RESEARCHERS at Onderstepoort Veterinary Institute are working on a new vaccine that could open up South African horse-racing to international competition.
South Africa is home to a virus called African horsesickness, which is endemic in most of sub-Saharan Africa. Horses are infected by a species of blood-sucking midges called Culicoides.
In trekker days, it led to the wholesale deaths of horses on the trail, making oxen the preferred beasts of transport and leading to unsuccessful experiments with zebras as replacements. Today, the disease is the cause of severe restrictions on the import and export of horses.
Although there are vaccines for African horsesickness, they are problematic because they cause the horses to test positive for African horsesickness antibodies – but the current tests can’t distiguish between an infected horse and a vaccinated one. This creates difficulties in exporting local horses, and makes overseas horse trainers and owners reluctant to send their horses here for the racing season.
However, the type of vaccine currently in development – known as a recombinant subunit vaccine – would not have this problem, researcher Albie van Dijk told the conference this week.
Another reason Van Dijk and her collaborators are working on recombinant vaccines stems from problems in a vaccine factory in the 1980s. Some workers from the packaging section suffered encephalitis and chorioretinitis and lost their sight after being accidentally infected by two old vaccine strains of the live attenuated type.
These vaccines were immediately withdrawn and new vaccine strains were developed to replace them, but there are still problems with one of the strains.
Live attenuated vaccines are weakened versions of the virus – they have been grown in laboratories in tissue cultures and weakened to the point where they no longer cause the disease, but stimulate the immune system to develop antibodies.
Recombinant subunit vaccines, however, are a small piece of the genetic material of the virus – usually the outside protein. It cannot cause the disease because the whole virus isn’t there, but it causes antibodies because the body recognises the outside protein as the virus.
Horses injected with a recombinant subunit vaccine would, theoretically, also test positive for African horsesickness antibodies. But new testing procedures are also being developed in conjunction with the new vaccine that can show the horses are testing positive for the vaccine rather than an infection.
Van Dijk stressed the vaccine is still in the development phase. But if it works, it will be the first recombinant vaccine to be developed in South Africa. And perhaps one day we’ll have a race of the stature of Ascot.
ENDS