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The relative amount of RNA measured by qRT-PCR cycles ranged from 8.2 to 37.0 cycle threshold (Ct) and formed a bimodal frequency distribution, with maxima at 20 and 36 Ct and minima at 28\u201330 Ct. On the basis of frequency distributions among different avian species with different responses to infection following experimental inoculation, field serological data indicating survival of infection, and the discovery of persistent RNA in experimentally infected birds, dead birds collected in nature were scored as \u201crecent\u201d or \u201cchronic\u201d infections on the basis of Ct scores. The percentage of birds scored as having chronic infections was highest during late winter\/spring, when all birds were after hatching year, and lowest during late summer, when enzootic transmission was typically highest as indicated by mosquito infections. Our data indicated that intervention efforts should not be based on dead birds with chronic infections unless supported by additional surveillance metrics.<\/jats:p>","DOI":"10.1089\/vbz.2012.1097","type":"journal-article","created":{"date-parts":[[2013,3,14]],"date-time":"2013-03-14T09:26:14Z","timestamp":1363253174000},"page":"401-405","update-policy":"https:\/\/doi.org\/10.1177\/sage-journals-update-policy","source":"Crossref","is-referenced-by-count":25,"title":["Chronic Infections of West Nile Virus Detected in California Dead Birds"],"prefix":"10.1177","volume":"13","author":[{"given":"William K.","family":"Reisen","sequence":"first","affiliation":[{"name":"University of California"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kerry","family":"Padgett","sequence":"additional","affiliation":[{"name":"California Department of Public Health"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ying","family":"Fang","sequence":"additional","affiliation":[{"name":"University of California"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Leslie","family":"Woods","sequence":"additional","affiliation":[{"name":"University of California"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Leslie","family":"Foss","sequence":"additional","affiliation":[{"name":"California Department of Public Health"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jaynia","family":"Anderson","sequence":"additional","affiliation":[{"name":"California Department of Public Health"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Vicki","family":"Kramer","sequence":"additional","affiliation":[{"name":"California Department of Public Health"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"179","published-online":{"date-parts":[[2013,6,1]]},"reference":[{"key":"e_1_3_3_2_1","article-title":"West Nile virus chronic positive infections in dead birds in California 2010\u20132011","author":"Anderson J","year":"2012","unstructured":"Anderson J, , Foss L, , Fang Y, , Woods L et al. 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