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Serological and molecular prevalence of swine influenza virus on farms in northwestern Mexico
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... Corzo et al. (2013a) reported an individual prevalence level of 4.6% in the USA pig population, and a 90.6% herd prevalence in the participating farms with a period of 12-24 months using a real-time reverse transcription polymerase chain reaction (real-time RT-PCR). A cross-sectional study in northern Mexico reported that more than 50% samples tested from commercial farms with between 300 and 2500 sows were seropositive to either H1 or H3 subtype SIV (Lopez-Robles et al. 2014). However, the seroprevalence may have been overestimated because these authors primarily sampled pigs less than ten weeks of age and maternally derived antibody (MDA) can last up to ten weeks in pigs and potentially have resulted in false positive results (Cador et al. 2016). ...
... This assumption was also supported by the finding of decreasing antibody titres with increasing age of the sampled pigs. The authors also reported that 16.7% (25/150) sampled pigs were positive for type A influenza with a RT-PCR test (Lopez-Robles et al. 2014). ...
... Furthermore, it is often difficult to culture SIVs and therefore subtype them when the viral load in samples is low. For example, Lopez-Robles et al. (2014) reported that even when clinical signs were present in 22 of 25 pigs that were positive for viral RNA, only isolates from 6 affected pigs were able to be subtyped by RT-PCR. ...
Globally swine influenza is one of the most important diseases of the pig industry, with various subtypes of swine influenza virus co-circulating in the field. Swine influenza can not only cause large economic losses for the pig industry but can also lead to epidemics or pandemics in the human population. We provide an overview of the pathogenic characteristics of the disease, diagnosis, risk factors for the occurrence on pig farms, impact on pigs and humans and methods to control it. This review is designed to promote understanding of the epidemiology of swine influenza which will benefit the control of the disease in both pigs and humans.
... Further, a significant number of swine experiencing respiratory illness had H1N1 or H3N2 virus antibodies in commercial piggeries in Sonora Province of Mexico during October 2008-March 2009. The molecular diagnostics and subtyping determined four H1 and two H3 viruses while 19 other IAV positive samples could not be subtyped given the low viral load [306]. ...
... The molecular detection approaches followed by sequencing are largely used for the research focusing on the influenza virus epidemiology [73,78,82,87,94,128,146,150]. [5,37,43,45,46,61,74,88,137,157,171,176,188,191,199,207,215,[219][220][221]241,243,248,250,263,289,290,301,306,307,326,334] 2. [37,38,46,52,59,70,79,96,97,135,138,153,186,195,200,215,291,306] 9. Lung/liver/internal organ tissues RNA extraction, real-time RT-PCR, reverse transcription-PCR, ligation, HI assay, virus isolation (MDCK cells/SPF chicken eggs), Sanger and Next-generation sequencing, hematoxylin-eosin staining, immunohistochemistry, Immunofluorescence H1N1, H1N2, Reassortant H1N1, H3N2, H2N3, A(H1N1)pdm09, H7N2, IDV [45,121,127,128,130,201,203,243,245,248,274,314,320,325,327] 10. Lung homogenate RNA extraction, real-time RT-PCR, multiplex RT-PCR, single step RT-PCR, virus isolation (MDCK cells/Caco-2 cells/SPF chicken eggs), Sanger sequencing, membrane enzyme immunoassay, HI assay H1N1, H1N2, H3N2, Reassortant H1N2, A(H1N1)pdm09 [130,213,218,292] 11. ...
... The molecular detection approaches followed by sequencing are largely used for the research focusing on the influenza virus epidemiology [73,78,82,87,94,128,146,150]. [5,37,43,45,46,61,74,88,137,157,171,176,188,191,199,207,215,[219][220][221]241,243,248,250,263,289,290,301,306,307,326,334] 2. [37,38,46,52,59,70,79,96,97,135,138,153,186,195,200,215,291,306] 9. Lung/liver/internal organ tissues RNA extraction, real-time RT-PCR, reverse transcription-PCR, ligation, HI assay, virus isolation (MDCK cells/SPF chicken eggs), Sanger and Next-generation sequencing, hematoxylin-eosin staining, immunohistochemistry, Immunofluorescence H1N1, H1N2, Reassortant H1N1, H3N2, H2N3, A(H1N1)pdm09, H7N2, IDV [45,121,127,128,130,201,203,243,245,248,274,314,320,325,327] 10. Lung homogenate RNA extraction, real-time RT-PCR, multiplex RT-PCR, single step RT-PCR, virus isolation (MDCK cells/Caco-2 cells/SPF chicken eggs), Sanger sequencing, membrane enzyme immunoassay, HI assay H1N1, H1N2, H3N2, Reassortant H1N2, A(H1N1)pdm09 [130,213,218,292] 11. ...
The global anxiety and a significant threat to public health due to the current COVID-19 pandemic reiterate the need for active surveillance for the zoonotic virus diseases of pandemic potential. Influenza virus due to its wide host range and zoonotic potential poses such a significant threat to public health. Swine serve as a “mixing vessel” for influenza virus reassortment and evolution which as a result may facilitate the emergence of new strains or subtypes of zoonotic potential. In this context, the currently available scientific data hold a high significance to unravel influenza virus epidemiology and evolution. With this objective, the current systematic review summarizes the original research articles and case reports of all the four types of influenza viruses reported in swine populations worldwide. A total of 281 articles were found eligible through screening of PubMed and Google Scholar databases and hence were included in this systematic review. The highest number of research articles (n = 107) were reported from Asia, followed by Americas (n = 97), Europe (n = 55), Africa (n = 18), and Australia (n = 4). The H1N1, H1N2, H3N2, and A(H1N1)pdm09 viruses were the most common influenza A virus subtypes reported in swine in most countries across the globe, however, few strains of influenza B, C, and D viruses were also reported in certain countries. Multiple reports of the avian influenza virus strains documented in the last two decades in swine in China, the United States, Canada, South Korea, Nigeria, and Egypt provided the evidence of interspecies transmission of influenza viruses from birds to swine. Inter-species transmission of equine influenza virus H3N8 from horse to swine in China expanded the genetic diversity of swine influenza viruses. Additionally, numerous reports of the double and triple-reassortant strains which emerged due to reassortments among avian, human, and swine strains within swine further increased the genetic diversity of swine influenza viruses. These findings are alarming hence active surveillance should be in place to prevent future influenza pandemics.
