Last update: September 2, 2011 10:27:24 AM E-mail Print



J Joubert


After abundant rains, there are pools of standing water everywhere and many mosquitoes and midges hatch. Mosquitoes are the carriers of Rift Valley fever and Wesselsbron viruses, while midges carry the blue tongue virus. Autumn is the season when these troublesome insects are liable to present a problem, and only after the occurrence of severe frost do they disappear again.

Rift Valley fever is the most drastic of the three diseases, says Dr Johan Joubert, Acting Head of the Regional Veterinary Laboratory at Grootfontein. In susceptible animals this disease can cause up to 95% of the lambs to die, most ewes to abort and up to 30% of the adult animals to die, he says. This applies to sheep, goats and cattle.

According to Dr Joubert, Wesselsbron disease has very much the same effect as Rift Valley fever but in a lighter degree, it also causes many abortions, but fewer deaths. Blue tongue can result in death, mainly in sheep, and can affect many animals, causing them to walk and eat with difficulty,

"As conditions have been very favourable for these three diseases, the Regional Veterinary Laboratory at Grootfontein wishes to draw the attention of farmers to the prevention and control thereof", Dr Joubert says.

There is a live virus vaccine available against Rift Valley fever and Wesselsbron disease. The vaccine can be used for both sheep and goats. It does however cause abortions in pregnant animals and must therefore not be used for animals in that condition. The two vaccines can be mixed and injected simultaneously. One ml is injected under the skin. It affords life-long protection.

If ewes are already pregnant, the dead or inactive Rift Valley fever vaccine, which is actually intended for cattle, should be used. This vaccine gives protection for about 9 months.

Blue tongue vaccine for sheep is now packed in A, Band C packages. This is done because there are so many types of blue tongue virus. Five different types are included in each of the A, Band C vaccines. The A, Band C vaccines can be used at least 2 or 3-week intervals. Doing this, the widest possible protection against a large number of blue tongue strains can be achieved.

Dr Joubert reminds that pregnant ewes should not be vaccinated during the first half of gestation. Furthermore, rams ought not to be vaccinated before the mating season, but thereafter.

The dipping of sheep about once every two weeks can keep mosquitoes and midges away. This treatment can be a useful aid in the present circumstances.

Animals can also be moved to hill and mountain veld where there will be fewer mosquitoes and midges. In this way the danger of contracting diseases can be minimized. Dr Joubert warns that horse sickness virus is also transmitted by midges. The danger thus exists that horse sickness can spread after rains. The same preventative measures exist for horses: a vaccine is available and dip remedies may also be used. "As a preventative measure, horses should preferably be stabled early in the afternoon and allowed out again only when the dew is off the grass", says Dr Joubert.



Karoo Regional Newsletter 1