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The Behavior of Murray Valley Encephalitis Virus in Culex Tritaeniorhynchus Giles and Culex Pipiens Quinquefasciatus Say^*

Robert M. Altman

Studies were conducted with Culex tritaeniorhynchus and Culex pipiens quinquefasciatus to ascertain the behavior of Murray Valley encephalitis virus in these two species of mosquitoes and to determine if they could transmit this virus. Virus multiplication was demonstrated in both species of mosquitoes following ingestion of blood from viremic chicks. The multiplication of virus in mosquitoes followed an "eclipse" period during which it could not be detected. The rate of multiplication was similar in both species and the virus increased to approximately the same titer in each, although a higher percentage of C. tritaeniorhynchus became infected.

Specimens of both species of mosquito could transmit the virus after being held for extended periods of time which indicated the possibility that, once infected, they were capable of transmitting the virus for the duration of their lives. Serial transmission was obtained with C. tritaeniorhynchus after short periods of time and by both species after long periods of time.

Transmission experiments by individual feedings of the two species of mosquitoes were conducted. For more precise comparison of the two species they were infected simultaneously, whenever practical, by feeding them on viremic chicks. A total of 317 transmission attempts was made with C. tritaeniorhynchus of which 111 were positive. The mosquitoes were infected by feeding on donor chicks with viremia levels ranging from less than 1.0 log to more than 5.5 logs. The transmission attempts were made following extrinsic incubation periods ranging from 6 to 79 days.

A total of 351 transmission attempts was made with C. pipiens quinquefasciatus; 56 were positive. The mosquitoes were infected by feeding on donor chicks with viremia levels ranging from less than 1.0 log to more than 5.5 logs. The transmission attempts were made following extrinsic incubation periods ranging from 6 to 62 days. C. tritaeniorhynchus was a much better laboratory vector especially when the combined effects of dosage of virus and various periods of extrinsic incubation are considered.

Two experiments were conducted to determine if Japanese B encephalitis virus could interfere with the transmission of Murray Valley encephalitis virus by C. tritaeniorhynchus infected sequentially. The results are interpreted as having yielded evidence of viral interference.

^* Part of a thesis submitted to the Faculty of the Graduate School of the University of Maryland in partial fulfillment of the requirements for the degree of Doctor of Philosophy in 1961. Scientific Article No. A1003, Contribution No. 3391 of the Maryland Agricultural Experiment Station, Department of Entomology.

This work was conducted at the Department of Entomology, Walter Reed Army Institute of Research, Washington, D. C.

Present address: U. S. Department of Agriculture, P. O. Box 3391, Orlando, Florida.