Categories: Horses

Underestimate AHS at your peril

If sources in the local horse fraternity are to be believed, the official statistics of African horse ­sickness are just…

doug walsh, ceo of the
african horse sickness trust

If sources in the local horse fraternity are to be believed, the official statistics of African horse ­sickness are just the tip of the iceberg, with the real death toll being up to 1 000 horses in the last year. The African Horse Sickness Trust was set up two years ago to coordinate efforts to contain this deadly disease. Lloyd Phillips reports.

African Horse Sickness (AHS) is endemic to SA, yet every year there are hundreds of officially confirmed cases of this disease infecting horses, donkeys and mules, many of which end up dying a ­horrible death as a result of severe damage to their circulatory and respiratory systems.
According to National Department of Agriculture (NDA) records, 851 cases of this notifiable disease were reported in the 2005/06 AHS season, which tends to run annually from December until the cold snaps of June. The NDA’s records further indicate that 274 horses in these cases died.
Yet, according to some people in the local horse fraternity, these figures are just the tip of the iceberg. An anonymous source who is well placed in national equine circles told Farmer’s Weekly they had heard that AHS infections for 2005/06 were more around the 1 500 to 1 800 figure, with deaths totalling between 750 to 1 000 horses.
The source added, “The Department of Agriculture only officially records an AHS case once a blood ­specimen has been taken from an equine suspected of having the disease, a vet has signed for the specimen, the specimen has been couriered to Onderstepoort Veterinary Institute, and the institute has confirmed AHS in the specimen. Many equine owners can’t afford the vet and testing fees, so these cases go unrecorded, ­giving a skewed view of the impact that this disease is actually having on the equine ­population. The figures I’ve heard are probably also only 30% to 40% of the true number of AHS cases out there every year.”
The time frame during which AHS tends to manifest is linked to the lifecycle of the disease’s vectors – the midge species Culicoides imicola and Culicoides bolitinos. These midges begin ­breeding during the warm, moist months of the year, and the females require a blood meal before laying their eggs. In SA their ­populations begin growing exponentially from about the end of November, peaking during ­February, March and April, and dropping to negligible levels during the cold months of winter.
It is when these female midges begin seeking their blood meals that AHS begins to find its way into equines. Zebras can carry the AHS virus while suffering no ill effects, as can donkeys. However, there have been recorded cases where even donkeys have become ill or died from the disease.
According to a research paper by Philip Mellor and Christopher Hamblin of Pirbright Laboratory’s Institute for Animal Health in the UK, female midges require a number of blood meals during their breeding cycle. If a female feeds on an infected equine first and on an uninfected equine next, she is highly likely to transfer the AHS virus into the uninfected animal. Huge populations of these midges participating in ongoing breeding, combined with the females’ ability to fly an average distance of 2km, enable the AHS virus to rapidly find its way into equines all over SA every year.
The African Horse Sickness Trust was set up two years ago by concerned members of the equine fraternity to work with relevant public and private institutions to determine the true extent of AHS’s impacts on its target species, and to promote closer cooperation in finding ways to reduce the high number of infections and deaths around the country.
The trust’s CEO, Doug Welsh, explains, “Most of these infections and deaths are totally unnecessary. In the past, people have said that the AHS vaccines from Onderstepoort Biological Products have been ineffective against the disease. From my research into the causes and impacts of the disease in SA, I have found that the vaccines work very well provided that they are used properly by horse owners.”
The first common mistake that many equine owners make when handling the two vaccines is breaking the cold chain. Vaccines 1 and 2 contain ­attenuated live strains of the AHS virus and need to remain refrigerated right up to being administered, or they will die and lose their effectiveness.
A second mistake deals with when to administer the vaccinations. “It takes five months from being administered into an equine for the vaccines to be working at their peak,” Welsh says. “We have found that cases of AHS peak in the months of March and April every year, so it’s better to administer the vaccines during September, October and November of the previous year so that the vaccine is working at full strength during the months when Culicoides populations are at their peak, and the threat of AHS transmission is at its greatest.”
Properly vaccinated equines may still become ill from AHS, but it is unlikely that they will die. During the AHS ­outbreak in George, Western Cape earlier this year, not a single properly vaccinated infected equine died of the disease. Yet, according to Welsh, the majority of unvaccinated infected equines in that area during the outbreak did die.
He warns that equines with compromised immune systems from injury and illness ­ should receive additional protection against contracting the disease during the AHS season. In these cases it is ­recommended that the affected equines be stabled at night when the Culicoides midges are at their most active; to use insect repellents on the animals or in the stables; to use fans or have good ventilation in the stables to disperse the carbon dioxide and equine odours that attract the midges; to cover the animals with blankets; and to cover all openings in the stables with shade netting. Welsh says 70% shade cloth has been proven to reduce indoor midge counts by seven times if used to cover all a stable’s openings.
The trust is in discussions with ­government and other stakeholders to develop a programme to send teams to blanket-­vaccinate equines in tribal ­authority areas. Welsh hopes this programme will kick off before the upcoming AHS season by ­starting to vaccinate equines in the ­communal lands of northern KwaZulu-Natal.
The African Horse Sickness Trust relies on donations to cover the costs of all its ­activities. Doug Welsh requests that ­concerned citizens or organisations use the following details to make donations: account name: African Horse Sickness; bank: FNB; branch: Durban Main; account number 62098357885; branch code: 221–426.
Contact the trust on 086 114 735 (24 hours) or visit www.africanhorsesickness.co.za. |fw

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Tags: African Horse Sickness;Animal Health

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