Trypanosoma

(Trypanosoma evansi)

Trypanosoma evansi is a protozoal pathogen closely related to African trypanosomes which causes the disease ‘Surra’ in ruminants, horses and camels. Dogs are highly susceptible to T. evansi infection and they often exhibit severe clinical signs than can lead to death.

Parasite: Trypanosoma evansi
Common name: ‘surra’
Hosts: Ruminants, horses, camels, dogs, cats
Location in host: free in bloodstream
Distribution: Asia, Latin America, North Africa
Transmission route: biting insects (tabanids and stomoxes), iatrogenic, oral transmission.
Zoonotic: Yes

Distribution

The disease spread from North Africa towards the Middle East, Turkey, India, southern Russia, across all South-East Asia, down to Indonesia and the Philippines and into Latin America.

Clinical signs

T.evansi infection in dogs includes fever, anorexia, lethargy, lymphadenomegaly, hepatosplenomegaly, edema, ascites, petechial hemorrhages, uveitis, oculonasal discharge, corneal edema reminiscent of blue eye caused by canine adenovirus infection, and neurological signs associated with meningoencephalitis.

Diagnosis

The diagnosis of T. evansi trypanosomiasis involves detection of trypomastigote forms of the parasite by cytology of blood, body fluids or tissues by microscopy (Fig 1). Dogs may have anemia, leukocytosis or leukopenia and thrombocytopenia. Serum biochemistry abnormalities include increased activities or liver enzymes, azotemia, hypoalbuminemia and hyperglobulinemia.

PCR with sequencing are useful for detection of low parasitemias and for species determination.  ELISA, IFA and the card agglutination trypanosomiasis test (CATT) are available for the detection of antibodies against T. evansi.

Treatment

T.evansi infection in dogs can be treated with off-label use of diminazene aceturate at 5mg/kg IM or suramin (70 mg IV in 100 mL 0.9% NaCl TID every third day till resolution of parasitaemia)1, with variable responses noted.

Figure 1. Trypanosoma evansi in a stained blood smear from an infected dog. (Image credit: Dr Bui Khanh Linh.)

Control

Disallowing consumption of raw meat and eliminating dog contact with vectors by using topical repellants and insecticides such as collars and spot-on formulations (e.g. permethrin, flumethrin, deltamethrin).

Public health considerations

Rare zoonosis. To date, five human cases of T. evansi infection have been reported. Livestock are considered primary reservoirs.

References

[1]  Defontis M, Rochartz J, Engelmann N, Bauer N, Schwierk C, Buscher VM, Moritz A. Canine Trypanosoma evansi infection introduced into Germany. Vet Clin Pathol. (2012), 41(3), 369-74.