Vol. 38 Epidemiology of Colorado Tick Fever * LLOYD FLORIO, M.D., DR.P.H., F.A.P.H.A., AND MABEL STEWART MILLER Department of Public Health and Laboratory Diagnosis, University of Colorado Medical Center, Denver, Colo. A LL available evidence indicates that the transmitting agent for Colorado tick fever is the wood tick, Dermacentor andersoni Stiles.1-3 How- ever, the causative agent has never been isolated from ticks in nature. There are several areas in the mountains near Denver where a number of individuals probably become infected each year. These areas were " flagged" and ticks obtained. These ticks were divided into ten pools of approximately 25 each and then ground in small amounts of normal saline. The supernatant from the cen- trifuged specimens was injected in equal amounts into each of two hamsters. White blood cell counts and spleen studies were done on these animaL] and the succeeding carries according to technics previously established.3' Nine of the ten pools thus studied revealed the presence of Colorado tick fever virus on the basis of white blood cell counts and spleen studies. Neutraliza- tion tests were conclusive in five of the nine pools. The other four were not tested. Virus was demonstrated in the ticks from each of the three separate areas " flagged." The finding that some ticks in nature were infected with the virus of Colorado tick fever led to a study of laboratory infection of the ticks. Two strains of * Presented before the Epidemiology Section of the American Public ltealth Association, at the Seventy- fifth Annual Meeting in Atlantic City, N. J., October 10, 1947. virus were used. One was a long established laboratory strain that had undergone a great many hamster and some human passages. Results with this strain were inconsistent and incon- clusive. The other strain had had only several hamster passages. Clean adult male and female ticks were allowed to feed on infected hamsters. The fully engorged females were permitted to lay. The resultant larvae were divided roughly into equal parts. One portion was ground and in- jected into a number of. clean animals. The remainder were allowed to feed on clean hamsters. In both instances, the leucocyte count indicated infection. Some of the engorged larvae were also ground and injected into clean ani- mals. The resultant nymphs, engorged nymphs, and adults were handled in the same manner as the larvae. In each instance the hamsters showed infection with Colorado tick fever. The virus could never be demon- strated in the eggs from infected fe- males despite the fact that in the three different attempts that were made, the resultant larvae, nymphs, and adults were found to be infected. Clean larvae were allowed to feed on infected hamsters. In each instance the resultant engorged larvae, nymphs, NOTE: This work was aided by grants from James J. Waring, M.D. and the Lederle Lab- -oratories Division of the American Cyanamid Company. [2t 11
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Related Documents
