Parasites

(Platy)Helminths

Flatworms

Nematodes

Roundworms

Worms associated with foods

• Animal parasites: need animal host to develop - therefore worms are only found in meat products

• Life cycle: egg, intermediate stage(s), mature worm

• Classified according to shape adult worm:

  • Flatworms: Trematodes and Cestodes

  • Roundworms: Nematodes

• Do not grow in foods

The four most important worms, their hosts and the food vehicles.

Transmission cycle Taenia solium

• Pig tapeworm

• Only in humans the larvae will mature, not in the food.

• Similar cycle for T. safinata but instead it grows in beef.

Human health effect Taenia

• Mature tapeworm only develops in human hosts

• 4-12 m long (1000-2000 segments, proglottids)

• Symptoms: asymptomatic, nausea, abdominal pain, weight loss, anemia

• Effects more severe in young and immuno-compromised

• Efficient drugs are available.

Transmission cycle Trichinella spiralis

primary vs secondary source host parasites

A primary host, or definitive host, is where a parasite reaches sexual maturity and reproduces. A secondary host, or intermediate host, harbors the parasite during its development but not to sexual maturity, serving as a transition to complete its life cycle. The distinction is about the parasite's development and reproductive stage within the host. 

Trichinellosis

• Roundworm

• caused by consumption of Trichinella spiralis

• Encysted larvae released in stomach

• Larvae mature to adult worm (3-4 mm) in intestine

• Female worm releases larvae

• Larvae invading intestinal mucosa, causing symptoms

  • Incubation time: few days - month

  • Symptoms: abdominal pain, nausea, diarrhoea

• Larvae invade and encyst in muscle tissue

  • Symptoms: muscle pain, fever

• Efficacy of drugs uncertain

Contamination cycle of Echinococcus multilocularis

Echinococcossis

• Disease caused by consumption of Echinococcus multilocularis

• Which is a parasite found in foxes

• Alveolar cysts (lungs, liver), treatment may not be effective.

Fish parasites

• Anisakis: herring worm

  • Symtpoms: abdominal pain

• Therefore all freshly caught fish, has to be frozen for 24h at -18C which kills the worms

• This makes it safe to eat the fish raw.

Preventative measures against worms

• Examination of slaughter animals before and after slaughter

  • Multiple spots of parasites → rejection

  • Local contamination → approval after treatment

  • Severe cold treatment of contaminated fish or meat, e.g. Taenia saginata, -18C, 10 days in calf meat

• Educate consumers: adequate heating of food before consumption, wash (wild) berries