Surra in Horses: Trypanosoma evansi Tests

Surra is a blood infection caused by a tiny parasite called Trypanosoma evansi, which biting flies carry from one animal to another. In horses it may cause fever that comes and goes, weight loss and swollen legs. A blood smear, an antibody ELISA and RT-PCR can help detect it, and a registered veterinarian reads the results with the horse's signs.

What is surra and how does it spread?

The parasite is a single cell that swims in the liquid part of the blood. Biting flies, such as horseflies and stable flies, spread it. A fly feeds on an infected animal, is disturbed, and soon feeds again on another. Blood on a shared needle or tool can also carry the parasite.

Surra can be serious in horses, so a horse that may have it needs a vet promptly. It is a notifiable disease, so owners should tell their veterinarian or the animal husbandry department if they suspect it.

What signs may owners notice?

Common signs include a fever that comes and goes, weight loss even though the horse keeps eating, weakness, pale gums, and swelling of the legs or the underside of the belly. Between fever spells a horse may look almost normal, which is why owners sometimes wait too long.

Many other illnesses cause similar signs, tick fever among them, so a lab test is needed to tell them apart. A horse with these signs needs a vet promptly, and urgent care should never wait for a lab result.

How should the sample be taken?

Your vet draws the blood from a vein in the neck. A wet film needs fresh blood, so tell the lab if the horse is feverish when you book, and ask which tubes to use. Label each tube with the horse's name and the date, and keep it cool and out of the sun. Tell your vet about any medicine the horse has had lately, because it can change what the tests find.

Why can a blood smear miss surra?

The number of parasites in the blood rises and falls. A sample drawn when the number is low may show none, and a negative smear then proves little.

The Trypanosome Detection (Wet Film & Buffy Coat Smear) helps in two ways. In a wet film, a fresh drop of blood is watched under the microscope for parasites that are moving. In a buffy coat smear, blood is spun so that white cells and parasites gather in one thin layer, which makes the parasites easier to spot. A sample drawn while the horse is feverish may be more likely to catch them. Seeing the parasite supports the diagnosis, but not seeing it does not rule surra out.

What do the antibody and RT-PCR tests add?

The Trypanosoma evansi (Surra) Antibody ELISA looks for antibodies, the defence proteins a horse makes after meeting the parasite. A positive result shows contact with the parasite, though not always that the infection is active now. A negative result can happen early on, before antibodies have formed.

The Trypanosoma evansi (Surra) RT-PCR uses RT-PCR (real-time PCR) to look for the genetic material of the parasite in a blood sample. It can find small numbers when a smear sees none. A negative still does not always rule surra out. Your vet may use one test, several, or repeat a test after a gap. The lab confirms the method when you book.

How does a blood count help?

The Complete Blood Count (CBC) counts the red cells, white cells and platelets. In a horse with a long-running blood parasite it may show anaemia (too few red cells) and changes in the white cells. These are clues, not proof, because other illnesses do the same. A CBC also lets your vet follow how the horse is coping.

For several checks together, the Horse Disease Screening Pack typically includes a surra smear along with other horse disease tests. The exact list is confirmed when you book.

Read next

Older Horse Lab Tests: Kidney, Liver and Thyroid covers the organ checks a vet may add when an older horse loses weight or energy, since surra is only one of several possible causes. Online Lab Reports: My Reports and WhatsApp, How It Works explains how reports reach you, which helps when a horse needs more than one test.

Testing in Bhopal

Surra is a case where your vet and the lab should talk early. Phone or WhatsApp +91 88175 01118 and the team will guide you on the smear, the ELISA and the RT-PCR. The lab is at C-200, C Sector, Shahpura, Bhopal, with free sample collection anywhere in Bhopal, and your vet usually draws the blood from the horse. Samples from other districts can come by courier, bus parcel or through the local vet. The lab confirms the method, sample needs and reporting time when you book.