Confined Animal Feeding Operations as Amplifiers of Influenza

Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, UK.
Vector Borne and Zoonotic Diseases (Impact Factor: 2.3). 02/2006; 6(4):338-46. DOI: 10.1089/vbz.2006.6.338
Source: PubMed


Influenza pandemics occur when a novel influenza strain, often of animal origin, becomes transmissible between humans. Domestic animal species such as poultry or swine in confined animal feeding operations (CAFOs) could serve as local amplifiers for such a new strain of influenza. A mathematical model is used to examine the transmission dynamics of a new influenza virus among three sequentially linked populations: the CAFO species, the CAFO workers (the bridging population), and the rest of the local human population. Using parameters based on swine data, simulations showed that when CAFO workers comprised 15-45% of the community, human influenza cases increased by 42-86%. Successful vaccination of at least 50% of CAFO workers cancelled the amplification. A human influenza epidemic due to a new virus could be locally amplified by the presence of confined animal feeding operations in the community. Thus vaccination of CAFO workers would be an effective use of a pandemic vaccine.

Download full-text


Available from: Roberto A. Saenz, Jul 23, 2014
    • "They hypothesized that virus transmission to swine may occur via consumption of human feces, which contains infectious particles (Larison et al., 2014). However, this mode of transmission seems relatively unlikely in the Togolese context, swine production in Togo consists of small farms and free range pigs, with little to no importation from abroad, a setup unfavorable for sustained swine influenza virus transmission (Saenz et al., 2006). Taken together, the literature and our phylogenetic analyses results support the hypothesis of human-to -swine transmission of (H1N1)pdm09 in Togo; however, epidemiological studies are warranted to show the transmission route definitively. "
    [Show abstract] [Hide abstract]
    ABSTRACT: We collected 325 nasal swabs from freshly slaughtered previously healthy pigs from October 2012 through January 2014 in a slaughterhouse near Lomé in Togo. Influenza A virus genome was detected by RT-PCR in 2.5-12.3% of the pooled samples, and results of hemagglutinin subtyping RT-PCR assays showed the virus in all the positive pools to be A(H1N1)pdm09. Virus was isolated on MDCK cells from a representative specimen, A/swine/Togo/ONA32/2013(H1N1). The isolate was fully sequenced and harbored eight genes similar to A(H1N1)pdm09 virus genes circulating in humans in 2012-2013, suggesting human-to-swine transmission of the pathogen. Copyright © 2015 Elsevier B.V. All rights reserved.
    No preview · Article · Mar 2015 · Veterinary Microbiology
  • Source
    • "In general, it is difficult to measure the transmission probability per contact, and therefore, it is mostly derived from calibrating models to match either the cumulative number of cases or R 0 (basic reproductive number) of on-going or historical outbreaks (Saenz et al., 2006; Rahmandad and Sterman, 2008; Vynnycky and White, 2010). Given an R 0 , a contact rate (C) and an average duration of infectiousness of totally susceptible individuals (D), transmission probability per contact (P), which is the probability that infection will be transferred between an infected and a susceptible units given an adequate contact has been made can be Table 4. Contact structure and influenza transmission parameters used in the simulation of influenza spread between swine and human populations in a county of Ontario, Canada Contact type Mean contacts/ day Distance distribution of recipient units (km) Probability of infection (Low/ medium/high) References Swine to swine a (Christensen et al., 2008; Bates et al., 2001) and unpublished data from Ontario Veterinary College; b Assumption based on the informed judgement of co-authors; c Assumed based on based on experimental studies (Brookes et al., 2010; Lange et al., 2009; Vincent et al., 2010); d Bases on the assumptions explained in the main text; e Assumed once/week based on the informed judgement of co-authors and multiplied by half the individual contact rate from Lee et al. (2010a) and Mossong et al. (2008); f Derived from R 0 value of pH1N1 2009 as explained the text; "
    [Show abstract] [Hide abstract]
    ABSTRACT: Simulation models implemented using a range of parameters offer a useful approach to identifying effective disease intervention strategies. The objective of this study was to investigate the effects of key control strategies to mitigate the simultaneous spread of influenza among and between swine and human populations. We used the pandemic H1N1 2009 virus as a case study. The study population included swine herds (488 herds) and households-of-people (29 707 households) within a county in Ontario, Canada. Households were categorized as: (i) rural households with swine workers, (ii) rural households without swine workers and (iii) urban households without swine workers. Seventy-two scenarios were investigated based on a combination of the parameters of speed of detection and control strategies, such as quarantine strategy, effectiveness of movement restriction and ring vaccination strategy, all assessed at three levels of transmissibility of the virus at the swine–human interface. Results showed that the speed of detection of the infected units combined with the quarantine strategy had the largest impact on the duration and size of outbreaks. A combination of fast to moderate speed of the detection (where infected units were detected within 5–10 days since first infection) and quarantine of the detected units alone contained the outbreak within the swine population in most of the simulated outbreaks. Ring vaccination had no added beneficial effect. In conclusion, our study suggests that the early detection (and therefore effective surveillance) and effective quarantine had the largest impact in the control of the influenza spread, consistent with earlier studies. To our knowledge, no study had previously assessed the impact of the combination of different intervention strategies involving the simultaneous spread of influenza between swine and human populations.
    Full-text · Article · Sep 2014 · Transboundary and Emerging Diseases
  • Source
    • "Currently, the effects of animal husbandry practices on interspecies transmission are poorly understood. Models suggest that swine raised on large-scale commercial farms, where animals are confined and raised at high densities, could serve as an important source of novel influenza that might trigger a new pandemic by infecting agricultural workers who would serve as a bridge to spread the virus to the rest of the population [26]. Small-scale farms, where swine are largely free-ranging, are common in many developing countries [27]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The 2009 pH1N1 influenza pandemic resulted in at least 18,500 deaths worldwide. While pH1N1 is now considered to be in a post-pandemic stage in humans it has nevertheless spilled back into swine in at least 20 countries. Understanding the factors that increase the risk of spillover events between swine and humans is essential to predicting and preventing future outbreaks. We assessed risk factors that may have led to spillover of pH1N1 from humans to swine in Cameroon, Central Africa. We sampled swine, domestic poultry and wild birds for influenza A virus at twelve sites in Cameroon from December 2009 while the pandemic was ongoing, to August 2012. At the same time we conducted point-count surveys to assess the abundance of domestic livestock and wild birds and assess interspecific contact rates. Random forest models were used to assess which variables were the best predictors of influenza in swine. We found swine with either active pH1N1 infections or positive for influenza A at four of our twelve sites. Only one swine tested positive by competitive ELISA in 2011-2012. To date we have found pH1N1 only in the North and Extreme North regions of Cameroon (regions in Cameroon are administrative units similar to provinces), though half of our sites are in the Central and Western regions. Swine husbandry practices differ between the North and Extreme North regions where it is common practice in to let swine roam freely, and the Central and Western regions where swine are typically confined to pens. Random forest analyses revealed that the three best predictors of the presence of pH1N1 in swine were contact rates between free-ranging swine and domestic ducks, contact rates between free-ranging swine and wild Columbiformes, and contact rates between humans and ducks. Sites in which swine were allowed to range freely had closer contact with other species than did sites in which swine were kept penned. Results suggest that the practice of allowing swine to roam freely is a significant risk factor for spillover of influenza from humans into swine populations.
    Full-text · Article · Mar 2014 · BMC Veterinary Research
Show more