Sheep scab is regarded as the most serious threat to the sheep industry in Namibia, as well as neighboring countries. It occurs mainly in southern Namibia during autumn and winter, in large commercial sheep flocks.
The sheep farmers in the southern areas of Namibia are now well-seasoned in the management of this disease. However, it is always a nightmare when farmers are faced with the disease, as evidenced in the recent devastating outbreak on several farms in the Keetmanshoop district and in the Gochas area of the Mariental district.
Let’s discuss what causes sheep scab, and how we control it. Sheep scab is caused by mites (Afrikaans “muite’, OtjiHerero “ozona”) which are so small that we can’t see them with our naked eyes. It can only be seen with a microscope at veterinarians’ offices, or at the laboratory.
The sheep scab mite has a fancy name, Psoroptes communis ovis, and is quite specific to sheep of all ages. Even if you can’t see the mites, they are there on sheep. Goats are not as susceptible to these mites, and they only live for a short while on the hair of goats.
In the flock, the sheep scab mite is transmitted to other animals by direct contact. Farmers should be aware that just one infested sheep is enough to cause an outbreak in the flock. The mites can also be spread by means of vehicles, handling equipment, clothing and bedding.
In winter months, these mites become very active, and that’s when farmers will start noticing symptoms of this disease in their sheep.
The earliest signs to be noticed would be most likely the sheep scratching and biting or licking themselves, as well as rubbing themselves against fences and objects. This constant scratching leads to sheep losing wool. (This differentiates sheep scab from zinc deficiency, where animals’ don’t itch, although they lose hair). The intense itchiness is caused by mites sucking moisture from the skin of the animal. Due to the scratching and biting, you may find small pieces of wool/hair hanging on fences and objects and even in the mouths of sheep, and you will note that the sheep have patches of areas where there is no wool or discoloured fleece.
This condition derives its name from the dry crusty scabs with moist red borders (so-called scabs which form after the fluid leaks from the irritated skin of the animal. You will see bare, scabby patches and wool stuck or matted together.
The general signs which will be noted include affected sheep standing apart from the flock, dull and depressed, with weight loss over time and poor fertility. The intense itch can cause animals to stop feeding and mating. If left untreated, death may also occur in severe cases, especially in younger animals.
The economic impact of the disease is felt not only because of the affected health of the animal, but also the irreversible damage to the wool as well. The resulting quarantine which follows an outbreak of sheep scab can affect marketing in those designated areas. That’s why this disease is by law a notifiable disease, and farmers should report any suspected cases of this disease to the nearest veterinary official as soon as possible.
If sheep scab is suspected, farmers should immediately report to veterinary services for animal health technicians or veterinarians to take the relevant skin scab sample for definite diagnosis, and to assist with the control program.
In Namibia, sheep scab control programmes include an immediate quarantine of the designated farm, as well as neighbouring farms. In other words, no small stock may be brought in or may leave the farm. Every single sheep on these farms should be treated individually.
There are many dips compounds registered to treat sheep scab, including Amitraz, Deltamethrin, Diazinon and Cypermetrin. Make sure that the animal is immersed in the dip for at least one minute, and the heads submerged three times in the dip.
For our small-scale village farmers, a 200-liter drum can be cut in half, and used as a dip tank. Or you can inject with Ivermectin products or Dectomax, although this are more expensive.
All treatments are supposed to be done under veterinary supervision. In fact, the treatment of sheep scab without veterinary supervision is NOT allowed. Therefore, such treatment will be regarded as null and void until the farmer treated all his/her small stock under veterinary supervision.
It is important to give a second treatment after 8-10 days in order to kill the young hatching mites. Farmers are warned that it is no benefit using short-cuts with these treatments as an outbreak can re-emerge from following an ineffective control program.
It is also recommended to leave the affected kraals empty for about three weeks and also to spray disinfecting chemicals in houses where sheep are housed.
The owner of an animal which is infected or suspected of sheep scab must prevent access of other sheep and goats to the sick animal. The movement of people and equipment must be restricted and actively controlled. The disinfection of used equipment is also important to prevent the spread of the disease.
Finally, it is clear that of all the diseases of sheep affecting the skin known in Namibia, sheep scab is the most common and most devastating.
We cannot stress enough that farmers should be careful when introducing new sheep into their flock. The best way to prevent sheep scab introduction is to isolate and treat new sheep twice before they come into contact with the rest of your flock.
And remember to always report suspicious cases of sheep scab to veterinary services, more so since it is a notifiable disease. The early detection and reporting of outbreaks is also crucial in the containment of the disease and to prevent its spread.