Knowing about notifiable diseases

Working with horses, means that farriers should be aware of the notifiable and other diseases that affect their equid clients. Some of the diseases are so important that a local Animal Health office of Defra or the Divisional Veterinary Office in Northern Ireland must be notified if they are suspected. Here is a brief description of a number of these diseases, including more detailed information about African Horse Sickness and West Nile Fever. However, it is important to remember that if you have any concerns about the health of animals in your care, you should first consult a veterinary surgeon.

The Defra website www.defra.gov.uk has more detailed information on some of these diseases, in the form of factsheets or disease profiles. Some of the diseases can affect people and they may have links to the Department of Health or other medical sites. Good biosecurity is also a vital part of keeping new disease away from animals.
African Horse Sickness
African Horse Sickness is a highly fatal disease that affects horses, mules and donkeys. It is caused by an orbivirus. Dogs have been known to be infected by eating infected horsemeat. It has never occurred in the UK, but is found in Southern Africa. An outbreak occurred in Spain relatively recently, which was associated with the import of infected zebras from Africa. The disease is carried and spread by insects with the speed of the spread dependant on weather and wind conditions. Affected horses have a fever with laboured breathing, coughing and discharge from the nostrils. A less serious form can occur causing fever and swelling of the face. Any suspicion of this notifiable disease must be notified to the local Animal Health office.
Transmission
The spread of disease is influenced by climatic conditions, which favour the spread of carrier insects as well as spread by wind dispersal. It is likely that the virus overwinters in other, unknown species in Africa when the insect is not active.
Clinical signs
The clinical signs seen are different depending on what form of the disease is present.
◗ In the most acute form, which has a short incubation period of only 3 to 5 days, affected horses have a high fever, severely laboured breathing, coughing and profuse discharge from the nostrils. The mortality rate is very high with up to 95 per cent of horses dying within a week.
◗ In the cardiac form of the disease, which has an incubation period of from 7 to 14 days, swellings are present over the head and eyelids, lips, cheeks and under the jaw. The mortality rate is around 60 per cent and death results from heart failure.
◗ The mixed form of the disease is a combination of the above two types. It has an incubation period of from 5 to 7 days, and the disease shows itself initially by mild respiratory signs followed by the typical swellings of the cardiac form.
◗ Horse sickness fever is the mildest form, characterised by a fever with low temperatures in the morning rising to a high peak in the afternoon.
Equine housing vector protection
Housing horses in accommodation at times of peak midge activity reduces the likelihood of midge attack, but it is unlikely to fully protect horses against AHS. A combination of protection measures is recommended to ensure the highest possible degree of protection is achieved. Further details on these protection measures can be downloaded from Defra's website.
GB legislation
AHS is included in The Specified Diseases (Notification and Slaughter) Order 1992. Imported horses from at-risk countries outside the EU are routinely tested for this disease. The severity of disease and the controls to monitor and restrict movement of horses could significantly affect the UK equine industry, particularly in southern UK, where this disease is most likely to occur.
EU legislation
Council Directive 92/35 provides for compulsory notification, and the setting up of a protection zone of least 100 kilometres radius around and infected premises. This, together with a surveillance zone of at least a further 50 kilometres, would have to remain in force for at least 12 months.
Contagious Equine Metritis
Contagious equine metritis (CEM) is a reproductive disease of horses that is transmitted both at mating and indirectly, for example, through contaminated instruments and the hands of staff. It can be caused by three different species of bacteria, Taylorella equigenitalis, Klebsiella pneumoniae or Pseudomonas aeruginosa. The CEM organism was first reported in the UK in 1977 and periodic outbreaks continue to occur. CEM is present in other European countries, Morocco and Japan. Infected mares may have a discharge from the vagina and become temporarily infertile. Both mares and stallions can carry the organism without showing any signs.
Dourine
Dourine is a contagious disease of horses transmitted only at mating. It is caused by an organism called Trypanosoma equiperdum. It has never occurred in the UK, but is present in several other countries including Africa, Asia, parts of Europe and South America. The disease may be severe with many horses dying. However a milder form of the disease also occurs, especially in countries where it has been present for a long time. Both stallions and mares may have swelling and discharge from the sexual organs. Nervous signs and skin lesions have also been seen.
