Electron Micrographs of Erythrocytes from Swiss Albino Mice Infected with Semliki Forest Virus

Abstract

The Semliki Forest virus (6th passage MBB26146 in serum M494744958) (Public Health permit) was obtained from Dr. K. C. Smithburn of the Rockefeller Foundation Laboratories in New York. According to Rivers (1952) this virus was isolated by Smithbur and Haddow from Aedis abnormals mosquitoes found in Uganda. A viremia and encephalitis is produced in mice when inoculated with this virus by various routes. Guinea pigs, rabbits, rhesus and red tail monkeys develop the disease only after intracerebral inoculation. Chick embryos can be used to propagate Semliki Forest virus. Neutralization antibodies have been found in humans, but the virus itself has not been isolated from them (Rivers et al). EXPERIMENTAL METHODS AND RESULTS Lyophilized mouse brain of the 6th intracerebral mouse passage was diluted to a 10 percent suspension with sterile distilled water. Each of ten 3-week-old Swiss albino mice was inoculated intracerebrally with 0.03 cc of this suspension. On the 3rd day after inoculation the mice showed symptoms of central nervous system involvement. When symptoms appeared, the mice were sacrificed, and the brains were removed aseptically, pooled, ground, and diluted to a 10 percent suspension. This suspension was injected intracerebrally into 4 unvaccinated mice and into 4 mice which previously had been immunized intramuscularly with a higher dilution of Semliki Forest virus. After 4 days the unvaccinated mice showed symptoms of central nervous system involvement; while the immunized group showed no nervous symptoms. This confirmed the virus suspension to contain Semliki Forest virus, and for the present experiment, this was used as the inoculum which titrated 10-6 intracerebrally in Swiss albino mice. The present experiment was conducted in the following manner: Thirty 21day-old, healthy Swiss albino mice, (Webster and Dawson, 1935) were divided into 2 groups of 15 animals each. One group was designated as the control group and the other as the test group. One-tenth cc of a 10 percent suspension of the above described inoculum was injected intramuscularly into each of the 15 Swiss albino mice in the test group. Animals of the control group were inoculated intramuscularly with 0.1 cc of a 10 percent brain suspension prepared from normal Swiss albino mice of the same strain and age as previously mentioned. The animals of each group were further divided into 5 groups of 3 animals each. Three animals from the test group and 3 animals from the control group were bled from the heart 24 hours post inoculation. Approximately 0.06 cc of blood was drawn from each animal. The blood taken from 3 animals in the test group was pooled and added to 1 cc of normal physiological saline. The blood from the 3 animals of the control group was treated in the same manner. The cell