... This underscores the urgent need to mount a high level of scrutiny on the broad group of pathogens. The most notable examples of recent pandemics caused by zoonotic RNA viruses include but are not limited to: the "highly pathogenic avian influenza" (HPAI-H5N1) outbreak of 1997 which was first reported in Hong Kong [6]; the SARS-CoV-2 or COVID-19 pandemic which rapidly spread globally following its emergence at its epicenter in Hubei Province, China starting in late 2019 [7]; and the "swine influenza virus" (H1N1) outbreak of 2009 that spilled into the human population from pigs in Mexico [8]. After jumping the species barrier, this virus subsequently caused human-to-human transmission with deadly consequences [9]. ...
Pandemic zoonotic RNA virus infections have continued to threaten humans and animals worldwide. The objective of this review was to highlight the epidemiology and socioeconomic impacts of pandemic zoonotic RNA virus infections that occurred between 1997 and 2021.
Literature search was done from Web of Science, PubMed, Google Scholar and Scopus databases, cumulative case fatalities of individual viral infection calculated, and geographic coverage of the pandemics were shown by maps.
Seven major pandemic zoonotic RNA virus infections occurred from 1997 to 2021 and were presented in three groups: The first group consists of highly pathogenic avian influenza (HPAI-H5N1) and swine-origin influenza (H1N1) viruses with cumulative fatality rates of 53.5% and 0.5% in humans, respectively. Moreover, HPAI-H5N1 infection caused 90–100% death in poultry and economic losses of >$10 billion worldwide. Similarly, H1N1 caused a serious infection in swine and economic losses of 0.5-1.5% of the Gross Domestic Product (GDP) of the affected countries. The second group consists of severe acute respiratory syndrome-associated coronavirus infection (SARS-CoV), Middle East Respiratory Syndrome (MERS-CoV) and Coronavirus disease 2019 (COVID-19) with case fatalities of 9.6%, 34.3% and 2.0%, respectively in humans; but this group only caused mild infections in animals. The third group consists of Ebola and Zika virus infections with case fatalities of 39.5% and 0.02%, respectively in humans but causing only mild infections in animals.
Similar infections are expected in the near future, and hence strict implementation of conventional biosecurity-based measures and development of efficacious vaccines would help minimize the impacts of the next pandemic infection.
... SwIAV is endemic in several regions of high pig density, while epidemic outbreaks often occur in naïve pig herds [7]. In addition, swIAV is involved in porcine respiratory disease complex (PRCD), which is associated with important economic losses [7][8][9]. SwIAV is considered an important pathogen for animal and public health [1,10,11]. Pigs are susceptible to both human and avian influenza viruses [12] and may play the role of a "mixing vessel" for the emergence of a new influenza virus through genetic reassortment [13]. ...
Simple Summary
Our study aimed to assess the seroprevalence of Swine Influenza Viruses (swIAVs) in commercial pig farms in Greece. A total of 1416 blood samples were collected from breeding animals (gilts and sows) and pigs aged 3 weeks to market age from 40 different swIAV vaccinated and unvaccinated commercial farrow-to-finish pig farms. Of the total 1416 animals sampled, 498 were seropositive, indicating that the virus circulates in both vaccinated (54% seroprevalence) and unvaccinated Greek pig farms (23% seroprevalence). In addition, maternally derived antibody (MDA) levels in pigs at 4 and 7 weeks of age were lower in unvaccinated farms than in vaccinated farms. In conclusion, our results underscore the importance of vaccination for the prevention of swIAV infections in commercial farrow-to-finish pig farms.
Abstract
Swine influenza is a highly contagious respiratory disease caused by influenza A virus infection. Pigs play an important role in the overall epidemiology of influenza because of their ability to transmit influenza viruses of avian and human origin, which plays a potential role in the emergence of zoonotic strains with pandemic potential. The aim of our study was to assess the seroprevalence of Swine Influenza Viruses (swIAVs) in commercial pig farms in Greece. A total of 1416 blood samples were collected from breeding animals (gilts and sows) and pigs aged 3 weeks to market age from 40 different swIAV vaccinated and unvaccinated commercial farrow-to-finish pig farms. For the detection of anti-SIV antibodies, sera were analyzed using an indirect ELISA kit CIVTEST SUIS INFLUENZA®, Hipra (Amer, Spain). Of the total 1416 animals tested, 498 were seropositive, indicating that the virus circulates in both vaccinated (54% seroprevalence) and unvaccinated Greek pig farms (23% seroprevalence). In addition, maternally derived antibody (MDA) levels were lower in pigs at 4 and 7 weeks of age in unvaccinated farms than in vaccinated farms. In conclusion, our results underscore the importance of vaccination as an effective tool for the prevention of swIAV infections in commercial farrow-to-finish pig farms.
... Most studies show a higher H1N1 (Jolaoluwa et al., 2013) prevalence than for H3N2. The high prevalence of H3N2 in this study may reflect a shift in the dominant subtype among pigs in this region, although the antibody subtype in circulation is likely to be largely affected by the previous composition of vaccine (Choi et al., 2002) and for reasons unknown, the epidemiological status of certain SIV serotypes might vary from region to region (López-Robles et al., 2014). The former is ruled out as the government of Nigeria has always maintained a no influenza vaccine policy in livestock. ...
Influenza A virus presents a significant public health burden worldwide, with the 1918
Spanish flu pandemic being the most dramatic example. Swine influenza viruses can be
transmitted to humans through occupational exposures and in live pig markets. Novel
variants can emerge in pigs because they can be infected by human, avian and swine
strains. This study was carried out to determine the seroprevalence and serotypes of
swine influenza in pigs from a major slaughter slab in southern Kaduna. Using
competitive ELISA and haemagglutination-inhibition (HI) assays, 305 swine sera were
analysed. The result showed an overall seroprevalence of 28.20% (n=86), with H3N2
7.87% (n=24) emerging as the most dominant subtype in circulation. Concurrent
antibody detection of H1N1 in 5.26% (n=16) was also detected in boar 2.62% (n=8) and
sows 2.62% (n=8). This study revealed swine Influenza H1N1 and H3N2 serotypes are in
circulation in pigs in Kaduna State, and that reassortment in the instance of co-infection
of swine host is possible.
