Congenital Toxoplasmosis in Chronically Infected and Subsequently Challenged Ewes

Abstract

This experiment studied congenital transmission in sheep experimentally infected with oocysts of Toxoplasma gondii and reinfected at one of three stages of pregnancy. Twenty ewes were experimentally infected with T. gondii strain ME49 (day 0). After the T. gondii infection became chronic (IFAT≤512), the ewes were allocated with rams for coverage. After the diagnosis of pregnancy, these ewes were allocated into four experimental groups (n = 5): I-reinfected with T. gondii on the 40th day of gestation (DG); II-reinfected on DG 80; III-reinfected on DG 120; and IV-saline solution on DG 120 (not reinfected). Five ewes (IFAT<64) were kept as negative controls (uninfected, group V), therefore in groups I-III were infected prior to pregnancy and re-infected during pregnancy, group IV was only infected prior to pregnancy, and group V was not infected. Parasitism by T. gondii was investigated (histopathology, immunohistochemistry, mouse bioassay and PCR) in mothers and lambs tissue. All ewes produced lambs serologically positive for T. gondii. The results of the mouse bioassay, immunohistochemistry and PCR assays revealed the presence of T. gondii in all 20 sheep and their lambs. The congenital transmission of T. gondii was associated with fetal loss and abnormalities in persistently infected sheep and in ewes infected and subsequently reinfected by this protozoan. Therefore, congenital T. gondii infection was common when ewes were chronically infected prior to pregnancy, with or without reinfection during at various stages of gestation.

Ocorrência de anticorpos anti-Toxoplasma gondii e anti-Neospora caninum em ovinos com distúrbios reprodutivos e fatores de risco

“…Notou-se fator de proteção quanto a repetição de estro e animais soropositivos a T. gondii, provavelmente devido desenvolvimento de imunidade duradoura e protetora para re-infecções, após a fase aguda, tornando rara a repetição de quadros de distúrbios reprodutivos (Beverley & Watson 1971, Dubey & Kirkbride 1989. Santos et al (2016), em ovelhas Santa Inês primo-infectadas experimentalmente antes da prenhez e durante diferentes estágios gestacionais, apesar de nenhum caso de aborto, observaram distúrbios em cordeiros como; alterações locomotoras, malformações, natimortalidade e debilidade, indicando que nem sempre ocorra proteção do feto contra T. gondii nas reinfecções.…”

Modeling the Ruminant Placenta-Pathogen Interactions in Apicomplexan Parasites: Current and Future Perspectives

“…Endogenous transplacental transmission of the parasite has also been described in goats ( 38 ). Recent descriptions from Brazil seem to corroborate the relevance of this route of transmission associated to certain breeds or T. gondii strains or genotypes ( 39 , 40 ).…”

Congenital Transmission of Toxoplasma gondii After Experimental Reinfection With Brazilian Typical Strains in Chronically Infected Sheep

“…In our experiment, we estimated that at the time of reinfection the sheep were at a stage where vertical transmission would have a high chance of causing abortion. A study using laboratory reference strains (ME49 and VEG) for experimental infection and reinfection at various gestation stages of Santa Inês sheep reported a high occurrence of congenital transmission and clinical signs in fetuses (12). Evaluating transmission at different time points (40, 80, and 120 days), no abortions were reported in the study, and only one macerated fetus (from the group reinfected at 120 days of gestation) and one mummified fetus (from the group reinfected at 40 days of gestation) were found of the 25 lambs obtained.…”

“…Studies based on the molecular diagnosis of T. gondii , without its isolation, have suggested that primary infection fails to provide protection against subsequent infections, resulting in a risk of vertical transmission in chronically infected animals (6, 9–11). In Brazil, studies have also indicated that experimental congenital transmission of T. gondii commonly occurs during various stages of gestation in chronically infected sheep (12), but these studies did not identify the strain genotype responsible for infection.…”