Department of Animal Health and Biomedical Sciences, and Institute for Environmental Studies and School of Veterinary Medicine, University of Wisconsin, Virology Division, U.S. Army Medical Research Institute of Infectious Diseases, Fort Detrick, Madison, Wisconsin
The transplacental transmission of La Crosse virus (LACV) was evaluated in domestic rabbits (Oryctolagus cuniculus) and Mongolian gerbils (Meriones unguiculatis) as a potential mechanism for the maintenance of the virus. Rabbits were infected with LACV at different times of gestation by injection of viral suspensions or by exposure to LACV transovarially (TO) infected Aedes triseriatus. Pregnant gerbils were exposed between 16–24 days of gestation to LACV TO- infected Ae. triseriatus. Our results indicate that LACV can infect gerbils in utero. The LACV was isolated from the brain of suckling gerbils that died 3–5 days after birth from LACV-exposed mothers, representing the first evidence of LACV transplacental transmission. Microgliosis was found histologically in the cerebral cortex. In addition, LACV infection of both pregnant gerbils and rabbits resulted in in utero and neonatal mortality. La Crosse virus was not detected in surviving young of infected rabbits even after immunosuppression by administration of cyclophosphamide. Thus, there was no evidence of persistent infection of rabbits following in utero exposure. Surprisingly, some of the infected pregnant gerbils developed progressive paralysis 9–14-days postexposure, and LACV was isolated from the brains of these animals. Histopathologic studies of these tissue samples showed acute meningoencephalitis. The effects of natural LACV infection should be studied in pregnant amplifying hosts, such as chipmunks and squirrels, and in pregnant women.