Setaria equina: Abdominal worm

General Description: The adults are long and slender, reaching 8 cm. for males and 13 cm. for females. The microfilariae are about 0.25 mm. long.

Life Cycle: Larvae produced by adult worms in the body cavity circulate in the blood and are taken up by culicine mosquitoes, including Aedes and Culex species. Infective larvae develop in the mosquito muscles in 2 weeks, and are reinjected into horses when the mosquitoes feed. Adult parasites are present 8 to 10 months after infection.

Location: The adult worms live in the abdominal body cavity. Microfilariae occur in the blood. Occasionally, the adults invade the lungs and eyes.

Geographical Distribution: Common worldwide.

Significance: Setaria adult worms in the abdominal cavity are of no concern, but worms occasionally develop in the eye and cause damage.

Effect on Host: Adults in the body cavity are nonpathogenic, except in very heavy infections, which may cause mild peritonitis. Setaria developing in the eye may be very damaging, even leading to blindness.

Diagnostic Information: Detection of microfilariae in the blood.

Control: Mosquito control is important in the control of Setaria in horses. Topical insecticides may be useful in some cases.