Evaluation of vertical transmission of Toxoplasma gondii in Calomys callosus model after reinfection with heterologous and virulent strain.

Toxoplasma gondii is an obligate intracellular protozoan parasite that causes a variety of clinical syndromes, but the infection is severe in immunocompromised individuals and during pregnancy due to the possibility of transplacental transmission of the parasite causing congenital toxoplasmosis. Vertical transmission of the parasite usually occurs when females are primarily infected during pregnancy. Calomys callosus is resistant to T. gondii ME49 strain, which presents a moderate virulence and congenital disease occurs only during the acute phase of infection. The aim of this study was to determine whether vertical transmission occurs when females of C. callosus chronically infected with ME49 strain of T. gondii are reinfected with a highly virulent strain (RH, type I). Females were infected with cysts of the ME49 strain. On the 1st day of pregnancy, animals were reinfected with tachyzoites of the RH strain. In the 19th day of pregnancy, placentas and embryos were processed for morphological analysis, immunohistochemistry and for detection of the parasite by PCR and mouse bioassay. Morphological and immunohistochemical analyses revealed the presence of parasites only in placental tissues. Mouse bioassay results showed seroconversion only in mice that were inoculated with placental tissues. Also, T. gondii DNA was detected only in placental samples. Congenital toxoplasmosis does not occur in C. callosus females chronically infected with the moderately virulent ME49 strain of T. gondii and reinfected with the highly virulent RH strain, thus indicating that primary T. gondii infection before pregnancy leads to an effective long-term immunity preventing transplacental transmission to the fetus.

Azithromycin inhibits vertical transmission of Toxoplasma gondii in Calomys callosus (Rodentia: Cricetidae).

Toxoplasma gondii infection during pregnancy may cause severe consequences to the embryo. Current toxoplasmosis treatment for pregnant women is based on the administration of spiramycin or a drug combination as sulphadiazine-pyrimethamine-folinic acid (SPFA) in cases of confirmed fetal infection. However, these drugs are few tolerated and present many disadvantages due to their toxic effects to the host. The aim of this study was to evaluate the effectiveness of different treatments on the vertical transmission of T. gondii, including azithromycin, Artemisia annua infusion, spiramycin and SPFA in Calomys callosus as model of congenital toxoplasmosis. C. callosus females were perorally infected with 20 cysts of T. gondii ME49 strain at the day that a vaginal plug was observed (1st day of pregnancy - dop). Treatment with azithromycin, A. annua infusion, and spiramycin started at the 4th dop, while the treatment with SPFA started at the 14th dop. Placenta and embryonic tissues were collected for morphological and immunohistochemical analyses, mouse bioassay and PCR from the 15th to 20th dop. No morphological changes were seen in the placenta and embryonic tissues from females treated with azithromycin, spiramycin and SPFA, but embryonic atrophy was observed in animals treated with A. annua infusion. Parasites were found in the placenta and fetal (brain and liver) tissues of animals treated with SPFA, A. annua infusion and spiramycin, although the number of parasites was lower than in non-treated animals. Parasites were also observed in the placenta of animals treated with azithromycin, but not in their embryos. Bioassay and PCR results confirmed the immunohistochemical data. Also, bradyzoite immunostaining was observed only in placental and fetal tissues of animals treated with SPFA. In conclusion, the treatment with azithromycin showed to be more effective, since it was capable to inhibit the vertical transmission of T. gondii in this model of congenital toxoplasmosis.

Susceptibility to vertical transmission of Toxoplasma gondii is temporally dependent on the preconceptional infection in Calomys callosus.

Toxoplasma gondii is an obligate intracellular parasite that causes a variety of clinical syndromes, but the infection is more severe in immunocompromised individuals and in cases of congenital toxoplasmosis. This study aimed to verify if the susceptibility to vertical transmission of Toxoplasma gondii is temporally dependent on the preconceptional infection in Calomys callosus. Twelve C. callosus females were infected with 20 cysts of T. gondii ME49 strain and divided into three groups of four animals that were mated after approximately 10 days (group 1), 30 days (group 2), and 50 days (group 3) of infection. The animals were sacrificed from the 17th to 20th day of pregnancy, when placentas and embryos were collected for morphological and immunohistochemical studies, mouse bioassay for evaluating seroconversion and PCR for detecting parasite DNA. Serum samples from C. callosus females and mice used in bioassay were analysed for the detection of IgG antibodies to T. gondii by ELISA. Detection of T. gondii was observed by mouse bioassay and PCR in placentas and embryos from C. callosus females infected around 10 days pre-conception. However, only placentas, but not embryos, from females infected around 30 and 50 days pre-conception showed positivity for parasite DNA and seroconversion by mouse bioassay. In conclusion, this study model shows that vertical transmission of T. gondii may take place when maternal infection occurs within one month before conception, thus demonstrating the time of preconceptional seroconversion that rule out a risk of congenital toxoplasmosis.