Australian researchers have detected Toxoplasma gondii in more than one third of sampled ground lamb.
Toxoplasma is a parasite that causes inflammation of the retina, which is the nerve layer of the eye. Anyone may develop retinal inflammation after infection but it is more common and severe in babies, older adults and people with compromised immune systems.
Toxoplasma can be contracted from eating raw or undercooked meat, according to the study published in the Australian New Zealand Journal of Public Health. In Australia, toxoplasmosis is not a notifiable disease. Consequently, health care providers do not have to report confirmed cases to public health authorities for statistical purposes.
Ground lamb, known as lamb mince in Australia, was purchased at a supermarket in South Australia three times weekly for six months by Flinders University researchers. Toxoplasma gondii was detected by real‐time polymerase chain reaction (PCR) of DNA extracted from the meat.
Conservative interpretation of PCR testing gave a probability that 43 percent of samples were contaminated. None of the purchases were positive for Campylobacter jejuni, Salmonella species, or Salmonella Typhimurium, indicating sanitary meat processing. Toxoplasma gondii DNA detection reflects infection of livestock in the pasture, rather than introduction during processing, according to the researchers.
A total of 79 samples of lamb mince parcels of 500 grams were purchased between April and September 2017. The product was prepared from primary and secondary lamb cuts from between 15 and 20 animals, and contained meat from organically farmed South Australian livestock and conventionally farmed countrywide livestock.
DNA extracted from each parcel was tested for the Toxoplasma gondii B‐1 gene by quantitative PCR, including nested PCR. The B‐1 gene was detected in three or four of four tests for 34 samples. For 21 other samples, the B‐1 gene was found in two of four tests, and in 20 of these, the presence of the gene was confirmed by nested PCR.
The conservative interpretation of PCR testing indicated a probability of 43 percent that lamb mince was contaminated with Toxoplasma gondii. The more liberal interpretation indicated a probability of 68 percent that it was contaminated.
“Although the meat was purchased at one supermarket, located in South Australia, our findings are likely to be generalizable, because Australian supermarket retailers purchase their lamb across a range of farms throughout the country,” said researchers.
Flinders strategic research professor, Justine Smith, who led the research, said the findings were new for Australia, but were expected from work done in other parts of the world.
Twenty‐nine studies from countries in Africa, Asia, Europe, North and South America and Oceania provided a range for prevalence in lamb meat, from as low as 0.144 in North America, to as high as 0.271 in Asia.
Tissue cysts are rendered non‐viable by cooking meat to an internal temperature of 66 degrees C (151 degrees F) or it can be frozen overnight at −12 degrees C (10.4 degrees F) to destroy the cysts.
Researchers said Australian governmental recommendations do not advise on the need to cook fresh red meat thoroughly.
“Specific messaging that is sensitive to consumer cooking preferences may be helpful to educate the Australian population of the risk related to consuming undercooked lamb, which applies particularly to pregnant women, the elderly and immunocompromised persons.”
It is important to recognize detection of parasite DNA does not equate with human infection, said researchers.
“The method cannot distinguish between viable and non‐viable microorganisms and does not account for the fact that Toxoplasma gondii occurs as groups within tissue cysts, rather than individual parasites dispersed across the meat.”
The research team plans to test other red meats for Toxoplasma, especially those eaten rare, such as kangaroo and beef.
(To sign up for a free subscription to Food Safety News, click here.)