[Transovarial transmission of arboviruses by mosquitoes (author's transl)]

An important aspect of the epidemiology of arboviruses is the manner in which the viruses are maintained during winter, dry season, or other adverse environmental periods when their arthropod hosts are inactive. One possibility is that the viruses survive in arthropods. In the case of mosquito-borne viruses, it is probable that such viruses could be maintained in this manner only if they were transmitted from one insect generation to the next by transovarial transmission. Such transmission was reported in 1905 by Marchoux and Simond for yellow fever virus in Aedes aegypti. Other workers were unable to confirm this observation and, until very recently, it was believed to be in error. Interest in transovarial transmission of viruses by mosquitoes was reawakened with the recovery of La Crosse virus from field-collected larvae of Aedes triseriatus in 1972. Among bunyaviruses, transovarial transmission has been observed mainly among the California serogroup viruses in Aedes mosquitoes. Among flaviviruses, transovarial transmission has been demonstrated experimentally for the viruses of principal interest to man, namely, yellow fever, dengue, japanese encephalitis, and St-Louis encephalitis. Thus far, the only field evidence of transovarial transmission of flaviviruses is the isolation of yellow fever virus from Aedes furcifei/taylori males captured in nature in 1977. At present there is not conclusive evidence that transovarial transmission of alphaviruses occurs in mosquitoes. Among rhabdoviruses, transovarial transmission of vesicular stomatitis virus has been demonstrated experimentally at a relatively high rate in phlebotominae flies. Many factors are known to affect the experimental transovarial transmission of viruses. The significance of such transmission in nature can only be assessed by field studies.