Trypanosomosis is an infectious disease which infects cattle, buffalo, goat, sheep, pig, horse, donkey, camel and dog characterized by high rise of temperature, anaemia, wasting and cutaneous eruptions.
Distribution
The disease is widely distributed in tropical and subtropical countries. It is also prevalent in Middle East, Far East, Central and South America and Africa. In India, the disease has been recorded from all the states.
Aetiology
The disease is caused by protozoan parasite Trypanosoma evansi. This was first reported by Evans in 1918 in comes from India. T. evansi is long, slender organism having free flagillum. The organisms are actively motile. They divide by binary longitudional fission. T. evansi is indistinguisable from T. brucei and it is believed that T. evansi has evolved from T. brucie following its introduction into camel and its adaptation to direct transmission by Tabanus. Strains of T. evansi from various geographical areas vary in their virulence for animals. T. evansi can be grwon in Novy Macneal Niccolle (NMN) medium and in developing chick embryo. Nutrition of the protozoa occurs by pinocytosis (engulfing of liquid droplets) or by phagocytosis (engulfing of solid matter).
Susceptible Hosts
It is an important disease in camel and horse. Dog also suffer. Cattle and buffaloes show subclinical infection and act as carrier. But, clinically apparent infection is also possible. Besides, the disease is recorded in mules, donkeys, elephants, cats, sheep and goats. Experimental infection can be produces in rats, mice, rabbits and guinea pigs.
Mode of Transmission
The disease is transmitted echanically hrough the bites of flies. Tabanus, Haematopota, Lyperosia and Stomoxys spp. 30 species of Tabanus are able to transmit T. evansi.
Carriage by Ornithodorus spp. of tick has been suggested (phoretic transmission).
Vampire bat (Desmodus rotundus) can be infected from blood feeds and act as vector. It transmits trypanosome through saliva when feeds on new hosts.
Carrier animals remain as potential source of disease transmission. Close herding and stabling lead to increase transmision.
The disease can be transmitted experimentally in mice, rabbits, guinea pigs, rats, dog and cattle. Injection of hydrocortisone increases higher susceptibility and higher parasitaemia.
Pathogenesis
Anaemia is the perincipal pathological change which is attributable to extra-vascular destruction of RBC. The distruction of RBC may be through the process of erythro phagocytosis. This may be immune mediated. Metabolic products and toxins liberated from the protozoa may alter the blood-sugar level and glycogen reserve. Changes in plasma constituents include increase in fibrinogen degradation product and increased macroglobulin (IgM). The reason for this increase may be due to rapid succession of antigenic variants and non-specific stimulation to B-cell proliferation. Increased macroglobulin level causes increased viscosity of plasma resulting to stasis of blood. Kinins released from antigen-antibody complexes may cause increased endothelial permeability of vessels to oedema. Probable causes for death in trypanosomiasis are:
- Decreased blood glucose level (Hypoglycaemic shock).
- Toxaemia due to endotoxin liberation by the lysed parasites.
- Low glucose reserve due to hepatic changes (Hepatopathy).
- Respiratory distress due to elevated blood lactate level.
- Arrested erythrocyte production due to liberated toxin.
Clinical Findings
Cattle and Buffalo: In endemic areas cattle and buffalo usually carry subclinical infection but overt disease may ensue due to stress, inter current infection, starvation and debility. Subacute or chronic form is common. There is transient rise of the body temperature, enlargement of superficial lymph glands, emaciation, progressive weakness and anaemia. Animals continue to feed until signs of peripheral circulatory failure develops. Course ranges from 30 to 96 days in buffalo calves and 22 to 40 days in cross bred cow calves.
The symptoms in buffaloes are similar to cows. Chronic cases remain as asymptomatic for a long period. But, signs like progressive loss of body weight, mild anaemia and poor appetite will persist. There is muco-purulent discharge from the eyes. Oedema of the dependent parts may be the feature. Chronic form may interfere with reproductive performances comprising of delayed oestrous, abortion and still birth.
Acute form is characterized by elevation of temperature, congestion of conjunctival mucous membrane, erection of hairs and digestive disturbances. Keratitis and occasional blindness may occur. There is oedematous swelling of tongue. Nervous signs may be noted. The course is for 8 days. This form terminates fatally in young and debilited animals. Some animals show nervous manifestations characterized by convulsions, ataxia, apparent blindness and frenzy.
Horse and Donkeys: They suffer from acute, sub-acute or chronic form of disease. Severe infection occurs in horse characterized by fever, emaciation, oedema and death. Signs like sweating, rigors, lacrimation, nasal discharge and hyperaesthesia are seen. Animal may die all of a sudden. Urticarial plaques may be noted on the neck, back and flank region. Conjunctiva shows petechial haemorrhage. There is extreme emaciation. Muscles of hind quarters are atrophied and nerves are affected and paralysis supervenes.
Camel: Surra has got economic importance in camel. The disease is chronic in nature. There is intermittent fever, progressive anaemia, emaciation and oedema of the dependent parts.
Dog: The dog may suffer from acute form of trypanosomiasis. The disease can be produced experimentally. There is intermittent fever, anaemia, oedema, corneal opacity and poor appetite.
Diagnosis
The diagnosis is based on the following criteria:
- Demonstration of parasite in blood films.
- Movements of the parasites under hanging drop method.
- Biological test: Mice inoculation test
- Increased serum protein level: beta and gamma globulin levels have been found to increase in affected animals.
- Low blood glucose level
- Mercuric chloride test
- Formol gel test
- Stilbamidine test
Serological Tests
- Complement fixation test
- Passive haemagglutination test
- Indirect fluorescent antibody test
- Enzyme liked immunosorbent assay
- Polymerase chain reaction
Treatment
Drugs used against T. evansi infection:
- Quinapyramine sulphate (Antrycide) used as curative in camel, buffalo, pig @ 4 mg/kg body weight.
- Quinapyramine prosalt (Tribexin) is used in cattle and horse both as curative and prophylactic @ 3.5 mg/kg body weight.
- Diminazene aceturate (Berenil) is used in cattle, buffalo, pig, dog @ 8-10 mg/kg IM.
Control
- Detection of infected animals should be done promptly.
- Isolation of the positive animal should be made from rest of the herd.
- Treatment of the animal should be rendered as promptly as possible.
- Vectors should be controlled as far as practicable.
- Quinapyramine (suramin) can be used as prophylaxis in endemic areas.
