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Sheep scab Afrikaans | Xhosa

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Of all diseases caused by mites, sheep-scab is without a doubt the best-known, most dangerous, most destructive, and most dreaded condition.

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Sheep-scab is caused by the sheep-scab mite. The female mite lays between 40 and 90 eggs in her lifetime of about 30 days. A larva hatches from the egg, grows, and moults into a nymph, which develops into the adult mite. Under favourable conditions the life cycle from the new-laid egg to a mature, egg-producing female can be as short as nine days. The result is that an infested sheep can show severe lesions within four to six weeks.

In the herd the mites are transmitted from sheep to sheep through direct contact between animals. However, individual mites can remain viable, and capable of re-infection, for as long as 12 days after being separated from a sheep. They can be spread by means of vehicles, the sheep shearing process, handling equipment, the clothing and bedding of shearers, etc.

The following facts concerning scab should be borne in mind:


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Scab mites live and feed on the surface of the skin. The mites prick the skin with their mouth parts and feed off the lymph and tissue-fluids which flow from the pricks.

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The lymph and fluids mix with the dead tissue, dust and dirt, secretions of the mites, strands of wool and oil. When this dries it results in the characteristic scabbiness, which is clearly visible and from which the condition derives its name.

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Lesions formed by scab have a rosette-like shape, because the scabs hamper the feeding of the mites so that they have to continuously move out from under the scabs to find new areas of skin.

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Dormant mites can survive for 10 months in the folds of the sheep's skin, around the bases of the horns, and in the sheep's ears.

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Scab is accompanied by intense irritation, and causes the wool to break. Among the first visible symptoms are wads of wool which become detached when the sheep scratches or bites at the lesions.

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Usually lesions first appear on the shoulders and flanks of the sheep. Among rams lesions often appear first on the parts around the chest and neck, due to infection which takes place when they service ewes. During the time for service infected rams will, in turn, cause the first lesions to appear on the rumps and hips of ewes.
  • Scab is traditionally regarded as a winter disease. In the autumn, when the temperature in the fleece drops and the intensity of the sunlight decreases, the moisture level of the wool increases, the mites thrive, and an infestation often turns into an "outbreak" in the early to midwinter.

 

  • It has been found that poor feeding conditions are also related to scab. Summer outbreaks are not unknown in South Africa, and these are usually associated with sheep that are in poor condition or under nutritional stress.

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In terms of the Animal Diseases Act sheep scab is a controlled disease and any suspected or confirmed cases of this disease must be reported to the nearest state veterinarian, animal health technician, extension officer or police station. Neglect in this regard may lead to prosecution.

Since sheep scab is such a dangerous disease, which can easily assume epidemic proportions, everything must be done as quickly as possible to control the spread of the disease.

Here are a few important guidelines that the farmer should follow:


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Consult a veterinarian as soon as any skin condition or itching is observed among sheep, so that the responsible organism can be diagnosed timeously.
  • In cases of sheep scab no animals must be transported or moved from the farm. Doing this will cause the disease to spread. The farm will also be put under quarantine straight away by a veterinarian or animal health technician.

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Dip the sheep twice (with an interval of eight to ten days) using a registered sheep scab dip. Medicines that can be injected are also available. Be aware, however, that individuals that are skipped during the injection exercise and get mixed up with the treated animals can not be readily identified, as in the case of dipped animals. Such skipped individuals will soon infect the flock once again. It is advisable to spot-mark all stock in the kraal during a dipping exercise (use two paint colours, one for each treatment). Animals that were dipped only once, or not at all, will be identified at the second dipping, when they can be isolated and dipped immediately to avoid re-infection. 

Moreover, this way the cost of a third or fourth dipping can be avoided. During dipping each animal receives a full dose of dip commensurate with its body size. In the case of injections the dose is based on the animal's body weight. When large weight differences occur within a flock, care must be taken to ensure that the heavy animals receive the full dose. It takes only a few mites that are not killed, to re-infect the whole flock.

The following must also be kept in mind:

  • Carefully adhere to the instructions on the label.

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Follow the 4 x 100% rule when dipping, i.e. dip 100% of all small livestock (sheep and goats) on the farm in one session; immerse 100% of each animal's body in the dip mixture; keep the animals in the dip mixture for 100% of the recommended time (60 seconds); dip at 100% of the recommended strength of dip mixture until the last animal has been dipped.
  • Dip or treat all the sheep on the farm against scab once a year.

 

  • Rid all sheep that are brought onto the farm from elsewhere, for example breeding rams, of scab by dipping them and keeping them under quarantine for two weeks before releasing them into the flock.

 

  • Take the best possible precautions with shearing teams and equipment, as well as with all vehicles used during the shearing season. In this way infection can be avoided. Wash and disinfect equipment thoroughly.

 

  • Be aware of stray sheep and goats.

J du Plessis
ELSENBURG / NWGA Port Elizabeth