Prevalence in food anima

International Commission on

    Prevalence in Food Animals

Trichinella prevalence in pigs varies from country to country, and regionally within countries.  The lowest prevalence rates in domestic swine are found in countries where meat inspection programs have been in place for many years (including, in particular, countries of the European Union).  In some instances, countries with long-standing inspection programs consider themselves free from Trichinella in domestic swine.  In countries of eastern Europe, higher prevalence rates of Trichinella have been reported in pigs and this is supported by higher numbers of cases of human trichinellosis.  Increased prevalence of Trichinella infection in pigs in some of the Balkan countries is the result of changes from large government run farms to small holdings where pigs are raised outdoors.  In the United States, no formal inspection programs have been used to control Trichinella in pigs.  However, changes in the pork industry which focus on confinement housing and other measures of bio-security have essentially eliminated this infection from the domestic pork supply.  

Only sporadic information is available on the prevalence of trichinellosis in South America, Africa and Asia, but these limited reports suggest high infection rates occur in pigs in some countries.  For example, in rural areas of China where pigs are raised outdoors in uncontrolled environments, pig infection rates can be 50% or higher.  

Most evidence for infection in horses comes from the implication of horsemeat in human disease outbreaks.  Despite widespread testing, detection of natural infections in horses has been rare – only a few naturally infected horses have been identified, from Mexico, Romania, the former Yugoslavia and Poland.  However, due to the habit of eating horsemeat without thorough cooking, a single infected horse can cause a large outbreak in humans.  Horses implicated in human infections have generally been imported from countries where high infection rates occur in pigs.  Further, epidemiological studies suggest that horses may be deliberately fed pork scraps or other meat scraps (from wild animals) to increase their weight prior to sale.   

Trichinella infection in wildlife varies tremendously from region to region, but it is safe to say that no area is completely free from this parasite in nature.  The highest rates of infection are found in foxes, wolves and bear, where infection rates can reach 85-90% of the population.  It should be noted that infection rates in wildlife tend to increase in colder climates.  In the domestic pig cycle, rats, skunks, raccoons and other small mammals play an important role and are often found to have high infection rates.

Further Reading

Pozio, E. 2007. Taxonomy, biology and epidemiology of Trichinella parasites. In, (Dupouy-Camet, J and Murrell, K.D. eds.), FAO/WHO/OIE Guidelines for the Surveillance, Management, Prevention and Control of Trichinellosis, Rome, pp. 1-36. 

Pozio, E. 2007. World distribution of Trichinella spp. infections in animals and humans. Veterinary Parasitology, 149: 3–21.
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