Trypanosoma evansi and surra: a review and perspectives on origin, history, distribution, taxonomy, morphology, hosts, and pathogenic effects

Abstract

Trypanosoma evansi, the agent of "surra," is a salivarian trypanosome, originating from Africa. It is thought to derive from Trypanosoma brucei by deletion of the maxicircle kinetoplastic DNA (genetic material required for cyclical development in tsetse flies). It is mostly mechanically transmitted by tabanids and stomoxes, initially to camels, in sub-Saharan area. The disease spread from North Africa towards the Middle East, Turkey, India, up to 53° North in Russia, across all South-East Asia, down to Indonesia and the Philippines, and it was also introduced by the conquistadores into Latin America. It can affect a very large range of domestic and wild hosts including camelids, equines, cattle, buffaloes, sheep, goats, pigs, dogs and other carnivores, deer, gazelles, and elephants. It found a new large range of wild and domestic hosts in Latin America, including reservoirs (capybaras) and biological vectors (vampire bats). Surra is a major disease in camels, equines, and dogs, in which it can often be fatal in the absence of treatment, and exhibits nonspecific clinical signs (anaemia, loss of weight, abortion, and death), which are variable from one host and one place to another; however, its immunosuppressive effects interfering with intercurrent diseases or vaccination campaigns might be its most significant and questionable aspect.

Figure 1

Geographical distribution of Trypanosoma evansi in the world (data synthesis).

Figure 2

Hypothetical evolution tree for the Trypanozoon subgenus (data synthesis).

Figure 3

Morphological features of Trypanosoma evansi: classical forms in camel blood (M. Desquesnes). Legend: T. evansi in camel blood (France), Giemsa stained blood smear; typical morphology can be observed: large size (25–35 μm), small and subterminal kinetoplast, thin posterior extremity, large undulating membrance, central nucleus, and free flagellum.

Figure 4

Morphological features of Trypanosoma evansi classical and truncated forms (M. Desquesnes). Legend: T. evansi in cattle blood (Thailand), Giemsa stained blood smear; typical morphology can be observed: with thin posterior extremity (head of arrows), together with truncated forms (arrows) whose posterior extremities are truncated just below the kinetoplast location.

Figure 5

Chronic (up) and acute (down) evolution of surra in horses (M. Desquesnes).

Figure 6

Weight loss and testicular oedema in a horse infected with T. evansi in Thailand (M. Desquesnes).

Figure 7

Chronic evolution of surra in cattle and buffalo.

Figure 8

Hind leg paralysis in a pig naturally infected by Trypanosoma evansi in Malaysia (courtesy, Dr. Chandrawathani Panchadcharam).

Figure 9

Fibrin deposit in the anterior chamber of the eye, in a mixed German shepherd, naturally infected by Trypanosma evansi, Chiang Mai, Thailand (courtesy Miss April Terry).

Box 1

The main characteristics of Trypanosoma evansi.