Última actualización:
9/25/2025
Años publicados: 1990, 1999, 2006, 2007, 2009, 2025
NORD gratefully acknowledges Gioconda Alyea, MD (FMG), MS, National Organization for Rare Disorders, for the preparation of this report.
Summary
Lymphatic filariasis (LF), also known as filarial elephantiasis, is a neglected tropical disease caused by infection with thread-like parasitic worms (filarial worms) that are transmitted to humans through the bite of infected mosquitoes. Infection is often acquired in childhood, where it silently damages the lymphatic system, and later in life it can lead to severe and disfiguring manifestations such as lymphoedema, elephantiasis and hydrocele. These complications cause permanent disability, profound pain and visible swelling in different parts of the body, particularly the legs and scrotum. People suffering from LF not only have physical disability but also face social stigma, mental distress and economic hardship, further deepening cycles of poverty.1,2
In 2023, an estimated 657 million people across 39 countries lived in areas requiring preventive chemotherapy to halt its transmission. Globally, about 25 million males are affected by hydrocele and over 15 million people live with lymphoedema, while at least 36 million individuals endure chronic disease manifestations.¹ Despite being a preventable and manageable condition, LF continues to persist in impoverished communities where access to healthcare, sanitation and resources is limited.²
Because LF is classified as a neglected tropical disease, global health programs emphasize strategies such as mass drug administration (MDA), which provides safe and effective medicines to control its spread. Preventive measures also focus on reducing exposure to mosquitoes, as avoiding bites remains the most effective way to stop transmission.² Eliminating lymphatic filariasis would prevent unnecessary suffering, ease stigma, and contribute significantly to improve the living conditions in affected populations.1,2
Introduction
Lymphatic filariasis is the most common cause of elephantiasis (see below) so the terms are often used interchangeably. However, elephantiasis can also be caused by other factors such as non-filarial causes like podoconiosis, leprosy, or tuberculosis, which affect the lymphatic system differently.
Most people with lymphatic filariasis (LF) do not have symptoms (asymptomatic). Other people can have sudden episodes of illness (acute) or long-lasting problems (chronic). Even without symptoms, the parasite can still damage the lymphatic system, which is the network of vessels that helps circulate fluid and fight infections, as well as the kidneys, and it can affect the body’s immune system.1
The acute (sudden) episodes of illness often involve pain, fever and swelling of the skin, lymph nodes (small glands that help fight infection) and lymphatic vessels. They are sometimes caused by the body’s reaction to the parasite, but more often they result from secondary bacterial infections which can occur because the damaged lymphatic system no longer protects the skin effectively. These episodes are very painful, may last for weeks and often prevent people from being able to work.1
In the early stages of infection, some patients may develop inflammation of lymphatic vessels (lymphangitis), swelling of lymph nodes (lymphadenopathy) and an increased number of a type of white blood cell called eosinophils that usually increase in parasitic infections or allergies (eosinophilia).3
When LF causes chronic illness it can lead to several noticeable problems:
These physical changes can cause not only health problems but also social and emotional difficulties, such as stigma, reduced job opportunities and financial strain due to medical costs and caregiving needs.1
A rare but serious complication is tropical pulmonary eosinophilia, most often seen in South and Southeast Asia. This condition affects the lungs and is linked to certain LF parasites (Wuchereria bancrofti and Brugia malayi). Symptoms include coughing, wheezing, chest pain, coughing up blood, an enlarged spleen (splenomegaly) and very high levels of eosinophils in the blood.3,4
Lymphatic filariasis is caused by infection with thread-like parasitic worms called nematodes (roundworms) from the Filarioidea family. There are three main species that infect humans: Wuchereria bancrofti (about 90% of cases), Brugia malayi and Brugia timori.¹
These parasites are transmitted to humans through the bites of infected mosquitoes. Several mosquito species can carry the infection, including Culex (common in towns and cities), Anopheles (more common in rural areas), Aedes (often seen in Pacific Island regions) and Mansonia.⁴
The worms require both humans and mosquitoes to complete their life cycle. When a mosquito bites a person already infected with lymphatic filariasis, it ingests microscopic larvae called microfilariae, which circulates in the person’s blood. Inside the mosquito, the microfilariae develop in stages over 10 to 14 days, eventually becoming third-stage larvae, known as L3 larvae.⁴
These L3 larvae are the infectious form of the parasite. They move to the mosquito’s mouthparts and are passed onto another person’s skin the next time the mosquito bites. From there, the L3 larvae enter the body through the bite wound. Once inside, they travel to the lymphatic system, which helps regulate fluid balance and supports the immune system. Over several months, the larvae mature into adult worms.⁴
Adult worms can live in the lymphatic vessels for 5 to 8 years or more.¹,⁴ During that time, they reproduce and release millions of microfilariae into the bloodstream. These offspring are most active in the blood at night; a behavior called nocturnal periodicity and can survive in the body for up to two years.⁴
The cycle continues when another mosquito bites the infected person, takes in the microfilariae and becomes capable of spreading the disease after the larvae mature to the L3 stage.