... ). Por ende, los sueros porcinos evaluados recibieron un tratamiento previo.En el presente estudio, el 56.52% de los porcinos fueron seropositivos contra el subtipo H1N1, el 26.95% contra el subtipo H3N2 y el 26.08% contra ambos subtipos. Estos resultados son similares a los reportados previamente en el noreste de México con alta seropositividad a los subtipos H1N1 (55%), H3N2 (59%) y hacia ambos subtipos (38%)(López-Robles et al., 2014). Asimismo, la falta de seropositividad contra el subtipo H5N2 evidenciada en el presente estudio es consistente con un estudio realizado en Egipto, cuya área de estudio estaba cerca al sitio principal de paro de aves migratorias, se encontraba próxima a un foco de infección de VIA y los cerdos eran alimentados con restos orgánicos incluyendo aves muertas. ...
Los sistemas productivos de traspatio contribuyen de manera significativa en la producción animal global y son una fuente importante de proteína en áreas rurales de México. Sin embargo, estas producciones familiares representan una interfaz que propicia interacciones entre animales domésticos, silvestres y humanos, favoreciendo la emergencia y propagación de agentes virales como el virus de influenza A (VIA). A pesar del papel de aves acuáticas como reservorios naturales de la mayoría de los subtipos de VIA y la participación de los cerdos en la ecología viral, se conoce poco acerca de la circulación viral en la interfaz cerdo doméstico - fauna silvestre en México. Por lo cual, el objetivo del presente estudio fue realizar diagnóstico serológico y molecular de VIA en cerdos de traspatio en una interfaz con patos silvestres en el Municipio de Lerma, Estado de México. Durante la temporada invernal 2016 - 2017, se colectaron 175 muestras nasales con hisopo y 115 muestras sanguíneas de porcinos de granjas de traspatio cercanas a la Ciénega de Atarasquillo (Chiconahuapan), considerada un área natural protegida y zona de conservación de aves. Se efectuó diagnóstico molecular por qRT-PCR y diagnóstico serológico mediante la técnica de IH contra los subtipos H1N1, H3N2 y H5N2 detectados en patos silvestres de la Ciénega en la misma temporada. Todas las muestras con hisopo resultaron molecularmente negativas a VIA. Sin embargo, se obtuvo una seropositividad de 56.52%, 26.95% y 0% para los subtipos H1N1, H3N2 y H5N2, respectivamente. Las granjas presentaron bajo nivel de bioseguridad, cría simultánea de diversas especies animales, falta de vacunación contra influenza porcina y una distancia de 0.8 a 2.7 km lineales respecto a otra granja, los cuales son factores de riesgo para la emergencia de VIA. Este estudio evidenció la presencia de anticuerpos en cerdos contra los virus aislados en patos silvestres de la ciénega de Atarasquillo y destaca la importancia de entender la dinámica de transmisión de VIA entre patos silvestres, aves de corral y cerdos mediante una aproximación integral con la combinación de datos serológicos y moleculares junto con información medioambiental y socioeconómica.
... Swine influenza is one of the most ubiquitous diseases circulating in the global pig population. Corzo et al. (2013a) reported a 90.6% herd prevalence in USA using a real-time reverse transcription polymerase chain test and a cross-sectional study in northern Mexico reported that more than 50% of pigs from commercial farms were seropositive to H1 or H3 subtype SIV (Lopez-Robles et al., 2014). Swine influenza is also widespread in Europe. ...
A cross-sectional study was undertaken to better understand the husbandry, management and biosecurity practices of pig farms in Guangdong Province (GD), China to identify risk factors for farmer reported swine influenza (SI) on their farms. Questionnaires were administered to 153 owners/managers of piggeries (average of 7 from each of the 21 prefectures in GD). Univariable and multivariable logistic regression analyses were used to identify risk factors for farmer reported SI in piggeries during the six months preceding the questionnaire administration. The ability of wild birds to enter piggeries (OR 2.50, 95% CI: 1.01–6.16), the presence of poultry on a pig-farm (OR 3.24, 95% CI: 1.52–6.94) and no biosecurity measures applied to workers before entry to the piggery (OR 2.65, 95% CI: 1.04–6.78) were found to increase the likelihood of SI being reported by farmers in a multivariable logistic regression model. The findings of this study highlight the importance of understanding the local pig industry and the practices adopted when developing control measures to reduce the risk of SI to pig farms.
... Consequently, it is expected that the overall percentage of positive and seropositive herds found in this study underestimates IAV prevalence. Nevertheless, the detection rates fall within the ranges reported for other countries in the region (27)(28)(29). Detection by rRT-PCR yielded 14% of positive samples over the two-year period, with more than 30% of positive herds each year. ...
Background:
Guatemala is the country with the largest swine production in Central America; however, evidence of influenza A virus (IAV) in pigs has not been clearly delineated.
Objectives:
In this study, we analyzed the presence and spatial distribution of IAV in commercial and backyard swine populations.
Methods:
Samples from two nation-wide surveys conducted in 2010 and 2011 were tested using virological (rRT-PCR and virus isolation) and serological (ELISA and Hemagglutination Inhibition) assays to detect IAV.
Results:
IAV was detected in 15.7% of the sampled pigs (30.6% of herds) in 2010 and in 11.7% (24.2% of herds) in 2011. The percentage of seropositive pigs was 10.6% (16.1% of herds) and 1.4% (3.1% of herds) for each year respectively. Three pandemic H1N1 and one seasonal human-like H3N2 viruses were isolated. Antibodies against viruses from different genetic clusters were detected. No reassortant strains with swine viruses were detected. The H3N2 virus was closely related to human viruses that circulated in Central America in 2010, distinct to the most recent human seasonal vaccine lineages. Spatial clusters of rRT-PCR positive herds were detected each year by scan statistics.
Conclusions:
Our results demonstrate circulation of IAV throughout Guatemala, and identify commercial farms, animal health status and age as potential risk factors associated to IAV infection and exposure. Detection of human-origin viruses in pigs suggests a role for humans in the molecular epidemiology of IAV in swine in Guatemala and evidences gaps in local animal and human surveillance. This article is protected by copyright. All rights reserved.
... The causative agent of SI is the swine influenza virus (SIV) which belongs to Orthomyxoviridae family and exists in three main different genotypes: H1N1, H2N1, and H3N2 (Simon-Grifé et al., 2011) These viruses are endemic in several pigproducing regions, and epidemic outbreaks of SIV infection often occur in naïve pig herds (Brown, 2000). Additionally, SIV is one of the agents involved in the porcine respiratory diseases complex (Brown, 2000;Thacker, 2001;López-Robles et al. 2014. ...
