Filariasis
Filariasis
Disease History, Characteristics, and Transmission
Introduction
Filariasis is a preventable parasitic disease caused by the threadworms Wuchereria bancrofti, Brugia malayi, and Brugia timori. It is endemic in over 80 countries and is considered to be the main cause of permanent disability worldwide.
When symptomatic, patients may present with severe lymphatic and limb swelling, commonly referred to as elephantiasis. The disfigurations resulting from elephantiasis and lymphodema raise issues among some communities and add to the socioeconomic impacts of this debilitating disease.
Infection is transmitted through mosquito bites, where both the vector (disease carrier) and the human host are necessary in the successful completion of the parasitic life cycle. Anti-parasitic treatment is available, but is expensive and can take around a year to eliminate the parasites. Filariasis infection has been successfully curtailed in countries such as China, which has given hope for the campaign of global eradication.
Disease History, Characteristics, and Transmission
Filariasis was first recognized in its infectious form in 1866 when filarial larvae were detected in urine and identified as the causative agent.
The infection is usually acquired in childhood, but takes years to manifest and usually remains asymptomatic until adulthood. Once developed, symptoms may include chronic swelling of the lymph nodes and swelling of the arms, legs, and genitals. Elephantiasis refers to the thickening of skin and underlying tissue and often accompanies symptoms. Without presentation of symptoms, internal damage to the kidneys and the lymphatic system may also develop.
Transmission of filariasis is through mosquito bites, whereby the larval form is drawn out of blood by mosquitos, develops to the infective stage, and is injected into a new host. Here the larvae develop into the adult form, migrate to the lymph nodes, mate, and release millions of larvae into the host's bloodstream. Adult worms may live up to six years, during which time the host will remain a source of infection for others.
Scope and Distribution
Filariasis is a disease largely associated with poverty with more than a billion people in over 80 countries at risk. Infection caused by W. bancrofti is endemic in tropical regions of Southeast Asia, Africa, India, and Central and South America, while B. malayi and B. timori are generally limited to areas of Southeast Asia. This disease state is rare in western countries with no cases having been reported within the United States.
Filariasis has been recognized as the leading cause of permanent disability worldwide. Of the 120 million people affected, 40 million have been left disfigured and completely incapacitated. Chronic disease symptoms present more in men than women as seen in endemic areas where from 10 to 50% of men are infected versus up to 10% of women.
Disease distribution is also affected by habitat suitability for the various forms of mosquito responsible for transmission of the parasite.
Treatment and Prevention
Treatment of this disease consists of a multifaceted approach. Treatment of the infection itself may be achieved with a concurrent dosage of strong anti-parasitic drugs such as diethylcarbamazine citrate (DEC), DEC fortified salt, and albendazole. This proves to be 99% effective in removing microfilaria from the blood after one year of treatment.
Lymphodema and elephantiasis are often exacerbated due to bacterial and fungal infections taking advantage of the patient's compromised lymphatic condition. Following rigorous hygiene routines as prevention against infection from opportunistic pathogens and completing exercises to improve lymph flow often helps to reduce these causes of swelling. Surgery may be necessary for treatment of severe genital swelling in men.
Prevention of filariasis is achievable by reducing exposure to mosquito bites and treating endemic communities, in total, to remove the pool of infection. Some means of prevention are relatively simple and inexpensive. Using mosquito netting in sleeping areas, wearing clothing that covers the arms and legs, applying mosquito repellant on exposed skin, and remaining indoors during peak times of mosquito activity all reduce the risk of exposure to filariasis. These measures are the basis of a global campaign to eradicate filariasis.
Impacts and Issues
Filariasis causes permanent—and often painful—disability in over 40 million people worldwide. Most cases occur in developing or underdeveloped regions. Many disabled by filariasis cannot regularly farm, work, or attend school. Malnourishment rates are often higher among those affected by filariasis than in the surrounding non-affected population.
The social impacts of filariasis present not only in the loss of work labor due to incapacitation, but also in community relations. People disfigured by the disease are frequently shunned by society and chronic complications are often deemed shameful. Marriage is considered a near impossibility among those suffering genital manifestations, which then puts growth and development of the community at risk.
Filariasis is a disease with potential for eradication, but one that remains endemic in poor communities. The continued increase in infection may be attributed to the rapid growth of cities and the resultant spread of poverty-stricken housing areas. These regions provide breeding sites for the mosquitoes and aid in disease transmission. It is for these reasons that endemic areas are trapped in a vicious cycle of infection that has proven difficult to break.
WORDS TO KNOW
LYMPHATIC SYSTEM: The lymphatic system is the body's network of organs, ducts, and tissues that filter harmful substances out of the fluid that surrounds body tissues. Lymphatic organs include the bone marrow, thymus, spleen, appendix, tonsils, adenoids, lymph nodes, and Peyer's patches (in the small intestine). The thymus and bone marrow are called primary lymphatic organs, because lymphocytes are produced in them. The other lymphatic organs are called secondary lymphatic organs. The lymphatic system is a complex network of thin vessels, capillaries, valves, ducts, nodes, and organs that runs throughout the body, helping protect and maintain the internal fluids system of the entire body by both producing and filtering lymph, and by producing various blood cells. The three main purposes of the lymphatic system are to drain fluid back into the bloodstream from the tissues, to filter lymph, and to fight infections.
SOCIOECONOMIC: Concerning both social and economic factors.
VECTOR: Any agent, living or otherwise, that carries and transmits parasites and diseases. Also, an organism or chemical used to transport a gene into a new host cell.
IN CONTEXT: RELATED DISEASE GROUPS
Filiariasis is a group of tropical diseases caused by thread like parasitic round worms (nematodes of the order Filaraiidae, commonly called filariae) and their larvae. The group affects humans and animals. The larvae transmit the disease to humans through a mosquito bite. Filariasis is characterized by fever, chills, headache, and skin lesions in the early stages and, if untreated, can progress to include gross enlargement of the limbs and genitalia in a condition called elephantiasis. There are hundreds of described filarial parasites, but only eight that cause infections in humans: Brugia malayi, Wucheria bancrofti, Brugia timori, Onchocerca volvulus, Loa loa, Mansonella streptocerca, Mansonella ozzardi, and Mansonella perstans.
See AlsoDemographics and Infectious Disease; Economic Development and Disease; Helminth Disease; Host and Vector; Opportunistic Infection; Parasitic Diseases.
BIBLIOGRAPHY
Books
Mandell, G.L., Bennett, J.E., and Dolin, R. Principles and Practice of Infectious Diseases. Volume 2. Philadelphia, PA: Elsevier, 2005.
Web Sites
Centers for Disease Control and Prevention (CDC). “Lymphatic Filariasis.” February 16, 2007 <http://www.cdc.gov/ncidod/dpd/parasites/lymphaticfilariasis/index.htm> (accessed March 5, 2007).
Directors of Health Promotion and Education (DHPE). “Lymphatic Filariasis.” 2005 <http://www.dhpe.org/infect/Lymphfil.html> (accessed March 5, 2007).
World Health Organization (WHO). “Lymphatic Filariasis.” September 2000 <http://www.who.int/mediacentre/factsheets/fs102/en/> (accessed March 5, 2007).