Epizootic Lymphangitis
Epizootic lymphangitis is a disease of horses and mules. It is caused by a fungus called Histoplasma farciminosum. The disease is present in Africa, the Middle East, Asia and India. It has not occurred in the UK since 1906. The fungus may be spread directly or indirectly by flies, or by the use of contaminated grooming equipment or tack. The disease causes ulcers and skin lesions. Affected animals may eventually die. The disease can be confused with glanders.
Equine Infectious Anaemia
Equine infectious anaemia or ‘swamp fever’ is a disease of horses, mules and donkeys. It is caused by a lentivirus and last occurred in Great Britain in January 2010. It is still present in many parts of the world. Affected animals develop a fever, become anaemic, lose weight and may die. Recovered animals can become carriers and infect others. The virus is spread between animals by biting insects that typically live in low-lying swampy areas. If you suspect this disease you must immediately notify your local Animal Health office.
Equine Influenza
Equine influenza is a disease of horses caused by one of the influenza viruses; Influenza A. The virus occurs worldwide. Two different subtypes of the virus can cause the disease. Affected horses may have mild signs such as a runny nose and coughing. Some animals are more severely affected, with a high temperature, dullness, reluctance to eat and a hacking cough. They may go on to develop bacterial infections. The disease spreads very quickly and easily to other horses via infected droplets from the nose and coughs, and by infected rugs and brushes. The disease can cause severe problems in susceptible groups of horses. The Animal Health Trust (AHT) has developed a surveillance network for equine influenza.
Equine Viral Arteritis
Equine viral arteritis is a disease of horses. The equine arteritis virus has been reported throughout the world (including the UK) and is present in mainland Europe. The most recent confirmed case in the UK was in August 2010. Infection can spread between horses at mating, by artificial insemination with contaminated semen, by contact with aborted foetuses, or by direct contact from droplets from the respiratory tract, ie, through coughing and snorting. The disease may cause abortion or pregnancy failure. Recovered stallions may continue to infect mares while showing no signs of the disease themselves.
EquineViral Encephalomyelitis
EVE causes encephalitis (a serious nervous disease), which can be fatal. It is a viral disease of horses and there are a number of different types of EVE viruses. The same viruses can also affect people, as well as poultry and wild birds. The disease is transmitted by mosquitoes and/or biting flies. It has never occurred in the UK, but has been seen in North and South America. It is present in Central America and has spread north as far as Texas. The severity of the disease depends on the type of virus involved but all will cause nervous signs. Any suspicion of this notifiable disease must be notified to the local Animal Health office.
Glanders and Farcy
Glanders is a disease of horses, mules and donkeys. Dogs and cats can also be infected. It is caused by a bacterium called Burkholderia mallei. It was finally eradicated from the UK in 1928, but is still present in other parts of the world. It can affect people who may be infected via wounds or by inhalation following contact with diseased horses and can cause death if untreated. In horses the disease cause nodules to form in the lungs and other internal organs (glanders) or on the surface of the legs and body (farcy). Horses may die or can recover and become carriers possibly infecting others.
Vesicular Stomatitis
Vesicular stomatitis is a disease of cattle, pigs and horses. It is caused by a rhabdovirus. The disease has never been reported in the UK but is present in North, Central and South America. It is transmitted between animals by biting flies. In cattle and pigs the clinical signs of the disease are identical to foot and mouth disease. The affected animal has a high temperature and blisters and vesicles appear on the lips, tongue and feet.
Warble fly
The warble fly is an insect that can cause severe damage to the hides of animals. It mainly affects cattle although horses and deer can also be affected. The disease caused by the fly has been eradicated from the UK, but still exists in many other parts of the world. The fly lays its eggs on the skin. This can cause the animal to become distressed. The larvae hatching from the eggs travel through the body towards the back, where swellings develop. The damage caused to the hides is usually permanent and has economic consequences. In severe cases of infestation, the animal may lose its appetite. Occasionally the pressure of the larvae on the spinal cord causes paralysis.
