Trypanosoma evansi (Trypanosoma equinum)

Location and host

• Found in blood of cattle, sheep, goat, horse, donkey, camel, pig, dog, cat.

Morphology

• These parasites are identical and structurally similar in appearance with selender forms of brucei
• Mean length varies with typical form (5-34 µm) long.
• Most are slender or intermediate in shape
• Kinetoplast is upto 4 µm from posterior end. Usually drawn out, tapering to point end and has well developed free- flagellum
• Undulating membrane is well- developed
• In intermediate form, free flagellum is shorter and posterior extremity is short and frequently truncated.
• Forms lacking kinetoplast may arise spontaneously especially after drug treatment.

Life-cycle

• Transmission is mechanically through biting flies such as Tabanus, Stomoxys, Haematopota. Chrysops, Lyperosia and Hippobosca
• Ticks of genus ornithodoros i.e. crossi and O. laborensis are involved in transmission of T. evansi.
• There is interrupted feeding habit of flies which go quickly from one host to other in order to multiply as parasite don not survive in the proboscis of flies for more than 10-15 minutes.
• No cyclical development

Pathogenesis

• Disease caused by this parasite is called ‘malde caderas’ in horse which is similar to surra. It is chronic wasting disease of horse.
• In other host such as dog, cattle, sheep, goat, camel, disease caused by evansi is called surra. Surra is derived from Hindi word meaning ‘rotten’.
• Depending on virulence of strain and susceptibility of individual host, disease may be acute in horses, camels and dogs. Other species are commonly affected, but overt (Clinically apparent) disease is uncommon and their main significance is as reservoir of infection.

Clinical signs

• All domestic animals are susceptible but disease is fatal in horses, camels and dogs

Horses

• Intermittent fever with temperature rising to 44 ⁰C
• Anemia, loss of condition
• Depression
• Oedema of leg and lower parts of body
• Transient local or general urticarial eruptions. This is followed by febrile paroxysm (recurrent fever attacks ), plaques are usually seen on neck and flanks
• Petechial hemorrhage on mucous membrane of eye particularly in nictitating membrane and sometimes vulva in mares. Mucous membrane becomes pale and at later stage appears dirty yellow.
• Animal becomes dull, listless and leg-weary ( tired or arching legs).
• Rapid and labored respiration, Pulse frequent and small.
• Staggering gait and ultimately paraplegia ( paralysis of both legs ) occurs
• Increased thirst, constipation and diarrhea in later stage
• Urine becomes viscid and dark yellow and contains albumin and blood.

Cattle and buffaloes

• Course of disease varies from asymptomatic state to per acute infection. Young and debilitated animals suffer severely.

In acute cases

• Affected animals appear dull and sleepy
• Animals show staggering gait.
• Eyes staring and wide open
• Hard breathing and noisy
• Circling movements
• Tilting of head against hard object
• Apparent blindness
• Stamping of feet, bellowing, grooming
• Frequent micturition, salivation, twitching of muscle
• Shivering of body followed by coma, collapse and death in 6-12 hours.

Per acute cases: Shows nervous signs within 2-3 hours

In sub-acute and chronic cases

• Animals are dull, sleepy and have bilateral lacrimation
• Progressive emaciation, rapid pulse, intermittent attacks of fever, oedema of legs, diarrhea and death from exhaustion

Dogs and cats

• Severe in exotic breeds of dogs. Disease is more severe in pups than adult. Incubation period is 6-10 days.
• Fever, anorexia
• Edema of head and throat
• Corneal opacity and blindness
• Oedema of larynx change voice of dogs similar in case of rabies
• Muscular spasm, staggering gait and excitement like biting of kennel bars
• Dogs die within 1-2 months
• Chronic case occur in cats and may be fatal

Camel

• Disease in camels is known as ‘fibersa’ meaning 2 years duration
• Intermittent fever
• Animal appear dull and listless
• Hump disappears and animal becomes anorectic
• Oedema on pads, abdomen, scrotum and sheath in males and on breasts in females. They may suppurate
• Nervous signs like periodic convulsion
• Similar signs and symptoms appear in elephants. Not much pathogenic in sheep and goat shows anemia and emaciation

Diagnosis

• Hostory of prevalece of evansi infection and biting flies especially tabanids.

Clinical signs

• Examination of blood and body fluids
• Chemical test
• Animal inoculation test
• Immunodiagnostic test : Indirect hemagglutination test (IHA), immunofluorescent antibody test (IFAT), Complement fixation test (CFT) and ELISA.

Treatment

• Suramin or quinapyramine (Trypacide) are drugs of choice for treatment. Suramin is given @ 10mg/kg body weight I/V in horses.