Lymphatic filariasis is generally not a risk for casual travelers, as infection requires repeated bites from infectious mosquitoes.² Travelers are most at risk when staying in endemic regions for prolonged periods.² Risk is also higher among individuals who live in tropical and subtropical areas where these parasites are common, and who experience frequent mosquito bites over months or years.²
Lymphatic filariasis (LF) affects over 120 million people in 72 countries, mainly in tropical and subtropical regions such as Sub-Saharan Africa, Southeast Asia, the Western Pacific, South America and the Caribbean. Wuchereria bancrofti is the most widespread cause, while Brugia malayi and Brugia timori are more geographically limited to Southeast Asia. Although global control efforts have significantly reduced transmission, resulting in a 74% drop in cases since 2000, LF remains endemic in several regions.1,4
The disease is rarely seen in short-term travelers and typically requires repeated mosquito exposure over time. People who live in or spend extended periods in endemic areas, such as aid workers or field researchers, are at the highest risk.²
One-third of children in these areas may be infected without symptoms, while adults in their 30s and 40s often develop more serious complications. Males are affected more frequently than females with a 10:1 ratio.⁵ Though often silent in early stages, LF can lead to long-term disability and disfigurement if left untreated, making ongoing prevention and treatment efforts essential.
Lymphatic filariasis is not endemic in the United States; therefore, its prevalence is extremely low to negligible. While few cases have been documented in the U.S., they are often linked to travel or exposure to endemic regions, such as military personnel in the South Pacific. These U.S. cases are typically zoonotic infections from the Brugia genus, which can cause symptoms like lymphadenopathy.6,7
The diagnosis of lymphatic filariasis (LF) involves several methods, ranging from simple blood tests to more advanced laboratory and imaging techniques. Traditionally, doctors have used blood smears, where a drop of blood is examined under a microscope to look for the tiny worms known as microfilariae (the immature stage of the parasite). This method can confirm infection, but it is most effective at night, when the parasites are usually present in the bloodstream. It is less helpful in people with long-term (chronic) disease or in those with very few parasites in their blood.2,4
In addition to microscopy, antibody tests may be used, which detect proteins that the immune system produces when it recognizes the parasite. These tests can indicate if someone has been infected, but they do not always distinguish between a current infection and one that occurred in the past.²
Over time, newer and more accurate tools have become available:⁴
The elimination of lymphatic filariasis (LF) is possible by interrupting the spread of infection through medicines and mosquito control. The World Health Organization (WHO) recommends a strategy called mass drug administration (MDA), where once a year, entire communities in affected areas are offered preventive treatment, regardless of whether individuals show symptoms.¹ These medicines do not completely kill the adult worms but greatly reduce the number of microscopic worms in the blood (called microfilariae), which prevents further transmission to mosquitoes.
