Wednesday, 22 January 2014

Elephantiasis and Wolbachia: The Bacteria Behind the Worms

Horrific parasites sometimes turn out to be mere vessels.

Filarial worms, nematodes that are transmitted by insects and live in the tissues, cause horrible disfigurement, disability, blindness. The common names for the diseases they cause are descriptive and apt: elephantiasis, and river blindness.

Wucheria bancrofti, and Brugia malayi nematode worms live in human lymph vessels. Prolonged presence of the worms there often results in the affected part – often a limb or the scrotum - becoming grossly enlarged and deformed. Microfilaria, the worm’s young, circulate in the blood.

Elephantiasis results in almost
unbelievable disfigurement of
various parts of the body.
Imagine living with this.
Tropenmuseum of the Royal
Tropical Institute (KIT)
CC BY-SA 3.0

Onchocerca volvulus adults live together in nodules in the skin. Their young migrate through the skin and, over the long term, can cause discoloration, aging, and sagging of the skin. Worse, microfilariae in the eyes cause blindness.

For a long time, we thought that the worms themselves, and the microfilariae, caused these terrible responses to infection – that the battle between the human body and the worms caused blindness and disfigurement. But now it’s becoming clear that the real culprit is not the worms, but a type of bacteria living inside the worms. The problem is Wolbachia pipientis.

Wolbachia and Filarial Worms

Wolbachia is best known for living in insects, where it is typically parasitic and sometimes causes fatal disease. In nematodes, the relationship is different. In nematodes, Wolbachia is a symbiont: the bacterium actually provides nutrients to the parasitic worm that the worm can’t otherwise get, and without the Wolbachia, the worm can’t survive.

Researchers now have compelling evidence that what the human immune system responds to is actually the Wolbachia, not the filariae or the microfilariae. It’s the Wolbachia that causes elephantiasis and river blindness.

Wolbachia, Filarial Nematodes’ Achilles Heel

Treatment of the diseases caused by filarial nematodes has proven difficult for many reasons, not the least of which is that few drugs kill the adult worms. The discovery of their reliance on Wolbachia reveals a weakness that may be the worm’s undoing: instead of finding a drug to kill the worms, we can use a drug to kill the Wolbachia.

Ironically, if it’s the Wolbachia that’s actually the culprit, the worms end up as collateral damage.