Aedes albopictus adult female mosquitoes, transovarially infected with San Angelo (SA) virus, were examined by fluorescent antibody technique during various stages of ovarian development to determine how the virus enters the egg. Upon emergence from the pupal stage, viral antigen was observed only in the oviduct and ovariole sheath. By the 4th day of adulthood, it was visible in the follicular epithelium, oocytes and nurse cells of the primary follicles. In the 72-hour period between the ingestion of blood and oviposition, there was a marked increase in the amount of viral antigen in the oocyte, indicating rapid virus accumulation. After oviposition, SA viral antigen was also seen in the secondary ovarian follicles. The observed sequence of infection of the mosquito ovariole with SA virus is analogous to that described with certain endosymbionts of insects.
Present address: Yale Arbovirus Research Unit, Department of Epidemiology and Public Health, Yale University School of Medicine, 60 College Street, New Haven, Connecticut 06510.