Scientists call for greater focus on the horse disease dourine

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Dourine has been described as a neglected horse disease by scientists, who believe greater efforts need to be put into diagnostic tests, and better drugs developed to treat it.

The need is even more compelling, they say, given the ever-increasing international movement of horses.

Dourine, or covering sickness, is a parasitic venereal disease of equines caused by a protozoan, Trypanosoma equiperdum.

Dourine is among a complex of infectious diseases known as Equine trypanosomosis, which also includes nagana and surra. They are caused by several species of the genus Trypanosoma that are transmitted cyclically by tsetse flies, mechanically by other haematophagous flies, or sexually.

They give rise to important economic losses in Africa, the Middle East, Asia, and Latin America.

“Nevertheless, they can be considered as animal diseases that are seriously neglected, both by the scientific community and by veterinary authorities and regulatory organisations,” Philippe Büscher and her colleagues wrote in a review published in the journal Parasites & Vectors.

“The situation is aggravated by the reluctance of many endemic countries to notify dourine and surra to the World Organisation for Animal Health.”

Vaccines against these diseases do not exist. Chemotherapy is able to clear the parasites from blood circulation. However, most of the organisms are known to live mainly outside the vascular system, including the central nervous system.

Evidence is accumulating that none of the chemotherapy drugs are effective in the neurological stage of the disease, since they are unable to cross the blood-brain barrier in sufficient amounts.

The international review team says major obstacles to the local and global control of these diseases are the lack of vaccines, the inability of drugs to cure the neurological stage of the infections, inconsistent case definitions and the limitations of current diagnostics.

“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.

“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 always clear, parasitological tests are not sufficiently sensitive, blood tests are not as sensitive as they could be, and molecular tests cannot distinguish the taxa within the Trypanozoon subgenus.

“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.”

Equine trypanosomosis: enigmas and diagnostic challenges
Philippe Büscher, Mary Isabel Gonzatti, Laurent Hébert, Noboru Inoue, Ilaria Pascucci, Achim Schnaufer, Keisuke Suganuma, Louis Touratier and Nick Van Reet. Parasites & Vectors 2019 12:234. https://doi.org/10.1186/s13071-019-3484-x

The study, published under a Creative Commons License, can be read here

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