West Nile virus detected in birds in San Diego

According to ProMedMail, West Nile virus was found in 6 birds in San Diego County, California. This is unusual as evidence of viral infection in birds usually doesn't show up until the summer or fall. Fifteen cases have been reported in humans in 2007, 14 of them in people aged over 50. [Actually, ArboNET reports 16 total human cases in San Diego County, California in 2007 up to March 4, 2008]. The report mentions that mosquitoes usually die off in the winter, but a wet winter and a warm spring may have helped them survive in recent months. While this might be true, it is also possible that WNV is maintained by direct transmission between birds during the winter period. Interestingly, looking at reports of WNV-positive birds in 2007 in California, a few cases occured as early as January and February. Undoubtedly, human cases were only reported starting in June. Interestingly, WNV-positive mosquitoes appeared in earnest in July as well, while a few were reported in January [a warm spell?] and May. This could support the idea that cases of West Nile in birds are due to direct transmission between birds, and not vector-borne. Agreeing with Mod TY in the ProMedMail report, it would be very interesting (and important) to know whether there are any WNV-positive mosquito pools in San Diego County at the moment.