These small worms (3 - 4 mm) are found embedded in the small intestine of dogs, pigs and occasionally humans. Outbreaks of trichinosis have been reported commonly in humans that eat contaminated pig and dog meat.
Intermediate hosts (including dogs, pigs and rats) become infected by eating infective third-stage larvae in raw-meat. Larvae penetrate the small intestinal mucosa. After 5 days, the viviparous females lay eggs, which are swept into the lymphatic system and transported to muscle. Dogs become infected by eating contaminated prey or uncooked food containing encysted striated muscle larvae. The parasite can complete all stages of development in one host. Infective larvae excyst in the gut of dogs that eat the infected meat. The worms mature and reproduce in the small intestine. Newborn larvae migrate to the muscles where they encyst. The intestinal phase in dogs can last 3 - 4 months, and immunosuppression may result in recrudescence of larvae in dog muscle.
Species which are pathogenic to dogs include:
Older dogs appear to have a higher seroprevalence, presumably due to length of exposure.
Clinical signs are often nonspecific and depend on the stage of infection. The intestinal phase may be marked by vomiting, diarrhea or abdominal pain. Systemic symptoms follow, with joint and muscle pain, edema, fever, and eosinophilia as larvae migrate and encyst.
Diagnosis is usually based on coprological identification of Trichinella eggs in feces and supprtive hematological changes such as eosinophilia, and elevated creatinine kinase (which appears to be unrelated to stage of infection). An ELISA has been produced but is not commercially available.
Muscle biopsies showing histological evidence of T. spiralis larvae are considered definitive. Parasitic larvae may be found in skeletal dorsal and limb muscles as well as the diaphragm.
Although adult Trichinella are sensitive to ivermectin and related macrocyclic lactones, treatment is difficult because of the encysted larval stages.
Palliative care is important in domestic dogs, with non-steroidal anti-inflammatory drugs indicated in acute trichinosis to alleviate fever and myalgia.
- Tropical Medicine
- Microbe World
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