Читать книгу Parasitology - Alan Gunn - Страница 117

Trypanosoma equiperdum is monomorphic and morphologically indistinguishable from T. equinum. It exhibits dyskinetoplastidy – that is, it retains only fragments of kinetoplastid DNA. It parasitizes a range of equids although it affects the domestic horse (Equus cabalus) more severely than asses, donkeys etc. Some strains infect dogs and one can establish laboratory cultures in rats and mice. It is a sexually transmitted disease and causes a condition called ‘dourine’: a word deriving from the Arabic for ‘unclean’. The use of horses in agriculture and warfare spread T. equiperdum around the world. However, following breeding programmes aimed at eliminating infected horses, it currently has a restricted distribution in parts of Africa, Asia, southern Europe, and South America.

Dourine typically manifests itself in three stages. The first stage begins with swelling of the genitalia. There is patchy depigmentation of the penis and vulva, and there is vaginal discharge in mares. The horse may also exhibit a slight fever and loss of appetite. After about a month, the second stage of the disease begins with the development of circular fluid‐filled (oedematous) plaques 2.5–10 cm in diameter underneath the skin. They usually form on the flanks although they can develop on any part of the body. The plaques may last a few hours or days after which they disappear and then reappear again later. Because of the rash‐like swellings, this is called the ‘urticarial stage’. Plaques do not always form but if they do, they are a reliable indicator of the nature of the disease. The onset of paralysis marks the third stage of the disease. Often this begins in the nose and face. It then spreads to affect the rest of the body and can result in complete paralysis affecting all the limbs. The course of the disease may take as long as 2 years and mortality can be as high as 70%.

The relationship between T. equiperdum, T. evansi, and T. brucei remains uncertain. Molecular evidence indicates that T. equiperdum and T. evansi independently diverged from T. brucei on several occasions. According to Cuypers et al. (2017), T. equiperdum arose from an East African T. brucei ancestor whilst T. evansi derives from a West African T. brucei ancestor.

Trypanosoma equiperdum is primarily a tissue parasite and not usually present in the circulating blood, but it occurs in smears taken from the genitalia or plaques. Diagnosis has traditionally relied on serological complement fixation tests and in some countries where dourine is endemic, they are mandatory. However, such tests will not reliably distinguish T. equiperdum from other trypanosomes such as T. evansi and T. brucei – which is hardly surprising because they are all closely related.