Filariasis is an infectious disease that spreads through mosquito bites. Some people have no symptoms. Others may have inflammation, swelling or fever. Filariasis can lead to lymphedema (fluid retention) or hydrocele (swelling in the scrotum). You can prevent filariasis by avoiding mosquito bites if you live in or travel to tropical climates.


What is filariasis?

Filariasis (fill-a-RYE-a-sus) is an infectious disease. It can lead to inflammation, swelling and fever. Without treatment, filariasis can cause health complications.

In the most severe cases, it can cause disfigurement, such as thickening skin and swelling in your calves. Because of this disfigurement, some people refer to filariasis as elephantiasis.

You get filariasis through tiny parasitic worms (filarial worms) that infect your lymphatic system. The lymphatic system balances fluid levels and helps protect your body from infections. Healthcare providers sometimes call the condition lymphatic filariasis because it affects your lymphatic system.


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Who might get filariasis?

Filariasis is most common in tropical climates. Countries in Asia, Africa and South America have higher cases of filariasis infection. The condition is rare in North America. The worms that cause filariasis don’t live in the United States.

People rarely get a filariasis infection during a short visit to one of these countries. You are more likely to get filariasis if you stay in a high-risk area for months or years.

How common is filariasis?

About 120 million people worldwide — 1.5% of the world’s population — have a filariasis infection.


Symptoms and Causes

What causes filariasis?

Filariasis is a parasitic infection with a type of roundworm. Tiny worms, too small to see with the naked eye, invade your body. Under a microscope, the filarial worms look like threads.

There are several types of filarial worms:

  • Wuchereria bancrofti causes 9 out of 10 infections.
  • Brugia malayi leads to most of the remaining cases of the disease.
  • Brugia timori also can cause infection.

What are the symptoms of lymphatic filariasis?

About two in every three people who have lymphatic filariasis don’t have severe symptoms. But filariasis usually leads to a weakened immune system.

Some people may experience:

  • Inflammation — an overactivated immune system.
  • Lymphedema — fluid buildup in your lymphatic system.
  • Hydrocele — swelling and fluid buildup in the scrotum.
  • Edema — swelling and fluid buildup in your arms, legs, breasts and female genitals (vulva).


What are the complications of lymphatic filariasis?

Over time, damage to your lymphatic system may make it difficult for your body to fight infections. Because of this lowered immune response, you may develop:

  • Frequent bacterial infections.
  • Elephantiasis — thickened and hardened skin and fluid retention, leading to painful, swollen and enlarged body parts.
  • Tropical pulmonary eosinophilia syndrome — an increase in white blood cells that causes coughing and difficulty breathing.

How does filariasis spread?

Filariasis spreads through mosquito bites. When a mosquito bites someone who has filariasis, the filarial worms in the person’s blood infect the mosquito. Then, when the infected mosquito bites another person, the worms pass into that person’s bloodstream.

When these worms enter your bloodstream, they travel to your lymphatic system. There, they grow into adult worms. The adult worms stay alive for up to seven years. The filarial worms reproduce and release millions of worms into your bloodstream.

Diagnosis and Tests

How is filariasis diagnosed?

To diagnose lymphatic filariasis, healthcare providers need to examine a blood sample. They may use:

  • Microscopic testing: Providers may view your blood sample under a microscope. The microscope allows them to see if your blood has any filarial worms. Filarial worms are nocturnally periodic, meaning they only move in your blood at nighttime. Because of this, you may need to get your blood drawn at night.
  • Antibody testing: Providers may measure your blood sample for antibodies. Your body creates antibodies in response to an infection. You can have this test during the day.

Management and Treatment

How is filariasis treated?

Your treatment plan varies depending on what symptoms you have and how severe they are. In general, filariasis treatment may include:

  • Medication: You may take anti-parasitic medicines such as ivermectin (Stromectol®), diethylcarbamazine (Hetrazan®) or albendazole (Albenza®). These drugs destroy the adult worms in your blood or keep them from reproducing. Taking these medicines can also prevent passing the infection to someone else. Because the worms may still live in your body, you take these medicines once a year for a few weeks at a time.
  • Surgery: You may have surgery to remove dead worms from your bloodstream. If filariasis has caused hydrocele, you may also have surgery to relieve fluid buildup in your scrotum.
  • Elephantiasis management: Your healthcare provider may also recommend strategies to manage swelling, such as elevation or compression garments.

Are there side effects of filariasis treatment?

If you're taking filariasis medications, you need careful monitoring from a healthcare provider. Anti-parasitic medications can lead to severe side effects. Some of these side effects include:

How can I keep lymphedema from worsening?

Even if medication kills the filarial worms, you can still develop lymphedema. To manage lymphedema symptoms, you can:

  • Disinfect and cover any wounds.
  • Elevate (raise) swollen arms or legs.
  • Exercise to improve the flow of lymphatic fluid.
  • Wash and dry swollen areas of your body daily.
  • Wear properly fitted shoes to reduce your risk of falling and getting injured.

Is there a cure for lymphatic filariasis?

There's no vaccine or cure for filariasis. Medication can kill many of the worms and keep you from spreading the infection to someone else. Treatment can also reduce filariasis symptoms.


How can I prevent filariasis?

The best way to prevent filariasis is to avoid mosquito bites, particularly in tropical areas. If you live in or travel to places where a filariasis infection is possible, take the following steps to prevent mosquito bites:

  • Sleep under a mosquito net.
  • Use insect repellent on exposed skin, especially at night.
  • Wear long pants and long sleeves.

In parts of the world where filariasis is common, the World Health Organization recommends treating whole regions with preventive chemotherapy. With this prevention strategy, people at risk of infection take an annual dose of specific chemotherapy medications.

The medications have a small effect on adult worms but can keep younger worms from reproducing. They can also prevent the parasites from spreading to mosquitoes.

Outlook / Prognosis

Are there long-term effects of lymphatic filariasis?

Filariasis may develop into chronic conditions such as lymphedema or elephantiasis. These conditions have no cure, although you can manage them and reduce symptoms.

People who have these chronic conditions often experience negative social impacts. If they have very visible, severe symptoms such as extreme swelling, they may experience social stigma. Chronic swelling or pain may also impact a person’s ability to work.

Living With

What else should I ask my doctor?

You may also want to ask your healthcare provider:

  • What is the most likely cause of filariasis infection?
  • How can I manage symptoms related to filariasis?
  • What treatment do you recommend for filariasis?
  • Are there any side effects of treatment?
  • What are the chances that an infection will return after treatment?
  • How can I prevent lymphatic filariasis?

A note from Cleveland Clinic

Lymphatic filariasis is a parasitic infection. It is common in tropical climates and rare in North America. The disease spreads through mosquito bites. These mosquitos carry small worms that travel through your bloodstream to your lymph system. Many people have no visible symptoms, while others develop chronic inflammation and swelling. A yearly medication may reduce the number of worms in your bloodstream and reduce symptoms. To prevent infection, it’s important to protect yourself from mosquito bites.

Medically Reviewed

Last reviewed on 10/15/2021.

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