epidemiology

A cross-sectional coprological survey in the regions of Ada, Akaki, Bereh and Boset, and a retrospective postmortem investigation were conducted to study the epidemiology of Parascaris equorum in donkeys and horses in Ethiopia. Faecal samples from 803 working donkeys and 402 horses were collected, and the numbers of worms recovered from 112 donkeys examined postmortem between 1995 and 2004 were analysed. There was a high prevalence of infection and faecal egg output of Parascaris equorum in both donkeys and horses, and the severity of the infection in donkeys was increased irrespective of their age. The prevalence of the infection in the donkeys was 51·1 per cent and in the horses 16·2 per cent, and the prevalence in the donkeys examined postmortem was 55 per cent. There was no significant difference between different age groups of donkeys in either the prevalence or the intensity of the infection. The prevalence of the infection was significantly higher in the Ada and Akaki regions than in the Bereh and Boset regions.

Parascaris equorum is an important parasite of young horses, particularly sucklings and weanlings (Russell 1948, Soulsby 1982, Austin and others 1990, Southwood and others 1998). The parasite has a worldwide distribution, and is usually present wherever horses are raised (Clayton 1986, Southwood and others 1998). It can reduce the growth rate of foals and cause occasional deaths due to intestinal obstruction or rupture (Dipietro and others 1983, Clayton 1986, Ryu and others 2004).

Parascaris equorum has also been reported in donkeys from various regions of the world (Tolliver and others 1985, Vercruysse and others 1986, Pandey and Eysker 1990, Ricci and Sabatini 1992, Burgu and others 1995, Daoud and Al-Alousi 1995, Feseha 1998, Lewa and others 1998, Getachew 1999, Kotwal and others 2000, Matthee and others 2002). However, most of these reports concern only small numbers of animals, and the information is rather fragmentary. There have been no specific studies of the epidemiology, pathogenicity and immunology of parascarid infections in horses and donkeys under the tropical weather conditions of Ethiopia. The aim of the present study was to investigate the epidemiology of this parasite in working donkeys and horses in Ethiopia by means of a cross-sectional coprological survey and retrospective postmortem examination findings.

A 12/13 kDa antigen, tapeworm ELISA test, developed for use in horses, was used to detect parasite-specific serum antibody, IgG(T), in the serum of donkeys. In a pilot study the 12/13 kDa antigen was tested and proved to detect the antibody, IgG(T), in donkey sera. Blood samples from 797 donkeys, naturally exposed to cestode infection, from four geographical localities were collected and sera were prepared and analysed. There was substantial serological evidence that donkeys were potentially infected with A. perfoliata. A range of ELISA OD values were obtained from the serological assay. Over 26% and 7.5% of the donkeys were moderately and highly infected, respectively, showing at least a 34% sero-prevalence. The rest, 66.1%, were either with low infection intensity or negative for A. perfoliata infection. The risk of infections, both in sero-prevalence and intensity, as determined by ELISA optical density (OD), were highest in the highland areas of Ethiopia where pastures are low-lying and wet, and permanent pasture management is regularly practised. Sex, age and body condition of the donkeys had no significant effect either on prevalence of the infection or on the serum antibody level. These results indicate a risk of intestinal disorders, particularly, colic, associated with A. perfoliata infection in donkeys.

Over 38% of the world equine population (114 million) is made up of donkeys and more than 97% are found in developing countries and are specifically kept for work. Despite their significant contribution to the national economy, the attention given to study the infectious diseases of working donkeys is minimal. To address this The Donkey Sanctuary has been conducting studies in collaboration with Addis Ababa and Nairobi Universities, Central Veterinary Research Laboratory (CVRL) in Dubai and the Trypanosomosis Research Centre (TRC) in Kenya. These studies have shown a high prevalence of some important infectious diseases.

Helminthosis

Helminth infection profiles of working donkeys living in semi-arid or tropical conditions are often very different from those of equids in temperate climates. They are often diagnosed with a high worm burden or faecal egg count irrespective of their age. The high level of age-independent infection may show that donkeys either do not develop protective immunity or that they might have become immuno-compromised, consequent upon the stress of their work intensity and/or undernourishment and general poor husbandry.

Trypanosomosis

Although there is a general belief that donkeys are more resistant, trypanosomosis has been shown to cause severe clinical disease in working donkeys. Epidemiological studies in Ethiopia and Kenya have shown that the prevalence of trypanosomosis was as high as 65%, often with mixed infections of two or more species. In both countries T. congolense was the predominant species followed by T. brucei and T. vivax; often associated with anaemia and poor body condition. Trypanosomosis is claimed by local farmers as the major health constraint of donkeys in both countries. Recent serological studies by The Donkey Sanctuary in collaboration with the CVRL showed a sero-prevalence of 1.1% (n=662) T. equiperdum in Ethiopia.

Piroplasmosis

Equine piroplasmosis is one of the most significant tick-borne diseases of donkeys in Ethiopia and Kenya. Recent studies in Ethiopia in collaboration with CVRL showed sero-prevalence of 53.3% to 58% T. equi and 13.2%-13.3% B. caballi (n=15-395) Most of the cases were associated with anaemia. Similar studies in Kenya reported only T. equi with a sero-prevalence of 81.2% (n=314).

Viral and bacterial diseases

A recent study in Ethiopia in collaboration with CVRL showed a sero-prevalence of 8.5% (n=165) AHS, 84.6% (n=104) EHV-4, 20.2% (n=104) EHV-1, 0.5% (n=662) glanders and 0.2% (n=657) EIA. Similar study made in Kenya also showed a sero-prevalence of 35.2% (n=398) AHS. Donkeys showing typical clinical signs of AHS were noted in Kenya and Ethiopia. Although no epidemiological studies are available, cases of tetanus, strangles, rabies, anthrax and dermatophilosis are common occurrences in donkeys. These studies highlight how important infectious diseases in donkeys are and the need to consider them in overall epidemiological studies and for sound control and prevention strategies.