Swine influenza (SI) is a seasonal infectious disease highly important to the world pig industry. Loss of daily weight gain, increased costs for the prevention and treatment of secondary infections are the main economic losses associated with the presence of this disease. However, some epidemiological features of SI remain quite unclear. This study focused on assessing the prevalence of swine influenza virus (SIV) infection in intensive and extensive pig herds and associating risk factors. A set of 601 blood samples of five intensive farrow-to-finish farms and 361 blood samples from 56 extensive farms were analyzed using an indirect ELISA kit CIVTEST SUIS INFLUENZA®, Hipra (Amer, Spain), in order to detect anti-SIV antibodies. In total, 24.13 % of samples from intensive herds were positive, while no positive samples were detected in extensive rearing herds. Sow and weaning piglets had the highest prevalence values. In the intensive rearing system, occurrence of reproductive disorders and exposure to recently introduced animals were positively associated with the disease occurrence in swine herds. The findings highlight the importance of sows in the epidemiology of the disease and bring information about risk factors involved in the occurrence of swine influenza in intensive herds.
Influenza A virus (IAV) is a major cause of acute respiratory disease outbreaks in pigs, but infections are frequently subclinical. The epidemiology of IAV in swine (IAV‐S) encompasses a complex interplay of viruses of human, avian, and swine evolutionary origins. Genetic reassortment of human, avian, and/or swine IAVs is extremely common in pigs, and the resulting viruses have fundamentally altered the epidemiology of influenza in pigs in many parts of the world. Infections with any of the endemic swine IAVs are clinically similar, and all can produce acute respiratory episodes. There are no pathognomonic signs, and swine influenza must be differentiated from a variety of respiratory diseases of swine with similar clinical and pathologic presentation. A diagnosis is only possible through isolation of virus, through detection of viral proteins or nucleic acid, or by demonstration of virus‐specific antibodies. Vaccination is the primary means of preventing influenza in pigs.
The objective of this study was to evaluate the seroprevalence and identify the strains of swine influenza virus (SwIV), as well as the seroprevalence of porcine parvovirus (PPV), transmissible gastroenteritis virus (TGEV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine respiratory coronavirus (PRCV), porcine circovirus type 2 (PCV-2), and classical swine fever virus (CSFV) in pigs in Trinidad and Tobago (T&T). Blood samples (309) were randomly collected from pigs at farms throughout T&T. Serum samples were tested for the presence of antibodies to the aforementioned viruses using commercial ELISA kits, and the circulating strains of SwIV were identified by the hemagglutination inhibition test (HIT). Antibodies against SwIV were detected in 114 out of the 309 samples (37%). Out of a total of 26 farms, 14 tested positive for SwIV antibodies. HI testing revealed high titers against the A/sw/Minnesota/593/99 H3N2 strain and the pH1N1 2009 pandemic strain. Antibodies against PPV were detected in 87 out of the 309 samples (28%), with 11 out of 26 farms testing positive for PPV antibodies. Antibodies against PCV-2 were detected in 205 out of the 309 samples tested (66%), with 25 out of the 26 farms testing positive for PCV-2 antibodies. No antibodies were detected in any of the tested pigs to PRRSV, TGEV, PRCV, or CSFV.
Influenza A viruses (IAVs) cause one of the most important viral respiratory diseases in pigs. Repeated outbreaks and spread of genetically and antigenically distinct IAVs represent considerable challenges for animal production. Subtypes of H1N1, H1N2, and H3N2 are currently endemic in swine around the world, but they exhibit substantial diversity not only within the hemagglutinin (HA) and neuraminidase (NA) genes, but also in the other six gene segments. Human and swine IAVs have had a particular propensity for bidirectional interspecies transmission during the past century, demonstrated by regular virus incursion between the two hosts, and sometimes sustained virus circulation within the new host species. The diversity of IAV in swine remains a critical challenge in diagnosis and control of this important pathogen, both for swine health, and as a result of zoonotic risk to public health.
Se evaluó la prevalencia serológica del virus de influenza mediante las pruebas de inhibición de la hemaglutinación (IHA) y ELISA para los subtipos H1N1 y H3N2 en 13 granjas porcinas de Argentina. Se compararon los resultados obtenidos mediante ambas pruebas en términos individuales y de establecimientos. La prevalencia individual por la técnica de IHA fue de 38,46% a 100% para H1 y de 7,69% a 100% para H3. Por la técnica de ELISA, la prevalencia individual fue de 2,33% a 6,9% para H1 y de 9,65% a 48% para H3. No se observaron diferencias significativas entre ambas técnicas a escala de granja (H1: p=0,20; H3: p=0,11). La concordancia entre las pruebas fue nula al tomar como unidad de referencia el animal (H1: 0,005; H3: 0,070), mientras que en términos de establecimiento fue escasa (H1: 0,350; H3: 0,235). Considerando la alta prevalencia individual obtenida por la prueba de IHA y la alta sensibilidad de esta técnica, se podría sugerir que en las poblaciones porcinas de la Argentina circularon cepas virales humanas o cepas porcinas con gran proximidad filogenética a las utilizadas en este estudio desde el año 2002.
The A (H1N1) pdm09 influenza pandemic and, most recently, the A (H3N2) variant outbreak in several areas of the USA are examples of swine influenza viruses infecting humans. These cases highlight the need for reliable and rapid diagnostic tests to elucidate the epidemiology and evolution of swine influenza viruses (Smith and others 2009, Centers for Disease Control and Prevention 2012a, b, c). Currently, there are numerous commercial kits based on rapid-immunomigration techniques available for a fast detection of avian influenza viruses (Chen and others 2010). These rapid-immunomigration kits use specific antibodies against nucleoprotein (NP) of type A influenza viruses. Because the NP proteins are highly conserved between influenza viruses (Shu and others 1993, Li and others 2009), it is of relevance to assess if rapid-immunomigration kits designed for avian influenza are effective to detect influenza viruses in swine populations. Thus, the main goal of the present study was to evaluate the sensitivity and specificity of a commercial kit intended for avian samples, for samples obtained from backyard and commercial farm pigs.
All procedures in this study were performed following the Good Laboratory Practices and its recommended biosecurity guidelines (Centers for Disease Control and Prevention 2012a, b, c). Handling and sampling of animals were performed as indicated in the Mexican Official Regulation 062-ZOO-1999, which outlines technical specifications for the reproduction, care and use of laboratory animals (FMVZ 2012).
