EXPERIMENTAL TOXOPLASMOSIS

Effective factors in the pathogenesis of Toxoplasmagondii

Toxoplasma gondii (T. gondii) is a cosmopolitan protozoan parasite in humans and animals. It infects about 30 % of the human population worldwide and causes potentially fatal diseases in immunocompromised hosts and neonates. For this study, five English-language databases (ScienceDirect, ProQuest, Web of Science, PubMed, and Scopus) and the internet search engine Google Scholar were searched. This review was accomplished to draw a global perspective of what is known about the pathogenesis of T. gondii and various factors affecting it. Virulence and immune responses can influence the mechanisms of parasite pathogenesis and these factors are in turn influenced by other factors. In addition to the host's genetic background, the type of Toxoplasma strain, the routes of transmission of infection, the number of passages, and different phases of parasite life affect virulence. The identification of virulence factors of the parasite could provide promising insights into the pathogenesis of this parasite. The results of this study can be an incentive to conduct more intensive research to design and develop new anti-Toxoplasma agents (drugs and vaccines) to treat or prevent this infection. In addition, further studies are needed to better understand the key agents in the pathogenesis of T. gondii.

Resistance to avirulent Toxoplasma gondii in normal and vaccinated rats

Investigation of the innate resistance to infection with Toxoplasma gondii showed that the Toxoplasma-hostile factor present in rats has an important lytic effect on the parasites but is unable to prevent an infection alone. Vaccination experiments showed that innate resistance was also related to specific immunity, which appeared faster in rats than in rodents with less innate resistance. Complete resistance to toxoplasmosis was only present in rats vaccinated with live parasites. In rats vaccinated with killed parasites, avirulent parasites were able to encyst themselves almost as readily as in unvaccinated rats.

[Experimental study of the possible activity of gentian violet in preventing the transmission of toxoplasmosis due to blood transfusion]

Devido a evidências sugestivas da possibilidade de transmissão da toxoplasmose por transfusão de sangue, os autores se propuseram avaliar o papel preventivo da violeta de genciana, à semelhança do que já é estabelecido para a doença de Chagas. O experimento em camundongos revelou a ação profilática da violeta de genciana quando adicionado ao sangue a ser transfundido na concentração de 1/1000 e permanência por 48 horas na geladeira.

The course of Plasmodium berghei infection in mice latently infected with Toxoplasma gondii

The course of infection with 2 different virulent strains of Plasmodium berghei was investigated in mice latently infected with Toxoplasma gondii. When given the highly virulent ANKA strain of P. berghei all Toxoplasma-infected mice died but the survival time was prolonged. After infection with the less virulent strain K 173 mice could survive the subsequent infection. In these cases levels of parasitemia depended upon the duration of the T. gondii infection. Mice infected for about 6 weeks with T. gondii showed maximum protection.

The importance of trophozoites in transmission of toxoplasmosis: survival and pathogenity of Toxoplasma gondii trophozoites in liquid media

It has been generally assumed that Toxoplasma gondii trophozoites cannot survive long outside the body, and that toxoplasmosis is transmitted by transplacental infection, cysts and oocysts. We tested the survival and pathogenicity of separated Toxoplasma trophozoites in saline, colostrum, and solutions of albumen and serum, and the penetration of Toxoplasma trophozoites from infected secretions through mucous membranes of nose, conjunctiva, and mouth. The trophozoites survived 24 h in saline, 3 days in 3.5% serum albumen, 3 days in colostrum, and 17-43 days in serum solutions. The infectivity of the trophozoites was highest after nasal instillation, second highest after instillation into conjunctiva, and lowest after instillation into the mouth. The infective dose was calculated. The results show that Toxoplasma trophozoites survive and remain infectious for a relatively long time in biological liquid media and can easily penetrate mucous membranes, and suggest a revised hypothesis for the transmission of Toxoplasmosis with the trophozoites as one important source of infection.