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Common infectious diseases of working donkeys: their epidemiological and zoonotic role

Citation

Mulugeta Getachew, Faith A. Burden, Ulli Wernery. April 2016. Common infectious diseases of working donkeys: their epidemiological and zoonotic role. Journal of Equine Veterinary Science. 39:Supplement. 107.

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Publication details
Publication date: 
5 April 2016
Volume: 
39
Issue: 
Supplement
Page numbers: 
107
DOI number: 
10.1016/j.jevs.2016.02.225
Abstract

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 (DS) 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 DS 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.

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Equine central nervous system trypanosomosis in The Gambia is caused by genetically diverse populations of Trypanosoma brucei parasites

Citation

Demelza Kingston, Jan Rodgers, S. Sharpe, K. Berman, Liam Morrison, P. Kennedy, B. Bradley, David Sutton. April 2016. Equine central nervous system trypanosomosis in The Gambia is caused by genetically diverse populations of Trypanosoma brucei parasites. Journal of Equine Veterinary Science. 39:Supplement. 100-101.

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Publication details
Publication date: 
5 April 2016
Volume: 
39
Issue: 
Supplement
Page numbers: 
100-101
DOI number: 
10.1016/j.jevs.2016.02.214
Abstract

In many countries diseases affecting working equid performance and productivity are detrimental both to equid welfare and to local economic development. Central nervous system (CNS) trypanosomosis, caused by Trypanosoma brucei spp 1, is a severe manifestation of trypanosomosis, which is usually fatal. The causative agent of this condition in the Gambia was investigated further in this study, to determine genotypic variation, mode of transmission and future management interventions. The presence of trypanosomes in local tsetse flies (Glossina spp.) was also investigated due to suspected vector involvement in disease transmission. Working equids exhibiting signs of CNS trypanosomosis were clinically evaluated. Blood was stored in EDTA and on FTA® cards prior to DNA extraction. In advanced neurological disease where prognosis was hopeless euthanasia was performed. CSF and CNS tissue samples were collected post-mortem. CSF was stored on FTA® cards and tissue samples were collected in formalin and RNAlater®. To confirm CNS T.brucei spp infection, immunohistochemistry and T.brucei-specific PCR 2 was performed on tissue samples. DNA was also extracted from blood collected from patients with evidence of generalised T.brucei infection with normal neurological function, and from the midguts of locally caught tsetse. Parasite population structure was investigated using a panel of microsatellite markers 3 together with a reference strain of T.brucei equiperdum (OVI) and a T.b.brucei positive control.Ten cases (5 horses, 5 donkeys) with naturally occurring CNS trypanosomosis were included. Horses presented with rapidly progressive spinal ataxia while donkeys showed slowly deteriorating cerebral dysfunction and cranial nerve abnormalities. CNS trypanosomosis was confirmed post-mortem using immunohistochemistry and PCR. Histopathological evaluation revealed diffuse lymphocytic-plasmacytic meningoencephalomyelitis. Microsatellite fragment analysis showed a heterogenous parasite population with a large range of alleles present, inconsistent with a clonal population. Parasite populations from donkey versus horse, and from blood versus CNS tissue were not found to be significantly different, suggesting that host factors are important in progression of neurological disease. Of 405 tsetse trapped locally and dissected, 11 contained microscopically visible midgut trypanosome infections. DNA extracted from the positive tsetse midguts was positive for equid DNA in 3/11 cases, confirming vector involvement. 5/11 flies were positive for T.brucei but with different microsatellite patterns to that found in infected CNS tissue. Further work is required to develop an optimal panel for use in both tsetse and equine-derived samples. Continued efforts are required to improve understanding of the transmission of this disease to enable the development of effective preventative measures.

Acknowledgements

This work is funded by the Donkey Sanctuary.

Online references

Treatment efficacy in Equine Trypanosomosis: A prospective comparative study of three trypanocides in over 250 clinical cases in working equidae

Citation

Alexandra Rafferty, Jan Rodgers, David Sutton. April 2016. Treatment efficacy in Equine Trypanosomosis: A prospective comparative study of three trypanocides in over 250 clinical cases in working equidae. Journal of Equine Veterinary Science. 39:Supplement. S99.

