11 Genitourinary System
Only three agents cause primary infections of the genitourinary tract in mice and rats. Leptospira interrogans serovar ballum, an agent that causes renal infection, has been reported on a few occasions in laboratory mice. Mycoplasma muris, an anaerobic mycoplasma, has been isolated from the vaginas of mice in a single colony. Natural infections of M. pulmonis also occur in the genital tract of female rats. LEW rats are highly susceptible to severe genital (as well as respiratory) disease due to M. pulmonis, and this is characterized by purulent endometritis or pyometra, salpingitis, and perioophoritis. Similar genital lesions attributable to M. pulmonis are rare in rats of other strains (see discussion of this agent on pp. 42-48 for references).
Leptospira interrogans serovar ballum
Leptospira interrogans serovar ballum has limited significance as a naturally occuring infection.
Although its prevalence in contemporary stocks of mice is probably low, Leptospira interrogans serovar ballum has been reported as an indigenous
infection in a few colonies of laboratory mice in the United States and Europe. Several clinical cases of leptospirosis have occurred in personnel who worked in these colonies (Alexander, 1984).
Leptospira interrogans serovar ballum is a bacterium, order Spirochaetales, family Leptospiraceae. Members of the genus Leptospira are Gram negative, motile, helicoidal rods, measuring 0.1 x 6.0-12.0 µm. They are visible by dark-field illumination and phase-contrast microscopy. Parasitic members of the genus belong to the species L. interrogans, which is subdivided into approximately 180 serovars by cross-agglutination and agglutinin-adsorption tests. L. interrogans serovar ballum is one of many that occurs naturally in wild rodents (Johnson and Faine, 1984; Alexander, 1985).
Transmission of leptospiras is in part dependent on contamination of and survival in the environment. Conditions of moisture, warmth (25°C), and neutral pH favor survival. Leptospiras are inactivated by dessication, pH below 6.2 or above 8.0, and common disinfectants (Turner, 1967).
The methods of cultivation, identification, and serologic testing for leptospiral organisms are highly specialized and usually are performed by specialty laboratories (Sulzer and Jones, undated; Turner, 1968, 1970). Specimens from human patients are usually submitted through county and state departments of public health to the Centers for Disease Control, Atlanta, Georgia. Specimens from animals can be submitted to state veterinary diagnostic laboratories or to the National Animal Disease Laboratory, Ames, Iowa.
Wild mice are considered the primary reservoir hosts of L. interrogans serovar ballum for laboratory mice and people (Yager et al., 1953; Stoenner and Maclean, 1958; Hathaway et al., 1983; Alexander, 1984). However, wild rodents are considered the most important natural hosts of leptospiral organisms in general and have been found to be infected with numerous serovars of L. interrogans. Wild rats are considered the primary reservoir hosts of L. interrogans serovar icterohemorrhagiae for humans and other species (Turner, 1967; Feigin and Anderson, 1975).
Natural infections of L. interrogans serovar ballum in colonies of laboratory mice have been reported on several occasions (Stoenner and
Maclean, 1958; Boak et al., 1960; Kappeler et al., 1961; Barkin et al., 1974; Alexander, 1984). In addition, L. interrogans serovar ballum infection has been found in pet mice on one occasion (Friedmann et al., 1973).
There are two phases of infection: the septicemic and leptospiruric phases. During the latter phase the organisms occur in the renal tubules and are shed in the urine, contaminating the bedding and food. The organisms infect new hosts through skin abrasions, the nose, the mouth, or the conjunctiva (Turner, 1967). Bites have been associated with transmission of L. interrogans serovar ballum to people in some cases (Stoenner and Maclean, 1958; Boak et al., 1960; Kappeler et al., 1961; Barkin et al., 1974).
Natural infections of L. interrogans serovar ballum in mice are subclinical (Stoenner et al., 1959).
Clinical manifestations in personnel who contracted L. interrogans serovar ballum from infected mice have included fever, chills, headache, myalgia, and orchitis (Stoenner and Maclean, 1958; Boak et al., 1960; Kappeler et al., 1961; Friedmann et al., 1973; Barkin et al., 1974).
There are no descriptions of lesions associated with L. interrogans serovar ballum infection in mice. During the leptospiruric phase the organism can be demonstrated in renal tubules by using histologic sections stained by silver impregnation methods such as Warthin-Starry (Friedmann et al., 1973).
The most common diagnostic method is serology in which the microscopic agglutination test with live antigen is used. Definitive diagnosis requires isolation and serologic identification of the organism (Alexander, 1985; Sulzer and Jones, undated). These procedures are best performed by laboratories that specialize in these methods (see above).
Cesarean-derivation and barrier-maintenance methods are thought to be effective. Stoenner et al. (1959) claimed to have eliminated L. interrogans serovar ballum from a colony of mice by feeding them a pelleted diet containing 1 kg of chlortetracycline hydrochloride per ton for 10 days. On the seventh day of treatment the mice were transferred to autoclaved cages with water bottles that had been autoclaved.
Interference with Research
L. interrogans serovar ballum infection in mice has not been shown to alter the results of experimentation. However, it represents a serious zoonosis and is unacceptable in experimental animals.
The prevalence of Mycoplasma muris in mice is unknown.
M. muris is an anaerobic mycoplasma of a previously unrecognized species that was recently isolated from the vaginas of mice in a single laboratory (McGarrity et al., 1983).
Mycoplasma muris is a bacterium, class Mollicutes, order Mycoplasmatales, family Mycoplasmataceae (sterol-requiring mycoplasmas). M. muris is a recently described, new species of mycoplasma. It is a strict anaerobe that grows only on SP-4 medium (not on standard horse serum and yeast extract medium suitable for other rodent mycoplasmas), and hydrolyzes arginine. It hemadsorbs to guinea pig erythrocytes and is serologically distinct from all other known mycoplasmas (McGarrity et al., 1983).
M. muris has been isolated only from the vagina of pregnant RIII strain mice in one laboratory. Its prevalence in other strains and populations of mice is unknown.
M. muris has not been associated with clinical disease.
No data are available.
The only method available for diagnosis currently is culturing with SP-4 medium under strict anaerobic conditions. No data are available on the use of other methods such as the mycoplasma enzyme-linked immunosorbent assay for diagnosis of this infection (McGarrity et al., 1983).
No data are available. The agent presumably can be eliminated by cesarean derivation and barrier maintenance.
Interference with Research