Organism

These are a group of infections caused by small worms called Filaria. These may be up to several centimetres in length and are transmitted by insect bites. Adult worms live either under the skin or in the lymphatic system, and their larval form, or microfilariae, are released in large numbers into the blood stream from where they can be picked up when insects feed. Although infections can occur in travellers to areas of filariasis, these are rare, and significant illness tends to occur only in people living in high risk areas for prolonged periods.

Worms that live in the skin and underlying tissues include Loa-loa (the infection is loiasis) and onchocerciasis (discussed elsewhere), while lymphatic filarial worms include Wucheria bancrofti and Brugia malayi. Finally the worm Mansonella perstans lives in body cavities such as the abdomen or pleural cavities, usually resulting in asymptomatic infection.

Mode of Transmission

Lymphatic filariasis is transmitted by the bite of an infected mosquito which injects an immature form of the worm into the skin or blood. Worms migrate to lymphatic vessels particularly in the groin, where they live for up to 5 years, mating and producing large numbers of microfilariae which reach blood and can then infect mosquitoes taking a blood meal.

Loa loa is transmitted by bites of the deer fly chrysops, but the mature worms do not settle at any one location in the body but wander at will, sometimes producing nodules under the skin due to irritation of the tissues as the worm passes. Adult Loa loa worms can live for up to 17 years. Mansonella is transmitted by the bites of midges. In all of these infections there is no direct person to person spread.

Regions Affected

Wucheria bancrofti is found throughout sub-Saharan Africa, the Far East and South Pacific, and South America. Brugia malayi is limited to Asia, particularly south-west India, China, South Korea and south-east Asia. Loiasis is found in Central Africa, while Mansonella is limited to the northern regions of South America and West Africa.

Prevention

For all forms of filariasis, people should be educated about the importance of avoiding mosquito, midge or deer fly bites. Intermittent mass treatment of the local population can reduce the problems associated with long standing infection.

Immunisation

None available.

Symptoms and Signs

In lymphatic filariasis, patients may develop symptoms 9 to 12 months after infection, although many infections are asymptomatic. Symptoms include recurrent fever with shivering and sweating, inflammation of lymphatic vessels which results in pain and redness of the skin if these vessels are near the surface, mainly in the lower leg or thigh, and tender enlargement of the lymph nodes. Release of microfilariae may be accompanied by allergic symptoms such as wheeze.

 Over time with repeated infections, the lymphatic vessels become chronically scarred with blockage of lymphatic drainage, resulting in chronic swelling of the part of the body drained by that part of the lymphatic system. This is usually the leg or scrotum, and swelling can be massive - one famous patient from Africa required a wheelbarrow to transport his scrotum. This swelling is known as elephantiasis. The skin of the swollen area becomes thickened and rough with great potential for secondary bacterial infections. Very occasionally elephantiasis can affect the breast.

In loiasis, the Loa loa adult worms migrate through skin and deeper tissues and patients sometimes experience transient itchy swellings several centimetres in diameter, due to inflammation as the worm passes


Source: www.privatehealth.co.uk
Last Editorial Review: 25/1/2010