For the present study, we collected 48 nasal swabs …
Background:
On April 15 and April 17, 2009, novel swine-origin influenza A (H1N1) virus (S-OIV) was identified in specimens obtained from two epidemiologically unlinked patients in the United States. The same strain of the virus was identified in Mexico, Canada, and elsewhere. We describe 642 confirmed cases of human S-OIV infection identified from the rapidly evolving U.S. outbreak.
Methods:
Enhanced surveillance was implemented in the United States for human infection with influenza A viruses that could not be subtyped. Specimens were sent to the Centers for Disease Control and Prevention for real-time reverse-transcriptase-polymerase-chain-reaction confirmatory testing for S-OIV.
Results:
From April 15 through May 5, a total of 642 confirmed cases of S-OIV infection were identified in 41 states. The ages of patients ranged from 3 months to 81 years; 60% of patients were 18 years of age or younger. Of patients with available data, 18% had recently traveled to Mexico, and 16% were identified from school outbreaks of S-OIV infection. The most common presenting symptoms were fever (94% of patients), cough (92%), and sore throat (66%); 25% of patients had diarrhea, and 25% had vomiting. Of the 399 patients for whom hospitalization status was known, 36 (9%) required hospitalization. Of 22 hospitalized patients with available data, 12 had characteristics that conferred an increased risk of severe seasonal influenza, 11 had pneumonia, 8 required admission to an intensive care unit, 4 had respiratory failure, and 2 died. The S-OIV was determined to have a unique genome composition that had not been identified previously.
Conclusions:
A novel swine-origin influenza A virus was identified as the cause of outbreaks of febrile respiratory infection ranging from self-limited to severe illness. It is likely that the number of confirmed cases underestimates the number of cases that have occurred.
In the spring of 2009, swine-origin influenza H1N1pdm09 viruses caused the first influenza pandemic of this century. We characterized the influenza viruses that circulated early during the outbreak in Mexico, including one newly sequenced swine H1N1pdm09 virus and three newly sequenced human H1N1pdm09 viruses that circulated in the outbreak of respiratory disease in La Gloria, Veracruz. Phylogenetic analysis revealed that the swine isolate (A/swine/Mexico/4/2009) collected in April 2009 is positioned in a branch that is basal to the rest of the H1N1pdm09 clade in two (NP and PA) of the eight single-gene trees. In addition, the concatenated HA-NA and the complete whole-genome trees also showed a basal position for A/swine/Mexico/4/2009. Furthermore, this swine virus was found to share molecular traits with non-H1N1pdm09 H1N1 viral lineages. These results suggest that this isolate could potentially be the first one detected from a sister lineage closely related to the H1N1pdm09 viruses.
The prevalence of antibodies specific to swine influenza virus (SIV) among domestic pigs of different age, raised in large farms in Poland and Lithuania, was evidenced. Two thousand seven hundred and thirty five blood samples, taken from non-vaccinated animals were tested in HI assay against 3 SIV strains (H1N1, H1N2 and H3N2 subtypes). As a positive result the haemagglutinin titre ≥20 was estimated. Performed monitoring study showed that the most spread is H1N1 subtype of SIV. The occurrence of antibodies specific to SIV depended on the age of the tested animals. The first parity sows in Poland had low level of antibodies against H1N1 subtype (about 8%, at both -farm and individual levels) and no antibodies against H1N2 or human variant of SIV. In Lithuania, first parity sows presented the antibodies against H1N1 (27.3% of farms) and H1N2 (9.1% of farms) subtypes. The percentage of seroconversion among individual sows reached in this country 1.1 and 0.8 for H1N1 and H1N2 subtypes, respectively. It should be stressed that no antibodies against any of the tested subtypes of SIV were detected in boars and suckling piglets. The highest percentage of animals producing antibodies to all 3 antigens was detected, in both countries, among weaners and fatteners. In Poland it reached the level 11.1, 5.5, and 2.8 while in Lithuania -18.2, 9.1, and 0, respectively against H1N1, H1N2 and H3N2 subtypes. The titre of the sera ranged from 20 to 160, but in the most samples it was low.
Prior to the introduction of the 2009 pandemic H1N1 virus from humans into pigs, four phylogenetic clusters (α-, β-, γ- and δ) of the haemagglutinin (HA) gene from H1 influenza viruses could be found in US swine. Information regarding the antigenic relatedness of the H1 viruses was lacking due to the dynamic and variable nature of swine lineage H1. We characterized 12 H1 isolates from 2008 by using 454 genome-sequencing technology and phylogenetic analysis of all eight gene segments and by serological cross-reactivity in the haemagglutination inhibition (HI) assay. Genetic diversity was demonstrated in all gene segments, but most notably in the HA gene. The gene segments from the 2009 pandemic H1N1 formed clusters separate from North American swine lineage viruses, suggesting progenitors of the pandemic virus were not present in US pigs immediately prior to 2009. Serological cross-reactivity paired with antigenic cartography demonstrated that the viruses in the different phylogenetic clusters are also antigenically divergent.
The seroprevalence of the Influenza virus against H1N1 and H3N2 was determined by the hemagglutination-inhibition test (HI) and a commercial swine influenza ELISA kit, in 13 Argentinean swine herds. The results of within-herd and between-herd prevalence obtained by both tests were statistically correlated. The within-herd prevalence observed by the HI test varied from 38.46 to 100% against H1 and 7.69 to 100% for H3. When the within-herd prevalence was measured with the ELISA test, it varied from 2.33 to 6.9% for H1 and 9.65 to 48% for H3. No statistical differences were observed at herd level between HI and ELISA (H1: p = 0. 20; H3: p=0.11). No agreement between HI and ELISA detected prevalence was observed when the within-herd prevalence was compared (H1: 0.005; H3: 0.070), while the agreement at herd level was considered poor (H1: 0,350; H3: 0,235). The high within-herd prevalence values observed with the HI test and the high sensibility of this test might show that human strains or swine strains phylogenetically closely related to the humans strains used in the HI test in this study have been affecting the swine population since 2002.
