From the Guidelines
This positive Filariasis AB IGG4 test in a patient who has never left the United States is most likely a false positive result, and no treatment is recommended based solely on this serological finding without clinical symptoms or exposure history. The test should be repeated and additional diagnostic tests such as peripheral blood smear examination, antigen detection tests, or molecular tests should be considered if there is clinical suspicion 1. Filariasis is not endemic to the United States, and transmission requires specific mosquito vectors not commonly found in the US. False positive results can occur due to cross-reactivity with other helminth infections or autoimmune conditions. The IgG4 antibody test has limited specificity and can remain positive for years after infection, even after successful treatment.
- Key points to consider in the diagnosis of filariasis include:
- Microscopy of Giemsa-stained thick and thin blood films, which is the main diagnostic test for filariasis due to species of Wuchereria, Brugia, and Mansonella 1
- Examination of concentrated blood specimens, such as Knott, Nuclepore filtered blood, or buffy coat, which can increase sensitivity 1
- Serology does not differentiate between these filariae, and a positive test does not necessarily indicate active infection 1 If the patient has no symptoms such as lymphedema, elephantiasis, or recurrent fevers, watchful waiting with follow-up is appropriate rather than empiric anti-filarial treatment. Should symptoms develop or additional testing confirm infection, diethylcarbamazine, ivermectin, or albendazole might be indicated, but treatment should not be initiated based on this isolated serological finding alone. It is essential to note that the CDC provides a valuable telediagnostic consultation service that can be accessed through the DPDx website for both the laboratorian and clinician, which can aid in the diagnosis and management of parasitic infections, including filariasis 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.