A study was conducted in Hale County, Texas, during 1965 to obtain data on the arboviruses, arthropod vectors, and their reservoir hosts. Eleven cases in man of western encephalitis and four cases of St. Louis encephalitis were confirmed among 46 suspected cases reported by physicians from the Hale County area. A total of 128 virus isolations was obtained from Culex tarsalis; of these 81 were WE virus and four were SLE. There also were 37 isolations of Hart Park virus and six isolations of Turlock virus from C. tarsalis. Weekly transection counts of adult wild birds revealed that House Sparrows constituted 71% of the bird population—213 blood samples were obtained from nestling House Sparrows, and 51 arbovirus isolations were obtained. Thirty-eight of these were WE, seven were SLE, four were Turlock, and two were Hart Park virus. Ten virus isolations were made from 572 specimens of mammal blood; nine were WE, and one was Turlock. The data obtained on C. tarsalis seasonal populations and on the correlation between WE virus infection rates among C. tarsalis and P. domesticus nestlings provided new insight regarding the basic involvement of these nestling birds in the WE virus amplification cycle in this study area. Except for the index case in man, WE virus activity detected among sentinel chickens, wild mammals, and man commenced after that in C. tarsalis and P. domesticus. The data obtained in these studies further substantiate the fact that Hale County, Texas, is an area of hyperendemic arbovirus activity.
Disease Ecology Section, Ecological Investigations Program, National Communicable Disease Center, Public Health Service, U. S. Department of Health, Education, and Welfare, P. O. Box 1097, Greeley, Colorado 80631.
Community Studies Section, Office of Pesticides, National Communicable Disease Center Public Health Service, U. S. Department of Health, Education, and Welfare, Atlanta, Georgia 30333.