Managing a large Outbreak of Trichinellosis in Belgium associated with Consumption of Imported Wild Boar Meat

Background:

Trichinellosis is a parasitic zoonosis caused by ingestion of raw or undercooked meat containing larvae of the genus Trichinella. Since the implementation of European Union Directives requiring the examination of wild boar, domestic pig and horse meat for Trichinella species, there was a sharp decline in incidence rates. The last reported outbreak in Belgium occurred in 1979. In November 2014, 16 patients were diagnosed with trichinellosis after consumption of imported wild boar meat from Spain in three Belgian restaurants.

Methods:

All exposed persons were invited by the regional public health authorities to be clinically evaluated. Confirmation of probable cases required positive serological testing or a histological report of intramuscular parasites and/or detection of T.spiralis DNA from muscle biopsies. After informed consent, clinical and laboratory data from the files of confirmed cases were reviewed. All restaurants supplied by the importer of wild boar meat were investigated and samples systematically analyzed.

Results:

In the cluster, two groups could be distinguished: patients with heavy exposure (n=10) or mild exposure (n=6) with a median incubation period of respectively 9 days (IQR 8-10) versus 23 days (IQR 21-23). The most frequently reported symptoms included bilateral peri-orbital edema, fever and muscular tenderness (Figure 1). Muscle biopsy obtained from 3 patients revealed first stage Trichinella larvae, confirmed as T.spiralis by PCR in all 3 (Figure 2). After anti-helminthic treatment (mebendazole, n=14; albendazole, n=2), with or without prednisolone, all patients had an uneventful recovery except one with persistant neurological complaints of tremor and impaired coordination. Several batches of imported Spanish wild boar meat were recalled and tested negative. The public health authorities issued the destruction of the suspected lot number and heat treatment for all other supplies.

Conclusion:

Despite EU control measures, even in a non-endemic country an outbreak of trichinellosis should be suspected if patients are clustered and/or have been exposed to wild (boar) meat. This outbreak highlights the need for local networks and agencies which can take swift action when a food-borne outbreak is detected.

Figure 1

Figure 2