XIII. Transmission of plague by feeding rats with infected material

Extract

1. It is possible to infect wild rats of Bombay with plague by feeding them with the viscera of dead plague rats, 21·4% being susceptible to this method of infection. Bombay rats show a greater immunity to infection by feeding than rats of the same species, which have not been subjected to a plague epizootic.

A series of experiments were also done with Mus rattus caught in the Punjab. Of these rats 67·8% were susceptible. In this series a considerably larger dose of infected material was given.

We have infected a large number (38%) of wild Bombay rats by feeding them on the whole carcases of their plague-infected comrades. No difference as regards the post-mortem appearances or the distribution of the primary bubo was found between rats infected in this way and rats infected by feeding on soft viscera.

2. The general pathological lesions found in all rats infected by feeding are, in the main, the same as those found in rats naturally infected. There are, however, two striking differences:—

(a) The distribution of the primary bubo is different. The common site in naturally infected plague rats is in the neck, no mesenteric bubo having been seen out of 5000 post-mortems. In the case of fed rats the common site is the mesentery.

(b) In the case of naturally infected rats the stomach and intestines show no marked pathological change. In the case of fed rats well marked pathological lesions are found in the intestines.

3. It would appear that in nature intestinal infection rarely or never takes place, and that in consequence rats do not become infected by eating the carcases of their comrades.

4. A large series of rats were fed on the urine of plague cases. None of these contracted the disease.