Filarial infection can be acquired only from infective larvae deposited by infective mosquitoes. Therefore, prevention of infection can be achieved either by decreasing contact between humans and vectors or by decreasing the amount of infection the vector can acquire, by treating the human host.
Contact with infected mosquitoes can be decreased through the use of personal repellents and sleeping under bed nets. Any intensive vector control activity such as indoor residual spraying, impregnated and preferably long lasting bed nets (LLNs) can reduce transmission of W. bancrofti, and this is often achieved by collaboration with anti-malaria programmes in areas where the two infections are co-endemic.
The current strategy for preventing/interrupting transmission is an annual single co-administration of two drugs for at least five years. The two alternative regimens are:
· single doses of albendazole (400mg) plus Mectizan® (150-200 mg/kg/body wt) or
· single doses of albendazole (400mg) plus DEC (6mg/kg/body wt).
Alternative strategies are under investigation for specific situations. For example, in areas co-endemic with Loa loa where DEC and ivermectin cannot be used, twice yearly albendazole and the use of bednets is an already approved strategy and early studies have shown it to be effective. A further strategy recently recommended by WHO is triple drug therapy (IDA - Ivermectin, DEC and albendazole) to accelerate the global elimination of lymphatic filariasis where there is no onchocerciasis. Other strategies that are being considered to enhance the elimination of transmission include the use of different dose regimens of the above medicines.
Albendazole, donated by GlaxoSmithKline for LF prevention, is a well-established anti-parasitic treatment, given to an estimated 500-800 million people, mostly children, for intestinal infections over the past 20 years. The combination of albendazole with either Mectizan® or DEC has been proven to enhance the efficacy of the individual-drug treatments in reducing the numbers of parasites in the blood.
Mectizan® (generic name: ivermectin) is an oral anti-parasitic drug, discovered and developed by Merck & Co. Inc. which is effective against both LF and onchocerciasis. Mectizan® is provided free of charge by Merck & Co. Inc. for the treatment of onchocerciasis in all endemic countries and for LF in African countries where onchocerciasis and LF co-exist.
DEC, developed over 50 years ago, is an inexpensive and effective anti-filarial drug which is used to treat LF in many countries. However, DEC cannot be used in most of Africa as severe side reactions can occur when other infections, such as onchocerciasis (river blindness) are also present. DEC is now donated by Eisai Co. Ltd.
How can we manage LF?
As there are many different presentations of clinical disease related to LF, there is no single drug or treatment that is effective for all cases. However, for all patients, three issues should be considered (1) anti-parasitic drug therapy be given to patients with clinical disease to prevent potential transmission; (2) supportive clinical care and (3) patient education and counselling.