Trypanosoma evansi, a notorious blood-borne parasite

Trypanosomiasis is a disease of great economic importance in camels and other livestock. It causes severe economic losses. Trypanosoma evansi is considered a notorious blood-borne parasite

Trypanosoma evansi, a notorious blood-borne parasite

Trypanosomiasis is a disease of great economic importance in camels and other livestock. It causes severe economic losses. Trypanosoma evansi is considered a notorious blood-borne parasite that is responsible for this disease in camels.

Camels belong to camelidae family and are even-toed ungulates. Camels are mostly reared for drought purposes, but they serve humans with meat and milk in many areas of the world. They are friendly and gentle creatures. By natural default, camels have adaptations to survive in the harsh and dry environment with low water availability, such as deserts.

Just like humans, there are various diseases which affect the well-being and overall performance of camels. The diseases can be of different types such as infectious, metabolic, nutritional etc.

Here, we will discuss a parasitic disease “Trypanosomiasis” in camels and related facts and figures under the light of scientific literature.

What is Trypanosomiasis?

This is a parasitic disease that is caused by a hemoflagellate parasite (blood-borne) that is transmitted to the host with the help of a vector fly.

Epidemiological aspect:

Many hundred years ago, Trypanosoma was first discovered in India by Evans. This protozoan parasite was identified in various animals’ species including horses, camels and mules. That time, this disease was locally termed as “Surra”.

After that, this disease was widely discovered in Africa, America and other pockets of the world. This has been observed that dromedary camels are more susceptible to this disease as compared to other camels.

Causative agent:

There are many species of Trypanosoma which have been reported so far. In camels, Trypanosoma evansi causes this disease.


This protozoan parasite transmits from one camel to another camel via a blood sucking (hematophagous) fly. This has been scientifically documented that Tabanids (horsefly) are the major vectors which transmit T. evansi to the host animals.

Additionally, other flies such as Lyperosia and Stomoxys species are also involved in the transmission of this parasite.


Vectors feed on an infected camel and T. evansi get attached with the mouth-parts of the fly and subsequently the fly transmits it to another healthy animal. After getting entry into the healthy camel, this parasite replicates and manifestation of clinical signs and symptoms occurs.

However, severe clinical infestation has been reported in camels by this disease. But many veterinary scientists state that camels often carry this parasite and usually don’t show clinical signs and symptoms (Asymptomatic reservoirs).

Differentiation of Trypanosoma evansi from other related species:

T. evansi belongs to the subgenus “Trypanozoon”. This particular parasite makes slender which other species of this genus don’t actually form. Moreover, this species is not limited to the bloodstream of the host. T. evansi crosses the blood-brain barrier and enters in joint fluids, other body fluids and compartments.

Trypanosoma evansi usually becomes hard to distinguish from T. brucei. There is a technique named “Isoenzyme electrophoresis”. This molecular technique helps in differentiation of the both species.

Clinical manifestation:

Trypanosomiasis attacks the camels at any age (camels of all ages are susceptible). However, this has been observed that a high incidence of this infection prevails in juvenile camels after weaning.

There are a variety of signs and symptoms which infected camel shows. Here, we have summarized some key signs and symptoms:

1) Reduction in the body weight
2) Rough and dry body coat
3) Odema (accumulation of fluid) may occur in feet, eyelids, brisket and other areas of the body.
4) Fever with shivering. *Fluctuating fever is usually seen and can reach upto 41 ºC
5) Loss of appetite (Anorexia) along with mild diarrhea.
6) Lacrimation (watery/teary eyes) may be seen.
7) Camels become anemic progressively.
8) Pale mucous membranes due to anemia.
9) Characteristic smell/odor in the camel’s urine due to ketone bodies.
10) Abortion in pregnant female camels.

Death of infected newborn usually occurs within two weeks of age. However, reduction in milk production of nursing/lactating female camels along with abnormal lesions in the central nervous systems usually observed as sequela. Generally, this disease affects the overall productivity, performance and weight gain of a camel herd.


In severe waves of infection, mortality can reach up to 20%. But it depends upon other factors as well, such as:

1) Immune status of camel herd
2) Presence of other infection
3) Nutritional status
4) Stress
5) Age


There are various diagnostic tools which help in the better diagnosis of this disease. However, in field conditions, where there are no laboratory facilities, diagnosis is made on the basis of thorough clinical examination along with related signs.

Direct methods:

These methods include microscopy, Thick and thin blood smears, fresh lymph smears, thin lymph smears. Other methods include the direct inoculation of camel’s blood in the lab animals such as rodents, which just give the idea about the subclinical infection.

Other concentration based methods include Hematocrit centrifuge technique (HCT), buff coat technique and miniature ion-exchange centrifugation technique.

Indirect methods:

Mercuric chloride test and formal gel tests. These tests basically detect the high globulins levels in the infected camel’s serum. Remember, these tests are non-specific and high globulin levels are one of the major indicators of trypanosomiasis.

Molecular techniques:

DNA extraction and polymerase chain reaction (PCR) also show good results in diagnosis of the T. evansi.

Serological methods:

Best serological techniques include ELISA-T. evansi (Enzyme-linked immunosorbent assay T.evansi) with special use of a manufactured protein A-Peroxidase coagulate, passive haemagglutination test, capillary agglutination test, immunofluorescent antibody test and Card agglutination test (CAT).

This has been documented that ELISA-T gives the 90-95% specificity and sensitivity in the camels. Overall, these techniques give nice outcomes in detection of T. evansi in camels.

Treatment & prevention:

Two drugs which are usually recommended to treat trypanosomiasis are Quinapyramine and Suramin. But T. evansi has developed resistance against these drugs. To cope up with this drug resistance, Isometamidium is widely used to treat trypanosomiasis in camels.

Important note:

This is always recommended to consult a registered veterinary physician. S/he will suggest a better treatment protocol on the basis of the current health status of the camel. Don’t use any drug without the instruction/ prescription of a registered veterinary physician.

Prevention includes the effective control of vector flies and separation of the infected camel from the healthy ones.

Quick Review:

Name of disease Trypanosomiasis
Common names Surra, three years disease, Menchaca
Causative agent/vector Trypanosoma evansi/ tabanids flies
Host Camels (dromedary camels)
Anemia YES
Diagnosis ELISA, PCR. CAT, direct and indirect methods
Treatment Quinapyramine, suramin, Isometamidium and various trypanocides


Trypanosomiasis is a disease of great economic importance in camels and other livestock. It causes severe economic losses. Trypanosoma evansi is considered a notorious blood-borne parasite that is responsible for this disease in camels.

Camels show a variety of signs and symptoms including anemia, fever, tachycardia, dullness, loss of appetite and many more. There are various molecular, serological, direct and indirect tests which show varying levels of specificity and sensitivity in camels. Treatment includes use of several drugs only under the supervision of a veterinary expert.

This article is jointly written by Muhammad Jawad Bashir, Dr. Muhammad Ashraf and Zoha Naeem