Study suggests higher risk of Toxoplasma infection from venison

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A study on the presence of Toxoplasma gondii in retail meat in Scotland has highlighted venison as potentially high risk.

Toxoplasma gondii DNA was detected in 48 of 149 venison samples over two sampling periods. Consumption of undercooked meat is a known risk factor for toxoplasmosis infection.

Findings could be used to inform quantitative microbial risk assessments of foodborne toxoplasmosis in Scotland, according to the study published in the journal Food and Waterborne Parasitology.

Sampling results

Of the 300 meat samples purchased for testing in the first sampling period, 39 were positive for Toxoplasma gondii DNA. It was detected in one of 21 chicken samples, six of 87 lamb samples, three of 71 pork samples and 29 out of 82 venison samples. None of 39 beef samples were positive.

Some venison products in the first sampling period also contained pork. Of the 67 pure venison samples purchased in the second sampling period, 19 were positive for Toxoplasma gondii DNA.

Antibodies to Toxoplasma gondii were detected in the meat juice of two of 38 beef samples, three of 21 chicken samples, 14 of 85 lamb samples, two of 68 pork samples and 19 of 128 venison samples.

An average of 365 toxoplasmosis cases are clinically diagnosed in England and Wales each year and 33 infections are recorded annually in Scotland.

The first sampling period in April and November 2017 involved meat purchased from butchers, farmers markets, farm shops, and supermarkets. In the second round, 67 pure venison samples were bought from farmers markets, farm shops and supermarkets between June and August 2018. Of these samples, 28 were from wild deer and 39 from farmed deer.

All samples were purchased fresh and pre-packed except those from butcher shops which were packaged upon purchase. Different cuts were collected for each meat type.

When rearing conditions was available, 22 out of 39 beef samples were from pasture-reared animals, 10 of 21 chicken and 20 of 71 pork samples were from outdoor-reared animals and all lamb samples were from animals reared in the UK so were assumed to be outdoor-reared.

Venison market push

As part of Scotland Food and Drink Ambition 2030, there is planned expansion of the farmed venison sector with an emphasis on making it the main meat of choice for consumers. As it is common and sometimes recommended on packaging to consume venison undercooked, this meat could present a potentially significant source of foodborne toxoplasmosis, said researchers.

Out of three DNA isolates partially genotyped in the study, only one had Type II alleles at all the amplified markers and the others had Type I or a mix of alleles. Strains containing Type I or atypical alleles are more pathogenic or more likely to cause severe disease.

“The presence of Toxoplasma gondii with Type I alleles in a meat product which is commonly consumed undercooked, such as venison, could pose a potentially significant public health problem,” said researchers.

Further work is underway with additional fresh samples of venison to determine the viability of Toxoplasma gondii in these meat products to assess the foodborne risk.

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