The specific drug combinations used depend on the presence of other diseases in the area:1,4,5
Recent studies show that multiple doses of the triple-drug regimen (known as IDA: ivermectin, DEC, albendazole) clear microfilariae from the blood more effectively than two-drug regimens, especially within the first one to two years of treatment.5 The medicines are generally safe, though mild side effects such as fever, headache, or dizziness may occur, which can be managed with anti-inflammatory drugs or antihistamines.1,4
Alongside preventive treatment, individual care is essential for those already affected. Hydrocele can often be treated successfully with surgery, while lymphedema is managed through daily hygiene, skin care, exercise and limb elevation. These measures help prevent further damage and reduce painful inflammatory episodes. Advanced cases may require specialized surgical techniques. Antibiotics such as long-term penicillin may help prevent recurrent infections in patients with severe swelling.1,4
WHO also stresses the importance of providing an essential package of care (EPC) to all affected people. This includes:
In addition to drug therapy, mosquito control is essential. Using insecticide-treated bed nets, indoor spraying and repairing window screens can significantly reduce mosquito bites.² These measures not only protect against LF but also against other mosquito-borne diseases such as malaria and dengue.
Globally, the Global Programme to Eliminate Lymphatic Filariasis (GPELF) launched by the WHO in 2000 has achieved major progress. Over 20 countries, including Brazil, Sri Lanka, Thailand and Togo, have successfully eliminated LF as a public health problem, and many others are in the final surveillance phase.¹
WHO’s 2030 goals include ensuring all endemic countries either eliminate LF or maintain surveillance, while providing continuing care for affected individuals¹. Achieving this requires not only medicines and mosquito control but also broader public health efforts, such as improving sanitation, clean water access and cross-sector collaboration under the One Health approach.⁵ Sustained financing, community education and psychological support are also essential, as LF affects not just physical health but also mental well-being and social inclusion.4
LF impacts the quality of life due to both its physical and emotional consequences. Psychological support for affected individuals is crucial from diagnosis, and the education of transmission and treatment of LF in endemic communities is essential to prevent discrimination and exclusion.8
Research is underway on new approaches, including antibiotics like doxycycline that kill adult worms by targeting their bacterial partners (Wolbachia)⁴, and potential vaccines to provide long-term protection. Although vaccine development is challenging due to the parasite’s ability to evade the immune system, promising candidates are being tested in laboratory and animal studies.⁴
Information on current clinical trials is posted on the Internet at https://clinicaltrials.gov/. All studies receiving U.S. Government funding, and some supported by private industry, are posted on this government web site.
For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:
Toll-free: (800) 411-1222
TTY: (866) 411-1010
Email: [email protected]
Some current clinical trials also are posted on the following page on the NORD website:
https://rarediseases.org/living-with-a-rare-disease/find-clinical-trials/
For information about clinical trials sponsored by private sources, contact:
https://www.centerwatch.com/
For information about clinical trials conducted in Europe, contact:
https://www.clinicaltrialsregister.eu/
Please note that some of these organizations may provide information concerning certain conditions potentially associated with this disorder.
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Aprende más https://rarediseases.org/patient-assistance-programs/rare-disease-educational-support/Este programa de asistencia, primero en su tipo, está diseñado para los cuidadores de un niño o adulto diagnosticado con un trastorno raro.
Aprende más https://rarediseases.org/patient-assistance-programs/caregiver-respite/The information provided on this page is for informational purposes only. The National Organization for Rare Disorders (NORD) does not endorse the information presented. The content has been gathered in partnership with the MONDO Disease Ontology. Please consult with a healthcare professional for medical advice and treatment.
The Genetic and Rare Diseases Information Center (GARD) has information and resources for patients, caregivers, and families that may be helpful before and after diagnosis of this condition. GARD is a program of the National Center for Advancing Translational Sciences (NCATS), part of the National Institutes of Health (NIH).
View reportOrphanet has a summary about this condition that may include information on the diagnosis, care, and treatment as well as other resources. Some of the information and resources are available in languages other than English. The summary may include medical terms, so we encourage you to share and discuss this information with your doctor. Orphanet is the French National Institute for Health and Medical Research and the Health Programme of the European Union.
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