Prevalence and genotypes of Toxoplasma gondii in feline faeces (oocysts) and meat from sheep, cattle and pigs in Switzerland
Introduction
Toxoplasma gondii is one of the most prevalent zoonotic parasites worldwide. While only felidae can act as definitive hosts and thus shed oocysts in their faeces, almost all warm-blooded animals can serve as intermediate hosts. These, upon primary infection, will first undergo a tachyzoite stage infection by the parasite, followed by the formation of bradyzoite-containing tissue cysts, primarily in brain or muscles (Dubey and Beattie, 1988, Dubey, 1996; reviewed by Tenter et al., 2000). Humans may acquire a T. gondii infection via (1) oral uptake of sporulated oocysts from the environment, (2) consumption of raw or undercooked meat containing tissue cysts or (3) via transplacental transmission of the parasite from the non-immune mother to the foetus. Studies in Europe have shown that 35–58% of women at child-bearing age were seropositive for T. gondii (reviewed by Tenter et al., 2000). In Switzerland, 46% of women at child-bearing age presented a seropositive immune status (Jacquier et al., 1995), but seroprevalences are likely to have decreased in the last decade, following the general trend in Europe (reviewed in Pappas et al., 2009). In fact, two locally restricted studies carried out with women in child-bearing age in Switzerland detected seroprevalences of 35% and 8.2%, respectively (Signorell et al., 2006, Zufferey et al., 2007). In Europe, congenital toxoplasmosis affected approximately 1–10 out of 10,000 newborns, of whom 1–2% suffered from general health problems or even died and 4–27% developed ocular disease (Cook et al., 2000). The European Food Safety Authority (EFSA) has recognized toxoplasmosis as the parasitic zoonosis with the highest human incidence and has recently published a scientific opinion that clearly states the need of representative data on the occurrence of toxoplasmosis and the distribution of the parasite in Europe (EFSA, 2007). Recently, different options of obtaining T. gondii-free meat have been discussed (Kijlstra and Jongert, 2008). It is thus of great importance to collect reliable data on the actual prevalence of T. gondii in meat-producing animals, but also on the prevalence of oocyst-shedding by cats to assess the infection-risk for the human population.
In North America and Europe, mainly three T. gondii clonal lineages dominate, designated as clonal Types I, II and III based on PCR-restriction fragment length polymorphism (PCR-RFLP) and microsatellite typing (Howe and Sibley, 1995, Ajzenberg et al., 2002). These clonal types exhibit different levels of virulence in outbred mice. While clonal Type I always causes a lethal infection, the other two clonal types are far less virulent (Sibley and Boothroyd, 1992). In South America and Asia, however, T. gondii genotypes are predominantly atypical and of mixed clonal Types (Lehmann et al., 2006, Dubey et al., 2007). Such genotypes could arise when a feline host ingests prey infected with T. gondii of more than one of the three clonal Types I, II, or III. In these cases, the clonal types may undergo sexual recombination in the feline gut and the resulting progeny would thus represent a mixture of the two parental genotypes (Su et al., 2002, Saeij et al., 2006). More recently, T. gondii with atypical allele combinations have also been observed in Germany (Herrmann et al., 2010). As yet, nothing is known about the T. gondii genotypes present in the animal populations in Switzerland.
The aim of this study was to assess the prevalence of T. gondii oocyst-shedding in cats, using faecal samples obtained from animal shelters, catteries and routine diagnostic samples at the Institute of Parasitology in Bern, as well as the prevalence of T. gondii gDNA in diaphragm samples of cattle, sheep and pigs. In addition, and for the first time in Switzerland, genotyping of oocysts shed by cats and parasite gDNA detected in muscles of meat-producing animals was carried out. Furthermore, parasite gDNA detected in muscle of meat producing animals of a previous study (Wyss et al., 2000) was subjected to genotyping because at the time of that former study, genotyping was not yet done.
Section snippets
Diagnostic samples
A total of 252 cat faecal samples were collected between January 2007 and August 2008. Animal shelters and catteries in the region of Bern and Olten were contacted and offered a free coproscopical examination for their cats. Furthermore, cat faeces entering the routine analysis of the Institute of Parasitology in Bern were included in the study. Thus, faeces were obtained from stray animals (n = 43, 17%), healthy pet cats (n = 171, 68%) and of cats with diarrhoea or other gastrointestinal disorders
Results
Cats: Out of 252 faecal samples analysed, two samples contained oocysts of a diameter of 9–14 μm. PCR analysis of the recovered oocysts revealed one sample to be T. gondii, while the other sample was identified as H. hammondi. Thus, the prevalence of cats shedding T. gondii oocysts was 0.4% (95% CI: 0.0–2.2%) (Table 1). The cat shedding T. gondii oocysts was 11 years old and suffered from pneumonia accompanied by vomiting and anorexia. It was a pet cat with no outdoor access.
Porcines: Three of
Discussion
This study aimed at estimating the prevalence of oocyst-shedding by cats and at assessing the frequency of T. gondii-infections in meat-producing animals in Switzerland by detection of gDNA in muscle samples. Diaphragm was chosen because it is easily accessible upon slaughter and has been used in studies in pigs (Gajadhar et al., 1998), sheep (Da Silva and Langoni, 2001) and cattle (Dubey and Streitel, 1976) for the detection of T. gondii. We were aware that with using one gram of meat
Conclusions
In conclusion, this study shows that the estimated prevalence of oocyst-shedding in cats from Switzerland is 0.4% (95% CI: 0.0–2.2). gDNA of T. gondii has been detected in meat samples of all assessed animals (pigs, ovines and bovines), implicating that the consumption of meat from these species might pose a risk of infection with T. gondii in Switzerland. Furthermore, the study allows a first insight into the genotypes of T. gondii circulating in Switzerland, revealing that in addition to
Conflict of interest statement
None of the authors of this study has a conflict of interest.
Acknowledgements
We would like to thank Philipp Stünzi, Caroline Müller, Beatrice Zumkehr, Andrea Bärwald and Aline Maksimov for excellent technical support. We are also very indebted for the excellent collaboration of Dr. Töngi, Mr Diethelm, Dr. Rudelt, Dr. Amgarten, Mr Bauer and Mr Bärtschi for their help with the sample collection. Furthermore we thank Prof. Andrew Hemphill for carefully reviewing the language of this manuscript. This study was funded by the Swiss Federal Veterinary Office, Grant Number
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