Lymphatic filariasis

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Fri, 25 Aug 2006 16:06:39 -0000

Lymphatic filariasis

 

 

 

 

http://www.who.int/mediacentre/factsheets/fs102/en/

 

Lymphatic filariasis

 

Lymphatic Filariasis, known as Elephantiasis, puts at risk more than a

billion people in more than 80 countries. Over 120 million have

already been affected by it, over 40 million of them are seriously

incapacitated and disfigured by the disease. One-third of the people

infected with the disease live in India, one third are in Africa and

most of the remainder are in South Asia, the Pacific and the Americas.

In tropical and subtropical 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 is 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

defence 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 develop, inside the mosquito, into the

infective stage in a process that usually takes 7-21 days. The larvae

then migrate to the mosquitoes' biting mouth-parts, ready to enter the

punctured skin following the mosquito bite, 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 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 asymptomatic 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 lymphoedema 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 defences 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 occurred already.

 

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. Lymphoedema may

develop within six months and elephantiasis as quickly as a year after

arrival.

 

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 anytime of

the day has completely transformed the approach to diagnosis. With

this and other new diagnostic tools, it will now be possible both to

improve our understanding of where the infection actually occurs and

to monitor more easily the effectiveness of treatment and control

programmes.

 

Treatment

 

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 microfilaraemia 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 with DEC or 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.

 

Treating the individual. Both albendazole and DEC have been shown to

be effective in killing the adult-stage filarial parasites (necessary

for complete cure of infection), but ideal treatment regimens still

need to be defined. It is clear that this anti-parasite treatment can

result in improvement of patients' elephantiasis and hydrocoele

(especially in the early stages of 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 " superinfection " 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 promote

lymph flow, results both in a dramatic reduction in frequency of acute

episodes of inflammation ( " filarial fevers " ) and in an astonishing

degree of improvement of the elephantiasis itself.

 

WHO's strategy to eliminate lymphatic filariasis

 

The strategy of the Global Programme to Eliminate Lymphatic Filariasis

has two components: firstly, to stop the spread of infection (i.e.

interrupt transmission), and secondly, to alleviate the suffering of

affected individuals (i.e. morbidity control).

 

To interrupt transmission, districts in which lymphatic filariasis is

endemic must be identified, and then community-wide ( " mass treatment " )

programmes implemented to treat the entire at-risk population. In most

countries, the programme will be based on once-yearly administration

of single doses of two drugs given together: albendazole plus either

diethylcarbamazine (DEC) or ivermectin, the latter in areas where

either onchocerciasis or loiasis may also be endemic; this yearly,

single-dose treatment must be carried out for 4-6 years. An

alternative community-wide regimen with equal effectiveness is the use

of common table/ cooking salt fortified with DEC in the endemic region

for a period of one year.

 

To alleviate the suffering caused by the disease, it will be necessary

to implement community education programmes to raise awareness in

affected patients. This would promote the benefits of intensive local

hygiene and the possible improvement, both in the damage that has

already occurred, and in preventing the debilitating and painful,

acute episodes of inflammation.

 

The generous pledge in 1998 by the global healthcare company

SmithKline Beecham to collaborate with the World Health Organization

in its elimination efforts included the donation of numerous resources

(but especially albendazole, one of the mainstay drugs in the

elimination strategy), free of charge, for as long as necessary to

ensure success of the elimination programme. This donation, coupled

with the recent decision by Merck and Co., Inc., to expand its ongoing

Mectizan® (ivermectin) Donation Programme to include treatment of

lymphatic filariasis where appropriate, and the creation of additional

partnerships with other private, public and international

organizations, including the World Bank, have all further strengthened

the prospects for success of these elimination efforts.

 

Economic and social impact

 

Because of its prevalence often in remote rural areas, on the one

hand, and in disfavoured periurban and urban areas, on the other,

lymphatic filariasis is primarily a disease of the poor. In recent

years, lymphatic filariasis has steadily increased because of the

expansion of slum areas and poverty, especially in Africa and the

Indian sub-continent. As many filariasis patients are physically

incapacitated, it is also a disease that prevents patients from having

a normal working life. The fight to eliminate lymphatic filariasis is

also a fight against poverty.

 

Lymphatic filariasis exerts a heavy social burden that is especially

severe because of the specific attributes of the disease, particularly

since chronic complications are often hidden and are considered

shameful. For men, genital damage is a severe handicap leading to

physical limitations and social stigmatization. For women, shame and

taboos are also associated with the disease. When affected by

lymphoedema, they are considered undesirable and when their lower

limbs and genital parts are enlarged they are severely stigmatized;

marriage, in many situations an essential source of security, is often

impossible.

 

For more information contact:

 

WHO Media centre

Telephone: +41 22 791 2222

E-mail: mediainquiries