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The diagnosis of loaisis should be considered in any patient with a history of travel in an endemic area who presents with eye worm, Calabar swellings, or unexplained peripheral eosinophilia. Additionally any patient in whom therapy for lymphatic filariasis or onchocerciasis is anticipated who comes from a region of Africa co-endemic for loiasis should be screened for infection prior to initiating treatment because of the risk of fatal encephalopathy after treatment with diethylcarbamazine (DEC) or ivermectin.
The standard diagnostic test for the diagnosis of loiasis is demonstration of microfilariae (larvae) on a daytime (10AM to 2PM) Giemsa-stained thin or thick blood smear or demonstration of an adult worm removed from subcutaneous or subconjunctival tissue. It is important to note that the timing of the blood smear should be adjusted to reflect local time at the point of origin of a traveler who is still experiencing jetlag. Concentration techniques such as Nuclepore™ filtration (Whatman Inc, Florham Park, NJ), Knott's concentration, or saponin lysis may increase the diagnostic yield in person with low numbers of circulating microfilariae. Identification of microfilariae on blood smear is sufficient for diagnosis of the infection. Quantification of the number of microfilariae per mL would then be needed to direct treatment.
Identification of the adult worm on physical exam in a patient with significant exposure history or by a pathologist after its extraction from subcutaneous tissue would also be sufficient to make the diagnosis of infection. However, a blood smear would need to be performed for quantification of microfilarial load prior to the initiation of antiparasitic agents.
In patients in whom microfilariae are not visualized, blood tests are available to assist in making the diagnosis, though many are not available outside the research setting. There is a general screen for any filarial infection (including Wuchereria, Brugia, Onchocerca, and Mansonella infections) that is available in some specialty diagnostic labs. Because the test is highly sensitive, it is useful in determining if an individual has had filarial infection, but it is not specific enough to identify which filarial infection. As with any antibody test, the results indicate only that the patient has been exposed to the disease, but they do not indicate if the patient has an active infection. This distinction is less important in symptomatic travelers, but it limits the usefulness of the test in persons from endemic areas. One advantage of the test is that it can pick up evidence of infection in the pre-patent stage of infection. There are several Loa-specific serologic tests in existence, such as the tests for antibodies to the LlSXP-1 recombinant antigen which can be used in both an ELISA and a luciferase immunoprecipitation systems (LIPS) assay, but these are currently available only in the research setting and are not approved for diagnosis in the United States. There is one polymerase chain reaction (PCR) test for loiasis approved for diagnosis in the United Stated.
In general the diagnosis of L. loa infection should be made with blood smear. However, when blood smears are negative and clinical suspicion of infection is high, the general antibody test could be used in an attempt to exclude infection. If the general antibody test were positive, then it might be necessary to consider seeking additional diagnostic information by enlisting the assistance of researchers who perform antibody and/or PCR tests.
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.
Surgical excision of migrating adult worms is an effective treatment for symptoms localized to the migrating worm and provides an opportunity for diagnosis. Systemic therapy would be required to cure the infection unless the patient is infected with only a single adult worm.
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.
Loa loa, unlike many other filarial parasites, do not contain Wolbachia so doxycycline is not an effective treatment.
|Treatment||Indication||Adult Dose||Pediatric Dose|
|Diethylcarbamazine (DEC)||Symptomatic loiasis with MF/mL <8,000||8–10 mg/kg orally in 3 divided doses daily for 21 days||8–10 mg/kg orally in 3 divided doses daily for 21 days|
|Albendazole||Symptomatic loiasis, with MF/mL <8,000 and failed 2 rounds DEC
Symptomatic loiasis, with MF/ml ≥8,000 to reduce level to <8,000 prior to treatment with DEC
|200 mg orally twice daily for 21 days||200 mg orally twice daily for 21 days|
|Apheresis* followed by DEC||Symptomatic loiasis, with MF/mL ≥8,000||N/A||N/A|
MF = microfilariae of L. loa
* Apharesis should be performed at an institution with experience in using this therapeutic modality for loiasis.
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. Please see the onchocerciasis web pages for treatment recommendations.
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.
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