COMPARISON OF IMMUNE RESPONSES OF BROWN-HEADED COWBIRD AND RELATED BLACKBIRDS TO WEST NILE AND OTHER MOSQUITO-BORNE ENCEPHALITIS VIRUSES

• Published in: Journal of wildlife diseases Vol. 43; no. 3; pp. 439 - 449
• Main Authors: Reisen, William K, Hahn, D. Caldwell
• Format: Journal Article
• Language: English
• Published: United States Wildlife Disease Association 01-07-2007; Wildlife Dis Assoc
• Subjects: Agelaius phoeniceus; Animals; Antibodies, Viral - blood; Bird Diseases - epidemiology; Bird Diseases - immunology; Bird Diseases - transmission; Birds; Blackbirds; Brown-headed Cowbird; Disease Reservoirs - veterinary; disease resistance; Disease Susceptibility - veterinary; Encephalitis Virus, St. Louis - immunology; Encephalitis Virus, Western Equine - immunology; Encephalitis Viruses - immunology; Encephalitis, Arbovirus - epidemiology; Encephalitis, Arbovirus - immunology; Encephalitis, Arbovirus - transmission; Encephalitis, Arbovirus - veterinary; Encephalitis, St. Louis - epidemiology; Encephalitis, St. Louis - immunology; Encephalitis, St. Louis - transmission; Encephalitis, St. Louis - veterinary; Encephalomyelitis, Equine - epidemiology; Encephalomyelitis, Equine - immunology; Encephalomyelitis, Equine - transmission; Encephalomyelitis, Equine - veterinary; EPIDEMIOLOGY; Euphagus cyanocephalus; hosts; Icteridae; immune response; immune system; indigenous species; Insect Vectors - virology; introduced species; life history; Molothrus ater; mortality; parasite-mediated selection; public health; Saint Louis encephalitis virus; Species Specificity; United States - epidemiology; Viremia - veterinary; West Nile Fever - epidemiology; West Nile Fever - immunology; West Nile Fever - transmission; West Nile Fever - veterinary; West Nile virus; West Nile virus - immunology; Western equine encephalitis virus; Western equine encephalomyelitis; western equine encephalomyelitis virus; wild birds; California; United States
• ISSN: 0090-3558; 1943-3700
• DOI: 10.7589/0090-3558-43.3.439

The rapid geographic spread of West Nile virus (family Flaviviridae, genus Flavivirus, WNV) across the United States has stimulated interest in comparative host infection studies to delineate competent avian hosts critical for viral amplification. We compared the host competence of four taxonomically related blackbird species (Icteridae) after experimental infection with WNV and with two endemic, mosquito-borne encephalitis viruses, western equine encephalomyelitis virus (family Togaviridae, genus Alphavirus, WEEV), and St. Louis encephalitis virus (family Flaviviridae, genus Flavivirus, SLEV). We predicted differences in disease resistance among the blackbird species based on differences in life history, because they differ in geographic range and life history traits that include mating and breeding systems. Differences were observed among the response of these hosts to all three viruses. Red-winged Blackbirds were more susceptible to SLEV than Brewer's Blackbirds, whereas Brewer's Blackbirds were more susceptible to WEEV than Red-winged Blackbirds. In response to WNV infection, cowbirds showed the lowest mean viremias, cleared their infections faster, and showed lower antibody levels than concurrently infected species. Brown-headed Cowbirds also exhibited significantly lower viremia responses after infection with SLEV and WEEV as well as coinfection with WEEV and WNV than concurrently infected icterids. We concluded that cowbirds may be more resistant to infection to both native and introduced viruses because they experience heightened exposure to a variety of pathogens of parenting birds during the course of their parasitic life style.