Cultivation of Certain Viruses Using Yolk of Chick Embryo as Route of Injection

Abstract

Cox 1 recently reported the use of the yolk sac of the developing chick embryo as a medium for growing rickettsiae of Rocky Mountain spotted fever and typhus fever. Success was also attained in the cultivation of Eastern and Western strains of equine encephalomyelitis by the same worker (personal communication May 2, 1939).

This preliminary report confirms the results of Cox with the Eastern and Western strains of equine encephalomyelitis virus and in addition summarizes the results obtained with the virus of St. Louis encephalitis and 3 strains of poliomyelitis virus recovered locally.

In essentials the method employed is the same as that described by Cox. Fertile eggs were incubated at 39°C until injected and then at 37.5°C for the cultivation studies. Injections of the inoculum in doses of 0.1 to 0.5 cc were made directly into the yolk through a small opening in the air sac end of the egg which would just allow the passage of a 21 gauge needle. The opening was then closed with melted paraffin. Three to 4 eggs were used for the same inoculum in each passage and infectivity tests of the embryonic tissues, except when titrating for end point infectivity, were made from 10% ground suspensions. Intracerebral doses of 1.0 cc were given to Rhesus monkeys for testing infectivity in the experiments with poliomyelitis virus and 0.03 cc given to white mice for the other viruses. One monkey as compared with 2 to 4 mice was used for each suspension as required.

Three series of egg passages, represented by different doses of original infective mouse brain inoculum—0.1, 0.2, and 0.5 cc were maintained for each of the following viruses: Eastern equine encephalomyelitis, Western equine encephalomyelitis and St. Louis encephalitis.