As a natural infection, glanders occurs only in horses, mules, and donkeys. Other animals occasionally become infected from contact with infected solipeds. The most susceptible of these occasionally infected species are ferrets, moles, field mice, cats, and dogs. Sheep, goats, hogs, rabbits, white, mice, and house mice are reported to be less susceptible, and cattle are iune (Hutyra and Marek, 1926). The guinea pig is considered to be the most susceptible laboratory animal. The virulence of various strains of Malleomyces mallei has been reported to vary widely (Bernstein and Carling, 1909; Dudgeon et al., 1918), but in the virulence tests recorded in the literature large doses were given, and evaluation of virulence was made solely on the severity of disease produced. The wild rats of southeastern Asia constitute a natural reservoir of melioidosis. The disease, chronic in the rat, is thought to be transmitted to other animals, and to man, by ingestion or inhalation of materials contaminated with rat exereta. Rabbits, dogs, and cats have been found infected naturally, and an occasional case of infection has been reported in other domestic animals. Guinea pigs, mice, and rabbits have been used in studies of the experimentally produced disease (Stanton and Fletcher, 1932). Guinea pigs were reported to be almost universally susceptible, dying of a fulminating infection within 24 hours after a massive inoculation and within 3 weeks after a smaller inoculation. Monkeys were more resistant, developing fatal infection only after ingestion of massive doses. Rabbits and guinea pigs were susceptible to inoculation by the intraperitoneal or subcutaneous routes and by ingestion and inhalation. Although the organisms were reported as highly virulent, the inoculum always contained thousands to millions of organisms (0.01 to 1 ml of a 48-hour broth culture-Stanton and Fletcher, 1932). No reference to a more quantitative evaluation of virulence by MLD or LDr0 determinations was found in the literature.
