Onchocerca gibsoni, O. lienalis O. stilesi:

General Description: Long roundworms, 30 to 60 millimetres in length.

Life Cycle: Not completely known; indirect; the midge (Culicoides) is the intermediate host for O. gibsoni and Simulium is the intermediate host for O. gutturosa.

Location: O. gibsoni are found in nodules under the skin, especially on the brisket and outside surfaces of hindlimbs. O. linealis are found in the cervical and femuro-tibial ligaments.

Geographical Distribution: Widespread in the Far East, Australia, North and South Africa, Europe and USA.

Significance: Skins of infected carcasses are not suitable for sale.

Effect on Host: Adult worms of O. gibsoni are localised under the skin. The host, in reaction to them, surrounds them with skin. This produces nodular swellings under the skin up to 5 cm. in width, located especially on the brisket and the outer areas of rear limbs. O. linealis adult do not cause clinical manifestations.

Diagnostic Information: Larvae (microfilariae) of Onchocerca may be found in tissue near nodules where adults live.

Control: Reduce midge populations; protect animals from them.

Onchocerca Microfilariae in tissues		Clulicoides fly		Tissue section – Adult Onchocerca in – situ