Abstract
Toxoplasma gondii is an important cause of reproductive failure in small ruminants that also poses a risk to consumers who consume undercooked meat. However, little is known about sheep toxoplasmosis in China for the world. Therefore, this study was conducted to assess the prevalence of T. gondii infection in sheep from China, to isolate T. gondii via bioassay in mice and to evaluate the virulence of the isolated T. gondii based on vero cell invasion and mice. A total of 840 samples (304 unfrozen hearts and 536 sera) from sheep in China were collected from 2014 to 2016. Heart samples (n = 36) of T. gondii seropositive sheep (MAT, ≥25) were bioassayed in mice individually. DNA derived from cell cultured tachyzoites of the isolated T. gondii was characterized by PCR-RFLP of 10 loci (SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and Apico). The virulence of the T. gondii was evaluated based on the mortality and encystation in mice, as well as their growth characteristics in cell culture. Antibodies to T. gondii were found in 174 of 840 (20.71%, 304 hearts juice and 536 sera) sheep by the modified agglutination test (cut-off 1:25). Viable T. gondii was isolated from the hearts of two of 36 seropositive sheep hearts. Both genotypes of the sheep heart isolates were ToxoDB#9. The virulence of the two ToxoDB#9 isolations varied significantly. To the best of our knowledge, this is the first report of isolation of ToxoDB#9 strain of T. gondii from sheep in China.
Highlights
The parasite Toxoplasma gondii is a major cause of reproductive failure in small ruminants, including sheep
Seropositivity rates varied with respect to source of sheep
Female sheep (18.64%, 74/397) shows a tendency to be more susceptible to T. gondii than male sheep (15.20%, 19/125), but this difference was not significant
Summary
The parasite Toxoplasma gondii is a major cause of reproductive failure in small ruminants, including sheep. Veterinary Investigation Diagnosis Analysis data from 2014 showed that about 25% of ovine production problems were caused by T. gondii (www.gov.uk/government/ statistics). Viable T. gondii has been isolated from goat meat, milk and cheese (Dubey et al, 2014a,b). T. gondii infection is widespread among humans. The prevalence of T. gondii is higher in Latin America than in North America and East Asia (Dubey, 2010); the cause of this difference is not known. T. gondii cause lymphadenopathy, Abbreviations: MAT, modified agglutination test; DPI, days post-inoculation; PCR, polymerase chain reaction; ROP, rhoptry protein; GRA, dense granule
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