African horse sickness (AHS) is an infectious disease that can affect all species of equidae (for example, horses, donkeys, zebras, ponies).
The clinical signs seen are dependant upon which form of the disease is present:
Acute respiratory form
High fever, difficulty breathing, coughing and frothy discharge from the nostrils, mouth open and head hanging down. The mortality rate is very high with up to 95% of severely affected animals dying within a week.
Fever, followed by swelling of the head and eyes, lips, cheeks and under the jaw. Loss of the ability to swallow and possible colic symptoms, pinpoint bleeding in the membranes of the mouth and eyes. The mortality rate is around 60% and death results from heart failure.
Mild respiratory signs followed by the typical swellings of the cardiac form.
Fever with low temperatures 40 to 40.5 degrees celcius in the morning rising to a high peak in the afternoon. Horse generally unwell.
In the majority of cases, the subclinical cardiac form is suddenly followed by marked shortness of breath and other signs typical of the pulmonary form.
How African horse sickness is spread
The primary way this virus is transmitted is through midges (Culicoides Spp). The spread of disease can be influenced by climatic conditions that favour the proliferation of the vector midges, including warm, moist weather and high rainfall, as well as spread by wind dispersal.
Once a horse has been bitten by a carrier midge, the incubation period of AHS is usually 7 to 14 days, but may be as short as two days.
Although AHS is not directly contagious (i.e. it is not transmitted directly between horses), it can remain in infected horses for a few weeks, enabling it to be transferred via blood-sucking midges or even contaminated hypodermic needles.
It is possible for disease to be transmitted by equipment such as dental, obstetric and veterinary instruments, for example needles and scalpels.
Vaccination of horses
Although attenuated live vaccines are available internationally, these are not considered to be sufficiently effective or safe to be suitable for use in Europe.
Human health implications
There are no human health implications because the disease is not zoonotic.
How to control the disease
The African Horse Sickness Control Strategy for Great Britain describes how an outbreak would be managed. This document sets out the measures applied in the event of an outbreak and summarises the wider framework aimed at preventing and limiting an incursion.
If the disease is confirmed the outbreak will be controlled in line with the contingency plan for exotic notifiable diseases.
Since AHS could spread throughout GB, this framework is endorsed by Scottish Government, Defra, and Welsh Government, although responsibility for management of an outbreak in respective regions falls to the respective governments.
The African Horse Sickness (Scotland) Order 2012 provides for declarations of infected premises, slaughter of infected animals, investigations by veterinary inspectors and certain movement restrictions.
Biosecurity for horses
The Government's policy on disease control is that prevention is better than cure. This approach works by reducing the chances of a disease entering the animal population, and if it does then it can be quickly spotted and dealt with through the preventative measures.
Biosecurity is about being aware of the ways disease can spread, and taking every practical measure to minimise the risk of disease spreading.
If you suspect signs of any notifiable diseases, you must immediately notify your Scotland: field service local office at the Animal and Plant Health Agency (APHA). Failure to do so is an offence.
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