Filariasis is an infectious tropical disease caused by any one of several thread-like parasitic round worms. The two species of worms most often associated with this disease are Wuchereria bancrofti and Brugia malayi. The larval form of the parasite transmits the disease to humans by the bite of a mosquito. In the early stages of the infection, the patient characteristically complains of fever, chills, headaches and skin lesions. Any one of several antiparasitic agents may be effective in eliminating the worm. However, if the disease is left untreated, obstruction of the lymph flow will cause particular areas of the body especially the legs and external genitals, to swell profoundly. Symptoms are primarily a response to adult worms that cause inflammation. Chronic inflammation may progress to hardening of the lymphatic vessels (fibrosis) and obstruction of the lymph flow.
Some people with filariasis have no symptoms. Other affected individuals may have episodes of acute inflammation of lymphatic vessels (lymphangitis) along with high temperatures, shaking chills, body aches, and swollen lymph nodes. Excessive amounts of fluid may accumulate (edema) in the affected areas (i.e., arms and/or legs), but the accumulation typically resolves after the other symptoms are gone. Attacks may also be accompanied by acute inflammation of the genitalia leading, in males, to inflammation, pain and swelling of the testes (orchitis), sperm track (funiculitis), and/or sperm ducts (epididymitis). The scrotum may become abnormally swollen and painful.
Bancroftian filariasis affects both the legs and the genitals. The Malayan variety affects the legs below the knees.
Some people with filariasis have abnormally high levels of certain white blood cells (eosinophilia) during acute episodes of symptoms. When the inflammation resolves, these levels return to normal.
Filariasis may cause chronic lymph node swelling (lymphadenopathy) even in the absence of other symptoms. Longstanding obstruction of the lymphatic vessels may lead to several other conditions. These include accumulation of fluid in the scrotum (hydrocele), the presence of lymphatic fluid in the urine (chyluria), and/or abnormally enlarged lymphatic vessels (varices). Other symptoms may include progressive edema (elephantiasis) of the female external genitalia (vulva), breasts, and/or arms and legs. Chronic edema may result in skin that is abnormally thick and has a “warty” appearance.
Filariasis is a rare infectious tropical disorder caused by the round worm parasites (nematode) Wuchereria bancrofti or Brugia malayi. Symptoms result primarily from inflammatory reactions to the adult worms. Some people may also develop hypersensitivity reactions to the small larval parasites (microfilariae).
Filariasis is common disease in tropical regions of the world. The organism W. bancrofti is present throughout Africa, Asia, China, and South America. B. malayi is found in southern and southeast Asia. Filariasis is extremely rare in North America and occurs only when these organisms are imported from tropical regions. The infection is transmitted by several different types of tropical mosquitos which transfer the larval stage of the organism (microfilariae) from one host to another. Lymphatic filariasis affects about 120 million people worldwide. Short-term travelers to areas where it is endemic are at low risk for this infection. People who visit endemic areas for extended periods of time, and especially those who are in areas or situations in which they are intensely exposed to infected mosquitoes, can become infected. Most infections seen in the U.S. are in immigrants from endemic countries, according to the Centers for Disease Control and Prevention (CDC).
The diagnosis of filariasis requires examination of a blood smear for the presence of the larval round worm W. bancrofti or B. malayi. Since the number of parasites (parasitemia) in the blood is higher during the night, blood samples are best obtained at night. When parasites are not found in the blood, the adult worms may occasionally be found in a lymph node sample from an infected individual.
A somewhat easier diagnostic test was recently developed that may be used at any time during the day. It is based on detecting the presence of antibodies generated in reaction to the foreign bodies, the parasites themselves.
Progressively increasing doses of any one of the major anti-parasiticide drugs is the treatment for the disorder. Among these drugs are: ivermectin, albendazole, and diethylcarbamazine. These drugs work to get rid of the larval worm, to inhiobit reproduction of the adult worm, or to kill the adult worm. Notwithstanding that these drugs are effective they do, the use of each is subject to substantial side effects (adverse reactions). These side effects may be alleviated by using antihistamines and/or anti-inflammatory drugs.
The elimination of adult worms must be undertaken with care because high concentration of dead worms in the lymph or blood can provoke dangerous allergic reactions and abscesses.
Surgery may be used to treat some people with filariasis who develop an abnormal accumulation of fluid in the scrotum (hydrocele). Surgery may also be performed to remove the remains of adult worms and calcifications developing around them. Treatment of elephantiasis of the legs usually consists of elevation and support from elastic stockings.
In the tropical areas of the world, mosquito control is an important part of prevention of filariasis. Filariasis is usually a self-limited disease unless reinfection occurs. Therefore some cases, especially those brought into temperate regions of the world (i.e., North America), may be left untreated because there is no danger of spreading the disease.
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Research on tropical diseases is ongoing. The development of vaccines is also being investigated. For more information, contact the World Health Organization (WHO) listed in the Resources section below.
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