Medical Care
Currently, three drugs are used to treat loiasis: diethylcarbamazine (DEC), albendazole (ALB), and ivermectin (IVM). The treatment strategy depends on the risk of adverse events, which is related to the patient’s microfilarial (mf) density. [33]
Microfilarial density below 2000 mf/mL
DEC can be administered straightaway. DEC is the only drug of the three to have a proven macrofilaricidal (lethal to adult worms) and microfilaricidal effects.
Start with 3 or 6 mg/day if microfilaremic or 50 mg/day if amicrofilaremic, divided into 2-3 doses. The dosage is doubled every day until 400 mg/day (or 8-10 mg/kg/day) is reached, lasting 3-4 weeks.
Antihistamines or corticosteroids may be useful initially to reduce the severity of adverse effects (eg, pruritus, angioedema, fever). However, a 2020 study found that, by one year following the first round of DEC treatment, L loa infection in both microfilaremic and amicrofilaremic patients had resolved to levels seen in uninfected individuals, with pretreatment corticosteroids or apheresis not affecting the efficacy of DEC. [34]
Several courses of DEC may be needed, although more than four courses is rarely indicated. In patients with DEC-refractory loiasis, a course of ALB (200 mg twice a day for 21 days) can be useful. Short courses of ALB likely have an embryotoxic effect (interrupts embryogenesis in adult female worms) and a macrofilaricidal effect.
Microfilarial densities between 2000 and 8000 mf/mL
Begin with a single dose of IVM of 150 µg/kg. Treatment with IVM can be repeated at intervals of 1-3 months to further reduce the microfilarial loads.
When the microfilaremia is less than 2000 mf/mL, a course of DEC can be started using the protocol above.
Microfilarial densities between 8000 and 30,000 mf/mL
IVM can also be given to reduce loads below 2000 mf/mL, with close surveillance/hospitalization during the first few days.
Alternatively, start with a course of ALB (200 mg twice daily for 21 days) to reduce the microfilarial load; then, continue with IVM treatment until 2000 mf/mL is reached.
Microfilarial densities above 30,000 mf/mL
ALB is probably the best option, although the effect of long courses of ALB has never been evaluated in patients with such high loads. DEC and IVM can induce potentially fatal encephalopathy in patients with loads over 30,000 mf/mL.
Apheresis, which rapidly reduces microfilarial loads by 75% after three sessions, has also been proposed but is expensive and unnecessary given the usually mild manifestations of loiasis.
DEC is not FDA-approved and is not readily available or sold in the United States but can be obtained through the CDC Drug Service after confirmed diagnosis (telephone: [404] 718-4745; email: parasites@cdc.gov). [35]
Surgical Care
To be surgically removed from a patient's eye, the L loa worm should be forcibly immobilized with forceps over the conjunctiva. An incision is then made in the conjunctiva to remove the worm. Surgical removal of the L loa worm from the eye is a temporizing but not definitive treatment, as the risk of invasion by other worms in the body persists. Surgery to remove migrating worms from the eye is generally safe and relieves symptoms from the transiting adult worm and allows for a definitive diagnosis with pathologic review of the specimen. Pilocarpine should not be used, since it is a known irritant to the adult L loa worm and may cause it to disappear into deeper tissue. [36]
Complications
In patients with high microfilarial loads, the administration of rapidly microfilaricidal agents, such as ivermectin and DEC, may cause serious adverse effects, often resulting from the immune response to dead microfilariae. These adverse effects may include encephalitis, [22] cardiomyopathy, [18] renal failure, and even death. [19] To avoid adverse reactions in these patients, albendazole or apheresis is first used to reduce microfilarial loads before other agents are given. [33]
However, a 2016 study showed that even 6 doses of 800-mg albendazole every 2 months for 24 months was not sufficient to reduce microfilaricidal loads to below 8100 mf/mL in patients whose initial levels exceeded30,000 mf/mL, suggesting a need to further study pretreatment methods. [37]
Co-infection with onchocerciasis (river blindness) is notable because ivermectin, the major treatment for onchocerciasis, often leads to severe or fatal complications in patients coinfected with L loa. Conversely, DEC, the primary treatment for low-level L loa infection, can result in a severe systemic reaction (Mazzotti reaction) in individuals with onchocerciasis. [38] In areas with high co-infection rates, a test-and-not-treat (TaNT) strategy may be used to exclude those with high L loa microfilarial density from ivermectin treatment. As shown in a 2017 study in Cameroon, such exclusions of those with over 20,000 mf/mL resulted in no serious adverse events. [39] Although more costly than routine ivermectin mass drug administration (MDA) ($2.20 per person in the population versus $4), the TaNT strategy remains affordable and offers significant safety and elimination benefits. [40]
In most patients, comorbid loiasis and onchocerciasis can also be treated safely via clearance of some microfilariae with ivermectin prior to DEC treatment. Alternatively, doxycycline, which has both microfilaricidal and macrofilaricidal activity in onchocerciasis owing to its effect on the intracellular bacteria Wolbachia can be used safely in patients coinfected with low levels of L loa. [41]
Consultations
The following specialists may be consulted in the management of loiasis:
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Ophthalmologist
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Infectious disease specialist
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Dermatologist
Prevention
L loa infection and loiasis are prevented by avoiding the bites of daytime biting competent vector flies in endemic areas. [7] This can be done using permethrin-treated clothing or screening, as well as DEET-containing repellents.
Chemoprophylaxis strategies have also been described, using diethylcarbamazine (DEC) 300 mg PO once weekly or DEC 200 mg twice daily for 3 days each month while in an endemic area for long periods. [42] Mass drug administration (MDA) of DEC may reduce transmission in these areas but is complicated by the high rate of coinfection with onchocerciasis and, in some cases, lymphatic filariasis, which introduces the risk of severe adverse effects. [7] However, MDA of ivermectin to treat onchocerciasis has also been shown to substantially reduce microfilarial density for L loa for at least one year with no risk of severe adverse effects in patients with a microfilarial density of less than 20,000 mf/mL. [43]
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Giemsa stained blood showing microfilaria of Loa loa with white blood cells present. Courtesy of Wikimedia Commons [Stefan Walkowski].
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A fly of the Chrysops genus. Courtesy of Flickr [Judy Gallagher].
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Map of the estimated prevalence of eye worm history in Africa. Courtesy of PLoS Neglected Tropical Diseases.
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Live adult Loa loa worm in the anterior chamber of the eye. Courtesy of PLoS Neglected Tropical Diseases.
