# Toxoplasmosis in Sheep Caused by Toxoplasma gondii Clonal Type I

## TL;DR

This study reports the first isolation of a Toxoplasma gondii Type I strain from sheep in China, which was found to be non-lethal in mice.

## Contribution

The first isolation and characterization of a viable T. gondii Type I strain from sheep with avirulence in mice.

## Key findings

- A T. gondii Type I strain (TgSheepCHn15) was isolated from sheep tissues in China.
- The isolated strain was avirulent in Swiss mice, with a survival time of 97 ± 31 days.
- The overall T. gondii prevalence in sheep was 16.4% based on PCR testing.

## Abstract

Toxoplasma gondii infects many warm-blooded animals, including sheep. Humans can be infected with T. gondii by consuming undercooked sheep tissues containing cysts. Type II (ToxoDB #3 or #1) and Type III (ToxoDB #2) varieties are the epidemic genotypes of viable T. gondii strains in sheep. Until now, no viable T. gondii Type I (ToxoDB #10) strain has been found in sheep tissues. Type I is usually associated with the highly virulent strain in mice. A viable T. gondii strain (TgSheepCHn15), ToxoDB #10, was isolated from the tissues of sheep at a veterinary clinic. This is the first report of a viable T. gondii clonal type I genotype that correlates with avirulence in mice.

Ovine toxoplasmosis has a significant negative impact on sheep farming, and abortion is the main clinical manifestation. The objective of the present study was to survey ovine toxoplasmosis and assess its potential harm T. gondii in sheep. Sheep serum or heart fluid was collected from 1035 sheep, along with the tissue or blood samples collected from 164 of them. We investigated ovine toxoplasmosis by a modified agglutination test (MAT) (n = 1035 sheep) and by a polymerase chain reaction (PCR) (n = 164 sheep) in China. The results showed that 75 sheep were seropositive (titer ≥ 1:100), with a prevalence of 7.2%, as assessed by MAT. The molecular prevalence of T. gondii in sheep was 16.4% (27/164), as assessed by PCR. From these 164 tissue or blood samples, 22 tissues and 2 blood samples were selected in order to isolate T. gondii by mouse bioassay. A viable T. gondii strain (TgSheepCHn15, ToxoDB #10) was isolated from sheep tissues in the veterinary clinic. This strain was avirulent for Swiss mice, and the survival time of mice was 97 ± 31 days. This is the first instance of the isolation of a Type I strain from sheep with avirulence in mice. The prevalence of T. gondii has been decreasing in sheep from China. However, T. gondii remains present in sheep herds and should not be ignored.