Laboratory Investigations on the Role of Bird Mites in the Transmission of Eastern and Western Equine Encephalitis 1

Abstract

Summary Large numbers of Dermanyssus gallinae, Bdellonyssus bursa, and B. sylviarum were fed upon chicks infected with the viruses of eastern and western equine encephalitis, then refed periodically in mass upon normal chicks. Samples of mites were tested for virus at different periods of incubation. Chicks ½-day-old proved to be more sensitive in detecting virus than mice. The viruses usually could not be recovered from the mites for more than a few days following the infected blood meal. After numerous trials involving mass feedings of many thousands of mites upon 125 chicks, two apparent virus transmissions to chicks by mite bite were accomplished, one of EEE by D. gallinae after 26 days extrinsic incubation, and one of WEE by this same mite species after 13 days extrinsic incubation. On one occasion, a trace of WEE virus was detected in excrement of 50 D. gallinae, tested after 6 days accumulation at 80°F. following an infected blood meal. A low concentration of WEE virus was also recovered from B. sylviarum protonymphs hatched from eggs laid as a result of an infected blood meal by parent mites. All other similar tests were negative. In view of the low susceptibility of these three species of mites to EEE and WEE infection, it is concluded that any role they might play in perpetuating these viruses in nature must be minor.