Worm Nodules Disease
Worm Nodule Disease is an infestation of the skin of cattle, horses, and camels with small, long (up to 60mm), slender Onchocerca worms. The disease occurs worldwide, but is more common in the tropics and sub-tropics. In livestock, infestations are rarely a problem but it may be necessary to differentiate them from other more serious skin diseases such as Mange and Skin Tuberculosis. The wounds in the skin contain the microscopic larvae of the worms, called microfilariae. Midges and small biting black flies ingest the microfilariae, which develop into infectious larvae in the flies. The flies then pass the infection to another host when feeding. The infectious larvae migrate to the place where nodules develop and adult females produce microfilariae.
Signs of Worm Nodule Disease
- Clinical signs are minimal, consisting of nodules up to 3cm in diameter under the skin and internally. In cattle skin nodules are found in the brisket, lower limbs and ligaments of the neck whereas in horses they are found in the ligaments of the neck and lower limbs.
- Animals have small lumps (called nodules) just under the skin. The lumps are full of worms and worm larvae.
- Cattle usually have lumps on the legs, around the genitals, on the neck and between the front legs.
Skilled vets can check a piece from one of the lumps for these worms with a microscope. The microfilariae can be easily seen in biopsies of nodules examined under the microscope.
Prevention - Control - Treatment
- Ivermectin works well against the microfilariae. Other medicines are less effective.
- Control of the vectors is usually impracticable.
Two other species of worm affect the skin of cattle:
Parafilaria bovicola occurs in the subcutaneous tissue (beneath the skin) and is carried there by face flies. Mature female worms puncture the skin to lay eggs on the surface and there is a heavy discharge from the wounds. The inflammation and swelling at the sites of infection resemble subcutaneous bruising and such areas have to be trimmed off at meat inspection and the hides downgraded
Ivermectin is effective as a treatment.
Rhabditis bovis is a worm which normally lives in the soil, but has become adapted to living in the ears of cattle in East and Central Africa. Signs include a putrid discharge from the ear, continual wasting, and a severe drop in milk yield. Central nervous signs and death may result.
Treatment of affected cattle with Ivermectin is effective.