A cheap antibiotic not only prevents but also relieves the symptoms of a disfiguring tropical disease called elephantiasis, scientists say.
LF causes swelling in the limbs
The condition - also known as Lymphatic Filariasis - causes severe swelling in the limbs or scrotum and affects 120m people globally, mainly in the tropics.
A Liverpool School of Tropical Medicine team found that doxycyline gave relief to those with advanced disease.
The same antibiotic also kills the worms that cause the disease.
People affected by Lymphatic Filariasis (LF) often cannot work or marry, and can be shunned by others in their village because of their disfigurement.
It is caused by parasitic worms invading the body's lymphatic system - the network of vessels carrying infection-fighting cells.
The worm is spread by mosquitoes, who pass it on when they take blood from humans.
The bacteria-containing worms lodge in the lymphatic system, producing millions of minute larvae which spread throughout the bloodstream.
It is unclear whether the swelling, or lymphoedema, that occurs results from the obstruction of the lymphatic vessels or from the response of the body's immune system to the worms and the bacteria within them.
Secondary bacterial infections, resulting from long-term damage of lymphatic vessels caused by the adult worms, could also play a role.
Existing LF treatments kill the worm larvae to prevent transmission. But they have little or no effect on the adults worms.
Nor do they halt the progression of the symptoms once the disease has developed.
Trials in Ghana on 51 patients by Dr Mark Taylor, from Liverpool, and an international team of scientists from Bonn and Ghana showed doxycyline, which attacks the bacteria inside the worm, not only kills adult worms but also helps to relieve symptoms in those who have already developed the disease.
Dr Taylor said: "The important breakthrough with this trial is to show that in addition to the anti-parasitic effects of antibiotic treatment, we can also improve the lives of individuals suffering from the stigmatizing elephantiasis."
Dr David Addiss said: "The cause of elephantiasis is still a matter of debate.
"We used to think the worm itself switched the immune system somehow and the immune system damaged the skin.
"Work in the last decade has shown that it is really secondary bacterial infections that are a major cause of the disease progression.
"It's possible doxycylin is decreasing the secondary bacterial infections. Antibiotics have been shown to reduce the inflammation in the skin of people with lymphoedema."
He said there were other treatments of proven benefit, including good hygiene, skin care and physiotherapy.
The work is published in PLoS Pathology.