Atlas of foodborne infections
transmitted by contaminated food and water

Atlas of Patogens Contents Information sources Glossary Administration

Food-borne nematodes

CZ: hlístice
EN: roundworms

Occurrence:
Meat and Meat Products
Fish and Fish Products
Fruits and Vegetables
Water and Beverages
Delicatessen


Category:
Parasites


Foodborne Disease:
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anisakiosis, trichinellosis


Description:
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The food-borne roundworms of primary importance in humans belong to the phylum Nematoda and are known as nematodes. Undercooked or raw fishery products and pork meat are the usual foods involved.

Where fishery products are the food vector, the definitive hosts of roundworms causing disease in humans are piscivorous marine mammals such as seals. Marine invertebrates and fish are the two intermediate hosts and humans are infected when they consume raw or minimally processed products. Fish are the secondary hosts and are infected when they consume the invertebrate primary host or fish that are already infected.

There are many species of nematodes and a very large number of species of fish, worldwide, that are known to act as intermediate hosts. The most common species of nematode causing disease in humans is Anisakis simplex, sometimes referred to as the herringworm. The other species involved in anisakiasis in North America, Europe and japan is Pseudoterranova decipiens (the cod- worm or sealworm).

Nematodes are commonly present in fish caught in the wild, most frequently in the liver and belly cavity, but can also occur in the flesh. Anisakiosis is an uncommon disease because the parasite is killed by heating (55°C for 1 min), and by freezing ( — 20°C for 24 h). There is a risk of illness from fishery products consumed raw, for example sushi, or after only mild processing, such as salting at low concentrations or smoking. Many countries now require that fish used for these mildly processed products be frozen before processing or before sale.

Trichinella spiralis is the cause of trichinosis in humans. This most commonly results from the consumption of contaminated raw or undercooked pork or pork products. Isolated cases have been reported from the consumption of bear meat and ground beef in the USA.

The incidence of trichinosis can be controlled by avoiding feeding infected waste foods to pigs or by fully cooking pig swill. Freezing pork products ( — 15°C for 20 days) or thorough cooking (78°C at the thermal center) before human consumption will destroy trichina larvae.


Pictures:

Anisakis simplex
Source: Anisakis simplex
Trichinella spiralis
Source: Trichinella spiralis larvae in muscle

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