Results and discussion

A 24-year-old female patient from the Moscow region was admitted to a polyclinic, with fever and mild abdominal pain. She was diagnosed with yersiniosis and treated with antibiotics and antipyretics for seven days (table 1). Following a lack of improvement, she was admitted to the outpatient department of the First Moscow Infection Hospital, with fever (up to 37.8°С), facial (mainly para-orbital) oedema, fatigue, weakness, pain in muscle and joints of limbs, abdominal discomfort and mushy stool. A blood test revealed leukocytosis (11.8 × 10⁹/l) with 17% (2.0 × 10⁹/l) eosinophils. Biochemical markers of liver damage (ALT, AST, bilirubin, alkaline phosphatase) were within normal limits. Testing for creatine phosphokinase and aldolase was not done. Tests for HIV, syphilis, yersiniosis, viral hepatitis and rotaviruses were negative. No pathogenic bacteria were found in stool. Helminth eggs and pathogenic protists were not found during stool microscopy. Lung X-ray, oesophagogastroduodenoscopy, abdominal ultrasound and ECG did not find any pathological changes.

Table 1. Timeline of the suspected case of trichinellosis associated with consumption of beaver meat in Moscow, Russia.

The patient reported a single episode of consumption of about 100–150 grams of stewed beaver meat. According to the patient, her father regularly hunts beavers in the Moscow region for meat. Preference towards beaver meat was justified by its ‘ecological cleanness’ because ‘beavers eat only tree bark.’ According to the patient, her father consumed the same meal and had similar symptoms at the same time, but refused to be admitted to the hospital for examination. Her mother never consumed beaver meat and did not have any health problems.

Clinical manifestations and food anamnesis suggested trichinellosis. The patient was positive for IgG antibodies to Trichinella spiralis (titer 1 : 600, the cut-off value for this test), using a Trichinella-IgG enzyme-linked immunosorbent assay (ELISA) kit (Vector-Best, Novosibirsk, Russian Federation). Unfortunately, the beaver meat was not available for testing because it was consumed two days before the onset of disease. Muscle biopsy was not carried out because this invasive procedure would not benefit the patient, and relatively mild clinical manifestations suggested a low chance of trichinellae detection.

The patient was treated with albendazole at 10 mg/kg/day for ten days. After ten days of treatment, all symptoms disappeared; leukocyte and eosinophil counts returned to normal four weeks after the start of treatment. According to the patient, her father recovered at the same time without albendazole treatment.

Diagnosis of trichinellosis requires confirmation by either muscle biopsy or a confirmatory Western blot following a screening ELISA. In this case, clinical manifestations were compatible with trichinellosis. A single detection of IgG provided only indirect support. Unfortunately, no additional test, such as a confirmatory Western blot, IgM test or paired serum (seroconversion) was done.

Beavers have not been implicated as a source of human trichinellosis; therefore, this case required an additional analysis. Beavers are amongst the largest rodents and can weigh up to 32 kg. The species Castor fiber is common in Europe and North Asia, whereas the species Castor canadensis is prevalent in North America. Beaver diet includes tree bark, leaves and other plants (Krojerová-Prokešová et al., Reference Krojerová-Prokešová, Barančeková, Hamšíková and Vorel2010), and does not contain an obvious source of trichinellae. However, there is indirect evidence that beavers occasionally consume meat, as rat liver parasites Capillaria hepatica and fish/crab parasites Paragonimus westermani have been detected in beavers (Craig & Faust, Reference Craig and Faust1958). Trichinellae have been found in beavers (Castor canadensis), but the prevalence and larval load were low: one of 29 beavers with a load of 3.0/g in one report (Rausch et al., Reference Rausch, Babero, Rausch and Schiller1956) and 5.3% positive beavers in another (Zimmermann et al., Reference Zimmermann, Hubbard, Schwarte and Biester1962). The contemporary literature contains only one report from Latvia, describing detection of 5.96 larvae/gram of muscle tissue in just one of 182 beavers tested (Seglina et al., Reference Seglina, Bakasejevs, Deksne, Spungis and Kurjusina2015). In Russia, beavers have been mentioned in trichinellosis surveillance reports. In 2006, a total of 201 cases were registered in Russia, and 5% of these cases were associated with beavers (Guzeeva, Reference Guzeeva2008); however, no supporting evidence for these cases was published. Our patient did not report consuming other game meat. Farm pigs, which were the major source of trichinellosis in the 20th century, are implicated in less than half of cases nowadays (Guzeeva, Reference Gottstein, Pozio and Nöckler2008), and the patient did not acknowledge consumption of privately produced pork.

Beaver meat is consumed in many countries where beavers occur. In particular, in the USA and Canada beavers are a part of the diet of the indigenous population, and are among the most common game animals (Rinella, Reference Rinella2011). It is therefore surprising that they have not been implicated as a source of trichinellosis in the USA, although other game meat was the source of roughly half of the cases (Kennedy et al., Reference Kennedy, Hall, Montgomery, Pyburn and Jones2009; Wilson et al., Reference Wilson, Hall, Montgomery and Jones2015). In Russia, beaver meat is also traditionally consumed for food. In the 20th century its popularity declined but in recent years it has been increasing. There is potential for an increase in the role of beavers (and other game animals) as a source of trichinellosis because beaver meat is commonly available as raw meat, sausage and stewed meat, and is marketed as organic, which raises the risk of under-cooking. Beaver hunting is often carried out without due licensing. Beaver farming is developing, too, but the extent of this industry is unknown, and meat is processed privately without appropriate control measures. At present, it is difficult to project the significance of beaver-borne trichinellosis for public health. A high level of trichinellae infection and a subsequent severe infection seems unlikely, and the moderate severity of the reported case can be ascribed in part to low infection levels reported in beavers. However, it is possible to imagine a scenario of poor farming practices leading to a beaver-borne trichinellosis outbreak. In any case, it is important to raise public awareness regarding beavers as a source of trichinellosis and to promote safe cooking habits among consumers of exotic meat.