Last updated:
9/25/2025
Years published: 1986, 1994, 1997, 2004, 2009, 2025
NORD gratefully acknowledges Gioconda Alyea, MD (FMG), MS, National Organization for Rare Disorders, for the preparation of this report.
Summary
Filariasis is a term that refers to a group of infectious tropical diseases caused by several thread-like parasitic round worms known as filariae. Filariae are spread to humans through the bites of infected insects such as mosquitoes or flies. These parasites are common in tropical and subtropical areas and cause diseases that are often preventable. Infections can range from having no symptoms at all to causing severe and visible physical damage that can lead to stigma and disability.1,2 Filarial diseases include:
Antiparasitic medications can treat early filarial worm infections. For people with advanced disease and chronic swelling, surgery or specialized lymphedema care may be required.1
Mass drug administration (MDA) campaigns currently target onchocerciasis and lymphatic filariasis. These programs distribute safe, low-cost drugs to curb or stop transmission. In some people, MDA also eases symptoms, but others may need additional treatment for relief.1
Filariasis is considered a neglected tropical disease. However, mansonellois remains one of the most neglected tropical diseases. It receives little attention from health programs, and it is not listed by the World Health Organization among neglected tropical diseases.
The signs and symptoms depend on the specific disease:1,2
The World Health Organization has updated information on:
Filariasis is caused by filarial nematodes transmitted by vectors such as mosquitoes (Anopheles, Culex), blackflies (Simulium) and biting midges (Culicoides). The specific parasites and the transmission of each subtype are as follows:1,2,5,6
The CDC has additional information:
While filariasis is rare in USA, it is endemic in many countries and represents a global health problem.1,2, 5,6
Onchocerciasis affects about 21 million people and more than 200 million need preventive treatment. Lymphatic filariasis affects about 51 million globally and there are about 863 million people at risk across 47 countries. Loiasis affects over 13 million infected in Central and West Africa. Mansonellosis affects more than 100 million people in Africa and other tropical countries and about 600 million people are at risk, mainly in Africa and parts of Latin America.1,2 In the U.S., the most common type of dirofilariasis that affects humans is Dirofilaria immitis. In Europe, it’s usually Dirofilaria repens. Both types have been found in human cases in other countries as well.5 There were an estimated 3.5 million Guinea worm cases occurring annually in 20 African and Asian countries in 1986, but today, through the Guinea Worm Eradication Program (GWEP), only a handful of countries continue to have the disease.6
Diagnosis can be made by examining a small blood sample under a microscope to identify the microscopic worms, called microfilariae. Doctors may also use a test that looks for antibodies that the immune system produces if a person is infected.1 Onchocerciasis is usually with a skin snip (thin skin biopsy) to look for immature worms through a microscope. Surgical removal of a lump (nodule) in the skin and examination for adult worms can also be useful. An eye exam can be done to evaluate signs of damage caused by immature worms, or for the worms themselves in both onchocerciasis and loiasis.1,4,5,6
Antibody tests against filarial antigens can also be useful. Other tests include molecular diagnosis such as PCR (polymerase chain reaction), a laboratory technique that can detect even small amounts of the parasite’s DNA for a more accurate diagnosis. Ultrasound for adult worms can be also used to evaluate organ damage.1
Human dirofilariasis is typically diagnosed by detecting coin lesions on chest X-rays, especially in infections caused by Dirofilaria immitis. Subcutaneous infections are identified by finding adult worms in biopsy samples. Diagnosis relies on examining the worm’s cuticle, muscles and lateral chords. Blood tests are not yet helpful in the diagnosis of dirofilariasis in humans.5
Dracunculiasis diagnosis is based on the typical appearance of a skin lesion with a protruding worm, commonly on a lower limb.6
Treatment
The primary aim of treatment for lymphatic filariasis is to eliminate the adult worms that cause the disease. The medication most often used is diethylcarbamazine citrate (DEC), which is effective against both the adult worms and their larvae, called microfilariae. In the United States, where lymphatic filariasis is very rare, DEC is not FDA-approved but can be obtained through the CDC after confirmed laboratory testing. Treatment usually involves either a single-day course or a 12-day course, both of which are generally equally effective. In cases of tropical pulmonary eosinophilia, a longer course of 14 to 21 days is recommended. DEC is typically well tolerated, though some people may have mild side effects such as headache, dizziness, nausea, fever, or muscle and joint pain.8,9
It is important to note that DEC is not safe for people who also have onchocerciasis (river blindness), as it can worsen eye and skin symptoms. Similarly, people with Loa loa infection may face life-threatening complications if treated with DEC, and specialist consultation is strongly recommended in these cases. Another drug, ivermectin, is effective against microfilariae but does not kill adult worms, while doxycycline taken for four to six weeks has shown some potential to reduce adult worm activity.4
For complications such as lymphedema or elephantiasis, antiparasitic medications are not helpful, as these conditions usually persist after the infection is no longer active. Instead, supportive care is recommended, including proper hygiene, exercise, wound care, infection prevention, limb elevation, appropriate footwear and in some people, specialized physiotherapy. Referral to a certified lymphedema therapist can be very beneficial. Limited evidence also suggests that doxycycline may help stabilize or slow the progression of lymphedema.4
When hydrocele develops, the most effective treatment is surgery (hydrocelectomy), as medications do not improve this condition.
