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African Horse Sickness

Written by  Dr Joan Kleynhans-Jordaan
| in Veearts
| April 8, 2014

African Horse Sickness was recently confirmed near Porterville in the Western Cape.

As a precaution against spread Veterinary Services established a Containment Zone, with a complete movement ban on all horses, mules, donkeys or zebras. 

    These animals may not be moved within, into, out of or through this area until the legislation has been repealed.  
The N7 forms the boundary of this area and the movement of horses from other areas on the N7 will be allowed during daylight hours on condition there is no stopping or deviation from the route.  If movement were to take place at night, or stops are made, it increases the risk of the travelling horses being bitten by Culicoides midges which may carry the virus. African Horse Sickness is spread by these midges.  
    The Chief Director of  Veterinary Services in the Western Cape, Dr. G. Msiza, has announced that restrictions have been placed on all direct horse movements to the Western Cape African Horse Sickness (AHS) Control Area from all other provinces, with immediate effect. These restrictions have been instituted due to the increasing number of reported and suspicious cases of AHS in the rest of South Africa. At this stage it is wise to check with your nearest state veterinarian before moving any horses, as the situation is dynamic and may change. Any outbreak in the Control Zone will impact severely on equine exports.
    Dogs that eat the raw meat of horses that died of African Horse Sickness, may also contract the disease. Recent evidence has also shown that dogs can contract horse sickness from Culicoides bites, although generally these midges do not seem to bite dogs.
    To limit risk of infection all horses should be stabled from 2 hours before sunset until two hours after sunrise. The reason for this is that Culicoides midges generally don’t enter buildings and are most active outside around dawn and dusk.  Further control involves treating the horses with effective insecticides. Any sick or dying horses must be reported to the closest State Veterinarian.  The above applies to all areas.
    The symptoms of African Horse Sickness include fever of up to 41° C, coughing, discharge from the nostrils, pneumonia, loss of appetite, ataxia (difficulty in moving), swelling of supraorbital fossa (the hollow above the eyes), and acute death before showing obvious symptoms.  Horses which contract the “dikkop” form with facial swelling, have a longer course and slightly better prognosis than those with the “dunkop” form, which mostly affects the lungs.
    In the Porterville outbreak, serotype 1, which is part of bottle 1 of the vaccine, is involved. In this area, the State Vets have requested that owners who wish to vaccinate should only use bottle 1 at this stage and administer bottle 2 after the outbreak has died down.
    Normal vaccine recommendations are that all horses should be vaccinated annually, preferably in early summer, with bottle 1, followed by bottle 2 after 3 weeks. There are 9 serotypes present in South Africa.
    How does horse sickness suddenly appear after it has been absent from an area for many years? Movement of infected horses usually account for spread over large distances. Culicoides midges may also blow many kilometres in the wind, or travel in horse boxes.  Under certain climatic conditions, midge numbers may explode; increasing the risk – such as good rains after a dry spell, followed by warm weather. Recently, there have been several outbreaks of horse sickness in other parts of the country. Even so, there is some evidence that climate change may be playing a role in the changing epidemiology of African Horse Sickness.  Zebras are natural reservoir hosts.  Prior to 1953, major epidemics occurred every 20 to 30 years. In 1855 nearly 70 000 horses died. This was more than 40% of the entire horse population of the Cape of Good Hope at the time.  A fairly effective vaccine has only been available since 1974.
    The best you can do to protect your horses is to have them vaccinated by a veterinarian every year in early summer, and stable them from 2 hours before sunset until two hours after sunrise during high risk periods. Also use effective insecticides on the animals and buildings to kill the midges.  
If stabling is not possible, move them to high lying areas away from standing water. When I first practised in Clanwilliam in the early seventies, farmers told me that they saved their horses during outbreaks by moving them out of the valleys and into the Cederberg Mountains. 

Dr Joan Kleynhans-Jordaan is ’n ervare veearts en het tydens haar loopbaan wat reeds oor vier dekades strek, met plaasdiere, huisdiere en wild gewerk. Sy doen tans lokums in die Wes-Kaap en elders en skryf graag oor haar wedervaringe. Sy is ook ’n ywerige fotograaf en kunstenaar. Sy skilder veral graag kleurvolle hondeportrette.