In a recent communication, the writers (1) have reported upon the discovery of the virus of Mexican typhus fever in wild rats trapped in the City of Mexico. Two strains of the virus were obtained by injecting into guinea pigs, intraperitoneally, emulsions of brain material of rats trapped upon premises in which typhus fever had appeared during the epidemic which was going on at the time the work was done, that is, April, 1931. Particulars concerning this investigation are given in the paper referred to.Our own observation, as cited, taken together with the recent observations of Dyer and his coUaborators (2), definitely establish the wild rat as a reservoir of the disease and probably the most important means by which the infection is kept alive in communities during interepidemic periods. The problems which now arise are, in the first place, the exact method by which the disease is, under practical conditions, transmitted from rat to man, and, in the second place, the method of transmission from rat to rat. There is, of course, no question in our minds concerning the importance of the human louse in transmission from man to man in times of epidemic, a fact first established by Nicolle.In order to throw additional light upon the two problems stated above we began, together with our search for the virus in the rats themselves, to carry out surveys of the ectoparasites found upon the captured rats, classifying the insects, and injecting them into guinea pigs, in the hope of discovering whether any of them, and if so which ones, were of importance in connection with virus transmission. 567on May 9, 2018 jem.rupress.org Downloaded from http://doi.org/10.1084/jem.54.4.567 Published Online: 1 October, 1931 | Supp Info:
TRANSMISSION OF MEXICAN TYPtt-US VIRUSThe present paper deals particularly with the question of transmission of typhus virus from rat to rat, that is, the mechanism by which the endozoic rat disease is kept going.
Insect DistributionIn an insect survey of about 100 wild rats, the following arthropods were found: The distribution of fleas on the wild rats was very irregular, even when the rats were caught at the same time and on the same premises. Some of them harbored numerous fleas, others one or two only, and some frequently carried none at all. The same observation was made with the mites, in which a similar irregularity was observed. In regard to the rat louse (Polyplax spinulosus), there was a difference in distribution to some extent related to the species of rat. The rats were Mus rattus and Mus decumanus. Polyplax spinulosus was found on most specimens of Mus rattus, while its distribution on Mus decumanus was extraordinarily irregular. Heavily infected specimens were caught, together with specimens on which few or no lice could be found. Summarizing our insect observations, however, we may say that Polyplax spinulosus was by far the most frequent ectoparasite found on the rats.
Results of Inoculation into Guinea Pigs of Ectoparasltes DirectlyCaught on Wild Rats.--Our method consisted in examini...
