Onchocerca is found widely in Central Africa and Central and South America, though the Americas have shown great progress in eradication. It's transmitted by riverine blackflies, which, surprise, hang out by rivers! Typically fast flowing ones, exactly the type people would live to build their settlements by. The adults live in nodules in the human skin, which are typically raised. Interestingly, these nodules favor the lower regions of the body in Africa and the upper regions of the body in the Americas. The microfilaria of this species migrate through the skin, which causes a very intense itching effect, to the extent that people frequently get permanently disfigured skin from the intensity of their scratching. Because they migrate through the skin, blood samples won't tell you anything. Instead, skin samples must be taken and processed to see if there's any microfilaria hanging out there. Fun!
Photo Credit: Emedicine.com
The most serious manifestation of Onchocerca volvulus is ocular lesions that lead to blindness. The microfilaria enter the eye, which causes irritation, which makes a tiny patch of scar tissue in the eye. Too many of these can lead to progressive blindness. These in the eye are diagnosed in an interesting manner - the patient is made to wait for a while with their eyes parallel with the floor. They then quickly raise their head up, and a doctor shines a light in their eyes and looks for falling particles.
Photo Credit: eyewiki.org
Mass Drug Administration has reduced the disease in many areas to the point that it can't be sustained anymore. Go public health!
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