Sheep scab mite

The sheep scab mite, scientifically known as Psoroptes ovis, belongs to the order Acariformes and the family Psoroptidae. It is a highly contagious ectoparasite that lives on the skin surface of sheep and other livestock.

These mites are microscopic, with adult females measuring approximately 0.6–0.7 mm in length. Their bodies are oval and flattened, and they possess specialized mouthparts used to pierce the epidermis and feed on tissue fluids.

The life cycle of the parasite consists of egg, larva, two nymphal stages, and adult. Under favorable environmental conditions, the entire life cycle can be completed in about two weeks.

They prefer areas of the host’s body where the wool is dense, as these regions provide the necessary warmth and humidity for rapid reproduction and mite survival.

While Psoroptes ovis cannot survive for long periods away from a host, they can persist in the environment in sheltered, humid conditions, creating a risk of re-infestation for several weeks.

It is important to clarify that this organism is an animal parasite and does not cause damage to plants. It is a significant health concern for the sheep industry worldwide.

The parasite causes a condition known as sheep scab. The mites feed on the skin, causing severe inflammation, allergic reactions, and intense irritation that manifests as uncontrollable itching.

As the mites feed, they secrete proteins that trigger a massive inflammatory response, leading to the formation of crusts and fluid-filled lesions on the animal's skin.

The damage to the skin surface leads to hair loss, destruction of the fleece, and overall poor physical condition, which significantly impacts the animal's growth and health.

In severe cases, the constant stress and discomfort caused by the infestation result in substantial weight loss, secondary bacterial infections, and, if left untreated, potential mortality.

The most prominent sign of infestation is extreme restlessness and constant scratching. Sheep will often rub against fences, troughs, or any available object to relieve the intense itch.

Visual inspection often reveals areas of broken, matted, or missing wool. The skin in these areas is typically thickened, inflamed, and covered with yellow or grey crusts.

As the infestation progresses, the lesions expand and may cover large parts of the animal's back and sides, causing the skin to become folded and cracked.

• Agitated and aggressive scratching behavior.
• Noticeable patches of hair loss or broken wool.
• Visible crusty lesions on the skin surface.
• Significant drop in weight and poor body condition.

Professional diagnosis is usually confirmed by taking skin scrapings from the edge of the affected area and observing the mites under a microscope to confirm their presence.

The primary control strategy involves systemic or topical application of acaricides. Dipping the entire flock in an approved chemical solution is a traditional and highly effective method.

Treatment programs must be strictly followed, ensuring that all animals in the flock are treated simultaneously to prevent re-infestation from untreated individuals.

Biosecurity measures, such as quarantining new arrivals and thoroughly cleaning and disinfecting pens and handling equipment, are essential to stop the spread of the disease.

In some regions, the use of macrocyclic lactones via injection provides an alternative control method, offering long-term protection against mite re-colonization.

Collaboration with local veterinary services is crucial for monitoring infestation levels and ensuring the correct application of chemical treatments to avoid the development of resistance.