Dourine is a chronic or acute contagious venereal disease of solipeds. The causative agent, Trypanosoma (T.) equiperdum (Doflein 1901) is transmitted directly from animal to animal during coitus. Humans are not susceptible to T. equiperdum infections.
Trypanosoma (T.) equiperdum
T. equiperdum is a protozoal, extracellular hemoflagellate (16-35µm of length) belonging to the family of trypanosomatidae, order of kinetoplastidae, parasitizing primarily in the tissue, invading the blood vessels only temporarily. According to the mode of transmission two sections are distinguished, one of which, the section of Salivaria, contains the subgenus Trypanozoon, including the species T. equiperdum, T. evansi and T. brucei. Recent molecular studies revealed that T. equiperdum and T. evansi may not be independent species, but rather types or subspecies of T. brucei, specifically adapted to solipeds. Up to now, T. equiperdum and T. evansi, both of which can be found in horses, cannot be differentiated by other means than PCR. T. equiperdum differs from other members of the subgenus Trypanozoon in that it is not transmitted by an invertebrate vector organism, but by coitus directly from animal to animal. A reservoir of the pathogen other than infected equine animals is not known.
Significance of T. eqiperdum as infectious agent
In the past dourine was present in many countries worldwide, nowadays it is eradicated in Central Europe, North America and Australia. In the beginning the disease manifests itself in a local inflammation of the genitalia with mucous excretions followed by oedematous cutaneous plaques at the neck, shoulder, breast and croup. Later motor nerve paralysis occurs. Clinical disease does not occur in Germany anymore. Here, horses in most cases are noticed by inconclusive or weakly positive serological reactions at trading or breeding examinations. Often these horses are imported from risk areas. A positive serological reaction has serious consequences for the animal (life, breeding) and the owner (financially) since the direct detection of the pathogen or of specific DNA in a country without endemic infections is unsuccessful in most cases.
In Germany dourine is a notifiable animal disease. The official diagnosis is conducted by complement fixation test (CFT), the method recommended by the OIE (world organization of animal health). According to OIE Manual of Standards for Diagnostic Tests and Vaccines 2008 serum titers equal or more than 1: 5 (serum dilution) 2+ are regarded as positive. According to EU commission decision 93/197/EWG (26/02/1996) serum titers from 1:10 (serum dilution) are regarded as positive for dourine.
The NRL produces the antigen used for CFT which is distributed to the veterinary public health institutes in Germany, as approved antigen is not commercially available in Germany. Furthermore, the NRL re-examines positive and inconclusive serological findings obtained by veterinary public health institutes and organizes inter-laboratory diagnostic trials.