Trypanosomiasis in Horses

Trypanosoma Infection in Horses:
Mal de Caderas, Dourine, Surra and Nagana

by Robert N. Oglesby DVM

Introduction

The Trypanosomatids are a rather large group of spindle shaped, flagellated protozoans that infect horses, livestock, and humans. Though trypanosomiasis is primarily a problem in the tropical and subtropical regions around the world the disease extends northward into Asiatic Russia and southern Europe. There are a number of different species that create slightly different clinical syndromes which are known as Dourine, Sura, and Nagana or African Animal Trypanosomiasis (AAT) however symptoms can overlap so clearly identifying the causative trypanosome may not be possible from clinical signs alone. In South America the disease is known as Mal de Caderas.

Clinical disease can vary from chronic to acute and usually typified with weight loss, anemia, and edematous swelling. In some syndromes you also will find fever, reproductive problems including swelling of the genitalia and abortion, and neurological problems. Though some species are not strongly pathogenic others can result in death. The species that infect horses do not infect humans and vice versa. Some of the diseases caused by Typanosoma sp. are:

Human
- Chagas, Trypanosoma cruzi, South and Central America Mexico and rarely the Southern US
- East African and Gambian Sleeping Sickness, several species related to T. brucei, 15 o N to 25 o S (Africa): central belt from the Atlantic to the Indian Ocean coasts and from the sub-Sahara to the northern border of S. Africa
Horse
- Dourine, T. equiperdum, Africa, Middle East, Asiatic Russia, Central and South America. Once found widespread in North America, it has been eliminated from the US and Canada.
- Surra, T. evansi, found throughout India, Far East, North Africa north of 15 o N; Central and South America
- Mal de caderas, T. equinum, Central and South America
- Sleeping Sickness or Nagana, T. brucei and other sp., 15 o N to 25 o S (Africa): central belt from the Atlantic to the Indian Ocean coasts and from the sub-Sahara to the northern border of S. Africa

This article is about the important diseases caused by trypanosmoes that effect horses. Included is geographical regions, symptoms, diagnosis, treatment and prevention.

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The Trypanosomatid Family

The organisms that infect horses are slender and 15 to 30 microns long. They have a undulating membrane and a well-developed flagellum.

Trypanosomatids are generally divided into three groups depending on their method of reproduction and subsequent transmission:

mechanical or venereal transmission
insect intermediate host localized in saliva glands (salivarian roup)
insect intermediate host in hindgut (stercorarian group)

With the exception of Sleeping Sickness and Dourine the groups that effect horses are mechanically transmitted to horses usually by biting flies. Dourine is a venereal disease. Sleeping sickness requires the intermediate host the tsetse fly and is spread when an infected fly bites a horse.

Pathogenesis/Clinical Signs

Dourine / T. equiperdum

Horses very susceptible with donkeys as symptomless carriers. There are 3 stages which proceed step wise in the horse:

Mild fever, swelling from edema of the genitalia including the vulva, prepuce, and scrotum. There is a mucoid vaginal/urethral discharge. This stage lasts 4 to 6 weeks.
Raised skin plaques 2 to 10 cm (1 to 4 inches) diameter. These urticaria appear for 3 to 4 days, may disappear only to later reappear. These characteristics lesions are considered pathognomonic and when present this disease can be diagnosed.
The last stage is paralysis which may just affect the head to the complete body. Horses that progress to this stage have a 50 to 70% mortality rate.

Mal de Caderas / T. evansi

Horses are mainly effected. This is a chronic fever and wasting disease which generally terminates in the horse becoming emaciated, going down, and being unable to rise. There is a high mortality after about a 2 to 6 month course. The incubation period is 1 week with pyrexia and parasitemia appearing. Other important clinical features are splenomegaly, enlarged lymph nodes, and ascites.

Surra / T. evansi

Surra effects camels and horses and is often fatal. In horses symptoms include hives, (urticarial plaques) on neck and flanks, ventral swelling from edema, enlarged lymph nodes, fever, and death. In camels symptoms are fever, progressive emaciation, anemia, edema.

Nagana Sleeping Sickness / T. brucei and less frequently T. gambiense, vivax, congolensei

Initially these is intermittent fever, rapid emaciation, ocular and nasal discharge, icterus, edema that lasts 2-4 weeks. This is followed by the chronic from which may last several months and often is terminal with mental changes and paralysis developing with cerebral lesions.

