Prevent and control parasitic mites that cause sheep scab and goat mange


By Nan Smith | 7 August 2017
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Psoroptes mites cause psoroptic mange, better known as sheep scab, in sheep and goats. Mite activity creates small lesions and sets up a severe itch. The constant itch causes animals to scratch, rub and bite the wound site and leads to a serious loss of condition. Untreated animals will eventually die.

Mites are ectoparasites that feed on the skin of the host animal and cause severe itching. This leads to scratching, rubbing and biting which, in turn, damages the skin, the wool and the hide. Stripped of hair and wool, bare patches of inflamed skin are crusted with weeping wounds and dry scabs. Head shaking is a sign of mites in the ears.

Sheep scab is caused by a psoroptic mite active in autumn and winter. It is a permanent parasite of sheep but it can survive briefly, on goats. Mange in the ears, on the legs and the fetlocks is more common in goats. Although the mite may come from a different family, the treatment is the same.

Scab is mostly spread through direct contact with infested sheep but the mites can survive in fabric, vehicles, wool and soil for up to two weeks. It is highly contagious.

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The picture at the top shows early scab. The ghastly progress of scab is illustrated in this picture. PICTURE: Alan R Walker – Wiki Commons

THE PARASITE AND THE SYMPTOMS

The scab mite is an adult in only 11 days. Mature adult mites bite through the skin and feed on the fluid that seeps from the bite wounds.

Within four days crusty sores form around the irritated bite area. These sores grow bigger as the mite keeps moving towards new feeding grounds on the edge of the wound.

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Mites have causes bare patches on this goat’s head, face and neck. In goats the mite infestation often begins in the ears and animals resort to constant head-shaking and rubbing. PICTURE: Alan R Walker – Wiki Commons.

To relieve the severe itching caused by mite activity, the animals rub, scratch, and pull at the affected area. The broken, exposed and sensitive skin is vulnerable to secondary bacterial infections and is the ideal site for blowfly strikes.

Infested sheep and goats lose weight, refuse to mate and avoid their lambs. Untreated, sheep scab will ultimately lead to the death of the animal. The production picture is horrific for large commercial operations, small-scale commercial farmers and subsistence farmers.

To add to the problem sarcoptic mange is a zoonotic parasite; which means the sarcoptic mite likes your skin as much as he likes the skin of your livestock.

TREATMENT

Plunge dipping is the only acceptable method of dipping for sheep scab say husband-and-wife vet team Peter and Pamela Oberem of Afrivet, and many other animal scientists. According to the Oberem’s disease manual for small-stock: “The animal must be immersed for at least 60 seconds and the head submerged three times.”

If we are to farm without excuses, then the dip tank must be built. There are several inspiring stories about small-scale sheep and goat farmers who have constructed plunge dips. When money is a major limiting factor farmers are incredibly innovative and creative.

Another solution may be to form a group and share the costs of building a dip. This would make a lot of sense to a group of farmers sharing communal grazing because all the animals would quickly be infested by the parasites.

PREVENTION

Prevention is always better than dealing with an outbreak. An annual dip against these parasites will protect your flocks.

First dip

To work properly and kill the mites there must be sufficient wetting of the hair, wool and skin. If this does not happen, the mites will be suppressed, not killed, and you will have a recurrence soon enough. All the money, time and energy you spent on dipping will have been wasted and you will have to start over.

Replenish. As you dip, animals take dip wash away; the volume in the dip tank gets lower and the concentration of the active ingredient diminishes. Let’s assume that your initial concentration was 500ppm (parts per million or mg per litre); you lose 15% of your volume and your concentration goes down to 100ppm (for example).

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Small-scale commercial and communal farmers will benefit enormously by sharing the costs of a small-stock dip tank. The mites must be properly exposed to the dip chemical and the heads of the animals submerged at least twice.

The animals dipped after the 15% reduction in volume will not have the same protection as those dipped at full concentration.

“Constant replenishment is the most effective method of maintaining the concentration,” say the Oberems in their small-stock disease manual. Progressive dilution of the active ingredients is called ‘stripping’. Because of the stripping, the replenishment dilution is often stronger than the initial dilution.

You must follow the instructions on the label to compensate correctly for the stripping effect.

Second dip

Dip again 8 – 10 days later. The second dip will wipe out survivors from eggs that may not have been killed in the first dip.

Once again – follow the replenishment instructions carefully and diligently carry out these instructions. Some products will tell you to put fresh dip into the tank for the second dip, others will allow replenishment.