Equine trypanosomosis: enigmas and diagnostic challenges

Abstract

Equine trypanosomosis is a complex of infectious diseases called dourine, nagana and surra. It is caused by several species of the genus Trypanosoma that are transmitted cyclically by tsetse flies, mechanically by other haematophagous flies, or sexually. Trypanosoma congolense (subgenus Nannomonas ) and T. vivax (subgenus Dutonella ) are genetically and morphologically distinct from T. brucei , T. equiperdum and T. evansi (subgenus Trypanozoon ). It remains controversial whether the three latter taxa should be considered distinct species. Recent outbreaks of surra and dourine in Europe illustrate the risk and consequences of importation of equine trypanosomosis with infected animals into non-endemic countries. Knowledge on the epidemiological situation is fragmentary since many endemic countries do not report the diseases to the World Organisation for Animal Health, OIE. Other major obstacles to the control of equine trypanosomosis are the lack of vaccines, the inability of drugs to cure the neurological stage of the disease, the inconsistent case definition and the limitations of current diagnostics. Especially in view of the ever-increasing movement of horses around the globe, there is not only the obvious need for reliable curative and prophylactic drugs but also for accurate diagnostic tests and algorithms. Unfortunately, clinical signs are not pathognomonic, parasitological tests are not sufficiently sensitive, serological tests miss sensitivity or specificity, and molecular tests cannot distinguish the taxa within the Trypanozoon subgenus. To address the limitations of the current diagnostics for equine trypanosomosis, we recommend studies into improved molecular and serological tests with the highest possible sensitivity and specificity. We realise that this is an ambitious goal, but it is dictated by needs at the point of care. However, depending on available treatment options, it may not always be necessary to identify which trypanosome taxon is responsible for a given infection.

Trypanosome infections in naturally infected horses and donkeys of three active sleeping sickness foci in the south of Chad

“…Although molecular tests enabled, with relatively high sensitivity and excellent specificity, to identify T. congolense, T. vivax and Trypanozoon taxa, no single test is able to differentiate unequivocally trypanosomes of the sub genus Trypanozoon [24]. The presence of tsetse flies in HAT foci of Chad indicates that some trypanosomes belonging to the subgenus Trypanozoon may be due to T. brucei s.l.…”

“…These diseases are characterized by overlapping clinical features that can be defined by their mode of transmission [23]. They give rise to important economic losses in Africa, the Middle East, Asia and Latin America [24]. They can be considered as animal diseases that are seriously neglected, both by the scientific community as by veterinary authorities and regulatory organizations [24].…”

“…They give rise to important economic losses in Africa, the Middle East, Asia and Latin America [24]. They can be considered as animal diseases that are seriously neglected, both by the scientific community as by veterinary authorities and regulatory organizations [24]. Nagana is due to T. vivax, T. congolense and/or T. brucei subspecies and is transmitted by tsetse flies; Surra is caused by T. evansi and is mechanically transmitted by biting flies while dourine is due to T. equiperdum and is sexually transmitted [23].…”

Noninvasive Biological Samples to Detect and Diagnose Infections due to Trypanosomatidae Parasites: A Systematic Review and Meta-Analysis

“…In addition to human African trypanosomiasis, animal trypanosomiasis (AT; nagana, surra, dourine) affects livestock (cattle, small ruminants, and pigs), equids (horses, donkeys) and camelids (camels, dromedaries, llamas and alpacas). They give rise to important economic losses in Africa, the Middle East, Asia and Latin America [7,43]. In addition to their cyclical transmission by tsetse flies (Glossina sp.…”

“…In addition to their cyclical transmission by tsetse flies (Glossina sp. ), trypanosomes infecting animals can also be transmitted mechanically by blood-sucking insects (mainly stomoxines and tabanids) and even directly via venereal transmission in the case of dourine [43][44][45]. In cattle and small ruminants, most cases are caused by Trypanosoma congolense and T. vivax, but infection by a variety of other trypanosomes and mixed infections are also frequent.…”