Introduction
This section briefly discusses a range of infections not usually found in the UK and, hence, referred to as exotic. The geographic distribution of these infections may be limited for two main reasons. Firstly, transmission of infection may depend on specific arthropod vectors that occur only outside the UK. Secondly, concerted disease control efforts may have led to eradication of disease in the UK. However, resurgence of such diseases in the UK might be expected more frequently as a result of increased movement of people and animals, expansion of the European Union, where disease security is dependent on its weakest point, and the consequences of global warming.
Specific scientific information is lacking for many infections that affect donkeys. Therefore, relevant information on diseases as they manifest in the horse has occasionally been included. Diseases are discussed in outline only, with an emphasis on the factors relevant to donkeys. This section should, therefore, be read in conjunction with standard texts describing the diseases and their diagnosis and treatment in more detail.
Although the donkey shares a common ancestor with the horse (the Hyracotherium or the Dawn Horse), the evolution of these two species diverged approximately four million years ago. They then adapted to different environments and disease challenges, which may explain the different epidemiology observed with some infections.
| Disease | Infectious agent | Transmission | Notifiable to OIE | UK legislation | Last reported in UK | Signs in donkeys |
| African Horse Sickness | Orbivirus | Midges | Yes (A) | Specified Diseases (Notification and Slaughter) Order 1992 (as amended); Specified Diseases (Notification) Order 1996 (as amended) | Never | Subclinical to mild |
| Epizootic Lymphangitis/Histoplasmosis | Fungus - Histoplasma | Contact, or possibly flies | No | Infectious Diseases of Horses Order 1987 | 1905 | Ocular form (Egypt), Cutaneous form (Ethiopia) |
| Equine Infectious Anaemia (EIA) | Lentivirus | Biting insects | Yes (B) | Infectious Diseases of Horses Order 1987, Specified Diseases (Notification and Slaughter) Order 1992 (as amended); Specified Diseases (Notification) Order 1996 (as amended) | 2006 (Isolated case identified in N. Ireland after testing all horses in contact with infected horse in Eire.) | Usually subclinical, some strains more pathogenic |
| Equine Viral Arteritis (EVA) | Arterivirus | Respiratory/reproductive system | Yes (B) | The Equine Viral Arteritis Order 1995 | 2004 (Isolated case only of an imported stallion kept throughout in quarantine before being exported.) | Subclinical to mild, fever, depression, ocular, nasal discharge and conjunctivitis |
| Glanders (Farcy) | Bacteria - Burkholderia | Contact | Yes (B) | Infectious Diseases of Horses Order 1987 | 1928 | Fever, nasal discharge, enlarged lymph nodes and coughing |
| Rabies (terrestrial) | Lyssavirus | Saliva
Bites |
Yes (B) | The Rabies (Control) Order 1974 | (Eradicated in 1922) European Bat lyssavirus (EBL) is enzootic in the UK | Encephalitic and paralytic form |
| Venezuelan Equine Encephalomyelitis (VEE) | Alphavirus | Mosquitoes | Yes (B) | Infectious Diseases of Horses Order 1987 | Never | Fever, depression and neurological signs |
| West Nile Fever (WNF) | Flavivirus | Mosquitoes | Yes (B) | Infectious Diseases of Horses Order 1987 | Never | Fever, anorexia and neurological signs |
| Piroplasmosis | Babesia | Ticks | Yes (B) | . | . | Often subclinical unless other stress factors concurrent |
| Tsetse-transmitted Trypanosomosis
Surra Dourine |
T. brucei | Tsetse flies | No | . | Never | Anaemia, oedema, petechiation and weight loss. Milder signs compared to horse but variable depending on species of trypanosomes and host factors. |
| . | T. evansi | Tabanid flies/mechanical | Yes (B) | . | Never | . |
| . | T. equiperdum | Sexual | Yes (B) | Infectious Diseases of Horses Order 1987 | Never | Asymptomatic to mild signs of oedema with skin plaques in only few cases |
Note: In May 2004, the OIE (World Organisation for Animal Health) member countries approved the creation of a single list of diseases notifiable to OIE. A new list was approved in May 2005 by the International Committee, which came into force in 2006. Previously disease notifiable to OIE were classified into two lists:
- List A: Transmissible diseases that have potential for very serious and rapid spread, irrespective of national borders, that are of serious socio-economical or public health consequence and that are of major importance in the international trade of animals and animal products.
- List B: Transmissible diseases that are considered to be of socio-econimic and/or public health importance within countries and that are significant in the international trade of animals and animal products.
Diagnosis of infection
Diagnosis of a disease requires clinical examination and knowledge of the epidemiology, the environment and the animal’s history. Knowledge of exotic diseases in donkeys is often sparse. The scope of diagnostic methods is constantly evolving and developing. However, in field conditions in less economically developed countries, further diagnostic techniques may not be readily available.
Where further diagnostic tests are available they may be commercial or more experimental. Such tests can be used to improve both diagnosis and epidemiological understanding of the disease. Diagnostic tests for the diseases in this section are either serological (based on antibody detection) or aimed at detection of the infectious agents or their components.
