Loa loa filariasis medical therapy
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Kalsang Dolma, M.B.B.S.[2]
Overview
Treatment of loiasis involves chemotherapy or, in some cases, surgical removal of adult worms followed by systemic treatment. The current drug of choice for therapy is diethylcarbamazine (DEC). The recommend dosage of DEC is 8 - 10 mg/kg/d taken three times daily for 12 days. The pediatric dose is the same. DEC is effective against microfilariae and somewhat effective against macrofilariae (adult worms).[1]
In patients with high microfilaria load, however, treatment with DEC may be contraindicated, as the rapid microfilaricidal actions of the drug can provoke encephalopathy. In these cases, albendazole administration has proved helpful, and superior to ivermectin, which can also be risky despite is slower-acting microfilaricidal effects.[1]
Medical Therapy
The treatment of loiasis is complex and is best undertaken after consultation with experts who have experience in the treatment of the disease and prevention of complications of treatment. Additionally, there may be times when it is best not to treat the infection. The drug of choice for the treatment of loiasis in patients without detectable microfilariae is diethylcarbamazine (DEC). Most patients will achieve cure, defined as resolution of symptoms, resolution of eosinophilia, and decreasing antifilarial antibody titers, with one or two courses of DEC. Some will require additional courses of DEC or a trial of albendazole. DEC is the treatment of choice because there is solid evidence that it kills both the microfilariae and the adult worms, resulting in quicker resolution of the infection. DEC can also be used to prevent infection in long-term travelers to endemic areas. The prophylactic dose is 300mg orally once a week. There is some evidence that albendazole given 200mg twice daily for 21 days may be an effective treatment for loiasis that is refractory to DEC treatment. It may also be used to reduce microfilarial load prior to initiation of DEC treatment. As albendazole's mechanism of action is believed to be an embryotoxic effect and possibly a directly toxic effect on the adult worms, both of which reduce microfilaraemia levels more slowly than DEC, it does not appear to be prone to causing encephalopathy, though published data are limited. Treatment of loiasis with antiparasitic agents may result in a brief increase of symptoms, such as Calabar swelling or pruritus. Some authors suggest that these symptoms might be attenuated with the concomitant use of antihistamines or corticosteroids during the first seven days of treatment. There is also the risk of fatal encephalopathy with DEC treatment; this risk has not been shown to be eliminated by corticosteroid treatment. More details on this are given below the treatment table.
Note on Risk of Fatal Encephalopathy When Treating Loiasis
Available data demonstrate that the risk of fatal encephalopathy in patients treated with DEC with microfilarial loads <8,000 microfilariae per mL approaches zero. In those patients with microfilarial loads ≥8,000 microfilariae per mL, apheresis can be used in specialized centers to reduce the load below the 8,000 threshold prior to beginning treatment. Some authors suggest a more conservative threshold of 2,500 microfilariae per mL for the initiation of treatment of loaisis. This lower threshold would need to be balanced with the risk associated with apheresis. There are some data available that suggest treating the patient with albendazole, 200mg twice daily for 21 day, may reduce the microfilarial load to acceptable levels, though re-measurement of levels after albendazole treatment would be required prior to treatment with DEC.
Note on Treatment in Pediatric Patients
DEC is not typically given to children under 2 years old. Albendazole can be given to children as young as 12 months old, though a reduction in dose may be required.
Note on Treatment in Pregnancy
DEC and albendazole are contraindicated in pregnancy and should be used only if the benefit of treatment outweighs the risk. Both medications are pregnancy category C, though malformations have not been reported in humans.
Note on Treatment in Patients with O. Volvulus Co-infection
DEC is contraindicated in persons with onchocerciasis because of a risk of blindness and/or severe exacerbation of skin disease.
Note on Obtaining the Medication
Diethylcarbamazine (DEC) has been used worldwide for more than 50 years. Because this infection is rare in the U.S., the drug is no longer approved by the Food and Drug Administration (FDA) and cannot be sold in the U.S. Physicians can obtain the medication from CDC after confirmed positive lab results. Loa loa, unlike many other filarial parasites, do not contain Wolbachia so doxycycline is not an effective treatment.
- Shown below is a table summarizing the preferred treatment for Loa loa filariasis [2]
| Characteristics of the Patient | Possible Pathogens | Preferred Treatment | Duration of Treatment |
| Symptomatic loiasis with MF/mL <8,000 | Loa loa | Diethylcarbamazine (DEC)
8–10 mg/kg orally in 3 divided doses daily |
For 21 days |
| Symptomatic loiasis, with MF/mL <8,000 and failed 2 rounds DEC
OR Symptomatic loiasis, with MF/ml ≥8,000 to reduce level to <8,000 prior to treatment with DEC |
Loa loa | Albendazole
200 mg orally twice daily |
For 21 days |
| Symptomatic loiasis, with MF/mL ≥8,000 | Apheresis* followed by DEC | N/A | N/A |
(*)Apharesis should be performed at an institution with experience in using this therapeutic modality for loiasis.
References
- ↑ 1.0 1.1 The Medical Letter – Filariasis. Available online at: http://www.dpd.cdc.gov/dpdx/HTML/PDF_Files/MedLetter/Filariasis.pdf.
- ↑ http://www.cdc.gov/parasites/loiasis/health_professionals/index.html#tx