Seroprevalence and molecular epidemiology of Toxoplasma gondii in the Western Cape of South Africa

[摘要] ENGLISH SUMMARY: Toxoplasmosis is a disease caused by the obligate intracellular parasite Toxoplasmagondii and is one of the most widely occurring infections known to man, causing diseasein almost all mammals and warm-blooded birds. Toxoplasma gondii is an opportunisticpathogen, taking advantage of weakened immune systems to cause disease. The diseasetoxoplasmosis is known to occur in both active and latent or chronic forms. The latent orchronic form of toxoplasmosis is known to be the most common latent infection in man.Currently, the effects of the latent or chronic form of toxoplasmosis is neither properlystudied nor understood.In Africa, there is currently no systematic monitoring or reporting of toxoplasmosisincidence or T. gondii prevalence and this leaves health systems at a disadvantage. TheUnited States Centre for disease Control and Prevention (CDC) currently classifytoxoplasmosis as a neglected tropical infection.In this series of research projects, the seroprevalence of T. gondii antibodies and the riskfactors to infection were investigated. Following that, the molecular epidemiology andpopulation structure of the pathogen was also investigated. The investigations wereconducted in opportunistically selected human and animal populations within theWestern Cape Province of South Africa. The data obtained was analyzed from a 'OneWorld One Health perspective and conclusions were then documented.The selected human populations were, a cohort of human immunodeficiency virus (HIV)positive and human immunodeficiency virus (HIV) negative post parturient women andtheir HIV exposed and uninfected (HEU) and HIV unexposed and uninfected (HUU) infants, and a cohort of HIV positive and HIV negative male and female patientspresenting with a clinical diagnosis of uveitis at the Tygerberg academic hospitalopthalmology clinic. The selected animal populations were a population of feral cats inthe greater Cape Town metropole, a population of free ranging sheep on a single farm inBredasdorp and a population of free ranging caracals in the Cape peninsula region.Toxoplasma gondii seroprevalence was 23.3% in the cohort of post parturient women,whilst the seroprevalence in the infant cohort was 1.02%. The seroprevalence was 24.7%in the cohort of patients presenting with ocular infections. The seroprevalence was notassociated with HIV status but was associated with the consumption of unwashed fruitsand vegetables. The similarity between the seroprevalence in the post parturient cohortand the ocular cohort points to the lack of regional differences in seroprevalence rates,whilst the low seroprevalence in the infant cohort implies a low rate of congenitaltoxoplasmosis in the study area and this comforms to what is observed in other parts ofAfrica, Europe and North America.Seroprevalence was extremely high in the felid populations investigated (Feral cats -37.1% and Caracals- 69.6%). These justifies considerable attention since these felidswere free ranging and therefore have access to domestic human and animal populations.The seroprevalence in the sheep flock was also higher at 8.0% than the five point sixpercent (5.6%) reported in earlier studies in Cape Town.Current research has established that T. gondii genotypes vary in their geographicdistribution, with certain genotypes being more predominant in certain geographic areasthan others. To establish the genotypes of T. gondii present in our selected geographic area, we investigated the molecular epidemiology of the pathogen. The molecularepidemiology investigations revealed a predominance of Type II genotypes in bothhuman and animal samples. A Type III genotype was detected in human but not in animalsamples. Atypical genotypes were also identified in both human and animal samples.The observed population structure is similar to that of South America and other parts ofAfrica but differs from that observed in Europe and North America.We have demonstrated the presence of T. gondii as well as its active transmission withinselected human and animal populations in the Cape Town metropole of South Africa. Thepresence of atypical T. gondii genotypes was also demonstrated. The observedseroprevalence rates investigated in this study implies that more attention needs to bepaid to the disease as it could have implications for female reproductive health, infant toadolescent ocular health as well as overall economic losses due to an increase in diseaseburden in humans (reported as disability-adjusted life years) and for agriculture.

[发布机构] Stellenbosch University