The treatment of filariaisis consists of chemotherapy directed against the adult worms (macrofilaricidal) and against the microfilariae (microfilaricidal) combined with symptomatic treatment to relieve the damage caused by the body's immunological reaction to dead or dying worms.

Macrofilaricidal drugs:

Suramin:

Also known as Antrypol this drug has a lethal action on adult W. bancrofti and other filarial parasites as well as some effect on microfilariae. Suramin was introduced in the 1920s for the treatment of African trypanosomiasis but it was subsequently found to be an effective treatment for filarial infections. Its mode of action is unknown however its high toxicity and the availability of other filarialicides has drastically reduced its use.

Toxicity: Immediate reactions include nausea and anaphylactic shock; 24 hours later photophobia and peripheral neuritis may occur. Agranulocytosis and haemolytic are uncommon however death of adult worms can lead to swelling of the effected area and abscess formation.

Macro- and Micro-filaricidal drugs:

Diethylcarbamazine:

Also known as Heterazan, Banocide, and Notezine this piperazine derivative is used mainly as a microfilaricide even though it does have macrofilaricidal properties . It is usually effective in treating Tropical Pulmonary Eosinophilia (TPE) and its mechanism of action is thought to involve sensitizing the microfilariae to phagocytosis.

Toxic Effects: There are no toxic effects on uninfected individuals. However, systemic adverse reactions (fevers,malaise, headache) are seen in microfilaraemic patients in proportion to the intensity of blood parasitaemia. These can be minimized by spreading the treatment into weekly low doses. Localized adverse reactions also occur, apparently around dying adult worms.

Microfilaricidal drugs:

Ivermectin:

Also known as Mectizan (22,23-dihydroavermectin B1) this drug is a semisynthetic macrocyclic lactone derivative of avermectine. It is an effective microfilaricide for most filarial species and W. bancrofti seems to be especially sensitive to its effects. Its mechanism of action is thought to involve the activation of GABA (gamma-aminobutyric acid) pathways and chloride channel permeability.

Toxic Effects: The lack of severe side effects, microfilaricidal activity, and single oral dose administration have encouraged its use. Adverse effects which include fever, myalgia, headache, sore throat, and cough are usually more prevalent in individuals with higher microfilaremic levels. Clinical use indicates that invermectin does not have macrofilarical effects upon adult worms unless used in multiple doses over a period of months.

Metrifonate:

Also known as trichlorphon this organophosphorus insecticide is also effective in treating nematode infections. It acts by inhibiting cholinesterases and thus paralysising the worm. It has been used clinically in the treatment of W. bancrofti infections and is an effective microfilaricide.

Toxic Effects: Although plasma cholinesterase levels fall and remain low for several weeks after the treatment, side effects are not severe. If the dose is increased above 10mg/kg vomiting, nausea and abdominal pain are frequent.

Benzimidazole derivatives:

Mebendazole stops the development of the embryos in onchocerciasis and when given in conjunction with levamisole both microfilaricidal and embryostatic effects can be achieved. Microfilarial counts in the blood fall slowly and the effects may last for up to six months.

Mebendazole:

Mebendazole is a potent antihelmintic with a wide range of activity against both nematodes and cestodes, and against both tissue stages of the parasite as well as against worms in the lumen and gut.As a drug it is poorly absorbed so high doses must be used when treating tissue infections (like filarial infections).

Toxicity: Side effects are unusual at lower doses but common when higher doses are given and fatalities have occurred when patients have been treated with very high doses.

Levamisole:

Levamisole acts by interfering with the carbohydrate metabolism of the nematodes and inhibiting the production of succinate dehydrogenase, causing muscular paralysis of the worms. It also acts as a non-humoral immunostimulant in immunosupressed individuals. The mechanism of this stimulation is unknown.

Toxicity: Side effects from this drug are unusual; however, when they occur they include nausea, vomiting, abdominal pain, dizziness, diarrhea, skin rashes, and transient neutropenia.

Symptomatic Treatment:

Lymphatic incompetence due to filarial infection causes lymph stasis and allows opportunistic microbial infections to develop. Antiseptic hygiene minimises these complications. Surgery can remove and provide bypasses around the damaged lymphatics.

Prevention:

There are currently no vaccines available to prevent filarial infections however control of mosquito vectors as well as the reduction of human reservoirs (through mass DEC treatment) has been effective reducing infection rates and seems to be a viable method of control for filariasis.