About Filarial Worms

Key points

  • Filarial worms are a type of microscopic parasitic worm.
  • They mainly spread through insect bites.
  • Symptoms from filarial worm infections can be minor (e.g., itching or swelling) but may be severe (e.g., blindness).
  • There are antiparasitic drugs that can treat filarial worm infections.
Community health worker sitting outside home, writing in notebook with woman and child looking on.


Filarial worms are a family of parasites that are found in tropical regions. A parasite is an organism (a living thing) that lives on or inside another organism. Once they infect a person, they can cause diseases that attack different parts of the body.


Symptoms of filarial worm infections range from itching and swelling to disfigurement and blindness. However, many people infected with filarial worms will have no symptoms.

Diseases and common symptoms caused by filarial worms include

  • Onchocerciasis, also known as river blindness, can cause itchy skin and skin changes and damage the eyes and may lead to blindness.
  • Lymphatic filariasis, sometimes called elephantiasis, can cause severe swelling of body parts, particularly legs, arms, genital area, and other parts of the body.
  • Loiasis, also known as Loa loa or African eye worm, can cause itchy, non-painful swellings on limbs or worms that move across the eye.
  • Mansonellosis, which can cause fever, fatigue, and joint and abdominal (belly) pain.

Causes and spread

Filarial worm diseases affect millions of people a year in Africa, South America, the Pacific islands, and Asia. They spread mostly through the bites of insects like blackflies, mosquitoes, or midges.

Tiny immature worms, known as larvae, will enter a human body when the insect bites into the skin. Once inside a person, they spread throughout the body, grow, and reproduce. When an insect bites an infected person, the insect can ingest the new larvae and eventually infect another person.


In most cases, the best way to prevent most filarial worm infections is to avoid insect bites. Wearing long-sleeved shirts and long pants, using insect repellent on exposed skin, and sleeping under mosquito nets will help prevent insects from biting you.


Medications known as antiparasitic drugs can treat new filarial worm infections. In people with advanced disease-causing chronic swelling, surgery or lymphedema care may be needed.

Onchocerciasis and lymphatic filariasis are currently the target of mass drug administration (MDA) campaigns. These campaigns deliver safe and inexpensive drugs aimed at reducing or eliminating transmission of these infections. For some, filaria MDA will reduce symptoms as well. For others, other treatments are needed for symptoms.