Last week, Steve Williams was gracious enough to take time out of his busy
schedule and help us out with the pronunciation guide for Parasites Unleashed. This involved reading parasite species names into a microphone, which he did with grace and good humor, even though some of the names are real tongue-twisters. He was happy to find out that the game includes Wuchereria bancrofti -- one of his favorite parasites (and a subject of his own research).
W. bancrofti is a filarial worm that lives in the tropics of Africa, Asia, and Central and South America. It’s the most common cause of lymphatic filariasis, a disease that affects about 100 million people worldwide.
The worms themselves don’t look particularly exciting. Adult males are about 4 cm long and about 1 mm thick. Adult females are much larger – reaching 10 cm in length. A female is also 3 times as thick as a male, probably because her body is jam-packed-full of baby worms.
W. bancrofti doesn’t look exciting, but what it can do to people is grotesque. The adult worms live inside lymph nodes. That in and of itself might not be so bad, if the immune system didn’t react to them. But it does. And when the killer white cells show up for extermination duty, they inflame the tissue around the worms and lay down fibrous tissue in an attempt to encapsulate them. Repeat this enough and the fibrous tissue builds up in the lymph vessels, blocking them and keeping lymphatic fluid from flowing. The fluid backs up into the tissues, causing the swelling characteristic of elephantiasis.
How does W. bancrofti get into the lymphatic system in the first place? Thank a mosquito.
Female worms give birth to millions of larvae called microfilariae. These first stage larvae are truly tiny – about as long as a Paramecium and 10 times thinner than a human hair. Their first stop is the bloodstream of their human host, but if they’re going to grow up into bigger worms they need to get into a mosquito. Fortunately for them, blood is the highway to their next host. The larval worms commute. During the day, they hide out in the arteries deep inside the lungs, but when night falls and the mosquitoes come out looking for blood meals they migrate to the blood vessels underlying the skin. If a mosquito bites the human host, they’ve got a better chance of sucking up a mouthful of tiny worms.
Once the larval worm is inside a mosquito, it digs through the mosquito’s gut wall and burrows into its wing muscles. Over the next 2 weeks it will molt twice more. The larger worm will then migrate to the mosquito’s mouth and wait for it to bite another person. When the mosquito eats, the worm enters its new human host through the wound. Within a year, it will find its way to the lymph nodes, molt into an adult, and start having microfilariae of its own.
Image above from the CDC's Parasite Image Library.
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