Pandemic influenza viruses cause significant mortality in humans. In the 20th century, 3 influenza viruses caused major pandemics: the 1918 H1N1 virus, the 1957 H2N2 virus, and the 1968 H3N2 virus. These pandemics were initiated by the introduction and successful adaptation of a novel hemagglutinin subtype to humans from an animal source, resulting in antigenic shift. Despite global concern regarding a new pandemic influenza, the emergence pathway of pandemic strains remains unknown. Here we estimated the evolutionary history and inferred date of introduction to humans of each of the genes for all 20th century pandemic influenza strains. Our results indicate that genetic components of the 1918 H1N1 pandemic virus circulated in mammalian hosts, i.e., swine and humans, as early as 1911 and was not likely to be a recently introduced avian virus. Phylogenetic relationships suggest that the A/Brevig Mission/1/1918 virus (BM/1918) was generated by reassortment between mammalian viruses and a previously circulating human strain, either in swine or, possibly, in humans. Furthermore, seasonal and classic swine H1N1 viruses were not derived directly from BM/1918, but their precursors co-circulated during the pandemic. Mean estimates of the time of most recent common ancestor also suggest that the H2N2 and H3N2 pandemic strains may have been generated through reassortment events in unknown mammalian hosts and involved multiple avian viruses preceding pandemic recognition. The possible generation of pandemic strains through a series of reassortment events in mammals over a period of years before pandemic recognition suggests that appropriate surveillance strategies for detection of precursor viruses may abort future pandemics.
In March and early April 2009, a new swine-origin influenza A (H1N1) virus (S-OIV) emerged in Mexico and the United States. During the first few weeks of surveillance, the virus spread worldwide to 30 countries (as of May 11) by human-to-human transmission, causing the World Health Organization to raise its pandemic alert to level 5 of 6. This virus has the potential to develop into the first influenza pandemic of the twenty-first century. Here we use evolutionary analysis to estimate the timescale of the origins and the early development of the S-OIV epidemic. We show that it was derived from several viruses circulating in swine, and that the initial transmission to humans occurred several months before recognition of the outbreak. A phylogenetic estimate of the gaps in genetic surveillance indicates a long period of unsampled ancestry before the S-OIV outbreak, suggesting that the reassortment of swine lineages may have occurred years before emergence in humans, and that the multiple genetic ancestry of S-OIV is not indicative of an artificial origin. Furthermore, the unsampled history of the epidemic means that the nature and location of the genetically closest swine viruses reveal little about the immediate origin of the epidemic, despite the fact that we included a panel of closely related and previously unpublished swine influenza isolates. Our results highlight the need for systematic surveillance of influenza in swine, and provide evidence that the mixing of new genetic elements in swine can result in the emergence of viruses with pandemic potential in humans.
An H1N2 influenza virus was isolated from a pig during an outbreak of respiratory disease and abortion on an Indiana farm in November 1999. Results of phylogenetic analyses indicate that this virus is a reassortant between a recent classical H1 swine virus and the reassortant H3N2 viruses that have emerged among American pigs since 1998.
A real-time reverse transcriptase PCR (RRT-PCR) assay based on the avian influenza virus matrix gene was developed for the
rapid detection of type A influenza virus. Additionally, H5 and H7 hemagglutinin subtype-specific probe sets were developed
based on North American avian influenza virus sequences. The RRT-PCR assay utilizes a one-step RT-PCR protocol and fluorogenic
hydrolysis type probes. The matrix gene RRT-PCR assay has a detection limit of 10 fg or approximately 1,000 copies of target
RNA and can detect 0.1 50% egg infective dose of virus. The H5- and H7-specific probe sets each have a detection limit of
100 fg of target RNA or approximately 103 to 104 gene copies. The sensitivity and specificity of the real-time PCR assay were directly compared with those of the current
standard for detection of influenza virus: virus isolation (VI) in embryonated chicken eggs and hemagglutinin subtyping by
hemagglutination inhibition (HI) assay. The comparison was performed with 1,550 tracheal and cloacal swabs from various avian
species and environmental swabs obtained from live-bird markets in New York and New Jersey. Influenza virus-specific RRT-PCR
results correlated with VI results for 89% of the samples. The remaining samples were positive with only one detection method.
Overall the sensitivity and specificity of the H7- and H5-specific RRT-PCR were similar to those of VI and HI.
We announce the release of the fourth version of MEGA software, which expands on the existing facilities for editing DNA sequence data from autosequencers, mining Web-databases, performing automatic and manual sequence alignment, analyzing sequence alignments to estimate evolutionary distances, inferring phylogenetic trees, and testing evolutionary hypotheses. Version 4 includes a unique facility to generate captions, written in figure legend format, in order to provide natural language descriptions of the models and methods used in the analyses. This facility aims to promote a better understanding of the underlying assumptions used in analyses, and of the results generated. Another new feature is the Maximum Composite Likelihood (MCL) method for estimating evolutionary distances between all pairs of sequences simultaneously, with and without incorporating rate variation among sites and substitution pattern heterogeneities among lineages. This MCL method also can be used to estimate transition/transversion bias and nucleotide substitution pattern without knowledge of the phylogenetic tree. This new version is a native 32-bit Windows application with multi-threading and multi-user supports, and it is also available to run in a Linux desktop environment (via the Wine compatibility layer) and on Intel-based Macintosh computers under the Parallels program. The current version of MEGA is available free of charge at (http://www.megasoftware.net).
In 2004, 803 rural Iowans from the Agricultural Health Study were enrolled in a 2-year prospective study of zoonotic influenza transmission. Demographic and occupational exposure data from enrollment, 12-month, and 24-month follow-up encounters were examined for association with evidence of previous and incident influenza virus infections. When proportional odds modeling with multivariable adjustment was used, upon enrollment, swine-exposed participants (odds ratio [OR] 54.9, 95% confidence interval [CI] 13.0-232.6) and their nonswine-exposed spouses (OR 28.2, 95% CI 6.1-130.1) were found to have an increased odds of elevated antibody level to swine influenza (H1N1) virus compared with 79 nonexposed University of Iowa personnel. Further evidence of occupational swine influenza virus infections was observed through self-reported influenza-like illness data, comparisons of enrollment and follow-up serum samples, and the isolation of a reassortant swine influenza (H1N1) virus from an ill swine farmer. Study data suggest that swine workers and their nonswine-exposed spouses are at increased risk of zoonotic influenza virus infections.
In the present study, we analyzed the presence of antibodies to four different influenza viruses (pH1N1, hH1N1, swH1N1, and swH3N2) in the sera of 2094 backyard pigs from Mexico City. The sera were obtained between 2000 and 2009.
The aim of this study was to perform a retrospective analysis of the 2000–2009 period to determine the seroprevalence of antibodies against pH1N1, hH1N1, swH1N1, and swH3N2 viruses in sera obtained from backyard pigs in Mexico City.
Antibody detection was conducted with hemagglutination inhibition assay (HI) using four influenza viruses. We used linear regression to analyze the tendency of antibody serum titers throughout the aforementioned span.
