Lymphatic Filariasis
Lymphatic filariasis (LF) is a major tropical disease caused by thin parasitic roundworms that are transmitted by mosquitoes in tropical countries. LF is a formidable foe that affects approximately 120 million people in 80 countries around the world; about one in five people on Earth are at risk of contracting this disease.
LF parasites are cousins of the dog heartworm, which is one of the worst enemies of “man’s best friend”. Unlike heartworms, the human parasites live in lymphatic vessels and cause the deforming and disabling conditions of elephantiasis (severely swollen legs with secondary skin changes) and hydrocele (a massive accumulation of fluid in the scrotum). Many patients with LF also suffer repeated “filarial fever” attacks with shaking chills, painful swollen lymph nodes and inflamed lymphatic vessels.
Adult filarial worms release microscopic larvae that circulate in the blood of infected humans. Mosquitoes ingest these “microfilariae” with their blood meals. Microfilariae develop in mosquitoes over a period of two weeks into larger (one millimeter long), infective stage parasites that are transmitted by mosquitoes to people. Infective larvae develop in humans over a period of months to become adult parasites that are several centimeters long; they reside in lymphatic vessels and have a lifespan of five to 10 years.
Traditional control methods for LF depended on mass screening of exposed populations to detect parasites in the blood and selective treatment of infected people with pills for two weeks. Mosquito control also had a role, but this was expensive and difficult to implement and sustain. These control measures were helpful in many areas. However, in most cases they did not eliminate disease transmission, and they comprised a perpetual care program that consumed lots of time and resources.
By the mid 1990s, technical advances (improved treatments and diagnostic methods) led to a paradigm shift that turned the LF control world upside down. The new strategy called for selective diagnosis (screening small population samples) to identify infected areas and mass drug administration (MDA) with new single-dose treatment regimens. The goal of MDA is to reduce human infection rates below levels required for sustained parasite transmission by mosquitoes. The World Health Assembly supported this strategy by passing a landmark resolution in 1997 that called for global elimination of LF as a public health problem by 2020.
The Global Programme to Eliminate Lymphatic Filariasis (GPELF) was developed by the World Health Organization in partnership with health ministries, academia, aid agencies, and industry to achieve this ambitious goal (see www.filariasis.org). GPELF is largely based on mass drug administration with medications donated by GlaxoSmithKline (albendazole) and Merck (ivermectin). The program also provides guidelines and resources for management of people who are living with LF disease.
The “Target LF” video was produced by GlaxoSmithKline to emphasize the impact of LF on individuals in endemic areas around the world. Its very positive conclusion celebrates the initiation of GPELF and the promise of MDA as a tool for eliminating this disease. GPELF is the largest infectious disease intervention ever attempted based on mass drug administration; more than one billion doses of antifilarial medications have been distributed in 45 countries since 2000.
GPELF faces many challenges, and it will not be easy to achieve LF elimination in all endemic countries. We have already picked the low-hanging fruit. Additional resources and untiring efforts will be needed to consolidate recent advances and to extend the program to the difficult regions that remain.
However, it is also important to focus on the positive achievements of this program. The campaign has ramped up at an amazing rate, and the impact of MDA has been dramatic; LF infection and disease rates are falling rapidly in many areas around the world, and several countries have initiated surveillance activities to document elimination of the disease. We hope that these early and impressive successes can provide enough steam and momentum to attract the resources and sustained effort that will be needed to finish the job by the target date of 2020.
Return to video.
References
World Health Organization, 2007. Global Programme to Elimination
Lymphatic Filariasis. Wkly Epidemiol Rec 82: 361-380.
EA Ottesen 2006. Lymphatic filariasis: Treatment, control, and elimination. Adv Parasitol 61:395-441.