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Publication details
Publication date: 
5 April 2016
Volume: 
39
Issue: 
Supplement
Page numbers: 
S99
DOI number: 
10.1016/j.jevs.2016.02.211
Abstract

Trypanocides are essential in trypanosomosis management, but evidence regarding treatment efficacy in equids is scarce. The objective of this study was to establish the relative efficacy of three trypanocides (Diminasan® 3.5 mg/kg IM, Cymelarsan® 0.25 mg/kg IV and Samorin® 0.5 mg/kg IV) with respect to improvement of clinical parameters and parasitic burden and to evaluate adverse drug reactions. A prospective randomised clinical efficacy study was performed in ten villages in The Gambia. Owners were invited to present horses and donkeys for free examination (history, clinical examination and jugular blood sample for packed cell volume (PCV) and total serum protein). Horses and donkeys were enrolled if they fulfilled at least 2/5 inclusion criteria for trypanosomosis (anaemia (PCV<24%), poor body condition (≤1.5), limb or ventral oedema, abortion or pyrexia). Randomised trypanocide treatment was administered and the animals were observed for adverse reactions. Follow up evaluation was performed at one and two weeks to assess treatment effect. Blood samples for each animal collected at weeks 1, 2 and 3 underwent PCR analysis with validated specific primers1 for T. vivax west (TVW), T. congolense savannah (TCS) and T. brucei (TBR).

254/710 animals examined fulfilled study inclusion criteria with follow up data obtained for 243. Age, gender, species, median PCV (22%; range 8-26) and body condition score (median 1.5/5; range 0.5-2.5) were comparable between treatment groups (p>0.1). No immediate adverse reactions occurred following Cymelarsan® or Diminasan®. Immediate reactions occurred in 12/45 (27%) of donkeys treated with Samorin® ranging from neck scratching, lip smacking to tachycardia, cold extremities, sweating and hypothermia. Demeanour classifications improved following treatment with Samorin® or Diminasan® (p=0.002). PCV increased at 1 and 2 weeks post treatment for all treatment groups (p<0.001). On preliminary analysis of PCR results (n=65), animals representing four villages were positive before treatment (week 1) for TVW (55/65; 85%), TCS (44/65; 67%) and TBR (17/65; 26%) with mixed infection common (45/65; 69%). Trypanosome species profile varied between villages (p<0.05). Post treatment positives occurred in all groups for all Trypanosoma sp but with a marked decrease in prevalence (Fig 1). Positives were most common in the Cymelarsan® group, particularly for TCS (7/13; 54%). Two weeks post treatment Diminasan® (15/19; 79%) and Samorin® (19/23; 83%) had reduced parasitaemia below the threshold of detection in most cases. The data support the continuation of treatment with Diminasan® and Samorin® (with careful titration of dosing in donkeys). Further investigation to quantify parasitaemia in post treatment positives will aid differentiation between treatment failure, reduced parasitaemia, new infections and residual non-viable parasite DNA.

Acknowledgements

This work was funded by The Donkey Sanctuary.

Online references

Donkeys - a unique and challenging endoparasite host

Citation

Faith A. Burden, Mulugeta Getachew. April 2016. Donkeys - a unique and challenging endoparasite host. Journal of Equine Veterinary Science. 39:Supplement. S102-S103.

