The flies have it: River blindness and the communities it affects

November 2, 2014 by PATH

In many areas of the world, a blackfly bite can cause more than temporary discomfort. River blindness infects 18 million people a year.

Rivers are a water source near many homes in Africa. They’re also home to the blackfly and a parasite they carry that causes river blindness. Photo: PATH/Will Boase.

Rivers are a water source near many homes in Africa. They’re also home to the blackfly and a parasite they carry that causes river blindness. Photo: PATH/Will Boase.

Editor’s note: This week PATH is announcing the launch of a new diagnostic test for river blindness with manufacturing partner Standard Diagnostics, Inc. Our blog series will explore how river blindness affects communities, how the diagnostic test works, and why diagnostic tools are the next wave in global health innovation.

Part 1: The water: a gift and a curse

Let’s say you’re a farmer. What’s the best resource you could hope for next to your land? Water. Right?

Let’s take it deeper: as a farmer, you’d prefer a river, a rapidly flowing water source with no stagnation. Flowing water helps flush impurities downstream, provides fish to eat, and limits breeding opportunities for the mosquito, an insect that can spread illnesses such as malaria and encephalitis. Yes, a river would be ideal. Which is why communities have settled by rivers for thousands of years.

So why is it that having a fast-flowing river near an agricultural area may cause people to abandon productive fields? If you’re thinking floods, think again.

It’s the flies.

A blackfly magnified at 100X actual size.

Adult blackfly magnified 100X using conventional scanning electron microscopy with parasite (Onchocerca volvulus) emerging from the insect’s antenna. The parasite is responsible for the disease known as river blindness. Photo: US Department of Agriculture

Meet the culprit

Flies do more than pester people—they can spread disease.

Across wide swaths of Africa, one such nasty illness is a parasitic infection called “river blindness” (onchocerciasis). The parasite is found in more than 100,000 communities in 31 African countries, 6 Latin American countries, and Yemen. Estimates of the number of people affected are mind-boggling: 120 million people remain at risk for the disease and 18 million people are infected, typically in poor, rural communities in remote low-resource settings.

The blackfly breeds in the fast-flowing waters of rivers. It’s generally a harmless insect, unless it’s carrying the river blindness parasite. When a fly with the parasite bites a human, it passes along the microscopic parasitic worm which multiplies under the skin of their hosts, causing their skin to become painfully itchy. Without treatment, this condition can become chronic. Eventually the worms can migrate to the cornea of the eyes resulting in scarring and permanent blindness.

This Carter Center video takes you to the Nebbi District in Uganda, where one family has suffered the devastating effects of river blindness. Video length: 3:08 minutes.

And so the lifecycle continues, resulting in blindness among affected people and transmission of the parasite to others.

Before you think all is lost

There is a medicine called ivermectin that paralyzes and kills the offspring of adult worms in humans, halting their lifecycle. And for nearly 20 years, the African Program for Onchocerciasis Control has helped map transmission zones and treat communities by mobilizing local agencies and networks to identify the disease’s prevalence. Then it’s usually local volunteers who give out the medicine and keep track of who has been treated.

However, it’s hard to know when to stop treating communities with ivermectin. When successful, ivermectin breaks the transmission of river blindness so fewer and fewer people are exposed over years of treatment. But current tests to see if a person has antibodies to the parasite (a sign they’ve been exposed to the disease) often require sending blood samples to a lab, waiting weeks for evaluation by a highly trained technician, and using expensive equipment. And the most common test to see if a person has an active infection is an invasive skin snip. This is a painful test that provides results within 24 hours but exposes people to infection. Because of these challenges testing has been difficult to administer, especially among families with children.

Programs are committed to treating entire communities until they’re sure the disease is gone, and there’s no doubt that this reduces the suffering caused by river blindness. But until they can confirm that transmission has been irreversibly stopped, the overarching problem remains: the disease cannot be eliminated if it risks being reintroduced.

The lifecycle of river blindness: bite from parasitized blackfly, infection by larvae under the skin, reproduction of worms, proliferation of microfilariae, and transport of microfilariae to the cornea.

This infographic details the lifecycle of river blindness. Illustration: PATH.

To speed elimination efforts, these programs need a new diagnostic tool that’s less invasive and provides faster results in the field. A test that is easier to use and less expensive. One that won’t dissuade people from being tested.