Lymphatic Filariasis [Archives:1998/07/Health]
Lymphatic Filariasis, known as Elephantiasis, puts at risk more than a billion people in 73 countries. Over 120 million have already been affected by it, 43 million of them seriously. One-third of the people infected with the disease live in India, one-third are in Africa and most of the remainder is in Southeast Asia, the Pacific and the Americas. In tropical and sub-tropical areas where lymphatic filariasis is well established, the prevalence of infection is continuing to increase. A primary cause of this increase is the rapid and unplanned growth of cities, which creates numerous breeding sites for the mosquitoes that transmit the disease.
In its most obvious manifestations, lymphatic filariasis causes enlargement of the entire leg or arm, the genitals, vulva and breasts. In endemic communities, 10-50% of men and up to 10% of women can be affected. The psychological and social stigma associated with these aspects of the disease are immense. In addition, even more common than the overt abnormalities are hidden, internal damage to the kidneys and lymphatic system caused by the filariae.
Cause: The thread-like, parasitic filarial worms Wuchereria bancrofti and Brugia malayi that cause lymphatic filariasis live almost exclusively in humans. These worms lodge in the lymphatic system, the network of nodes and vessels that maintain the delicate fluid balance between the tissues and blood and are an essential component for the body’s immune defense system. They live for 4-6 years, producing millions of immature microfilariae, minute larvae, that circulate in the blood.
Transmission: The disease is transmitted by mosquitoes that bite infected humans and pick up the microfilariae that develops into the infective stage in a process that usually takes 7-21 days. The larvae then migrate to the mosquitoes’ biting mouth parts, ready for inoculation into the bloodstream of the next unsuspecting individual, thus completing the cycle. Signs and Symptoms: The development of the disease itself in humans is still something of an enigma to scientists. Though the infection is generally acquired early in childhood, the disease may take years to manifest itself.
Indeed, many people never acquire the outward clinical manifestations of their infections. Even though there may be no clinical symptoms, studies have now disclosed that such victims, outwardly healthy, actually have hidden lymphatic pathology and kidney damage as well. The symptomatic form of infection is most often characterized by the presence in the blood of thousands or millions of larval parasites (microfilariae) and adult worms located in the lymphatic system. The worst symptoms of the chronic disease generally appear in adults, and in men more often than in women. In endemic communities, some 10-50% of men suffer from genital damage, especially hydrocoele (fluid-filled balloon-like enlargement of the sacs around the testes) and elephantiasis of the penis and scrotum. Elephantiasis of the entire leg, the entire arm, the vulva or the breast — swelling up to several times normal size — can affect up to 10% of men and women in these communities.
Acute episodes of local inflammation involving skin, lymph nodes and lymphatic vessels often accompany the chronic lymph edema or elephantiasis. Some of these are caused by the body’s immune response to the parasite, but most are the result of bacterial infection of skin where normal defenses have been partially lost due to underlying lymphatic damage. Careful cleansing can be extremely helpful in healing the infected surface areas and in both slowing and, even more remarkably, reversing much of the overt damage that has already occurred. In endemic areas, chronic and acute manifestations of filariasis tend to develop more often and sooner in refugees or newcomers than in local populations continually exposed to infection. Lymph edema may develop within six months and elephantiasis as quickly as a year after contact.
Diagnosis: Until very recently, diagnosing lymphatic filariasis had been extremely difficult, since parasites had to be detected microscopically in the blood, and in most parts of the world, the parasites have a ‘nocturnal periodicity’ that restricts their appearance in the blood to only the hours around midnight. The new development of a very sensitive, very specific simple ‘card test’ to detect circulating parasite antigens without the need for laboratory facilities and using only finger-prick blood droplets taken any time of the day has completely transformed the approach to diagnosis. With this and other new diagnostic tools, it will now be possible to both improve our understanding of where the infection actually occurs and to monitor more easily the effectiveness of treatment and control programs.
Treatment in communities where filariasis is endemic: The primary goal of treating the affected community is to eliminate microfilariae from the blood of infected individuals so that transmission of the infection by the mosquito can be interrupted. Recent studies have shown that single doses of diethylcarbamazine (DEC) have the same long term (1-year) effect in decreasing microfilaraema as the formerly recommended 12-day regimens of DEC, and, even more importantly, that the use of single doses of 2 drugs administered concurrently (optimally albendazole or DEC with ivermectin) is 99% effective in removing microfilariae from the blood for a full year after treatment. It is this level of treatment effectiveness that has made feasible the new efforts to eliminate lymphatic filariasis.
Treatment of the Individual: Both albendazole and DEC have shown to be effective in killing the adult-stage filarialparasites (necessary for complete cure of infection), but ideal treatment regimens still need to be defined. Clearly this anti-parasite treatment can result in improvement of patients’ elephantiasis and hydrocoeles (especially in the early stages of the disease), but the most significant treatment advance to alleviate the suffering of those with elephantiasis has come from recognizing that much of the progression in pathology results from bacterial and fungal ‘super infection’ of tissues with compromised lymphatic function caused by earlier filarial infection. Thus, rigorous hygiene to the affected limbs with accompanying adjunctive measures to minimize infection and promotes lymph flow result in both a dramatic reduction in frequency of acute episodes of inflammation (‘filarial fevers’) and in astonishing degree of improvement of the elephantiasis itself.
WHO’S Program to Eliminate Lymphatic Filariasis The strategy of the program in the Division of the Control of Tropical Diseases (CTD) to eliminate lymphatic filariasis has two components: first to stop the spread of infection (i.e., interrupt transmission) and, second, to alleviate the suffering of affected individuals (i.e., control morbidity).
To interrupt transmission, communities where lymphatic filariasis is endemic must be identified, and then community-wide (‘mass treatment’) programs should be implemented to treat the entire population at risk of infection. In most countries, annual administration of one or two medications given together will be required for four to six years. To alleviate the suffering caused by the disease, efforts must be made to educate communities and affected patients about the tremendous value of intensive local hygiene and the improvement possible both for the damage that has already occurred and for prevention of the debilitating acute episodes of inflammation that accompany it.
Working with WHO’s country, regional offices and collaborating centers, CTD encourages and supports endemic countries in their efforts to revise national programs and formulate plans of action that take advantage of the new tools and approaches to eliminate lymphatic filariasis. By January 1998, 13 countries had revised their national plans of action, and elimination programs had already been initiated in seven of these. To provide much needed support for these filariasis elimination efforts, SmithKline Beecham PLC has generously agreed (in January 1998) to collaborate with WHO/CTD in the program to eliminate lymphatic filarial disease. The company will donate through WHO quantities of albendazole sufficient to eliminate the disease globally and will, additionally, provide financial support, human resources and expertise in support of this elimination goal.
The World Bank and the Arab Fund for Economic and Social Development have joined these collaborative efforts. WHO has invited both organizations of the UN family and other partners in health to join similarly in this international program to eliminate lymphatic filariasis. Indeed, it is this new partnership now being forged among scientists, health workers, the public and private sectors, affected communities and patients themselves that will provide the necessary impetus to achieve by 2020 the goal, recently enunciated by the 50th World Health Assembly, of eliminating lymphatic filariasis as a public health problem from all endemic countries.
WHO Fact Sheet No. 190 January 1998
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