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. The patient's lack of travel history outside the US, combined with the fact that filariasis is not endemic to the US, makes it unlikely that they have a true infection 1.
Key Considerations
- The IgG4 antibody test can show significant cross-reactivity among helminths, including filaria, which can lead to false positive results 1.
- The patient should undergo further evaluation, including:
- A complete blood count with differential to check for eosinophilia
- Possibly a more specific test such as PCR or microscopic examination of blood for microfilariae if clinically indicated
- Filariasis transmission requires specific mosquito vectors not commonly found in the US, making it unlikely that the patient contracted the infection domestically.
Next Steps
- Observation without antiparasitic treatment is appropriate if the patient has no symptoms such as lymphedema, skin thickening, or recurrent fevers, and no eosinophilia is present.
- Should further testing suggest true infection despite no travel history, consultation with an infectious disease specialist would be warranted before initiating any treatment such as diethylcarbamazine, ivermectin, or albendazole.
Important Notes
- Antigen and nucleic acid detection methods should not be used to monitor response to therapy, since antigen or DNA may be detectable for days to weeks after successful treatment 1.
- NAATs for detecting blood and tissue parasites are currently available only from specialized laboratories and turnaround time may be prolonged 1.
From the Research
Filariasis AB IGG4 Test Results
- A patient has tested positive for Filariasis AB IGG4, indicating exposure to filarial parasites 2.
- 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
- Filariasis can be diagnosed through various methods, including identification of microfilariae in blood or skin samples, antigen detection, radiographic imaging, or polymerase chain reaction 2.
- Treatment options for filariasis include mass drug administration with diethylcarbamazine, ivermectin, and albendazole, which have been shown to be effective in reducing microfilarial levels 3, 4, 5.
IgG4 Response
- The kinetics of circulating human IgG4 after treatment of bancroftian filariasis have been studied, showing that IgG4 levels increase markedly after treatment and then decrease 6.
- The decrease in IgG4 levels is associated with treatment response, and posttreatment microfilaremia is inversely correlated with the decrease in IgG4 6.
Local Acquisition in the United States
- There is limited information available on locally acquired filariasis in the United States, and further investigation would be necessary to determine the source of the patient's infection.
- It is possible that the patient may have been infected through a rare case of local transmission or through travel to an endemic area prior to diagnosis.