West Nile Virus (WNV)
WNV is one of the equine encephalitides and can cause encephalitis (a serious nervous disease) in horses, which can be fatal. It is caused by a flavivirus, which can also infect birds and people. It is spread by insects, generally mosquitoes, which have bitten infected birds. It may cause central nervous signs in horses and people. Most birds that carry the virus remain unaffected. However some species, such as the crow family, are more susceptible to the disease. The clinical disease has never been reported in the UK. However, some blood samples recently taken from migratory birds have demonstrated that they have been exposed to the virus. The virus itself has not been isolated from these birds. Clinical disease has been diagnosed in many other countries including the USA, France and Italy. It is also present in Africa, Asia and the Middle East.
Spread of disease
WNV can be transmitted to humans and animals via the bite of an infected mosquito. A mosquito becomes infected by biting wild birds that carry the virus. The infection is a zoonosis, ie, a disease the causative agent of which can be transmitted between animals and humans. In the case of WNV, the virus is transmitted between birds and man, though a wide range of other animal species can also become infected. The mosquito vectors primarily involved are Culex species which are known to occur in some parts of the UK. Migrating birds are the most likely mechanism of the infection being introduced into the UK. Humans, horses and other animal species are believed to be dead-end hosts, ie, there is no spread from them to other people or animals. It is possible that a recently infected horse or person, incubating the infection, could have the virus in their bloodstream for a short time and during that time be bitten by a mosquito, but the risk of this is thought to be remote.
Since WNV was first recorded in the USA in 1999, it has spread throughout much of the country where it is now considered to be endemic. A vaccine is now available in the UK to protect horses against the emerging disease threat of WNV. It has been licensed via the European Medicines Agency (EMEA).
Animals it affects
The horse seems the most susceptible to infection but most cases are subclinical, with the horse showing no obvious signs of disease but becoming seropositive (ie, positive to the blood test for antibodies to the virus). The incubation period is 5 to 15 days and mortality rate in the USA is about 35 per cent of the animals, which show signs of disease. Affected animals develop a fever and often encephalitis with nervous signs. While birds are the main carrier and most remain apparently unaffected, some species are susceptible to disease – especially corvids (crow family). Mass die-offs can occur in these species. Other animals that can be infected are cats, bats, chipmunks, skunks, squirrels, rabbits and dogs (rarely).
WNV is primarily an infection of birds and although a range of other animal species, such as goats and sheep can be infected, these species only develop low levels of virus. To date there have been no reports that cattle have been affected by the virus. The main route of transmission of WNV is through mosquitoes and the risk of humans acquiring WNV through consumption of food is extremely low. The virus is destroyed by standard cooking methods and pasteurisation and there have been no reports of the virus infecting people following consumption of meat and milk from infected animals.
Human health
In 2004, the Department of Health published a comprehensive contingency plan for West Nile virus to protect the public's health. Many infected people show no symptoms. When disease does occur, it is usually a flu-like illness with fever. A small proportion of cases (less than 1 per cent) develop meningo-encephalitis which produces nervous signs and may be fatal. In the USA in 2002, 4161 people were reported as infected with the disease, of which 277 died.
There is currently no evidence that WNV can be spread directly from birds to people. However, dead birds can carry a variety of diseases and, therefore, should never be handled with bare hands. Always use gloves, and carefully place dead birds in double-plastic bags.
Infected mosquitoes are thought to be the primary source of the disease. Ticks have been found to be infected in Asia and Africa but their role in spreading the infection is unknown.
There is currently no licensed vaccine to protect humans against WNV, although there are experimental vaccines in development.
Disease prevention
In the absence of a vector, there is no evidence of direct person to person, person to animal, or animal to animal transmission, under natural conditions.
◗ Vector control - eliminate breeding sites of mosquitoes (stagnant water, rainbutts etc) with possible use of insecticides.
◗ Vector avoidance - for animals keep them away from vector sites, apply insect repellent, house in insect proofed accommodation when mosquitoes are active.
The Department of Health (DH) has commissioned research to evaluate the population size, species, biting behaviour and temporal and spatial characteristics of mosquitoes in GB. Tests for the presence of WNV in mosquitoes will also be carried out by the Health Protection Agency (HPA) Porton Down.
DH is identifying multilevel control measures to be used should disease caused by WNV or infection in mosquitoes be confirmed in GB. These include source control (reducing breeding habitats), advice to the public on how to avoid mosquito bites and consideration of appropriate pesticide control measures. The Health and Safety Executive (HSE) has undertaken an evaluation of the approved pesticides for use in the control of mosquitoes.

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