Toxoplasma gondii infection in impala (Aepyceros melampus) from the Timbavati abattoir

Abstract

Toxoplasma gondii (T. gondii) is a protozoon parasite with a worldwide distribution that infects mainly domestic and wild felids, with virtually all mammal and avian species acting as intermediate hosts. Clinical manifestation known as toxoplasmosis causes encephalitis as well as infertility, abortion or the birth of offspring with central nervous system abnormalities. The feline definitive host ingests the parasite when consuming intermediate hosts with tissue cysts containing T. gondii bradyzoites. Considering the possible presence of the parasite in production and wildlife species, the consumption of undercooked game meat by people, should be regulated because of the potential risk of T. gondii transmission to humans.

In this study the prevalence of infection and the tissue cyst predilection sites was determined through serological and molecular assays performed on impala antelope (Aepyceros melampus) samples collected from the Timbavati abattoir, located within the Timbavati Private Nature Reserve (TPNR), on the western boundary of the Kruger National Park (KNP). Impala samples (n = 138) were collected within the TPNR over six months. Serum was used in two serological assays, the Modified Agglutination Test (MAT) and the Latex Agglutination Test (LAT), for assessing the seroprevalence. An optimised in-house sodium acetate method was used to extract DNA from the triceps brachii, cardiac muscle, tongue, diaphragm, spleen, liver, and brain samples, followed by quantitative polymerase chain reaction (qPCR) to amplify an 81-bp fragment of the Repeat element 529-bp sequence to confirm the presence of T. gondii DNA. Due to the limited research on T. gondii in wildlife species in Africa, in terms of both clinical significance and the interface between humans and wildlife in the rural setting, the main focus of the current study was to determine whether the rural communities in and around the Mnisi area are at risk of contracting T. gondii by consuming game meat, and to determine if specific organs/tissues were more prone to containing T. gondii cysts than others. Based on a seroprevalence of 8.70% (MAT) and

13.77% (LAT) in impala in the Mnisi area, the risk of infection via environmental (faecal) contamination is quite low, but still noteworthy. In both assays the two strong positive impala individuals were F18 and F29. When comparing the results between MAT and LAT using the McNemar’s test and Kappa statistics, the LAT yielded a higher seroprevalence, alluding to the possibility of it being the less specific test of the two, however the MAT is more subjective in terms of interpretation of the results. When evaluating the presence of T. gondii DNA using qPCR, 7.25% of individual impala contained T. gondii DNA in at least one of the seven tissues that were sampled, and of these the only samples to have Ct values consistently below 35 were F18 (brain) and F29 (tongue). The presence of DNA within specific tissues (tongue, heart, brain, triceps brachii, and diaphragm) correlates directly with the risk of infection via ingestion of tissue cysts. Undercooked game meat is often sold to nature reserves as biltong or carpaccio, but is most often consumed locally by the population around Timbavati. A lack of resources in the rural community often leads to ingestion of raw or undercooked game meat, and therefore poses a significant risk of contracting toxoplasmosis. Since treatment of T. gondii using drugs such as sulphadiazine, pyrimethamine, clindamycin, or toltrazuril is challenging in people, a better understanding of the prevalence of this parasite within the wildlife population can lead to advances in prevention of disease in and around the Mnisi community. Furthermore, investigating the different strains of T. gondii circulating in wildlife species might shed some light on its genetic diversity within the South African population, and will also help to assess the clinical importance of this disease.