Trichinella spp

From Dog
Encysted larval stage of T. spiralis in muscle[1]
Adult T. spiralis[2]

Trichinella are a parasitic nematode of most carnivores, including dogs.

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[3].

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[4].

Species which are pathogenic to dogs include:

  • Trichinella spiralis[5]
  • Trichinella nativa[6]
  • Trichinella murrelli[7]

Older dogs appear to have a higher seroprevalence, presumably due to length of exposure[8].

Clinical signs are often nonspecific and depend on the stage of infection. The intestinal phase may be marked by vomiting, diarrhea or abdominal pain[9][10]. 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)[11]. An ELISA has been produced but is not commercially available[12].

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[13].

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.

References

  1. Tropical Medicine
  2. Microbe World
  3. Cui J & Wang ZQ (2001) Outbreaks of human trichinellosis caused by consumption of dog meat in China. Parasite 8(2):S74-S77
  4. Bowman, DD (2009) Georgis' parasitology for veterinarians. 9th edn. Elsevier Saunders, Missouri. pp:222-223
  5. Franco Sandoval LO et al (2012) Molecular similarities and differences between Trichinella spp., isolated from canine skeletal muscle in Zacatecas, Mexico. Exp Parasitol 131(2):148-152
  6. Lu Y et al (2011) Molecular identification of three Trichinella isolates from Heilongjiang Province, People's Republic of China. Exp Parasitol 129(3):299-302
  7. Dubey JP et al (2006) A Trichinella murrelli infection in a domestic dog in the United States. Vet Parasitol 137(3-4):374-378
  8. Oivanen L et al (2005) The prevalence of Trichinella infection in domestic dogs in Finland. Vet Parasitol 132(1-2):125-129
  9. Rice L et al (1990) Trichinosis in a dog. J Am Vet Med Assoc 197(4):480-482
  10. Bowman DD et al (1993) Treatment of experimentally induced trichinosis in dogs and cats. Am J Vet Res 54(8):1303-1305
  11. Bowman DD et al (1991) Signs, larval burdens, and serological responses of dogs experimentally infected with Trichinella spiralis Owen, 1835. Folia Parasitol (Praha) 38(3):245-253
  12. Yang SM (1989) A preliminary study on the use of enzyme-linked immunosorbent assay (ELISA) for detection of Trichinella spiralis infections in dogs. Vet Parasitol 31(2):165-171
  13. Mikhail EM et al (1994) Identification of Trichinella isolates from naturally infected stray dogs in Egypt. J Parasitol 80(1):151-154