Confirmed Eastern Cape AHS virus outbreak: Weathering the storm

Due to the African horse sickness (AHS) outbreak in the Eastern Cape, movement restrictions have been imposed in the Grahamstown state veterinarian area. After consulting with nearby state veterinarians, it was agreed that no horses or donkeys should be transported in or out of the Kleinemonde, Port Alfred, Bathurst, Alexandria, Seven Fountains, Grahamstown and surrounding areas at this time.

Dr Gabriel Mutero, the state veterinarian in Grahamstown, said some horse owners do not report possible AHS cases and mortalities, which prompted a strict warning to halt any horse travel and show participation. He urged everyone who deals with equines to familiarise themselves with the Animal Diseases Act, 1984 (Act 35 of 1984), and warned that non-compliance could lead to legal action.

It is a horse owner’s responsibility to:

  • Prevent the spread of AHS by not moving animals of unknown disease status onto their property.
  • Refrain from moving animals off a property affected by AHS for 30 days after the last case.
  • Ensure their equines receive annual vaccinations with a registered vaccine.
  • Inform the state veterinarian or a local veterinarian of any suspected cases.

“We care for your equines and we want to limit the spread to more animals,” said Dr Mutero. “We are therefore putting down strict rules at this point in order to protect your animals. Thus, we genuinely hope and trust that horse and donkey owners will abide by this request.”

First AHS cases confirmed

Plaas Media enquired about the situation at Kowie Veterinary Clinic in Port Alfred, where Dr Leon de Bruyn reported the first (fatal) case, confirmed by Grahamstown Veterinary Clinic, near Kleinemonde on 21 January. Dr De Bruyn diagnosed the subsequent cases, including a non-fatal case at South Seas East of Kleinemonde and another fatal case on the same farm on 3 February. The last two horses had not received vaccinations for four years. Meanwhile, there was a possible case north of Bathurst, and an unconfirmed fatal case near Cannon Rocks on 7 February.

A horse in Bathurst survived a confirmed case of AHS on 12 February, followed by two more survivors in Port Alfred and its vicinity on 16 and 17 February. “The last three horses had received proper vaccinations. However, another horse near Salem died of AHS and a suspected case was fatal west of Alexandra on 29 February.”

Clinical signs and diagnosis of AHS

Horse owners are strongly advised to report suspected cases of AHS to their local veterinarian who will take the necessary samples, prescribe treatment and report any confirmed cases to the state veterinarian.

“AHS is regulated by the state, so owners have to inform the state veterinarian or a private veterinarian who will then report any cases to the state veterinarian,” Dr De Bruyn says. “Suspected live cases are tested by sending blood samples to the Equine Research Centre Veterinary Genetics Laboratory for testing to verify the AHS virus.”

The disease can manifest in different ways, such as:

  • The peracute ‘dunkop’ cardiac form, which is often fatal in a short time.
  • The sub-acute ‘dikkop’ or pulmonary form, which has a higher survival rate.
  • The intermediate, mixed form.

The virus damages the lining of the blood vessels, which causes the swelling and the fluid on the brain and lungs.

Clinical signs of AHS include the following:

  • Fever.
  • Lethargy.
  • A tendency to lie down.
  • Supraorbital swelling – The sunken cavities above the eyes actually swell quite dramatically.
  • Laboured breathing.
  • White or pink foam out of the nose.

Precautionary measures

Dr Cebisa Mnqeta, chief director of veterinary services at the Department of Rural Development and Agrarian Reform (DRDAR), advises horse owners to also avoid low-lying and marshy areas where possible and if possible, to stable animals in insect-proof stables.

To prevent AHS infection during an outbreak, the Culicoides midges that carry the virus should be away from horses. Dr De Bruyn advises that the midges bite more at dusk, night and dawn, so spray horses should be sprayed with an insect repellent. He recommends using repellents with DEET, which work best, but horse owners can also try pyrethroids or citronella.

“Midges obviously don’t respect boundary fences, which is why the strong state veterinarian advisory has been issued to the horse owners and competitor community of the Grahamstown state veterinarian district,” he says. “This could have major implications for the horse section of the Bathurst Agricultural Show, which will be taking place 22 to 24 March. The last case in Bathurst was over 30 days from the start of the show, but if we keep getting AHS cases in the area then the equestrian component of the show may unfortunately have to be cancelled.”

Vaccination frequency and effectiveness

Annual AHS vaccination is recommended. “Foals born from unvaccinated mothers can be vaccinated at any age, preferably from one month of age, while those from vaccinated mothers can be vaccinated when they are at least six to seven months old,” says Dr Mnqeta. “Vaccination of mares should be avoided in the first three months of pregnancy. Vaccination is strongly recommended to be carried out when vector populations are low, from 1 June to 31 October. Please consult your veterinarian for any vaccination advice.”

The AHS vaccine is a modified live virus vaccine made by the state vaccine manufacturer Onderstepoort Biological Products (OBP). It is, in the words of Dr De Bruyn, “reasonably effective, but vaccinated horses can still get sick and die. However, vaccinated horses tend to be better protected and have milder disease than unvaccinated horses.”

There are nine strains of the AHS-virus, and the vaccines are divided into two doses containing four strains each. These doses are administered preferably four weeks, but at least three weeks, apart to prevent interference between the different viral strains, which would compromise the immune response.

Dr De Bruyn says it is important to note that the vaccines must not be administered during an outbreak since the live virus in the vaccines can revert to virulence and be transmitted by the Culicoides midge vector to cause AHS disease outbreak.  “It is therefore preferred that AHS vaccines are administered between the end of June and end of October when the midges are generally dormant. This vaccination period is mandatory in the AHS-free, protection and surveillance zones of the Western Cape.”

A broken freeze dryer caused a shortage of AHS vaccines from OBP in the past few years. The repair was delayed because the technicians had to come from Europe and a new freeze dryer takes two years to order. OBP used the smaller research freeze dryer, which reduced vaccine production significantly. This also affected other vital livestock vaccines such as the bluetongue vaccine, which is also freeze-dried.

Act 35 of 1984 does not make provision for a movement ban within the AHS infected zone in the country, apart from off the property where the cases occurred, but the onus still lies with horse owners to act responsibly to prevent further spread of AHS. – By Carin Venter, Plaas Media

For more information, please contact the DRDAR call centre on 0800 203 025 or send an email to customercare@drdar.gov.za.

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