Experimental Observations on the St. Louis Epidemic of Encephalitis

Abstract

Through the kindness of Dr. E. V. Cowdry and Dr. Ralph S. Muckenfuss of the School of Medicine, Washington University, we have been permitted to study brain tissue from 2 fatal cases of the recent epidemic of encephalitis in St. Louis. When received by us, these 2 brains were immediately cultured anaerobically and aerobic-ally in several different mediums to determine the presence or absence of visible microorganisms, such as the streptococcus. All cultures were entirely negative. Emulsions prepared with these 2 brains were then injected intracerebrally into a large number of different animals, including Rhesus and Cebus monkeys, rabbits, guinea pigs, kangaroo rats, white rats and mice, canaries, pigeons, ferrets, dogs, puppies, cats and kittens. None of these animals or fowls inoculated has developed any symptoms definitely characteristic of encephalitis after 47 days. On the twenty-fifth day following inoculation one of the kittens died with what appeared to be cerebral involvement, but upon autopsy, and after examination of sections of the brain, no evidence of encephalitis was demonstrable. On the twenty-seventh day one of the kangaroo rats died, but this brain was also negative. Later a pigeon died, which was negative for any suspicious lesions and on the thirty-eighth day a Cebus monkey died, the brain of which at first looked suspicious, but later it was decided that we had little, if any, evidence of encephalitis. Cultures of this brain, however, have shown a luxuriantly growing staphylococcus to be present in the tissue, though direct smears from the surface of the brain and pipettings of the brain substance are negative for this organism. This organism is regarded only as a secondary invader as we 1 , 2 have emphasized in previous work in regard to green streptococci when these organisms occur in the brains of such animals. Even with the presence of this organism in the central nervous system at death the absence of definite pathology of an encephalitis is noteworthy and confirms the interpretation placed upon its presence as a secondary invader.

That the above explanation is the true one is emphasized further by the fact that cultures from the brains of other animals dying during these experiments have been entirely negative. Furthermore, the other monkeys have had no symptoms referable to a central nervous system involvement and one Rhesus monkey, which was sacrificed 18 days following inoculation, gave negative cultures from both brain and heart blood.