Monday, June 27, 2011 - Mark Humph
Italy recently reported two outbreaks of dourine in horses in Sicily and on the mainland. This is the first report of the disease in Europe for many years (Italy, 1996). However, the disease was recognised as being endemic in Southern Italy after the Second World War and there are no (easily accessible) reports of stringent surveillance and control programmes.
While there has never been a case of dourine reported in the UK, it is a notifiable disease (Infectious Diseases of Horses Order 1987 - http://www.legislation.gov.uk/uksi/1987/790/contents/made) and so it is important to be aware of the disease and to consider it in your list of differential diagnoses.
Dourine is considered endemic in parts of Africa, South America, parts of south eastern Europe, parts of Asia, including Russia and occasionally the Middle East.
Dourine is caused by the protozoan Trypanosoma equiperdum. A recent study suggests that T. equiperdum (along with T. evansi) is a subspecies of T brucei. This trypanosome does not live for long outside its host and is unusual for a trypanosome in that it does not require a vector. There are no other animal reservoirs of infection other than infected equidae. It is transmitted during mating and by AI; and from infected mares to their foals at foaling, or via infected milk. Approximately 50% of cases will die. The incubation period is highly variable and may be days to months.
Clinical signs are vague and not pathognomic. They frequently progress and include intermittent pyrexia, conjunctivitis, emaciation, swelling of the external genitalia and discharge from the urethra and vulva, skin plaques which may become de-pigmented and neurological signs (weakness and paralysis) leading to death. Infected animals excrete parasites in genital fluids in the acute stage of the disease; but in chronic cases, this may be intermittent. Sub-clinically infected and recovered equidae may act as inapparent carriers. Donkeys and mules are more resistant to the disease.
Diagnosis is based on a combination of clinical signs and laboratory results.
The most widely used diagnostic test (also used for international trade) is the complement fixation test (CFT). However, false positives and cross reactivity with other Trypanosoma spp. are common. Indirect fluorescent antibody (IFA) may be used. Other tests are available, including enzyme inked immunosorbent assays (ELISAs), radioimmunoassay and agar gel immunodiffusion (AGID). Definitive diagnosis is only by identification of the parasite in blood films or genital secretions (Giemsa) but this is very difficult to achieve.
The sensitivity of the CFT has never been characterised.
Prevention and Control
Treatment has been attempted and the most commonly used products are quinapyramine sulphate or melarsamine hydrochloride. Therapeutic regimes have not been thoroughly investigated and treatment is usually discouraged because many treated animals become symptomless carriers. Slaughter is usually recommended. There is no vaccine available.
It is widely recommended and good husbandry that any horse being brought to new premises is quarantined for a period before being introduced to the 'herd'. If dourine is suspected or diagnosed, the local office of the Animal Health Veterinary Laboratories Agency (AHVLA) must be notified urgently http://animalhealth.defra.gov.uk/about/contact-us/postcode.asp. All mating must cease immediately and all affected and in contact animals put into quarantine. Official restrictions will be put in place on all equidae on the premises and an official disease investigation will be initiated and serological tests will be performed to try to determine which animals have been exposed to infection. There is strong evidence to advise that these animals should be euthanased; however, there is no statutory requirement for compulsory humane destruction at this time; however, any infected equidae that are not humanely destroyed are likely to remain under official restrictions for life
Under the requirements for the importation from third countries of horses for breeding or production to the UK, horses must originate from countries where dourine is notifiable and the region of origin must be free of dourine for at least 6 months prior to export. (93/197/EC). For most countries, the horses must have a pre-export test for dourine within 21 days of export. For horses travelling from within the EU, each must be accompanied by a certificate stating that the region of origin has been free from dourine for 6 months, that the animal must not have had actual or possible contact with another animal with dourine and, if the animal is a stallion, he must have been castrated since the contact.
Deidre Carson, President
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