Models of mycoplasma respiratory and genital tract infections.

Animal models for the study of human diseases must be replaced by in vitro methods, whenever possible. However, when critically evaluated, they remain indispensable for the solution of some specific problems in infectious diseases. These include the pathogenesis, the host response, as well as the study of antimicrobial agents and vaccines. Under these conditions animal models, which closely reflect the situation in man, are especially valuable. Two models may serve as "ideal" examples for the study of human diseases: firstly mouse typhoid for the study of systemic infections with Salmonella typhimurium. This model has been employed for many decades to examine various aspects of human typhoid fever. A second model is the experimental infection of hamsters with Mycoplasma pneumoniae as a model of local infection in the respiratory tract. Mycoplasma and ureaplasma infections of man are frequent, but rarely life threatening. Chick embryos, rats, hamsters, guinea pigs, and monkeys (rhesus monkeys and chimpanzees) are susceptible to experimental infection with M. pneumoniae. Some mouse strains are also colonized with M. pneumoniae after intranasal inoculation, but histopathological alterations similar to the hamster model have not been established in a reproducible way in mice. Hamsters have, therefore, been important for the evaluation of antibiotics and vaccines. Local immunity in the respiratory tract, the possible contribution of the immune response to disease pathogenesis, persistence of the organisms in the respiratory tract after clinical symptoms are cured by antibiotic therapy, and the role of cytokines in protection or disease pathogenesis remain interesting areas for future research, which could be addressed in animal models. The evaluation of the role of mycoplasmas and ureaplasmas in genital tract infections is by far more complex and even more difficult in AIDS and rheumatoid arthritis, because several species of mycoplasmas and Ureaplasma urealyticum can be isolated from a large proportion of healthy individuals. Furthermore, good models for the study of these infections are not available.