Evira survey on the occurrence of muscular parasites in ducks

23.8.2013

<p>In autumn 2013, the Finnish Food Safety Authority Evira aims to involve hunters in collecting information on the occurrence of muscular parasites in ducks. Since the lifecycle and main host species of the protozoan parasite <em>Sarcocystis</em> in ducks is unknown in Finnish nature, all information on this topic is vital to wildlife health research.</p>

A similar survey will be conducted in Sweden, to gain a better insight into the parasite situation in the environs of the Baltic Sea. For the time being, few observations have been made in Sweden.

Observations and samples received by Evira indicate that the parasite mainly occurs in mallards in the southern parts of the country. However, infected wigeons and teals have also been found in Finland. While the parasite is also known to occur in other parts of Europe, particularly in the Baltic countries, observations are rare in Western Europe.

Muscular parasites of ducks are not known to infect humans
Thorough cooking or freezing will destroy parasites in meat, thereby eliminating all risk of infection. However, in the worst cases the meat may be so infested by cysts that it is unfit for human consumption.

Assist wildlife health research
Information on infected birds are most welcome as well as photos of infected birds or muscles. The maximum size of such photos is 1Mb. Photos should be sent to researcher Marja Isomursu, marja.isomursu at-merkki-kapea.gif : 0 kB evira.fi

Birds infected by parasites hard to identify visually
Birds seem to suffer relatively little from the parasite infection, even in severe cases. The muscles of the duck may be full of cysts, but its ability to fly seems normal in the hunting context.

In principle, the parasite can cause the bird disease at the early stages of infection, when spreading to various parts of the body. In primary hosts, an infection limited to the intestines can cause diarrhoea, but in most cases there are no symptoms.

The Parasite needs two animal host species
Parasites of the genus Sarcocystis are microscopic unicellular protozoans, whose lifecycle includes at least two animal species: the main host, a carnivore, and the intermediate host, which is the prey of the main host. In the main host, the parasite lives and reproduces only in the intestinal wall. Infectious forms of the parasite are released into the environment in the main host's excrement. The intermediate host is infected by swallowing the excrement in water or food.

In the intermediate host, parasites find their way to the muscles, where they reproduce asexually through fission. Sarcocystis in ducks forms large cysts in the muscle cells, visible as light formations like rice grains running in line with the muscle fibres. Each cyst contains masses of unicellular parasites. The main host is infected with the parasite when consuming meat that includes cysts.

Finnish and American muscular parasite closely related
The Finnish parasites studied were found to be of the species Sarcocystis rileyi, originally described in the United States. There, the intermediate hosts of the species are chiefly the same as in Finland, but the American skunk is regarded as the main host. In Finland, and Europe, the main host species is unknown. The purpose of this survey is to gain a better understanding of the parasite's distribution.

Research on muscular parasites in ducks forms part of the extensive project Studies on wildlife parasites in Finland

Further information:
Marja Isomursu, Researcher,
Production Animal and Wildlife Health Research Unit,
Tel. +358 (0)40 512 1248
Antti Oksanen, Research Professor
Research and Laboratory Department,
Tel. +358 (0)44 561 6491


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