Studies on Medical and Veterinary Students Skin Tested for Toxoplasmosis

Abstract

MORE THAN 25 years have passed since Toxoplas8m gondii was first established as causing clinical disease in man (1). Nearly every discipline that deals with the health of man and animals has conducted research on toxoplasmosis. The number of articles published in the world literature increases each year, and thus keeping abreast of new developments has become increasingly difficult. However, several publications review recent advances in toxoplasma research (2,5). The success of this ubiquitous parasite is exemplified by (a) its dubious role as a protozoan parasite-the fact that it is not host-specific; (b) its wide distribution in nature, both zoologically and geographically; (c) its ability to parasitize nearly every body cell type with the possible exception of nonnucleated red blood cells, thus causing protean clinical manifestations in man and animals; (d) the inability to define completely its true life cycle; and, (e) the lack of success in establishing definitive proof of the modes of transmission in man, with the exception of the congenital route. Toxoplasma is an obligate intracellular parasite. In addition to reproduction by longitudinal binary fission (6, 7), recent studies have described two additional methods. Goldman and co-workers (8) have described the process of internal budding which they call endodyogeny (meaning birth of two from within). Gavin and co-workers (9) have described a third method whereby at least four progenies are delineated within a rosette-shaped multinucleated toxoplasma cell, following which they eventually separate to become individual parasites. Morphologically and immunologically, the toxoplasma organisms found in various hosts are considered to be of the same species, the main difference being in the virulence of the strain of organism -for different animal species (10). In general, the young of animal species are more severely affected than the old. Infection appears to be the rule; disease the exception. Toxoplasma occurs in two forms, the crescentshaped free proliferative form (fig. 1) and the cyst form (fig. 2). Presently, the modes of transmission must be considered in light of knowledge of these two forms. The proliferative form is considered to be sensitive to changes in osmotic pressure, to drying, and to exposure to artificial gastric juices. This form apparently dies rapidly once it leaves the animal host. The cyst form appears to be more resistant and is considered by maniy to play a All the authors are with the Institute of Agricultural Medicine, State University of Iowa College of Medicine, Iowa City. Dr. McCulloch is assistant professor and public health veterinarian; Mr. Braun is medical field epidemiologist; Mr. Heggen is statistician; and Dr. Top is professor and head of the department of hygiene and preventive medicine and director of the institute. The paper was presented at the Midwest Interprofessional Seminar held at Iowa State University, Ames, on September 16-17, 1962. The study was supported in part by Public Health Service Grant E-3023, National Institute of Allergy and Infectious Diseases.