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.
Highlights
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
Substitution to a proline in position 249 of the non-structural protein NS3 has been associated with increased virulence in WNV lineage 1 strains in American crows (Corvus brachyrhynchos) and the same substitution has been detected in recent lineage 2 strains causing important outbreaks in Europe [15,21,22,23,24]
Some studies conducted in Africa in the 1950’s underlined the role of birds as amplifying hosts and mortality was reported in host competence studies, especially in hooded crows (Corvus corone sardonius) [46], prior to 1997 WNV was considered low-pathogenic for birds [47]
Summary
West Nile virus, a pathogen considered of little importance for birds before the 1990’s [47], is nowadays one of the most widely distributed arboviruses in the world that causes thousands of bird deaths, with a locally significant impact on populations of native species in North America [9,125]. Passeriformes develop necrosis and mild inflammation in the heart, spleen, liver or kidney, they show only mild encephalitic lesions and neuronal necrosis is absent [71,80,121] This may be related to the higher susceptibility of this order to WNV infection leading to rapid viral distribution and host death that does not allow development of encephalic lesions [118]. The reason why most studies about the pathology of WNV infection have been carried out in raptors and owls may be related to the higher visibility of dead or clinically affected animals of these species in the field These animals are frequently maintained in facilities such as zoos or rehabilitation centers where they are observed daily allowing to perform necropsies of fresh carcasses in case of death. Her supervisor UH investigates and teaches on infectious diseases in wild birds
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