More than 120 million people worldwide suffer from Filarial infection and some get grotesque condition called elephantiasis, where their legs resemble that of an Elephant. The condition is caused by a pathogen called wuchereria bancrofti, this is a threadlike worm They go and house themselves in the body's lymph nodes where they cause the blockage of the flow of lymphatic fluids and cause swelling of an organ like the legs or genitalia like the scrotum, penis or vulva.
The adult wuchereria worms have a lifespan of up to five years. And during this time they produce millions of offspring known as microfilariae. These micro-filarae from an infected patient find themselves infecting another person when the mosquito has another go at the blood pf these individuals. Once in the blood circulation they mature into adult worm and settle in their lymph nodes and the cycle keeps repeating.
"Although the drugs currently in use kill the micro-filariae, they largely leave the adult worms unscathed," Bonn parasitologist Professor Achim Hörauf explains. "Due to the long lifespan of the wuchereria worms, therapy lasts several years, during which time the symptoms continue to persist." The drug to treat the micro-filariae can also cause severe side-effects.
In an interesting find it was realized that the filarial threadworm is dependant on a bacteria to survive and if the bacteria is killed the worm also will die. "This is why wuchereria is susceptible to antibiotics which are normally used against bacterial infections," said Professor Hörauf emphasizes. In their study in Tanzania they treated 72 male patients for eight weeks with doxycyclin or a placebo.
What they found was that initially the patients blood was swarming with micro-filariae and the researchers counted on an average up to 1,300 of them per milliliter of blood. However in patients treated with doxycylin the micro-filariae had almost completely disappeared when the blood was re-examined at eight months. At fourteen months after being treated with doxycyclin the doctors were only able to detect the typical movements of the worms (the dance of the filariae) on ultrasound in one in five patients. In the placebo group the rate was 89%.
"The importance of these findings for therapy should not be underestimated," Professor Hörauf emphasizes. "The mature worms are after all responsible for such symptoms of the disease as the extreme swelling of the limbs. In the past there was no effective and reliable method of combating them." The effectiveness of the antibiotic might be even greater than what was measured: "we cannot exclude the possibility that several patients became re-infected in the months following treatment with doxycyclin. It is therefore quite possible that all the worms were killed and the remaining 20% are the result of re-infection, which would no longer occur if infection was effectively prevented.
Doxycyclin has been used a safe and cheap drug and has been around for many years. however a note of caution is warranted when it is used in children. In them it may cause irreparable damage to the teeth and slow down growth of the bones. The antibiotic should not be used also during pregnancy. The drug is harmless in adults and adolescents. "Its biggest advantage is that it is already licensed for medical use," Professor Hörauf points out. "Elephantiasis hits the poor most of all. It is therefore not likely that the pharmaceuticals industry will develop completely new drugs."
The Lancet (vol. 365, May 2005).
Contact: Professor Achim Hörauf
University of Bonn