Diseases often manifest subclinically in donkeys. Hence, auxiliary blood tests are useful to provide evidence of current or past infection. Serologic tests must be carried out after an adequate time period following infection. For donkeys, the required time lag may differ from horses. For example, studies show that, when using the agar gel immunodiffusion test (AGID) or Coggins test, antibodies for Equine Infectious Anaemia (EIA) are detected later in the donkey than in the horse (Rattan et al., 1998; Cook et al., 2001). In complement fixation tests, the sera of donkeys and mules may give inconsistent or non-specific reaction because of the anti-complementary effect.
Results of serologic tests must be considered in context. For example, antibodies can be present for significant and variable periods following infection and also in response to vaccination. The analytical and diagnostic sensitivity and specificity of such tests must also be considered when interpreting individual status and when investigating seroprevalence. Many of the tests have been validated for horses but not donkeys and so caution is needed in interpretation.
The OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals (OIE, 2009) provides a comprehensive review of the tests available.The development, validation and investigative use of diagnostic tests would be invaluable in providing information on disease and infection prevalence, enabling clinical decision-making and intervention objectives to be improved. However, it is unlikely that there will be any major increase in the regular use of diagnostic testing for the majority of the world’s donkeys in the foreseeable future.
Treatment and control
Medical treatment
Most viral conditions have no specific treatment. Management depends on the severity of the condition and clinical signs, and involves supportive treatment, nursing care and analgesia. Euthanasia is an important, humane option for irreversible, deteriorating conditions or diseases that are a serious, uncontainable risk to other animals.
Although medicines prescribed for horses are not usually authorised for use in donkeys, they are often suitable. However, for some medications the pharmacokinetics vary between species and dose rates should be adjusted accordingly.
Quality, efficacy and safety requirements for pharmaceutical products are not consistent internationally. In less economically developed countries, where donkeys are most numerous, the medicines locally available may be sub-optimal quality, with variable availability and, perhaps, also compromised by poor pharmacy practice.
Disease control
Disease control should follow standard epidemiological principles and what is currently known about the disease in equines.
Due to economic constraints, commercially available vaccines are not likely to be authorised for use in donkeys or readily available to poor donkey owners. Field tests of vaccine safety and efficacy are usually performed for the horse and it is sometimes assumed that results are applicable to donkeys. However, this is uncertain as the donkey’s immunological response may be different from that of the horse.
Biosecurity and hygiene are crucial components in the control of contagious diseases such as glanders and epizootic lymphangitis. An effective cleansing and disinfection programme should be established in advance.
Diseases such as glanders, rabies and certain equine encephalitides are zoonoses. Hence, particular care has to be exercised when handling diseased animals. Rabid donkeys can be very dangerous and extreme care should be taken when handling infected animals to prevent bites and infection from saliva. Wherever possible, all personnel dealing with potentially rabid animals should be appropriately vaccinated.
A major concern regarding some vector-transmitted equine encephalitides is human infection due to spread of the virus by insects. People at risk should use appropriate insect repellents and barriers.
Where disease is transmitted through insects or ticks, appropriate attention must be directed at vector control. Knowledge of the behaviour and bionomics of a particular vector is essential for effective control. The practicalities of such control will depend on the individual situation and can include techniques such as insecticide, housing donkeys at night or mass spraying of insect habitat.
National legislation specifies the procedures to follow if a notifiable disease is diagnosed or suspected. Many of the diseases included in this chapter are also notifiable to the OIE by its member countries.
References
- Anzuino, J. (2008) Exotic infections In Svendsen, E.D., Duncan, J. and Hadrill, D. (2008) The Professional Handbook of the Donkey, 4th edition, Whittet Books, Chapter 14
- Cook, S. J., Cook, R. F., Montelaro, R. C., and Issel, C. J. (2001). ‘Differential responses of Equus caballus and Equus asinus to infection with two pathogenic strains of equine infectious anaemia virus’. Veterinary Microbiology 79. pp 93-109.
- Rattan, B., Gupta, A.K., Yadab, M.P., Uppal, P.K., and Praveen, M. (1998).‘Lower susceptibility of donkeys to equine herpes virus and equine infectious anaemia in comparison to horses’. Proceedings of the 3rd International Colloquium on Working Equids. UNAM, Mexico.
General References
- Anon. (1998). Foreign Animal Diseases. Richmond, Virginia, USA. Available on the Internet at: http://www.vet.uga.edu/vpp/gray_book/pdf/1998_edition.htm. (currently not available)
- Coetzer, J.A.W. , Erasmus, B.J. (eds).(2004). Infectious Diseases of Livestock. 2nd Edition. Oxford University Press Southern Africa, Cape Town, South Africa.
- Kaufmann, J. (1996). Parasitic Infections of Domestic Animals. Birkhauser Verlag. Basel, Switzerland.
- OIE. Terrestrial Animal Health Code (2007). Paris, France. (Office International des Epizooties). Available on the internet at http://www.oie.int/eng/normes/mcode/en_sommaire.htm.
- Radostits O.M., Gay, C.C., Blood, D.C., and Hinchcliff, K.W. (eds). (2003). Veterinary Medicine. A textbook of the diseases of cattle, sheep, pigs, goats and horses. 10th edition W.B. Saunders Company Ltd, London, UK.
- Sellon, D.C., Long, M.T. (2007). Equine Infectious Diseases. Saunders Elsevier, St. Louis, Missouri, USA.
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