Experimental Results on Possible Arthropod Transmission of Toxoplasmosis

Abstract

The most commonly recognized manifestation of toxoplasmosis in humans is a severe disease of the central nervous system in newborn infants. Neonatal toxoplasmosis is definitely of congenital origin; yet the mother shows no history of illness preceding delivery. Thus, in adults, Toxoplasma infection may be entirely asymptomatic, and the occurrence of the disease in infants is due to the unfortunate circumstance that the mother acquires the infection during the gestation period. On the basis of survey data, it appears that Toxoplasma infection is widespread in man (Feldman and Sabin, 1949) and animals (Jacobs, Melton, and Jones, 1952). The mode of transmission, however, is still a matter of conjecture. The organism, in the stage in which we know it, is not resistant to environmental conditions outside the host, and there is little evidence that the contaminative method could serve for its spread. Transmission by bloodsucking arthropods has been postulated by several investigators, and a few experimental attempts have been made to test various arthropods as vectors. References to the pertinent literature are included in the bibliographies of Weyer (1951), Piekarski (1950), Blanc, Bruneau, and Chabaud (1950), and Jacobs (1953). This article summarizes the results of an extensive series of experiments which were made to test a number of arthropods (17 species) as possible vectors of Toxoplasma gondii. As donors in attempts to infect arthropods, rabbits, guinea pigs, chicks, and pigeons were used. These animals were infected by intraperitoneal or intradermal inoculation with the RH strain of Toxoplasma. This strain of the parasite was isolated by Sabin (1941) from a fatal human case and has since been carried in mice; it is highly virulent for all of the animals used, except chicks. Assurance that the donors actually carried the infection is given by the fact that all rabbits and guinea pigs died within the expected period following inoculation; acute infections in rabbits have been demonstrated always to result in a high parasitemia. The same has been found true of acute infections in birds (Jacobs and Jones, 1950). The chicks and pigeons that did not die were shown to have an infection by inoculation of their blood into mice.