Onchocerca reticulata

Onchocerca reticulata	Contents	Rev 10/27/2026
	Classification	Hosts
	Morphology and Anatomy	Life Cycle
Return to Onchocerca Menu	Economic Importance	Damage
	Distribution	Management
Return to Onchocercidae Menu	Feeding	References
	Nemaplex Home Page	Go to Dictionary of Terminology

Classification:

Nematoda
Chromadorea
Rhabditida
Spirurina

Filariidae or Oncho cercidae

Onchocerca reticulata (Diesling, 1842) Railliet & Henry, 1910

Type species of the genus

Synonyms:

Morphology and Anatomy:

Adults up to 50 cm long.

Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:

Distribution:

Onchocerca reticulata infects cattle, horses and water buffalo worldwide. As a parasite of the definitive host, it is located in or around the ligamentum nuchae, a fibrous ligamernt of the neck that supports the cervical spine, and in the gastroplenic ligament which connest the stomach and the spleen.

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Economic Importance:

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Feeding:

Biology and Epidemiology

Adult worms are up to 60 cm in length and live in connective tissue of the ligamentum nuchae of horses. Adult parasites produce microfilariae (200-230 um long) that are most numerous in the dermis of the face, neck, back, and ventral midline. A number of Simulium spp. and Culicoides spp. may serve as intermediate hosts.

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Hosts:

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Life Cycle:

In filarial nematodes, two hosts are necessary to complete the life cycle; an intermediate host (often an arthropd) and a primary or definitive host (usually a vertebrate). The juvenile stages occur in the intermediate host and the reproductive adult in the definitive (primary) host.

In Onchocerca reticulata, the intermediate hosts are Simulium spp (blackfles) and heleomyzid flies,

The female nematode lays eggs in the host blood stream and these enter fly when it bites the human, Changes into larval stage (the microfilariae) within 24 hours after fly has first blood meal. Spreads throughout hosts muscles (vector is the Simulium commonly known as "the black fly" - vector bites the definitive host and microfilariae enter through wound; gradually grow into adult stages;

Ecophysiological Parameters:

For Ecophysiological Parameters for this species, click	If species level data are not available, click for genus level parameters

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Damage:

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Management:

Ivermectin at a dose of 200 ug/kg orally is the treatment of choice for elimination of microfilariae in the skin or ocular tissues. A single dose may result in improvement in clinical signs within 2 to 3 weeks, with complete resolution in 2 months.

Some horses may remain free of cutaneous microfilariae for 4 to 5 months or longer after treatment with injectable ivermectin. Some horses may require two or three monthly treatments before clinical signs resolve.

Approximately 10% to 25% of horses with onchocerciasis have an adverse reaction (e.g., ventral midline edema or pruritus) to ivermectin treatment within 7 to 10 days (Sellon, 2014).

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References:

Dzimianski, M.T., Marchiondo, A.A., Cruthers, L.R. 2020. Nematoda, Filarioidea. Chapter 2 in Marchiondo, Cruthers and Fourie (eds) Parasiticide Screening Vol 2. Academic Press.

Peters, W. and Gilles, H.M. 1991. A Colour Atlas of Tropical Medicine and Parasitology. Third edn., Wolfe, London.

Sellon, D.C. 2014. Nonenteriv nematodes. . Chapter 57 in Sellon, D.C. and Long, M.T.(eds) Equine Infectios Diseases. W.B. Saunders.