Lymphatic filariasis

Causes and risk factors of lymphatic filariasis

LF is caused by microscopic, thread-like parasitic worms invading the body's lymphatic system - the network of vessels that drain fluid from the tissues and carry infection-fighting cells. The two species of filarial worms that cause the condition, Wuchereria bancrofti and Brugia malayi, are spread by mosquitoes, who pick it up from an infected person when they feed on blood as they bite. The tiny worms develop in the mosquito over the next seven to 21 days into a larval stage which can be passed on to another human when the mosquito bites them.

The bacteria-containing worms lodge in the lymphatic system, producing millions of minute larvae which spread throughout the bloodstream. These worms disrupt the balance of the lymphatic system, which helps maintain the fluid balance between the tissues and the blood.

What is still not clear is how much this is down to the worms causing obstruction of the lymphatic vessels, or the immune response their presence triggers in the body. However, once the tissues have been damaged, they also become vulnerable to other bacterial and fungal infections, which are often responsible for much of the disease seen in LF patients.

In some high altitude areas of Africa, including Ethiopia, Kenya, Tanzania and Rwanda, a similar lymphatic condition resulting in elephantiasis limited to the lower leg and affecting nearly one in ten of the population, has been described. This doesn’t result from filarial worm infections but instead has been linked to walking barefoot on red clay soil derived from volcanic rocks, especially basalt. Metallic ions in the soil are known to be toxic to human tissues.

Who is most at risk of lymphatic filariasis?

Over 120 million people have already been affected by it, and over 40 million of these 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. Millions of other people in these areas are at risk.

In communities where the condition is endemic, ten to 50 per cent of men and up to ten per cent of women can be affected.

Symptoms of lymphatic filariasis

It’s thought that most people pick up the infestation during childhood, and it can take years for the symptoms to appear. Many people never have obvious outward signs of the condition although deep inside the body there are millions of larval parasites or microfilariae in the blood, adult worms in the lymphatic vessels, and extensive damage to the lymphatic system and kidneys.

More visible symptoms include huge and disfiguring enlargement of a limb, or areas of the trunk or head. These swellings are known technically as lymphoedema. In addition, the skin usually develops a thickened, pebbly appearance and may become ulcerated and darkened. This appearance of swelling and skin changes gives the condition its common name, elephantiasis.

Other symptoms can include fever, chills and a general feeling of ill health. The disease may also affect the sexual organs. In a man, the scrotum may become enlarged, and the penis may be retracted under the skin. In women the external genitalia may be covered in a tumourous mass.

People with the condition often have to contend with social as well as physical problems. Communities frequently shun women and men disfigured by the disease. Many women with visible signs of the disease will never marry, or their spouses and families will reject them. They are also frequently unable to work because of their disability.

Treatment and prevention of lymphatic filariasis

LF can be treated, but the drugs aren't always available to those most at need.

The World Health Organisation is running a ‘Global Programme to Eliminate Lymphatic Filariasis’, which aims to stop the spread of infection and help improve life for those already affected.

In areas where LF is common, mass treatment programmes are being put into place to treat the entire at-risk population. In most countries, treatment involves a once-yearly single dose of two drugs given together: albendazole plus either diethylcarbamazine (DEC) or ivermectin (ivermectin is given in areas where other infectious diseases such as onchocerciasis or loiasis are common). This single dose combination is 99 per cent effective in removing microfilariae from the blood for a full year after treatment. An alternative, and equally effective strategy, is to give communities cooking salt fortified with DEC for a period of one year.

These drugs can improve the patients' elephantiasis especially in the early stages of disease, and prevent further deterioration. But it's now recognised that much of the tissue damage results from secondary bacterial and fungal infection in the damaged areas. Rigorous hygiene and careful cleansing of the affected limbs can lead to a dramatic reduction in the frequency of acute episodes of inflammation (‘filarial fevers’) and a huge improvement in the elephantiasis. Measures to improve the flow of the lymphatic fluid, such as raising and exercising the swollen body part can also help.