Poliomyelitis Virus from Flies. ∗

Flexner and Clark 1 and Howard and Clark 2 have demonstrated that artificially contaminated house flies can carry the virus of poliomyelitis. Rosenau and Brues 3 and Anderson and Frost 4 allowed stable flies to bite poliomyelitis-infected monkeys first and then non-infected animals, which subsequently came down with poliomyelitis. Rosenow, South and McCormack 5 were able to produce the disease by injecting filtrates of flies collected in epidemic areas, although the disease was not transferable to other monkeys. Recently, Paul, Trask and associates 7 isolated virus from flies obtained from two widely separated areas—Connecticut and Alabama.

During the past 10 years, 20 experiments were done in this laboratory to recover poliomyelitis virus from house flies, all of which were unsuccessful. Dead flies were washed and the suspension filtered. The filtrate was injected either intracerebrally or intranasally, or both, into M. mulatta monkeys. A few experiments with filtrates of ground stable flies were also unsuccessful.

Although the disease morbidity decreases after the first frost and the fly population is minimal at the same time, and although virus might be found in or on flies during large epidemics, these facts seemed to be of slight epidemiologic importance because: (1) the virus could not be consistently recovered from these insects during either epidemic or non-epidemic years; (2) the disease did not always occur in crowded communities infested with flies, but more often in clean surroundings devoid of flies; (3) the peak of the disease and that of the greatest fly population did not correspond. 6

It was thought, nevertheless, that it should be possible to isolate the cirus from some flies, especially from those which in epidemic areas would become grossly infected. Thus, if flies were selected from areas contaminated with sewage, positive results might be obtained