EXPERIMENTAL CYCLIC TRANSMISSION OF ST. LOUIS ENCEPHALITIS VIRUS IN CHICKENS AND CULEX MOSQUITOES THROUGH A YEAR1

Abstract

Culex tarsalis and Culex quinquefasciatus infected with St. Louis encephalitis (SLE) virus in October were incubated outdoors through the winter at Bakersfield, California. Virus infection persisted in C. tarsalis for up to 8 months and in C. quinquefasciatus for over 7 months. C. tarsalis transmitted virus to chickens after incubation periods of 5, 6 and 7 months and C quinquefasciatus after 5 months. Virus was carried through the winter in 1 or 2 infection cycles and through a year in 7 infection cycles between C. tarsalis and chickens. Experimental overwintering of SLE virus in mosquitoes is contrary to most evidence from field studies and does not prove its natural occurrence. Most chickens infected through mosquito bites had detectable viremias for 3 successive days and viremia was usually greatest the second and third day. C. tarsalis that fed on blood containing over 100 MLD₅₀ of virus usually became infected.