Heterobilharzia spp

From Dog
Egg of H. americana under light microscopy[1]
Adult female residing within the gynaecophoral groove of the male fluke[2]

Heterobilharzia spp are a parasitic intestinal fluke of dogs.

Heterobilharzia are a trematode with sexual dimorphism. The male is the larger of the two, and has the gynaecophoral groove where the female resides following mating. Separate sexes are the distinguishing feature of the schistosomes.

The primary pathogenic species which affects dogs is:

  • Heterobilharzia americana.

This parasite is responsible for causing schistosomiasis and is found primarily in the mesenteric veins of canines across south-eastern USA.

The life cycle of this parasite involves snail intermediate hosts, the cercariae escape into water and penetrate the skin of dogs and other carnivores, where it migrates to the liver, mature, and move to the mesenteric vessels. Granulomas form around the eggs in the wall of the intestine, liver, kidney and other parts of the body[3].

Common clinical signs in infected dogs include glomerulonephritis[4], peritoneal effusion, anemia, anorexia, intermittent vomiting and diarrhea[5].

Systemic disease may occur due to mineralisation of extraintestinal fluke eggs, resulting in a wasting syndrome in heavy infections[6]. 'Water dermatitis' has been reported when cercariae penetrate the skin.

Lymphosarcoma has also been reported in a dog infected with this parasite[7], presumably arising from chronic inflammation of regional lymph nodes.

The eggs do not readily float and, if placed in water, hatch within minutes; therefore, a sedimentation method using 0.85% saline is useful in separating eggs from ingesta.

In infected dogs, eggs are passed intermittently, so on a given day they may not be found in feces.

Fenbendazole (40 mg/kg, PO, sid for 10 days) as well as Praziquantel appear to be effective against this parasite.

References

  1. Gastrointestinal Laboratory
  2. Uni of Pennsylvania
  3. Fabrick C et al (2010) Clinical features and outcome of Heterobilharzia americana infection in dogs. J Vet Intern Med 24(1):140-144
  4. Ruth J et al (2010) Heterobilharzia americana Infection and Glomerulonephritis in a Dog. J Am Anim Hosp Assoc 46(3):203-208
  5. Kvitko-White HL et al (2011) Imaging diagnosis-heterobilharzia americana infection in a dog. Vet Radiol Ultrasound 52(5):538-541
  6. Corapi WV et al (2011) Multi-organ involvement of Heterobilharzia americana infection in a dog presented for systemic mineralization. J Vet Diagn Invest 23(4):826-831
  7. Stone RH et al (2011) Lymphosarcoma associated with Heterobilharzia americana infection in a dog. J Vet Diagn Invest 23(5):1065-1070