What are filarial worms?
Filarial worms are a group of parasitic worms that can infest any part of the body, including the skin. Filarial worms are not like the large worms found in the soil. Even though the idea of worms crawling under the skin may seem scary, these parasitic worms are usually very tiny organisms. Filarial worms can reside either within an organ or in the bloodstream. Eventually, parasitic infestation with these worms causes skin problems.
Worm infestations of the skin are relatively rare in developed nations such as the United States. Most cases of skin problems due to worm infestation occur in developing nations. However, filarial worms were common at one time in North America, especially in the southern states. Skin worm infestations are not the same as the common ringworm infection of the skin. The ringworm is not actually a worm.
Ringworm refers to a fungal infection of the skin caused by a group of fungi known as the dermatophytes. These dermatophytes have a predilection for the human skin, and frequently cause skin infections of the feet (athlete’s foot), scalp (tinea capitis), and groin (jock itch) areas. The name “ringworm” refers to the characteristic ring-shaped red rash that appears on the skin upon infection with these fungi.
Parasitic worms (also known as helminths), are entirely different organisms. There are thousands of helminth species, including the filarial worms that can cause human diseases.
Read more on human intestinal worms.
A disease caused by a filarial worm is technically referred to as filariasis. Filarial worms can cause infection in many parts of the body, including the skin, body cavities, and lymphatic system. The skin manifestations of filariasis are referred to as cutaneous filariasis. Filarial worms are also known as roundworms (nematodes), which belong to the family filarioidea. There are hundreds of filarial worm species.
However, only a few (about 8) can parasitize humans. Out of these 8 filarial species, only 3 are thought to contribute significantly to cutaneous filariasis. The three filarial species mainly responsible for cutaneous filariasis include Mansonella streptocerca (causing mansonelliasis), Loa loa (causing loiasis), and Onchocerca volvulus (causing onchocerciasis). Apart from these three nematode species, two other species may also cause significant cutaneous symptoms.
Body cavity filariasis is caused by Mansonella perstans and Mansonella ozzardi species of nematodes. Lymphatic filariasis is caused by Wuchereria bancrofti, Brugia timori and Brugia malayi species of nematodes. The nematodes that cause lymphatic filariasis can also cause significant injury to the skin.
Two other types of worms that can cause human disease are Dirofilaria worms (causing dirofilariasis) and Dracunculus medinensis (causing guinea worm disease). Dirofilariasis is a relatively uncommon disease since humans are not ideal hosts for the Dirofilaria worms. However, a significant increase in the incidence of dirofilariasis has occurred in the past few years. Dracunculus medinensis can emerge through the skin surface in guinea worm disease.
Causes of Cutaneous Filariasis
As described previously, cutaneous filariasis in humans is caused by three species of filarial worms. These three filarial worms are Loa loa, Mansonella streptocerca, and Onchocerca volvulus. Although all three filarial worms cause cutaneous filariasis, they differ in terms of the responsible insect vector, geographical distribution, life cycle, and symptoms.
Infestation with Loa loa causes loiasis. This worm is transmitted by two species of flies belonging to the genus Chrysops. These vectors are mostly found in the rain forests and swamps of West and Central Africa. Loiasis affects the skin on the face, breasts, forearms, wrists and legs. The eyes are also affected. The symptoms of loiasis include painful, red swellings (referred to as Calabar swellings), hives (urticaria), itching, lumps (granulomas or abscess) under the skin, and fever (occasionally). These symptoms may arise many years after the initial infection.
Infestation with Mansonella streptocerca causes mansonelliasis. The vector that spreads Mansonella streptocerca is the biting midge of the Culicoides genus. This vector is found in the forested areas of Africa. The symptoms produced in mansonelliasis include elevated skin rash, lumps (granulomas/abscesses) under the skin, enlarged lymph nodes that become rubbery and mobile, hyperpigmentation and thickening of the skin.
Infection with Onchocerca volvulus causes onchocerciasis (also known as leopard skin and river blindness). The vector responsible for spreading this disease is a blackfly the belongs to the Simulium genus. This vector is mainly found in East, West, and Central Africa. The Middle East and South American regions also harbor this vector.
Onchocerciasis affects both the skin and the eyes. Symptoms include a mild form of flat red rash, itching, hyperpigmentation, fever, joint pain, muscle pain and weight loss. Inflammation occurs in both the inner and outer eye structures. The eye inflammation may be severe enough to cause blindness.
Treatment and Management
Drugs are available for the treatment of cutaneous filariasis. However, the initial symptoms may take anywhere from a few days to a few years to appear. During this time, the affected person is usually unaware of the infestation and rarely seeks treatment. In the early stages of infestation, a person may be asymptomatic. The initial symptoms may be mild or vague.
Death of the worm within the body causes immune reaction against the proteins and bacterial components released from the dead worm. Granuloma formation and scarring occur due to the body’s attempt to wall off the dead worm. The following are some of the drugs that are used in the treatment and management of cutaneous filariasis:
- Antiparasitic drugs: Antiparasitic medications are used to kill the worms. Diethylcarbamazine (abbreviated as DEC) is used to kill Loa loa worms. Ivermectin drug is used to kill the Onchocerca volvulus worm. Suramin drug is rarely used to treat onchocerciasis because of its toxicity.
- Antibiotics: Antibiotics such as doxycycline can be used to sterilize or kill the worms. Antibiotics are also used to treat secondary bacterial infections caused after the death of the filarial worms. Treatment of secondary bacterial infections of the skin may require intravenous administration of antibiotics.
- Antihistamines: Antihistamines are used to control itching and inflammation caused by the filarial worms.
- Corticosteroids: Corticosteroids are helpful in controlling the inflammatory immune response towards the dead worms.
- Analgesics: Analgesics are used to provide relief from pain.
Prevention of Cutaneous Filariasis
While travelling through the developing regions of the world, precautions can be taken in order to avoid being bitten by vectors (biting flies and midges) that carry filarial worms. Correct types of repellent creams and sprays can be used. Insect screens and nets can also be effective preventive measures against contracting filariasis. Any prophylactic treatment should only be prescribed by a qualified doctor.