St. Louis Encephalitis Transmission of Virus to Chickens by I17fected Mites Dermanyssus Gallin&e ~ Resulting Viremia as Source of Virus

Chicken mites (Dermanyssus gallinae) collected in several localities in St. Louis County have been fbund to be infected with the virus of St. Louis encephalitis (1, 2). The infection is probably permanent since congenital transfer of the virus in these mites has been demonstrated. Persistence of the virus in nature is indicated likewise by isolation of the virus from mites collected at a single site at intervals of 6, 8, and 16 weeks and by persistence of the virus for many months in laboratory colonies, one established with mites found infected in nature (31 months) and one established with experimentally infected mites (21 months). Experimental infection of mites from a homogeneous colony of uninfected mites derived from a single female, was accomplished by aUowing them to feed on chickens having viremia following subcutaneous inoculation of the virus. Transovarlan passage in these experimentally infected mites has been demonstrated (3). However, before these observations can be considered significant in the epidemiology of St. Louis encephalitis, it is necessary to show that infected mites are capable of transferring the virus of St. Louis encephalitis to chickens and that such chickens can serve as the source of virus for a blood-sucking vector. The present paper reports findings which show that infected mites, both those found infected in nature and those infected experimentally in the laboratory, are capable of producing viremia in chickens by bite and that these chickens in turn can serve as a source of the St. Louis virus for the infection of mites.