Have you ever been bitten by a gnat or blackfly? These little pesky flies are nothing but an annoyance in temperate area of the world. But imagine if such a bite could cause blindness? That is the case in some tropical areas of Africa and Central America because the blackfly of the Simulium species can carry a parasite that can have devastating effects.
These flies live along the banks of rapidly-flowing streams at low elevation. The fly leaves behind the Onchocerca volvulus parasite, which slowly grows, often forming a nodule under the skin of the neck or scalp. The adult parasite at some point releases larvae which swim around the blood stream, and frequently settle in the eye. The reaction of the body to these larvae may cause blindness. Below blind victims of onchocerciasis are lead in an old photo from Africa.
Today, river blindness can be prevented by treating every person in the at-risk areas with a once-yearly dose of ivermectin - the same medicine used to prevent the similar heartworm in dogs. Major successes in eliminating this disease have been carried out by the Carter Center and through the generosity and commitment of the Merck Corporation in donating one billion doses of the needed medication - "as much as necessary for as long as necessary".