Tissue Cultures as a More Sensitive Method Than Animal Inoculation for Detecting Equine Encephalomyelitis Virus

Abstract

Cultures consisting of minced chick embryo tissue suspended in Tyrode's solution 1 have been found favorable for the growth of equine encephalomyelitis virus. If it can be shown that cultures are equally or even more effective for revealing minimal quantities of virus in a material, or that cultures can bring to light the presence of virus when animal inoculation fails, a useful method will be available. Equally important is the fact that in a single test inoculum, a larger amount can be introduced into a culture than in an animal, since by intracerebral inoculation∗ a guinea pig can receive with safety a limiting quantity of only 0.2 cc., and a mouse 0.05 cc.

A comparison was therefore made of the relative sensitivity of cultures and of intracerebral inoculation of mice and guinea pigs for detection of the virus.

In Experiment 1, shown in Table I, a single disc Seitz filtrate of a 10% broth suspension of infected mouse brain tissue was diluted decimally to 10^-8 dilution. Each of 4 mice received an intracerebral injection of 0.05 cc. from each dilution and a like number of cultures were inoculated with the same quantity. After 72 hours'incubation at 37°C. each culture was tested for the presence of active virus by intracerebral injection of mice with 0.05 cc. of the centrifuged supernatant fluid. Active virus was detected up through 10^-5 dilution of the Seitz filtrate by animal test, and in 10^-6 dilution by inoculation of tissue cultures.

In Experiments 1 and 3 (Table I) the cultures revealed virus in dilutions tenfold greater than the limiting dilutions active by direct intracerebral injection of animals.