VPA 211: General Veterinary Parasitology and Helminthology (3+1)

ONCHOCERCA VOLVULUS

Host: Human being rarely in animals

Intermediate host: Black fly (Simulium ).

Morphology

• Adults of Onchocerca volvulus are long and slender, have a smooth cuticle, and have blunt anterior and posterior ends. There are no lips or buccal capsule, and the mouth is surrounded by 2 circles made up of four papillae each.
• The esophagus doesn't appear to be divided. Males range in length from 19-42 cm and range in width from 130-210 micrometers.
• Lacking alae, their tails are curled ventrally and bear 6 or 8 pairs of postanal and 4 pairs of adanal papillae. Females are larger than males, ranging in length from 33.5-50 cm and in width from 270-400 micrometers.
• Their vulva is directly behind the posterior end of the esophagus. The microfilariae released by adult females are 250-300 micrometers long, are unsheathed, and have sharply pointed and curved tails.

Life cycle

• O. volvulus begins when a parasitised female black fly of the genus Simulium takes a blood meal. The microfilariae form of the parasite found in the dermis of the host is ingested by the black fly.
• The microfilaria then penetrates the gut and migrates to thoracic flight muscles of the black fly, entering its first larval phase (J₁). After maturing into J₂, the second larval phase, it migrates to the proboscis where it can be found in the saliva . Saliva containing stage three (J_3S) O. volvulus larvae passes into the blood of the host.

Treatment and control

• Ivermectin
• Control of black fly formation
• Affected people treated by Ivermectin