A large study found that the most effective short-term treatment for lymphatic filariasis was taking multiple doses of diethylcarbamazine (DEC) with albendazole, which significantly reduced the number of microscopic worms in the blood within 6 to 12 months. Other regimens, like DEC followed by albendazole or the triple-drug combination therapy (ivermectin, DEC, albendazole) also showed good results but may not be suitable everywhere, especially in areas where onchocerciasis (river blindness) is common, since DEC can cause serious eye-related side effects. However, by 24 months, all treatments performed similarly, and no major differences in side effects were found between them, suggesting that several options are safe and effective, but the best choice depends on local health conditions and other co-existing infections.8
The World Health Organization (WHO) has the goal of eliminating these diseases as public health threats by 2030, but there is still much work to do and severe lack of resources for the people living in the endemic regions who need it the most.2,3
For additional information visit the WHO website about neglected tropical diseases.
For onchocerciasis, the main treatment is ivermectin. It kills the parasite’s larvae (microfilariae) but not the adult worms. Doxycycline can help by killing Wolbachia, a bacterium the adult worm needs to survive and to make new larvae. Older drugs like suramin and diethylcarbamazine are no longer recommended.5 Doxycycline needs extra caution. It can harm a fetus and should be avoided in pregnancy unless the situation is life‑threatening and no safer options work.10
The preferred treatment for loiasis is diethylcarbamazine (DEC). Most affected people are cured with one or two courses, meaning symptoms resolve, the high eosinophil count (a type of white blood cell) returns to normal and antifilarial antibody levels fall. DEC is favored because it kills both the larvae (microfilariae) and the adult worms, leading to faster recovery. Because of the risk of serious neurologic side effects, including rare fatal encephalopathy and rises with higher numbers of microfilariae in the blood, quantitative blood smears are required before starting treatment. For long‑term travelers to areas where loiasis is common, weekly DEC at 300 mg may be used to help prevent infection.11
If loiasis does not improve with DEC, a 21‑day course of albendazole taken twice daily may be helpful. Albendazole can also be used first to lower the microfilarial load before beginning DEC, but its effect is gradual and requires close, frequent monitoring to decide when DEC can be given safely. Short‑term worsening of symptoms such as Calabar swellings or itching can occur when treatment begins; some doctors use antihistamines or corticosteroids during the first week to ease these reactions, although steroids do not remove the small risk of encephalopathy with DEC. Loa loa does not carry Wolbachia bacteria, so doxycycline is not effective for this infection.11
For Mansonellosis (infections caused by Mansonella species, including M. perstans), there is no single established treatment. Drugs such as DEC and mebendazole have been used to reduce the number of parasites, but they may not fully clear the infection. Doxycycline is a more promising option when the parasites harbor the bacteria Wolbachia; studies in West Africa suggest many M. perstans do, and treatment with doxycycline lowered microfilariae levels, making it a reasonable first‑line choice when follow‑up testing is available. In places where Wolbachia status is unknown, testing can help guide therapy. Ivermectin, while widely used for other parasitic diseases, has shown limited benefit against Mansonella in many settings. In occasional cases, surgery may be needed to remove large adult worms, and mild cases may not require treatment.12,13,14
The definitive treatment of Dirofilaria infection in humans is surgical removal of lung granulomas and nodules under the skin; this treatment is also curative. In many people, no treatment with medicines is necessary.3,5
There is no effective medication or vaccine for dracunculiasis. Infected people do not become immune to subsequent infection. Treatment is a long painful process consisting of pulling out the emerging worm by rolling it around a piece of gauze or a small stick, a few centimeters a day, in combination with wound cleaning and dressing with antibiotic ointment to prevent secondary bacterial infection.6,7
For questions regarding diagnostic or treatment considerations, contact the CDC Division of Parasitic Diseases and Malaria: [email protected]. Diagnostic assistance is also available via DPDx.
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/
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