We modeled West Nile virus (WNV) movement rates and patterns based on a migratory bird agent (the Swainson's Thrush) and a resident bird agent (the House Sparrow), and compared the results of these models with actual movement data to investigate the likelihood that the pattern of WNV outbreaks observed in the New World was consistent with migrant bird-mediated spread, as reported from the Old World. We found that, contrary to Old World patterns, WNV activity in the Western Hemisphere does not seem consistent with movement by infected migrant birds. Instead WNV spread appears best explained by a non-directional movement, perhaps that of dispersing resident birds.
"The high rate of WNV dispersal in the U.S. could be explained by WNV infection of migratory birds that travel long distances annually (Dusek et al., 2009); however, evidence for infection in vernal north-bound migrants has been limited for WNV (Rappole and Hubalek, 2003; Reisen et al., 2010) as well as other North American encephalitides (Calisher et al., 1971; Lord and Calisher, 1970). In contrast, movements by resident birds have also been shown to be important for WNV enzootic maintenance and movement (Rappole et al., 2006). Furthermore, the phylodynamics of two emergent WNV genotypes, WN02 and SW03, have not been studied. "
"The virus is maintained in an enzootic ornitophilic-mosquito-bird cycle . Migratory birds are considered to play an important role in the local and long distance viral dispersal [32-35]. The most susceptible species to infection belong to the family Corvidae of the order Passeriformes such as the American crow, the blue jay (Cyanocitta cristata), the black-billed magpie (Pica hudsonia) or the fish crow (Corvus ossifragus) [9,36]. "
[Show abstract][Hide abstract] ABSTRACT: : West Nile virus (WNV) is a globally distributed arthropod-borne flavivirus capable of infecting a wide variety of vertebrates, with birds as its natural reservoir. Although it had been considered a pathogen of little importance for birds, from the 1990's, and especially after its introduction in the North American continent in 1999, thousands of birds have succumbed to West Nile infection. This review summarizes the pathogenesis and pathology of WNV infection in birds highlighting differences in lesion and antigen distribution and severity among bird orders and families. Despite significant species differences in susceptibility to infection, WNV associated lesions and viral antigen are present in the majority of organs of infected birds. The non-progressive, acute or more prolonged course of the disease accounts for part of the differences in lesion and viral antigen distribution and lesion severity. Most likely a combination of host variables and environmental factors in addition to the intrinsic virulence and pathogenicity of the infecting WNV strain influence the pathogenesis of the infection.
Veterinary Research 06/2013; 44(1):39. DOI:10.1186/1297-9716-44-39 · 2.82 Impact Factor
"Owing to the similarities in strains, the main theories of introduction of WNV not only involved intercontinental viremic migratory birds carrying the virus from the old world to the Western Hemisphere, but also zoo, pet or domestic birds introduced illegally to USA. There is also the possibility of a commercial flight transporting an infected mosquito into the country. Once the virus established its endemic cycle in NY, it started to spread through the rest of the country, south and westward. "
[Show abstract][Hide abstract] ABSTRACT: It has been 13 years since the first outbreak of West Nile Virus (WNV) occurred in the Americas. Since then, thousands of human cases have been reported in the United States. In contrast, there has not yet been an outbreak of WNV in any Latin American countries, including Mexico where <20 cases have been reported. We aimed to review publications to gather the main theories related to the fact that not all the countries of the continent reported human cases or that they have reported few cases since the introduction of WNV in the Western Hemisphere. We identified relevant publications using the PubMed database. Furthermore, we present on-line published information from Mexico. We found that researchers have tried to explain this phenomenon using several theories, like pre-existing antibodies against a heterotypical virus that have conferred cross protection in the population. Another explanation is that the strains circulating in Latin America are attenuated or that they came from a different origin of introduction in the continent. Another theory is that a conclusive diagnostic in regions where more than one Flavivirus is circulating results in cross-reaction in serological tests. Probably the sum of factors described by researchers in these theories in order to explain the behavior of the virus has resulted in the low number of reported cases in Latin America.
Journal of global infectious diseases 03/2013; 5(4):168-175. DOI:10.4103/0974-777X.122014
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