Nanophyetus spp

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Nanophyetus salmincola adult - the salmon poisoning fluke of dogs

Nanophyetus (Troglotrema) spp are a parasitic intestinal fluke of dogs.

The pathogenic species, Nanophyetus salmincola is responsible for 'salmon poisoning' of dogs and wild carnivores in the northwestern USA, Canada and Siberia.

This intestinal fluke measures 0.5 × 0.3 mm, ovoid in shape and resides in the small intestine of dogs where it is relatively nonpathogenic, although may cause enteritis and diarrhea in large numbers. However, coinfection of the fluke with Neorickettsia helminthoeca, an obligate intra-cytoplasmic bacterium may be fatal to some dogs[1].

Eggs are passed in the feces of infected hosts, are light brown, 55 × 45 µm, and indistinctly operculated with a small knob at one pole. The life cycle includes an extended period (up to 7 months[2]) of embryonation. The first intermediate hosts are snails found in endemic locations (eg, Oxytrema silicula in the USA). The cercariae from these snails penetrate the skin of young salmonid fishes and encyst as metacercariae in their muscles and organs[3]. Dogs and other animals become infected by eating raw or improperly prepared infected fish[4].

Because these flukes embed deeply between the villi of the intestine, infection with a large number may cause enteritis. Most infections, however, are complicated through development of the salmon poisoning complex caused by rickettsial organisms, which the fluke transmits.

Praziquantel (6.7-38.7 mg/kg, SC or IM, once) and fenbendazole (50 mg/kg, PO, sid for 10-14 days) are both effective treatments for dogs[5].

References

  1. Headley SA et al (2011) Neorickettsia helminthoeca and salmon poisoning disease: a review. Vet J 187(2):165-173
  2. Ferguson JA et al (2010) Persistence of infection by metacercariae of Apophallus sp., Neascus sp., and Nanophyetus salmincola plus two myxozoans (Myxobolus insidiosus and Myxobolus fryeri) in coho salmon Oncorhynchus kisutch. J Parasitol 96(2):340-347
  3. Ferguson JA et al (2011) Survey of parasites in threatened stocks of coho salmon (Oncorhynchus kisutch) in Oregon by examination of wet tissues and histology. J Parasitol 97(6):1085-1098
  4. Merck Veterinary Manual
  5. Fritsche TR et al (1989) Praziquantel for treatment of human Nanophyetus salmincola (Troglotrema salmincola) infection. J Infect Dis 160(5):896-899