African Horse Sickness

African Horse Sickness is a viral disease of horses, mules and donkeys and is transmitted by culicoides midges. Like the anopheles mosquito, which spreads the plasmodium malaria parasite, the culicoides midge also requires a blood meal from specific host animals in order to develop their eggs. Horses are most susceptible, mules less so, while donkeys and zebras are very resistant. Horses that have recovered from this disease do not remain carriers of the virus. However, like malaria, the virus requires a reservoir host to lie dormant in during the dry winter months. Zebras are thought to be a prime reservoir host, but it can lie dormant in other animals as well. It is therefore the transport of host animals that causes the large scale spread of the virus and the midge merely acts as a carrier from animal to animal over short distances.

African Horse Sickness does not affect any other animals, except that dogs have occasionally been fatally infected after having ingested diseased horse meat. The disease is generally more prevalent in low-lying moist areas, such as marshes and valleys. The period between sunset and sunrise, when culicoides midges are most active, is the time when most animals acquire infection in the open veld. There are three forms of the disease, namely the lung, heart and mixed form. The lung form
(Dunkop) is recognized by a high fever, difficult breathing and frothy discharge from the nose and is characterised by a very high death rate. The heart form (Dik kop) is recognised by a swelling of the head and eyes with only a 50% death rate in horses. In the mixed form of the disease, symptoms of both the heart and lung form could occur. A vaccine is available in South Africa; however, horses in the surveillance zone or sick- free zone may only be vaccinated with written approval of the Director of Veterinary Services.

The accidental transport of midges in airplanes and vehicles can also result in the actual midge transmitting the virus over long distances, providing that she has a blood meal soon after arrival at her destination. You will note that it is the female that spreads the virus, not the male! Similarly, the accidental transport of adult mosquitoes can also cause the widespread infection of malaria, otherwise known as airport malaria. In other words, an infection can take place at a destination miles away from an infected area simply by the arrival of an infected midge or mosquito via airplane or vehicular transport.

Midges can also transmit Rift Valley Fever, Akabane Virus and Bluetongue.

Culicoides bolitinos and Culicoides imicola are the main species involved in

the transmission of African Horse Sickness and normally breed in the dung
of large herbivores, e.g. cattle dung.

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Scientists believe that the Mpumalanga Lowveld and Zululand areas, with their warm winters and abundant game, are ideal environments for the maintenance of arboviral diseases such as African Horse Sickness.

The following points should be considered in the control of culicoides midges;

1. Breeding sites are often created on farms because of poorly constructed or poorly maintained watering points, and the increased use of irrigation in the production of crops may cause the further spread and escalation in their numbers.

2. Water leaks, manure and urine are ideal habitats for immature midges.

3. Dung pats, tree holes, rotting vegetation and stagnant surface water are ideal larval habitats, but they can be treated with various chemical methods.

4. As the biological control of midges has little prospect, it is essential that
horses be vaccinated against African Horse Sickness.
5. Valuable animals should be stabled at night, as the midges, which are

active at twilight and at night, are not inclined to enter buildings. Wet,
low-lying areas are dangerous areas, while dusk and dawn during the
mid-to-late summer are dangerous periods.

6. Screening stables with insect gauze or shadecloth treated with pyrethroids,
operating light-traps outside stables at night, switching off all internal lights
and the use of overhead or extractor fans should also be considered.

7. Culicoides prefer cattle and will thus rather feed on cattle than on horses.

8. One can also prevent the culicoides midge from biting animals by using an insect repellent, such as a Citronella Oil based product. Being herbal, it can be sprayed as much and as often as necessary and can also be used on your domestic pets as well as for human/personal use. One of the best methods of repelling such biting insects is to spray all horses with a Citronella Oil product every day before exercising and again in the evening after stabling. If it is sprayed on the legs, belly and rump of the horse, it will discourage the midge from adhering to the horses skin and passing on this dreaded virus. In order to make the contents adhere and spread further over the animal, dilute 50% of the repellent with 50% paraffin or water in a plastic spray bottle.

9. When sprayed in its concentrated form around the brim of a garden hat, pesky flies will also be kept at bay. If sprayed around the tops of socks or ankles, it will keep ticks and fleas at bay. When sprayed on exposed limbs and on clothing or bedding, it is most effective at preventing mosquito bites. Citronella Oil is a good
masking agent of Carbon Di-Oxide, Lactic Acid and other scents and aromas emitted by all animals which midges & mosquitoes use to find their blood-host.


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Email;
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