Clinical Treatment of Onchocerciasis

Ivermectin

The treatment of choice for onchocerciasis is ivermectin, which has shown to reduce the occurrence of blindness and to reduce the occurrence and severity of skin symptoms. Ivermectin kills the microfilariae but not adult worms. There is no evidence that prolonged daily treatment provides any benefit over annual treatment, as one dose results in a significant decrease in microfilarial load that lasts up to a year or more.

Treatment with higher-than-recommended doses is more likely to produce side effects and may be harmful. Although ivermectin does not kill the macrofilariae, it may does sterilize the adult female worms. There is evidence that treating people with ivermectin more frequently than once a year sterilizes the female worms , and that treating a person who no longer lives in an endemic area more frequently, such as every three to six months, could result in a shorter duration of symptoms.

Treatment for a patient who will not be returning to live in an endemic area should be given every six months for as long as there is evidence of continued infection. Dosing as frequently as every three months could be considered. Evidence of continued infection would include skin symptoms such as pruritus, microfilariae in skin biopsies, and microfilariae on eye exam.

Finding adult worms in nodules would not necessarily constitute evidence of the need for continued treatment, as ivermectin does not kill the adult worms and the adults do not cause symptoms. Treatment with ivermectin can cause mild symptoms associated with death of the microfilariae, such as increased itching, but there is no worsening of eye symptoms.

Severe adverse reactions to ivermectin in the absence of Loa loa co-infection are rare.

Doxycycline

Doxycycline has been shown in studies to kill Wolbachia, an endosymbiotic rickettsia-like bacterium that appears to be required for the survival of the O. volvulus adult worm and for embryogenesis. Treatment with a 6-week course of doxycycline has been shown to kill more than 60% of the adult female worms and to sterilize 80 – 90% of the females 20 months after treatment. Doxycycline does not kill the microfilariae, so treatment with ivermectin would be needed to result in a more rapid decrease of symptoms.

Most protocols that have examined the effectiveness of doxycycline had given treatment with ivermectin four to six months after treatment with doxycycline, so the safety of simultaneous treatment is not known. Treating with ivermectin one week prior to starting doxycycline would be reasonable. As doxycycline does not result in the rapid death of the parasites and as most of the mild side effects of ivermectin treatment are thought to be related to rapid release of Wolbachia antigens, the side effect profile of the medication when used for the treatment of onchocerciasis does not appear to be different than that of its use for other indications.

Older treatments for onchocerciasis, such as suramin and diethylcarbamazine, should not be used. Suramin has multiple systemic toxicities that limit its use in the presence of other less toxic and effective therapies. Diethylcarbamazine accelerates the development of onchocercal blindness.

*Doxycycline is not standard therapy, but several studies support its use and safety. Treatment with ivermectin should be given one week prior to treatment with doxycycline to provide symptom relief to the patient. If the patient cannot tolerate 200 mg PO daily of doxycycline, 100mg PO daily is sufficient to sterilize female Onchocerca.

Oral ivermectin and doxycycline are available for human use in the United States.

For questions regarding diagnostic or treatment considerations, contact the Division of Parasitic Diseases and Malaria: parasites@cdc.gov. Diagnostic assistance is also available via DPDx.

Care precautions

Ivermectin

Treatment during pregnancy

Ivermectin is a pregnancy category C drug. Data on the use of ivermectin in pregnant women are limited, though the available evidence suggests no difference in congenital abnormalities in the children of women who were accidentally treated during mass drug administration (MDA) campaigns with ivermectin compared with those who were not. The World Health Organization (WHO) excludes pregnant women from MDA campaigns that use ivermectin. In a pregnant woman infected with a soil-transmitted helminth, balance the risks of treatment for the fetus with the risks of disease progression in the woman in the absence of treatment.

Pregnancy Category C: Either studies in animals have revealed adverse effects on the fetus (teratogenic or embryocidal, or other) plus there are no controlled studies in women, or studies in women and animals are not available. Prescribe ivermectin only if the potential benefits in the woman justify the potential risks to the fetus.

Treatment during lactation

Ivermectin is excreted in low concentrations in human milk. Treat breastfeeding women with ivermectin only when the risks of disease progression in the untreated mother outweigh the risks to the infant.

Treatment in pediatric patients

The safe use of ivermectin in children weighing less than 15 kg (33 lbs) is unclear. According to the WHO guidelines for MDA campaigns, ivermectin can safely treat children at least 90 cm (35 in) tall. The WHO growth standard curves show that 50% of boys reach this height by age 28 months and 50% of girls by age 30 months. Some MDA campaigns use ivermectin to treat younger children who are able to swallow tablets safely, albeit at a reduced dose.

Doxycycline

Treatment during pregnancy

Doxycycline is in pregnancy category D. Doxycycline should not be used in pregnant women due to positive evidence of fetal risk. Doxycycline might be indicated in life-threatening situations where no other treatment is available.

Pregnancy Category D: There is positive evidence of human fetal risk, but the benefits from use in pregnant women may be acceptable despite the risk (e.g., if the drug is needed in a life-threatening situation or for a serious disease for which safer drugs cannot be used or are ineffective).

Treatment during lactation

Doxycycline is excreted in breast milk. The American Academy of Pediatrics classifies doxycycline as compatible with breastfeeding, whereas the World Health Organization (WHO) advises to avoid doxycycline in lactating women unless used for malaria. Dental staining and inhibition of bone growth in the infant may occur. Doxycycline should be used during lactation only if the potential benefit of therapy to the mother justifies the known risk to the infant.

Treatment in pediatric patients

Doxycycline is contraindicated in children aged eight years and younger as it may cause permanent discoloration of the teeth. The WHO recommends that doxycycline should be used only for life-threatening infections in children aged 8 years and younger. Use of doxycycline in children aged 8 and younger should be limited to instances when there are contraindications to the use of other appropriate antibiotics and the potential benefit justifies the known risk.