Ectoparasities of sheep and goats do not generally cause heavy mortalities unless the infestation is extreme, but they will cause unthriftiness and loss of production if not controlled. Animals in poor health or low levels of nutrition are more likely to be affected and young animals are more susceptible.
The main external parasites found in Southern Africa affecting sheep and goats are
1.    Ticks
2.    Mites
3.    Fleas and lice
4.    Nasal worm (Oestrus ovis)
 
Ticks
Ticks are more commonly found on goats and unwoolled sheep. They can cause anaemia resulting from blood loss, especially in lambs and kids, and open sores which then become a site for screw-worm infestation.
 
Ticks also transmit disease – the most common in Zimbabwe being heartwater. They also cause tick toxicosis (sweating sickness) and tick paralysis (also known as Karoo paralysis) These both affect young animals and may be fatal. Tick paralysis may also affect man.
 
To control ticks, sheep and goats must be dipped regularly with an approved acaracide. (See Dipping Cattle, Sheep and Goats) Most acaricides registered for sheep will control ticks, mites and lice.
 
Mites
There are many species of mites, but most are harmless. The two economically important conditions caused by mites are SHEEP SCAB and MANGE.
 
 
  • Mange is caused by several different species but the most important are Sarcoptes Spp which cause Sarcoptic Mange. This is a contagious condition more common in goats than sheep, and rarely seen in woolly sheep. The mites burrow into the skin of the animal causing thickening and wrinkling of the skin with thick crust formation. Other mites include Psoroptes caprae found in the ears of goats, which can result in deafness if not diagnosed and treated. Chorioptes Sp are found on the legs of goats and horses. It causes extreme itchiness and the affected animal will often stamp its legs continually.
  • Sheep scab (See picture) is a scheduled disease, luckily not commonly found in Zimbabwe. It is caused by the mite Psoroptes ovis and is highly contagious. It is found only in sheep and the mite does not live anywhere but on the body of the sheep. The life cycle is 10 days in optimum conditions so the spread of disease can be extremely rapid. The mite bites into the skin, feeding on lymph and causing inflammation and irritation. Lymph flows out of the bite wounds, forming thick scabs and causing the wool to drop out. It causes extreme itchiness and distress to the affected animal. DECTOMAX INJECTABLE controls Sarcoptic Mange mites and Lice

Fleas and Lice
These are found where animals are kept in close confinement, over-crowded and where the environment is warm and humid. Infestation cause anaemia, especially in young animals and damage to the skin leading to losses on hides and wool. Control is by dipping, avoiding over-crowding, regular cleaning of houses and changing of bedding if this is used. (See Flea Control in Dogs)
 
Nasal Bots (Oestrus ovis)
The fly deposits its larvae at the nostrils of the sheep. The larvae or maggots crawl up the nasal passage into the frontal sinuses. The worm grows rapidly in the sinuses, particularly in warm weather and may be fully grown in a month. It has two strong hooks at the front end and is covered in small spines. This obviously causes extreme irritation to the sheep and results in sneezing, head shaking, respiratory distress syndromes and copious nasal discharge. It also may cause secondary bacterial infections. Although the bot does not cause too much damage to the sheep, a heavy infestation causes such irritation that the sheep will feed poorly and lose condition. DECTOMAX INJECTABLE is effective against nasal bots.
 
Ref:    
•    Diseases of Small Ruminants Handbook - Common Diseases of Sheep and Goats in Sub-Saharan Africa by Lughano Kusiluka and Dominic Kambarage
•    Handbook on Stock Diseases – Monnig and Veldman