Ruffed Grouse Are Susceptible to Tularemia.

Abstract

The diminution in number of wild rabbits and ruffed grouse has occurred simultaneously in Minnesota during the last 4 years. Human cases of tularemia have occurred in Minnesota during the same period. The occurrence of specific agglutinins in the blood of many of the wild rabbits still remaining has been indicated by studies which we are carrying out in Hubbard County. This finding points to tularemia as the cause of the disappearance of the rabbit. The susceptibility of the ruffed grouse to tularemia has been studied, as it was felt that there was some relationship between the disappearance of grouse and the disappearance of the rabbit. At the outset of the work it was found that Parker and Spencer 1 had considered the possibility of grouse susceptibility, and produced an infection in blue grouse. They demonstrated that the rabbit tick Haemaphysalis leporis-palustris is an important carrier of tularemia, and further pointed out that this parasite is found on both rabbits and game birds. There is, therefore, a possible natural carrier of the disease between rabbits and grouse.

The grouse used in our transmission experiments were ruffed grouse (Bonasa umbellus) and were trapped wild in Hubbard County. Before inoculation they were tested for agglutinins and their blood did not agglutinate Bact. tularense antigen in dilutions of 1-10 or above.

The strain of Bact. tularense used for inoculation was obtained from a human case of tularemia originating in Hubbard County from the bite of a deer-fly. The organism was grown in pure culture on rabbit blood-cystin agar. At the beginning of this work it was inoculated into a guinea pig, which died on the 3rd day with liver and spleen studded with nodules. Material from this guinea pig was used to inoculate grouse No. 1.