Acute Encephalitis: T. evansi

Neuropathology of Naturally Occurring Trypanosoma evansi Infection of Horses.

Vet Pathol. 2009 Mar;46(2):251-258.
Rodrigues A, Fighera RA, Souza TM, Schild AL, Barros CS.
A. Rodrigues, Department of Veterinary Pathobiology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, 4467 TAMU, College Station, TX 77843-4467 (USA)Department of Veterinary Pathobiology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, 4467 TAMU, College Station, TX 77843-4467 (USA).

The clinical signs and pathology of the central nervous system in 9 horses with naturally occurring neurologic disease due to Trypanosoma evansi are described. The clinical course was 2 to 20 days; clinical signs included marked ataxia, blindness, head tilt and circling, hyperexcitability, obtundity, proprioceptive deficits, head pressing, and paddling movements. Grossly, asymmetric leukoencephalomalacia with yellowish discoloration of white matter and flattening of the gyri were observed in the brain of 7 of 9 horses. Histologically, all 9 horses had necrotizing encephalitis that was most severe in the white matter, with edema, demyelination, and lymphoplasmacytic perivascular cuffs. Mild to moderate meningitis or meningomyelitis was observed in the spinal cord of 5 of 7 horses. T. evansi was detected immunohistochemically in the perivascular spaces and neuropil of formalin-fixed, paraffin-embedded brain tissue in 8 of 9 horses.

Diagnosis

The clinical signs for Dourine in many horses are characteristic with the combination of history, venereal signs, and other symptoms providing a working diagnosis. But 1/2 of all horses with this disease may not show the genital swelling making further testing.

In endemic areas clinical signs for the other Trypanosoma diseases are suggestive but rarely diagnostic. Smears identifying the organism taken from exudates, lesions, or the blood can provide rapid diagnosis. The blood smears is most likely to be useful during febrile episodes. There are a number of good serological tests for the different forms of Trypanosomiasis. However cross reactivity with other pathogenic and nonpathogenic forms must be taken into account.

Treatment

Undefined drug failures and drug resistance have been common in the past but newer drugs may change this. Treatment in horses is generally considered impractical due to cost and failure rate. Instituting preventive strategies in large areas greatly attenuates the rate of new infection. The trypanocidal drugs for animal trypanosomiasis are either considered curative or prophylactic:

Curative:
- Sulfonated naphthylamine (Suramin R ) curative; IV; may need repeated doses
- Phenanthridine group:
- Homidium bromide (Ethidium) and
- Homidium chloride (Novidium) - given IM; often will sterilize infection
Prophylactic:
- Pyrithidium bromide (Prothidium) - SC or deep IM, preventative
- Quinapyramine chloride (Antrycide) - SC; preventative

Other control measures:

Under field conditions, largely dependent on prophylactic chemotherapy
Detect and destroy infected livestock
Control of biologic vectors such as the tsetse Glossina
Development of genetically resistant livestock

More Information on Treatment and Management

Vet Parasitol. 2008 Mar 14;
Health management of horses under high challenge from trypanosomes: A case study from Serengeti, Tanzania.

Auty H, Mundy A, Fyumagwa RD, Picozzi K, Welburn S, Hoare R.
Centre for Tropical Veterinary Medicine, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Roslin, Midlothian EH25 9RG, UK.

Horses kept for recreational riding purposes by a wildlife tourism company in a heavily tsetse fly-infested region of north-western Tanzania were systematically monitored to investigate the occurrence, presentation and management of tsetse-transmitted trypanosomosis. During a 23-month period, 18 clinical cases were diagnosed (Trypanosoma brucei or Trypanosoma congolense were identified) and treated and trypanosomes were implicated of involvement in four deaths. Pyrexia consistently aided early detection (17 cases). Ataxia, weight loss and anaemia were seen in chronic cases and conferred a poor prognosis. Delaying treatment by more than 2 days from the onset of clinical signs led to prolonged disease course and more severe anaemia. Early detection, prompt treatment, thorough post-treatment health monitoring and rigorous prophylactic measures helped keep clinical cases to manageable levels, but re-infection remained a constant, insidious threat.

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