We observed that the antibody titers for the pH1N1, swH1N1, and swH3N2 viruses tended to diminish over the study period, whereas the antibodies to hH1N1 remained at low prevalence for the duration of the years analyzed in this study. A non-significant correlation (P > 0·05) between antibody titers for pH1N1 and swH1N1 viruses was observed (0·04). It contrasts with the significance of the correlation (0·43) observed between the swH1N1 and swH3N2 viruses (P < 0·01).
Our findings showed no cross-antigenicity in the antibody response against the same subtype. Antibodies against pH1N1 virus were observed throughout the 10-year study span, implying that annual strains shared some common features with the pH1N1 virus since 2000, which would then be capable of supporting the ongoing presence of these antibodies.
A cross-sectional study was conducted to evaluate the transmission of swine influenza through occupational exposure and to assess some risk factors for zoonotic transmission in workers from commercial farms in Mexico. Seroprevalence to swine influenza subtypes was determined by hemagglutinin inhibition assay and was higher in exposed (E), in comparison with unexposed (UE) participants (P<0.05). Percentages of seropositivity between UE and E were 28.57% and 19.35% to A/NewCaledonia/20/99 (H1N1), 68.25% and 33.87% to A/Panama/2001/99-like (H3N2), 1.58% and 12.9% to A/Sw/England/163266/87 (H3N2), respectively. No antibodies were detected against A/Sw/Wisconsin/238/97 (H1N1) in the UE subjects, and only 3.22% were positive in the E group (P<0.05). A significant association between elevated antibody titres to swine influenza virus (SIV) H3N2 and the exposition to swine [OR 3.05, 95% (CI) 1.65-5.64] and to geographic location [OR 8.15, 95% (CI) 1.41-47.05] was found. Vaccination appeared as a protective factor [OR 0.05, 95% (CI) 0.01-0.52]. Farms with high number of breeding herd were associated with increased anti-SIV antibodies in the E group [OR 3.98, 95% (CI) 1.00-15.86]. These findings are relevant and support the evidence of zoonoses in swine farms and point out the need to implement preventive measures to diminish the occurrence of the disease and the potential emergence of pathogenic reassortant strains.
A literature review and pooled data analysis were carried out to examine the prevalence of antibodies against five influenza virus subtypes in pigs in China over a 10-year period (1999-2009). The average seropositive frequencies of subtypes H1, H3, H5, H7 and H9 were 3478/11,168 (31.1%), 2900/10,139 (28.6%), 77/5945 (1.3%), 0/1440 (0%) and 86/3619 (2.4%), respectively. There was a geographical variation in the seroprevalence of subtype H1, with the highest seroprevalence in pigs in South and East China. BLAST analysis of genetic sequences revealed that genome segments with moderate homology to the 2009 pandemic influenza A (H1N1) virus were present among swine influenza viruses isolated in China, especially in South and East China. It was concluded from both serological and genetic studies that subtypes H1, H3, H5 and H9 are currently co-circulating in pigs in China, with the H1 subtype most commonly detected, followed by H3.
Avian-like H1N1 and human-like H3N2 swine influenza viruses (SIV) have been considered widespread among pigs in Western Europe since the 1980s, and a novel H1N2 reassortant with a human-like H1 emerged in the mid 1990s. This study, which was part of the EC-funded 'European Surveillance Network for Influenza in Pigs 1', aimed to determine the seroprevalence of the H1N2 virus in different European regions and to compare the relative prevalences of each SIV between regions.
Laboratories from Belgium, the Czech Republic, Germany, Italy, Ireland, Poland and Spain participated in an international serosurvey. A total of 4190 sow sera from 651 farms were collected in 2002-2003 and examined in haemagglutination inhibition tests against H1N1, H3N2 and H1N2.
In Belgium, Germany, Italy and Spain seroprevalence rates to each of the three SIV subtypes were high (> or =30% of the sows seropositive) to very high (> or =50%), except for a lower H1N2 seroprevalence rate in Italy (13.8%). Most sows in these countries with high pig populations had antibodies to two or three subtypes. In Ireland, the Czech Republic and Poland, where swine farming is less intensive, H1N1 was the dominant subtype (8.0-11.7% seropositives) and H1N2 and H3N2 antibodies were rare (0-4.2% seropositives).
Thus, SIV of H1N1, H3N2 and H1N2 subtype are enzootic in swine producing regions of Western Europe. In Central Europe, SIV activity is low and the circulation of H3N2 and H1N2 remains to be confirmed. The evolution and epidemiology of SIV throughout Europe is being further monitored through a second 'European Surveillance Network for Influenza in Pigs'.
Pigs serve as major reservoirs of H1N1 and H3N2 influenza viruses which are endemic in pig populations world-wide and are responsible for one of the most prevalent respiratory diseases in pigs. The maintenance of these viruses in pigs and the frequent exchange of viruses between pigs and other species is facilitated directly by swine husbandry practices, which provide for a continual supply of susceptible pigs and regular contact with other species, particularly humans. The pig has been a contender for the role of intermediate host for reassortment of influenza A viruses of avian and human origin since it is the only domesticated mammalian species which is reared in abundance and is susceptible to, and allows productive replication, of avian and human influenza viruses. This can lead to the generation of new strains of influenza, some of which may be transmitted to other species including humans. This concept is supported by the detection of human-avian reassortant viruses in European pigs with some evidence for subsequent transmission to the human population. Following interspecies transmission to pigs, some influenza viruses may be extremely unstable genetically, giving rise to variants which could be conducive to the species barrier being breached a second time. Eventually, a stable lineage derived from the dominant variant may become established in pigs. Genetic drift occurs particularly in the genes encoding the external glycoproteins, but does not usually result in the same antigenic variability that occurs in the prevailing strains in the human population. Adaptation of a 'newly' transmitted influenza virus to pigs can take many years. Both human H3N2 and avian H1N1 were detected in pigs many years before they acquired the ability to spread rapidly and become associated with disease epidemics in pigs.
