appetite, weight loss, abortion, and incoordination,
followed by paralysis of the hind limbs. Researchers
divide these clinical signs in two or three stages
of the disease: subacute, acute, and chronic. In
the chronic stage, horses usually exhibit cachexia
(chronic wasting) associated with neurological signs
and limb paralysis. Neurological signs are the result
of the parasite travelling to the brain, where it causes
an inflammatory response leading to encephalitis
and cellular necrosis.
Trypanosomiasis caused by T. evansi can be clinically
confused with other diseases, including equine
protozoal myeloencephalitis in the chronic stages.
Where surra is suspected, it is important to rule
out other causes of equine neurologic disease.
Most available diagnostic methods include the
parasitological, serological, and polymerase chain
reaction (PCR). The parasitological test is fast, but it
lacks specificity and sensitivity due to low numbers of
the parasite in the bloodstream. Serology, employing
a card agglutination test kit known as CATT/T. evansi,
has been a method used for disease surveillance in
several countries. PCR testing on blood samples is a
specific and sensitive method; however, it is not 100
percent reliable since T. evansi may only be present
in the tissues.
Like any infectious agent, T. evansi stimulates an
immune response in the infected animal. While
this response is unable to clear the infection from
the host, it controls and maintains the parasitemia
at low levels, resulting in the disease becoming
chronic. In many countries, the disease is treated
with diminazene aceturate. However this drug,
even when used at the recommended dose, has
no significant curative