Robert B. Tesh

Transovarial transmission of viruses by phlebotomine sandflies.

Vertebrate viruses isolated from phlebotomine sandflies belong to three distinct arbovirus serogroups: 1-5 vesicular stomatitis, Phlebotomus fever, and Changuinola. In addition to their antigenic dissimilarities, the physicochemical properties and morphologic characteristics of these sandfly-associated viruses are also quite different.-1° However, one feature that they share in common, in contrast to most other vertebrate arboviruses, is their apparent inability to produce a significant viremia in infected animals or man. This characteristic suggests that vertebrates may be dead-end hosts for most sandfly viruses and that a maintenance mechanism other than the classic vertebrate-insect cycle must be postulated to explain their biologic survival. Accumulating evidence indicates that insect-to-insect (transovarial) transmission is the maintenance mechanism. In the present paper, we shall examine the field and laboratory evidence in support of this hypothesis and will present new data on the transovarial transmission of vesicular stomatitis virus, Indiana serotype (VSV-Indiana), by sandflies.

Failure of rubella virus to replicate in mosquitoes.

Rubella virus failed to replicate in mosquitoes (Aedes albopictus and Culex fatigans) following parenteral inoculation. The virus demonstrated in mosquitoes tested immediately after inoculation but was not detected in insects sampled 7, 14 and 21 days postinoculation. This experiment provides further evidence that rubella is not an arbovirus, but does not invalidate its classification as a togavirus.