A total of 360 type A swine influenza virus-positive samples including cell culture isolates, nasal swabs or lung tissues along with 30 virus-negative samples were tested for the detection and subtyping of H1N1, H1N2 or H3N2 by two multiplex reverse transcription (RT)-PCR assays. The positive samples had been collected between 1999 and 2001 from pigs with respiratory diseases, and type A influenza virus was isolated and subtyped by hemagglutination inhibition (HI) test at the Minnesota Veterinary Diagnostic Laboratory (MVDL). Two multiplex RT-PCR assays specific for H1 and H3, and N1 and N2 were developed. RT-PCR products with unique sizes characteristic of each subtype of influenza A virus were sequenced, and the sequences were demonstrated to be specific for H1N1, H1N2 or H3N2. Genomic RNAs or DNAs from 12 common swine pathogens other than type A influenza viruses were not amplified when the PCR assays were performed with these primer sets. Positive amplification reaction could be visualized with RNA extracted from up to 10(-5) dilution of each reference virus with original infectivity titer of 10(5) TCID(50)/ml. Of the 360 samples tested, swine influenza virus H1N1, H1N2 and H3N2 were identified in 200, 13 and 139 samples, respectively. The remaining eight samples were positive for both H1N1 and H3N2 viruses. The results of multiplex RT-PCR were 100% in agreement with those of virus isolation. These results demonstrate the usefulness of multiplex RT-PCR for detection and identification of influenza A virus subtypes. The results also indicate an increased occurrence of H1N2 in US swine population.
Serologic and virologic prevalence of infection with different swine influenza virus (SIV) subtypes was investigated using swine sera, nasal swabs and lung samples that had been submitted for a diagnosis to the Minnesota Veterinary Diagnostic Laboratory. A total of 111,418 pig sera were tested for SIV antibody between 1998 and 2000, and 25,348 sera (22.8%) were found to be positive by the hemagglutination inhibition (HI) test. Of the positive samples, 16,807 (66.7%) and 8,541 (33.7%) had antibody to H1 and H3 subtypes, respectively. Between January 1998 and May of 2001, a total of 3,561 nasal swabs or lung samples were examined for the presence of SIV, and SIV was isolated from 1,124 samples (31.7%). Of these isolates, 869 (77.3%) and 255 (22.7%) were subtyped as H1 and H3, respectively, by the HI method. For further characterization, 120 SIV isolates each from 1998 to 2001 were randomly selected from a culture collection and their hemagglutinin (HA) and neuraminidase genes examined by reverse transcription-PCR and sequencing. Of the 480 isolates, 322 (67.1%), 22 (4.6%) and 129 (26.9%) were subtyped as H1N1, H1N2 and H3N2, respectively. The remaining 7 samples (1.5%) were found to contain both H1N1 and H3N2 viruses. The SIV H1N2 subtype was isolated from 1, 8, and 13 samples in 1999, 2000, and 2001, respectively. The 22 H1N2 isolates originated from 9 different states of the United States. Genetic screening of the HA genes of 12 selected H1N2 isolates showed that 8 of them had a close phylogenetic relationship with the Indiana isolate of H1N2 (A/Swine/Indiana/9K035/99), while 4 isolates were closely related to classical SIV H1N1.
Since 1999 we have developed two computational mutation approaches to analyze the protein primary structure whose methodology and implications were reviewed in 2002. Our first approach is the calculation of predictable and unpredictable portions of amino-acid pairs in a protein, and the second is the calculation of amino-acid distribution rank in a protein. Both approaches provide quantitative measures to present a protein, which we have used to study a number of proteins with numerous mutations such as p53 proteins. More recently, we focussed our efforts on analyzing the proteins mutating frequently over time such as hemagglutinins of influenza A viruses. In this review we summarise our findings and their implications for hemagglutinin mutations in combination with some newly available data. Our approaches throw light on the true nature of genetic heterogeneity of influenza virus hemagglutinins; that is, the protein variability is highly relevant to its amino-acid construction. Using these approaches, we can monitor new mutations from influenza virus hemagglutinins and may predict their mutations in the future.
Swine influenza viruses (SIV) of the hemagglutinin subtype 1 (H1) isolated from the United States (U.S.) have not been well-characterized in the natural host. An increase in the rate of mutation and reassortment has occurred in SIV isolates from the U.S. since 1998, including viruses belonging to the H1 subtype. Two independent animal studies were done to evaluate and compare the pathogenesis of 10 SIV isolates dating from 1930 to currently circulating isolates. In addition, the hemagglutinin and neuraminidase genes of each isolate were sequenced for genetic comparison, and serological cross-reactivity was evaluated using all sera and virus combinations in hemagglutination inhibition and serum neutralization assays. Statistically significant differences in percentage of pneumonia and virus titers in the lung were detected between isolates, with modern isolates tending to produce more severe disease, have more virus shedding and higher viral titers. However, nasal shedding and virus titers in the lung were not always correlated with one another or lung lesions. Serologically, the classic historical H1N1 viruses tended to have better cross-reaction between historical sera and antigens, with moderate to good cross-reactivity with modern viral antigens. However, the modern sera were less reactive with historical viruses. Modern viruses tended to have less consistent cross-reactivity within the modern group. Overall, H1 isolates collected over the last 75 years from the U.S. pig population exhibit considerable variability in pathogenicity. There appears to be an increase in genetic and antigenic diversity coincident with the emergence of the swine triple reassortant H3N2 in 1998.
Influenza viruses are able to infect humans, swine, and avian species, and swine have long been considered a potential source of new influenza viruses that can infect humans. Swine have receptors to which both avian and mammalian influenza viruses bind, which increases the potential for viruses to exchange genetic sequences and produce new reassortant viruses in swine. A number of genetically diverse viruses are circulating in swine herds throughout the world and are a major cause of concern to the swine industry. Control of swine influenza is primarily through the vaccination of sows, to protect young pigs through maternally derived antibodies. However, influenza viruses continue to circulate in pigs after the decay of maternal antibodies, providing a continuing source of virus on a herd basis. Measures to control avian influenza in commercial poultry operations are dictated by the virulence of the virus. Detection of a highly pathogenic avian influenza (HPAI) virus results in immediate elimination of the flock. Low-pathogenic avian influenza viruses are controlled through vaccination, which is done primarily in turkey flocks. Maintenance of the current HPAI virus-free status of poultry in the United States is through constant surveillance of poultry flocks. Although current influenza vaccines for poultry and swine are inactivated and adjuvanted, ongoing research into the development of newer vaccines, such as DNA, live-virus, or vectored vaccines, is being done. Control of influenza virus infection in poultry and swine is critical to the reduction of potential cross-species adaptation and spread of influenza viruses, which will minimize the risk of animals being the source of the next pandemic.
Livestock Disease Surveys: A Field Manual for Veterinarians
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Characterization of an influenza A virus
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