Experiments on the Conversion of Typhus Strains

Abstract

Two types of strains of typhus virus are observed in Mexico: first the murine type which is obtained from wild rats in nature, from isolated endemic cases, and from cases during short epidemic outbreaks, and second, the epidemic type of strains which is obtained from long standing serious epidemics. Some of these epidemic strains correspond entirely to strains of historic Old World typhus. Other strains which in their experimental behavior are intermediate between these two types of strains were isolated from the same epidemic. A method is described by which these epidemic non-orchitic strains can be converted into murine strains regularly causing scrotal lesion in guinea pigs and a highly fatal disease in rats. The same results were obtained with an Old World strain of epidemic typhus. The method, which consists of daily blood injections into intraperitoneally inoculated rats, is based on the observation that Rickettsia prowazeki multiplies only within cells which come in constant or frequent contact with fresh blood. It is concluded from our experiments that there does not exist any real difference between the virus of historic Old World typhus and the murine New World typhus. Both are considered to be of murine origin. The murine strains represent the original form of the virus of typhus, whereas the epidemic strains are the result of a prolonged propagation in the cycle man-louse-man.

The in Vitro Cultivation of the Rickettsial Agent of Trench Fever

“…The photomicrographs of R. quintana grown in liquid medium by Pshenichnov et al, however, show the tight clusters of micro-organisms noted by Vinson & Fuller (1961) within cells cultivated in vitro and in colonies examined by Ito & Vinson (1965) During studies on the propagation of R. quintana in cell culture (Vinson & Fuller, 1961) The favourable influence of blood on the multiplication of other rickettsiae has been noted by several authors. Mooser, Varela & Pilz (1934) achieved heavy growth of R. prowazekii in the peritoneal cells of the rat by the daily intraperitoneal injection of guinea-pig blood. These authors stated that " R. prowazekii is able to develop in the mammal as well as in the insect only within those cells which come into constant contact with fresh blood".…”

Bacterial Type Transformation

“…is now known that type transformation can be induced artificially among pneumococci (Griffith 1928, Reimann 1929). It may occur spontaneously, as appears to be the case concerning murine and epidemic typhus (Mooser, 1934) and the rabbit papilloma virus of Andrewes and Shope (1936). Among most species of bacteria, type transformation is difficult to detect on culture media without laborious study since the separate types are seldom distinguishable by differences in colony structure or color.…”