Veterinary Epidemiology and Zoonosis

TRICHINOSIS

Synonym

• In humans: Raw pork disease
• In animals: Trichinellosis

Type of zoonosis

• Meat-borne zoonosis

Definition

• It is a type of food-borne helminthosis, caused by Trichinella spiralis. It is clinically characterized muscle soreness and pain due to irritation, enteritis, edema of upper eyelids, thirst, profuse sweating, chills and eosinophilia, and eventually, death due to myocardial and respiratory failure.

Etiology

• Trichinella spiralis , an intestinal nematode.
• Female worms are ovi-viviparous (eggs hatch in the uterus itself).
• Location of the parasite:
  • Adult worm in the small intestine.
  • Larvae in the striated muscles (diaphragm, tongue, intercostal and mandibular muscle)
• Common name of the parasite:
  • Garbage worm
  • Trichina worm

Reservoir and incidence

• Distributed worldwide.
• Pigs, rats, dogs, cats and many wild animals are susceptible.
• Eating of raw pork or under cooked pork results in development of trichinosis in humans.
• Sylvatic cycle involves jackals and wild boars by cannibalism.
• Synanthropic cycle involves wild and domestic cycles.

Transmission and life cycle

• Pigs generally become infected by feeding on garbage / uncooked scraps.
• In humans, infection occurs by eating raw or under cooked meat.
• Larvae develop into adults in the epithelium of the small intestine (L1 to L2 to L3) and then sexual differentiation occurs (L3 to L4).
• Copulation occurs in the intestine (male parasite will die after copulation) and the gravid female worms then produce larvae, which penetrate the lymphatics or venules and are disseminated via the bloodstream throughout the body. The larvae become encapsulated in skeletal muscle.

Disease in animals

• Usually subclinical

Disease in humans

• Number of larvae ingested by humans determines the clinical disease. Usually 10 to 100 parasite per gram of muscle causes clinical signs.
• Sudden appearance of muscle soreness and pain due to irritation, together with edema of upper eyelids, sometimes followed by subconjunctival and retinal haemorrhages, pain and photophobia.
• Thirst, profuse sweating, chills, eosinophilia, enteritis, fever, myocarditis, ascitis and peritoneal edema.
• Lastly, death due to myocardial and respiratory failure may occur.

Diagnosis

• Meat inspection.
• Larval examination by Baermann's apparatus.
• Muscle biopsy and trichinoscopic examination.

Treatment

• Infected persons recover spontaneously.
• Supportive treatment should be given.
• Anthelmintics like mebendazole, thiabendazole or albendazole can be given.

Prevention and control

• Cooking of pork at 77°C or above destroys the parasite.
• Freezing of pork at -10°C for about 30 days or -20°C for about 10 days destroys the parasite.
• Gamma irradiation destroys the parasite.
• Humans should not eat raw and/or insufficiently cooked Trichinella infested pork / meat.