Information on the following diseases can be found in the Related Disorders section of this report:

• Acanthocheilonemiasis
• Filarial Diseases (General)

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).

Symptoms of the following disorders can be similar to those of Filariasis. Comparisons may be useful for a differential diagnosis:

Acanthocheilonemiasis is a tropical infectious disease caused by a multicellular parasite (filarial worm [nematode]), called Acanthocheilonema perstans. This parasite is found most commonly in Africa. Initially people with Acanthocheilonemiasis may have no symptoms. Symptoms may include itchy skin (pruritis), abdominal pain, chest pain, muscle pain (myalgias), and/or areas of swelling under the skin. Other symptoms may include an abnormally enlarged liver and spleen (hepatosplenomegaly), and inflammation in the affected organs. (For more information on this disorder, choose "Acanthocheilo" as your search term in the Rare Disease Database.)

Filarial Disease, or the general term "filariasis," may also refer to a group of parasitic diseases caused by various species of filarial worms (nematodes). These include mumu, loiasis (Calabar swellings), dirofilariasis (human infection by dog heartworm), and onchocerciasis (river blindness). All these except dirofilariasis can be acquired only in the tropics, where they are common, but are extremely rare in temperate climates such as North America. Taken together, filarial diseases of all types affect approximately 100 million people worldwide.

Diagnosis
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.

Treatment
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.

Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government website.For information about clinical trials being conducted at the National Institutes of Health (NIH) Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222
TTY: (866) 411-1010
Email: prpl@cc.nih.gov

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.

TEXTBOOKS
Beers MH, Berkow R., eds. The Merck Manual, 17th ed. Whitehouse Station, NJ: Merck Research Laboratories; 1999:.

Berkow R., ed. The Merck Manual-Home Edition.2nd ed. Whitehouse Station, NJ: Merck Research Laboratories; 2003:.

Gorbach SL, Bartlett JG, Blacklow NR. Eds. Infectious Diseases. W.B. Saunders Company, Philadelphia, PA; 1992.

Mandell GL, Bennett JE, Dolan R. Eds. Mandell, Douglas and Bennett's Principles and Practice of Infectious Diseases. 4th ed. Churchill Livingstone Inc. New York, NY; 1995.

REVIEW ARTICLES
Michael E, Malecela-Lazaro MN, Simonsen PE, et al. mathematical modelling and the control of lymphatic filariasis. Lancet Infect Dis. 2004;4:223-34.

Walther M, Muller R. Diagnosis of human filariases (except onchocerciasis). Adv Paristol. 2003;53:149-93.

Taylor MJ. Walbachia in the inflammatory pathogenesis of human filariasis. Ann N Y Acad Sci. 2003;990:444-49.

Del Giudice P, Chosidow O, Caumes E. Ivermectin in dermatology. J Drugs Dermatol. 2003;2:13-21.

Horton J. Albendazole: a broad spectrum anthelminthic for treatment of individuals and populations. Curr Opin Infect Dis. 2002;15:599-608.

Shenoy RK. Management of disability in lymphatic filariasis-an update. J Commun Dis. 2002;34:1-14.

Lammie PJ, Cuenco KT, Punkosdy GA. The pathogenesis of filarial lymphedema: is it the worm or is it the host? Ann N Y Acad Sci. 2002;979:131-42; discussion 188-96.

Weil GJ, Lammie PJ, Weiss NW. The ICT Filariasis Test: A Rapid-format Antigen Test for the Diagnosis of Bancroftian Filariasis. Parasitol Today. 1997;13:401-05.

FROM THE INTERNET
Addiss D. Filariasis, Lymphatic. CDC TRAVELERS' HEALTH. Last reviewed June 30, 2003. 2pp.
www.cdc.gov/travel/diseases/filariasis.htm

Lymphatic Filariasis (Elephantiasis). National Institute of Allergy and Infectious Disease (NAID). Last updated March 12, 2003. 2pp.
www.niaid.nih.gov/newsroom/focuson/bugborne01/filar.htm

Nissen MD, Walker JC. Filariasis. emedicine. Last Updated: Oct 22, 2003. 24pp.
www.emedicine.com/med/topic794.htm

Turkington CA. Filariasis. Gale Encyclopedia of Medicine. 2002. 4pp.
www.healthatoz.com/healthatoz/Atoz/ency/filariasis.html

The Global Alliance to Eliminate Lymphatic Filariasis. nd.
Epidemiology. 1p
www.filariasis.org/index.pl?iid=1768
Pathogenesis and Pathology. 3pp.
www.filariasis.org/index.pl?iid=1769
Asymptomatic Presentations. 1p.
www.filariasis.org/index.pl?iid=1772
Clinical Features. 4pp.
www.filariasis.org/index.pl?iid=1771

Ottesen E, Karam M, Behbehani K. Lymphatic filariasis: in our lifetime. (c)1997 World Health Organization. 24pp.
www.filariasis.org/docs/Hope_Eng.pdf

Wuchereria bancrofti. Graphic Images of Parasites. nd. 2pp.
www.biosci.ohio-state.edu/~parasite/wuchereria.html

Lymphatic Filariasis Programme. (c)2001-2004. Glaxo, Smith Kline. Key Facts and Overview. Updated March 15, 2004. 2pp.
www.gsk.com/filariasis/