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why Elephantiasis is usually affecting the lymphatic vessels of the lower limbs?
Elephantiasis, or Lymphatic Filariasis, is a rare disorder of the lymphatic system caused by parasitic worms such as Wuchereria bancrofti, Brugia malayi, and B. timori, all of which are transmitted by mosquitos. Inflammation of the lymphatic vessels causes extreme enlargement of the affected area, most commonly a limb or parts of the head and torso. It occurs most commonly in tropical regions and particularly in parts of Africa. Elephantiasis is characterized by the gross enlargement of a limb or areas of the trunk or head. There is an abnormal accumulation of watery fluid in the tissues (edema) causing severe swelling. The skin usually develops a thickened, pebbly appearance and may become ulcerated and darkened. Fever, chills and a general feeling of ill health (malaise) may be present.
The lymphatic system is a complicated network of very fine tubes, about the diameter of a needle, which criss-cross body tissues to collect a fluid known as lymph. Lymph is a milk-like substance (containing white blood cells, proteins, and fats) that plays an important role in absorbing fats from the intestine, in fighting infections, and in the proper functioning of the immune system. Lymph is returned to the bloodstream via many vessels known as lymphatics. At various points, the lymphatics drain into masses of tissue known as lymph nodes or glands. If a blockage occurs, fluid may collect in the tissues, causing a type of swelling known as lymphedema (limf-e-DEE-ma). In the lymph system draining the legs, for example, few connections exist, and the legs often are a site of swelling when lymphedema occurs.

Worm larvae that make their way into lymph vessels can mature into adult worms. Male worms are long and slender, about 4 to 5 cm long, and 0.1 mm in diameter. Female worms are much larger, 6 to 10 cm long, and about three times wider than the males. The adults make their home mostly near the lymph glands in the lower part of the body. The adult female releases eggs enclosed within an egg membrane (microfilariae), and the microfilariae (mi-kro-fi-LAR-ee-i) develop into larvae to continue the life cycle.
Elephantiasis may also affect the male and female genital organs. In a male, there may be enlargement of the scrotum, and the penis may be retracted under skin which has become thickened, nonelastic, hot and painful. The spermatic cords may become thickened.

The external parts of the female genital organs (vulva) may also be affected by elephantiasis. A long, tumorous mass covered by thickened and ulcerated skin may develop between the thighs. There may also be an enlargement of the lymph nodes of the legs. The extreme enlargement of the limbs and other areas of the body characterized by elephantiasis, is the result of obstruction of the lymph flow and possibly of blood circulation. The lymphatic blockage can be due to recurrent attacks of a bacterial infection which causes inflammation of the lymphatic vessels (streptococcal lymphangitis). When the lymphatic obstruction is large enough, back pressure in the lymphatic channels produces dilation of the superficial vessels, resulting in extreme swelling. Without medical intervention, the cycle continues until the affected area is grotesquely enlarged. Death of surrounding tissues may also occur from an obstructed blood supply (gangrene).

Recent studies have shown that a possible cause of elephantiasis in Africa may be related to the red soil on which certain barefooted populations live. It is believed that small chemical particles found in the soil may enter the skin through the bare feet. These particles then lodge in the lymphatic tissues and produce irritating effects. The traumatized tissue is then vulnerable to streptococcal infection.

Lymphatic filariasis is the most common form, and it is caused by a parasitic disease resulting from a bite from an infected mosquito. This form is caused most commonly by the Wuchereria bancrofti parasite, but also can be caused by Brugia malayi and Brugia timori. These parasites are all nematodes, or roundworms, that inhabit the lymphatic vessels, resulting in their inability to drain the affected extremities.


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