The 10 Most Common Parasitic Infections

7. Onchoceriasis

Onchoceriasis spreads through the bite of a black fly infected by Onchocerca volvulus, a parasitic worm. An estimated 25 million people have this parasite, with the rate of prevalence highest in 30 African countries, Yemen, and parts of Venezuela and Brazil. Symptoms may include skin nodules, rashes, and lesions on the eye. Infected individuals are at high risk for blindness. Because of this, and because the black flies that transmit the infection breed in rivers, the infection is known also as river blindness. Over a million people worldwide have some degree of visual impairment due to this parasitic infection.