A genus of long, threadlike filarial nematodes of the family Onchocercidae.

They are found in subcutaneouis and connective tissue, or confined within tough, fibrous cysts. The most important species, Onchocerca volvulus is the cause of human onchocerciasis. Other species cause cutaneous diseases among domestic and wild herbivores.

A species found in cattle, sheep, and buffalo in India, southeast Asia, Egypt, and Australia. It forms hard nodules in the hides of cattle, thereby greatly reducing their commercial value.

A species found in cattle and buffalo in various sites in connective tissue, including the cervical or tibiofemoral ligament and the spleen capsule. It is distributed throughout most of the world, but it is not common in the United States.