Trichinella outbreak in France and Serbia linked to backyard pigs

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Backyard pork was the cause of an epidemic of trichinellosis in France and Serbia in 2017.Three patients were exposed in Serbia and brought pork back to France where they shared with relatives and friends. About 47 people received meat in France and Serbia and 20 cases of trichinellosis were reported, nine in France and 11 in Serbia. Nine of them were women.

While the cases in Serbia were moderate, those in France were serious, as all the patients were hospitalized but none had major complications. One of the reasons could be the case in Serbia where one ate mainly smoked pork, while the dried pork was consumed in France. The epidemic has shown that smoking and drying are not enough to inactivate the parasite, according to researchers in the journal Eurosurveillance.

In 2017, 15 European countries reported 224 cases of trichinellosis, of which 168 were confirmed. The incidence of trichinellosis in France is low, with only 68 cases reported from 2001 to 2016. Of these, 38 were linked to the consumption of infected meat abroad or illegally imported meat. However, Serbia is a country at high risk for trichinellosis. From 2001 to 2016, there were 2,897 cases, including three deaths in 2005.

The meat suspected in the 2017 outbreak came from three backyard pigs reared on a small family farm in a village near Belgrade. One pig’s meat was prepared as canned food – sausage and dried meat – the second was cooked and the third was prepared as smoked food.

French patients
A woman in her forties was hospitalized for two weeks on February 7, 2017, near Paris. Her symptoms started 11 days before she went to the doctor. A relative, a 30-year-old man and his friend, a 60-year-old woman, were hospitalized about two weeks later for seven and nine days, respectively.

The diagnosis of trichinellosis was delayed from the end of January to February 24 due to the time required to seek treatment, consult doctors who are unfamiliar with the rare disease in France and since antibodies generally appear a few days after the start of the acute phase of the disease, leading to frequent negative serology at the onset of symptoms. Some patients of Serbian origin did not speak French fluently, which could explain a misunderstanding of the symptoms.

During the Christmas holidays, patients went to Serbia where they ate pork from the farm three times and brought the meat of the first two pigs back to France. They shared the meat near Paris with 19 people between January 9 and 20. In Serbia, 25 people ate meat from three pigs during meals between December 31, 2019 and January 15 of this year.

Among the 19 others exposed in France, seven were asymptomatic and 10 presented clinical signs compatible with trichinellosis from mid-January to the end of February. Trichinellosis was excluded in four symptomatic people. Six other patients identified by the investigation had confirmed infection. For French patients, the incubation time was between 16 and 28 days and all required hospital treatment.

The pork was positive for the Trichinella larvae, identified as Trichinella spiralis. The sausages and dried meat contained 51 and 62 larvae per gram, respectively. The biological test on the mouse was negative, suggesting that the larvae were not infectious when the meat was analyzed – two months after the first consumption.

Serbian investigation
Out of 25 people exposed in Serbia, 11 suffered from trichinellosis. The infected were family members of the first two patients and eight family guests.

During examinations at a clinic in Serbia in early March, symptoms of Trichinella infection had passed. The symptoms described started between February 10 and February 18 and were mild. The incubation time has been estimated between 34 and 42 days.

According to the study, the Serbian cases could have had previous contact with Trichinella parasites and have developed immunity, leading to a longer incubation and milder symptoms in case of reinfection.

Trichinella larvae have been detected in samples of smoked and fresh meat from the third pig. The larval load varied from 21 to 61 larvae per gram.

According to the farmer, the hearth meat was sent after slaughter for analysis to a veterinarian who informed the family by phone that she was not infected, but did not send an official written confirmation. Although the analysis was performed by trichinelloscopy, a method not recommended, it would have been sensitive enough to detect the high larval load of the meat.

When comparing trichinellosis in the two countries, the researchers noted some differences such that most of the French patients were older than the Serbs because eight out of nine against four out of 11 were over 30 years old, therefore were more at risk complications.

During the outbreak, the smoked meat was prepared in less than 20 days, the sausages were only exposed to rapid cold smoking and the dried meat was prepared by rapid dry salting. The drying time may not have been long enough to inactivate the larvae, while smoking may have inactivated more larvae causing faster dehydration. The longer incubation time for trichinellosis in Serbian versus French cases suggested that the infectious dose was lower in smoked pork.

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