A probing ecologic study was conducted in south-central Florida during May, June and July, 1960, and August, 1961, to determine the nature and distribution of arthropod-borne viruses in this area. Collections for virus and/or antibody examination included 1380 specimens composed of arthropod pools, birds, small mammals, reptiles and sentinels (mice and chicks).
EEE virus was isolated from two pools of Culex mosquitoes (mixed species) and from a Common Grackle. WEE was recovered from a pool of Aedes taeniorhynchus, and the Highlands J strain of WEE from the blood of two Blue Jays and the brain of a sentinel mouse.
Antibody rates in birds which were high for EEE (21%) and WEE (23%) in the 1960 collection and indicated recent infections, were markedly lower (2.7% and 3.4%, respectively) in 1961. Bird plasma reactors to SLE were similar (8% in 1960, 5% in 1961), except positives were found with blood from juvenile birds in 1961 but not in 1960, indicating probably recent activity of SLE or a related group B arthropodborne virus in the 1961 bird population sampled. HI antibody rates in wild-caught rodents in 1960 were: WEE, 10%; SLE, 30%; EEE, 0%.
There were marked differences in two WEE strain antigens when used to measure antibody levels in birds. Forty-three or 10% of the samples were positive using the RI strain and 95 or 23% using the HJ strain of WEE. Moreover, a variance in the level of antibody was noted in bird plasmas examined by the HI and neutralization tests. These differences were attributed to the asynchronous development and/or disappearance of these antibody types.
Trainee in Epidemiology.
Connecticut Agricultural Experiment Station, New Haven, Connecticut.
Present address: University of California, School of Public Health, Berkeley, California.