Authors
Publication details
Publication date: 
5 April 2016
Volume: 
39
Issue: 
Supplement
Page numbers: 
S102-S103
DOI number: 
10.1016/j.jevs.2016.02.216
Abstract

Endoparasites in donkeys are ubiquitous and may cause serious disease. All common helminth parasites that affect horses also infect donkeys, therefore donkeys that co-graze can act as a significant source of infection for either species. Whilst donkeys are prone to the same parasite species as horses infection characteristics and presenting signs and symptoms of disease may differ. Large strongyles and cyathostomins are common in donkeys worldwide with Strongylus vulgaris causing significant disease in donkeys with poor anthelmintic treatment history. Cyathostomins infect the majority of donkeys globally and may rarely cause cyathostominosis or colitis; however signs and symptoms of both can vary significantly from those displayed in affected horses. The significance of low level cyathostomin infection on the donkey host is unclear, many donkeys appear to thrive with high faecal egg counts (> 3000epg) and when the donkey is in general good health they may exist with high cyathostomin burdens with little impact on their overall health. The donkey is renowned as the reservoir host for the lungworm, Dictyocaulus arnfieldi. Mature horses are not permissive hosts to the full life cycle of this parasite, but develop clinical signs on infection. In contrast, donkeys are permissive hosts without displaying overt clinical signs and act as a source of infection to co-grazing horses. Donkeys are also susceptible to the flukes, Fasciola hepatica and Fasciola gigantica and may be an important reservoir host for both human and herbivore infections particularly in developing countries. Finally, Parascaris spp. infections in donkeys are common, however infection is not only associated with young, immuno-compromised animals as seen in horses. Parascaris spp. infection is a frequent finding in all age groups of donkeys. The inability of many donkeys to develop lifelong immunity to Parascaris poses problems when attempting to reduce transmission of this parasite in herds which include adult and young donkeys. Anthelmintic treatment is challenging as many anthelmintics are not licensed for use in this species; however dosing should follow best practice used in horses. Anthelmintic resistance is of particular concern in donkeys with recent reports of lack of efficacy of all anthelmintic classes in cyathostomins infecting donkeys. Control of parasites in donkeys must primarily focus on reducing the risk of infection, maintaining good health and targeting drug treatments carefully. Donkeys can be co-grazed safely with other species but careful monitoring and control should be practiced to ensure that donkeys do not act as reservoirs of infection to other, more susceptible animals. The importance of parasite infection, particularly co-infection with multiple species must be appreciated. Donkeys under stress due to malnourishment, infectious disease, overwork or neglect are at a high risk of disease related to parasite infection and consideration must be given to targeted treatments in such circumstances. Whilst the donkey remains a challenging parasite host following simple control measures and improving the overall welfare of the donkey will undoubtedly serve both the donkey and other species grazing alongside.

Online references

Donkeys are Different

Citation

Faith A. Burden, Alexandra K. Thiemann. March 2015. Donkeys are Different. Journal of Equine Veterinary Science.

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Publication date: 
20 March 2015
Abstract

As a unique species of equine the donkey has certain specific variations from the horse. This review highlights the origins of the donkey and how this impacts upon its behaviour, physiology and propensity to disease. The donkey is less of a flight animal and has been used by humans for pack and draught work, in areas where their ability to survive poorer diets, and transboundary disease while masking overt signs of pain and distress has made them indispensable to human livelihoods.

When living as a companion animal however the donkey easily accumulates adipose tissue, this may create a metabolically compromised individual prone to diseases of excess such as laminitis and hyperlipaemia. They show anatomical variations from the horse especially in the hoof, upper airway, and their conformation. Variations in physiology lead to differences in the metabolism and distribution of many drugs. With over 44 million donkeys worldwide it is important that veterinarians have the ability to understand and treat this equid effectively.

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Clinical Approach to The Dull Donkey

Citation

Alexandra K. Thiemann. February 2013. Clinical Approach to The Dull Donkey. In Practice. 35. 470-476.

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Publication date: 
1 February 2013
Journal: 
In Practice
Volume: 
35
Page numbers: 
470-476
DOI number: 
10.1136/inp.f5262
Abstract

The ‘dull donkey’ is a general descriptive term used by owners and clinicians to identify a donkey presenting with varying degrees of depression, dullness and inappetence. These cases can be frustrating to diagnose and manage successfully. This article provides an overview of the most common causes of dullness in donkeys in the UK and suggests appropriate first-line diagnostic and treatment options. It should be appreciated that, in many cases, dull donkeys may be very sick and may require high levels of intervention to recover. Such cases should be seen as priority patients.

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