Diethylcarbamizine

Diethylcarbamazine (DEC) kills both microfilariae and adult Loa loa worms. Typical loiasis therapy consists of 6mg of DEC per kilogram body of weight per day administered orally for three weeks. DEC therapy is taken orally, three times per day following meals. A single course of DEC treatment typically resolves signs and symptoms of loiasis in half of those infected. A second course of DEC treatment cures half of remaining infected individuals. Levels of eosinophilia and antifilarial titters serve as indicators of treatment efficacy. No clinical or laboratory parameter appears to predict which patients will require multiple course of therapy (Klion et al., 1994). After DEC therapy dead worms sometimes surface and become visible under the skin. Mild side effects including pruritus and development of Calabar swellings (see Clinical Presentation section) have been reported with DEC use.

Patients with microfilaremia must use DEC with caution as the drug can cross the blood-brain barrier. Sudden death of many microfilariae can cause capillary blockage by dead and dying microfilariae in the brain, meninges, and retina, causing encephalopathy and death. In patients with more than 100 microfilariae per fifty cubic mm of afternoon blood, pretreatment with steroids should be considered before initiation of DEC therapy. Patients with extreme microfilaremia should be treated with 50 mg of DEC per day for several days before starting the typical three-week course of DEC treatment. Apheresis can be used to remove microfilariae from the blood before initiation of DEC therapy in highly microfilaremic individuals. Albendazole and ivermectin are also used to reduce microfilaremia prior to initiation of DEC therapy. Carme et al. report that even when precautionary measures such as small initials doses and steroid therapy are taken, DEC can still cause encephalitis (1991). This was found primarily in subjects presenting with high microfilarial loads.

Loa loa and Onchocerca volvulus have overlapping areas of endemicity and consequently many individuals are dually infected by both of these species. Diethylcarbamazine rapidly kills O. volvulus microfilariae, often resulting in severe side effects (Markell et al.). Therefore, coinfection with O. volvulus should be ruled out before DEC treatment is initiated. If co-infection with Onchocerca volvulus is suspected or verified, the Oxford Textbook of Medicine recommends that the patient be treated with ivermectin at the dosage of150 grams per kg of body weight to eliminate O. volvulus microfilariae before DEC therapy is initiated.

Ivermectin

Ivermectin is a semi-synthetic drug derived from avermactin, a macrocyclic lactone (Cully et al., 1994). Studies have shown that a single dose of 400 micrograms per kilogram of ivermectin is well tolerated and effectively reduces microfilaremia in subjects with parasitemia of under 7,700 microfilariae/ml (Martin-Prevel et al., 1993). Ivermectin effectively kills Loa loa microfilariae but has no apparent effect upon adult worms. Ivermectin appears to work by opening chloride-sensitive channels (Cully et al., 1994).

Ivermectin acts more slowly than DEC, so the acute reactions associated with rapid die off of microfilariae are typically avoided. Pruritius is the most common side effect of ivermectin use. However, patients with high levels of Loa loa microfilariae in the blood may develop encephalitis when treated with ivermectin (Gardon et al., 1997). Ivermectin has also been shown to induce hemorrhages of the palpebral conjunctiva in loiasis patients with high microfilaremia (Fobi et al., 2000).

Ivermectin is widely distributed throughout Central Africa through the World Bank's African Program for Onchocerciasis Control (Gardon et al., 1997). The program aims to eliminate Onchocerca volvulus from 19 African countries by means of community-based ivermectin treatment. In areas covered by the program where loiasis is also endemic, some patients with high levels of Loa loa microfilaremia develop encephalitis upon treatment with ivermectin (Gardon et al., 1997). Satellite maps have been created to identify regions of overlap between areas of high loiasis and onchocerciasis prevalence in order to modify plans for ivermectin distribution (Thomson et al., 2000).

Albendazole

A double-blind, placebo-controlled trail of Albenazole in subjects with loiasis found that the drug was capable of reducing levels of microfilariae, eosinophils, and anti-filarial IgG (Klion et al., 1993) at a dose of 200 mg twice daily for 21 days. No adverse side effects were noted. Albendazole appears to have a direct effect on adult Loa loa worms that results in a slow reduction in microfilaremia (Klion, 1993). Albendazole therapy appears to be effective in treating some loiasis patients that have remained uncured after multiple courses of DEC treatment (Klion et al., 1994). A single case of encephalopathy following treatment with albendazole has been reported (Blum et al., 2001). Further observation is needed to assess albendazole safety.

Surgical Removal

When migrating across the eye Loa loa are easily removed (as shown in the picture below) by pulling the worm through a small incision in the conjunctiva. Markell's Medical Parasitology suggests immobilizing worms with several drops of 10 percent cocaine instilled into the eye before excision.

Prophylaxis

Results of a double-blind placebo-controlled study of Peace Corps volunteers in Gabon, Cameroon, and the Central African Republic suggest that DEC effectively prevents infection with Loa loa in temporary residents of endemic areas (Nutman et al., 1988). The recommended dosage for use as prophylaxis is 300 mg DEC per week in adults during the period of possible exposure. To kill infective larvae and immature worms inoculated within the previous month, adults may take courses of 200 mg of DEC twice daily for three consecutive days. A possible side effect of this treatment is a minor papular reaction in the skin in the location of dead parasites.

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