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<ol> <li> Enhanced understanding of the pathogenesis of West Nile virus (WNV) infection in horses, wildlife, and other animal species; <li>Development of sensitive and specific methods of diagnosis of WNV infection in animals; <li>Surveillance of WNV infection in Michigan's animal populations. </ol> Specific objectives are: <OL> <LI> Characterization of WNV infection in animals through description of pathologic changes, detection of virus in tissues, and detection of antibodies in serum and CSF; <LI> Comparison of sensitivities and specificities of diagnostic tests in identification of WNV-infected animals.
NON-TECHNICAL SUMMARY: West Nile virus (WNV) infection in animals and humans has become an important disease in the United States since arrival of the virus in the Western hemisphere in 1999. Thorough characterization of WNV infection in animals by established techniques in diagnostic pathology and virology will increase understanding of the disease, and lead to improved surveillance methods.
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APPROACH: WNV infection in animals will be characterized by description of gross and histopathologic tissue changes and identification of WNV antigen in tissues by immunohistochemistry. Viral RNA will be detected in unfixed and formalin-fixed animal tissues by RT-PCR. Oral swabs from birds will be evaluated for the presence of WNV by virus isolation and RT-PCR, and by a commercially available enzyme-linked immunosorbent assay (ELISA). A comparison of diagnostic techniques in birds will establish which procedures are most practical and valuable as surveillance tools.
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PROGRESS: 2003/10 TO 2008/09<BR>
In 2006, Michigan State University's Diagnostic Center for Population and Animal Health (DCPAH) tested samples from 413 corvid birds (American crows, blue jays, common ravens), 131 noncorvid birds (21 different species), 92 horses, and1 white-tailed deer for evidence of West Nile virus (WNV) infection. There were 255 positive corvid birds, 34 positive noncorvid birds, and 46 positive horses. Compared to 2005 figures, these numbers indicate a 95% increase in the number of positive corvid birds (with a 35% increase in birds tested), a 10-fold increase in the number of positive noncorvid birds (and a 4-fold increase in the number tested), and a 2-fold increase in the number of positive horses in Michigan. Despite the rise in animal cases, the number of human cases of WNV infection was about the same as in 2005 (62 cases in 2005, 54 cases in 2006). Avian submissions (and thus, an increase in the number of positive cases) were believed to have increased because of the bird flu scare. The increase in equine WNV cases is uncertain, considering there is a widely used vaccine available for horses. Similar to previous years, the percentage of submitted corvids which tested positive for WVN began to increase toward the end of July and remained high through August. Then, in late August and September, the majority of positive equine cases were detected. In 2006, RT-PCR on oral swabs was the primary means of diagnosis in corvid birds, while detection of virus in feather follicles or pooled tissues by PCR was done with non-corvids. Horse sera and/or cerebrospinal fluid were tested by IgM capture ELISA for antibodies to WNV.
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IMPACT: 2003/10 TO 2008/09<BR>
WNV infection is now endemic in the 48 continental United States and most Canadian provinces, and has been reported in birds, horses, and people in several Central and South American countries. Active surveillance of infection in corvid birds (and mosquitoes) continues to be important, as detection of WNV in these species consistently precedes the appearance of equine and human cases in a given geographic area. Unfortunately, funding from the Michigan Department of Community Health will not be forthcoming in 2007, and thus Michigan's WNV surveillance program will be terminated.