This article is part of a series of informative animal health articles. The series goes hand in hand with the #VideoVet video series – watch the video below.
Sheep scab can cause devastating losses each year, mostly through losses in the wool clip. It is caused by the sheep scab mite (Psoroptes ovis), which lives on the discharge found on the skin of sheep. The mites prick the skin with their mouthparts and feed on the lymphatic and tissue fluids through the small holes. The lesions are rosette-shaped, because the scabs that form complicate the mites’ feeding ability. As a result, they constantly move from under the scabs to new, healthy parts of the skin.
Life cycle of the mite
The female mite lays 40 to 90 eggs in her 30-day life cycle. Larvae hatch from the eggs and develop into nymphs, from which mature mites develop. Under favourable conditions, the cycle from the egg being laid to becoming a mature egg-producing female can be as short as nine days. Sheep scab generally occurs in the winter months, but disease outbreaks during summer is not uncommon. In autumn, when the temperature in the wool fleece and surrounding atmosphere drops, moisture in the fleece increases, which creates favourable conditions for the mites to thrive and to infest the whole herd.
Poor grazing during this time, combined with less feed intake due to itchiness and scratching, can exacerbate the situation. Sheep can lose condition very quickly if they are not treated in time.
The presence of mites on the skin of sheep causes severe irritation. The animals start to scratch themselves against fences and other objects. They also tend to scratch with their teeth and bite the spots where irritation occurs, which leads to wool getting stuck between the teeth.
The scratching and severe irritation eventually leads to reduced grazing. This in turn leads to a loss of condition. The wool in the itchy spots start to fall out and bare patches with a scabby appearance become visible.
Spread of the disease
The disease is highly contagious. Mites can spread from one sheep to the next due to physical contact, as well as through clothing, equipment and vehicles. Infection via these secondary routes can continue for up to twelve days.
Appropriate hygiene and biosecurity measures should therefore be maintained during treatment of the disease.
All cases of fleece disturbance and suspected skin conditions in the herd must be reported immediately to the nearest state veterinarian for inspection. Once the condition has been confirmed, the Animal Diseases Act, 1984 (Act 35 of 1984) stipulates that all sheep on the farm must be dipped against sheep scab with a registered agent or treated with an injectable agent containing 1 % ivermectin.
The dipping or injection process should be repeated at least once within seven to ten days after the first treatment. If any animals are skipped during treatment, the entire herd can be reinfected. It is therefore important that all dipped animals are marked so that no animal is skipped. The animals must also be marked after the second dip.
Sheep scab mites can survive in a kraal for up to 17 days. For that reason, the kraals where infected animals were kept should not be used for at least three weeks.
By law, all sheep on the farm where the disease has occurred, as well as the sheep on neighbouring farms, must be treated twice with the prescribed agents.
Solution® 3,5 % L.A. Reg no: G3689 (Act 36/1947). Namibia reg no: V06/18.1.2/651 NS0. Composition: Ivermectin* 2,25 % m/v, abamectin* 1,25 % m/v (*macrocyclic lactone). Indications: An antiparasitic remedy for cattle and sheep.
Solution® 3,5 % L.A. kills sheep scab with a single injection and prevents re-infestation for up to 56 days. Controls important roundworms and is more than 90 % effective.
Dosage: 1 ml/50 kg body mass subcutaneously. Pack size: 50 ml and 500 ml vials.
For full details, please read product insert or visit www.msd-animal-health.co.za.