From the Guidelines
This is likely a false positive result for filariasis, and treatment should not be initiated without further confirmation. Since the patient has never left the United States, true filariasis infection is highly unlikely as the disease is not endemic to the US 1. The Filariasis Ab IgG4 test can cross-react with other helminth infections or produce false positives due to other immunological conditions.
Key Considerations
- The patient's lack of travel history to endemic areas makes filariasis infection unlikely
- The IgG4 antibody test for filariasis has good sensitivity but imperfect specificity, especially in non-endemic regions
- False positives can occur in patients without travel history to endemic areas
Recommended Approach
I recommend not treating for filariasis at this time, but instead conducting additional testing to rule out other parasitic infections that might be present in the US, such as strongyloidiasis or toxocariasis. A complete blood count with differential to check for eosinophilia would be helpful, as would stool examination for ova and parasites. If the patient has no symptoms consistent with helminth infection (such as skin lesions, lymphedema, or unexplained eosinophilia) and other tests are negative, clinical monitoring without antiparasitic treatment is appropriate.
Additional Testing
- Complete blood count with differential to check for eosinophilia
- Stool examination for ova and parasites
- Consider serology tests for other parasitic infections, such as strongyloidiasis or toxocariasis, if clinically indicated. According to the 2018 guide to utilization of the microbiology laboratory for diagnosis of infectious diseases, serology tests are available for these infections, but their interpretation should be done with caution and in the context of clinical presentation 1.
From the Research
Filariasis AB IGG4 Test Results
- A patient has tested positive for Filariasis AB IGG4, indicating potential exposure to lymphatic filariasis.
- The patient has never left the United States, which may suggest a rare case of locally acquired filariasis or a false positive result.
Treatment and Diagnosis
- According to 2, filariasis can be diagnosed through various methods, including identification of microfilariae in blood or skin samples, antigen detection, radiographic imaging, or polymerase chain reaction.
- The World Health Organization recommends mass drug administration, including albendazole, diethylcarbamazine (DEC), and ivermectin, to control and eliminate lymphatic filariasis 3, 4, 5, 6.
Efficacy of Albendazole
- Studies have shown that albendazole alone or in combination with DEC or ivermectin has limited efficacy in clearing microfilaraemia or adult filarial worms 5, 6.
- A 2019 review found that albendazole makes little or no difference in microfilariae prevalence, antigenaemia prevalence, or adult worm prevalence detected by ultrasound 6.
Safety and Adverse Events
- The safety profile of albendazole, DEC, and ivermectin has been evaluated in several studies, with most adverse events being mild and self-limiting 3, 4.
- A 2016 study found that triple-drug therapy with DEC, albendazole, and ivermectin was safe and effective in reducing microfilariae levels, but also increased the frequency of adverse events compared to two-drug therapy 4.