Differential Diagnosis for Positive Filaria IGG4 AB Test

When a person tests positive for the Quest diagnostics Filaria IGG4 AB test, it indicates exposure to filarial parasites. The differential diagnosis can be categorized as follows:

• Single Most Likely Diagnosis
  • Wuchereria bancrofti infection: This is the most common cause of filariasis worldwide and is likely to be the primary consideration in areas where this parasite is endemic. The IGG4 antibody response is a marker of current or past infection.
• Other Likely Diagnoses
  • Brugia malayi infection: Another common filarial parasite, especially in Southeast Asia, which can also induce an IGG4 antibody response.
  • Brugia timori infection: Found primarily in Indonesia, this parasite can cause similar symptoms and induce a positive IGG4 test.
  • Loa loa infection: Although less common, Loa loa can also induce an immune response that might cross-react with the Filaria IGG4 AB test, especially in individuals from Central and West Africa.
• Do Not Miss Diagnoses
  • Mansonella ozzardi infection: While less common, Mansonella ozzardi can cause filariasis and is found in the Americas. Missing this diagnosis could lead to untreated disease with potential long-term consequences.
  • Mansonella perstans infection: Similar to Mansonella ozzardi, this parasite can cause a milder form of filariasis but is important not to miss due to its potential for causing chronic disease.
  • Mansonella streptocerca infection: Found in Africa, this parasite causes a skin form of filariasis. Although rare, it's crucial not to miss due to its potential for causing significant skin lesions and discomfort.
• Rare Diagnoses
  • Dirofilaria infection: Typically found in animals, Dirofilaria can rarely infect humans, causing dirofilariasis. While the IGG4 test might not be specific for Dirofilaria, cross-reactivity could potentially occur.
  • Other non-filarial parasitic infections: Certain other parasitic infections might induce a cross-reactive immune response that could lead to a false-positive IGG4 test. These would be considered rare and would depend on the individual's travel history and exposure risks.

Each of these diagnoses should be considered in the context of the patient's travel history, symptoms, and exposure risks. Further testing and clinical evaluation may be necessary to confirm the specific type of filarial infection or to rule out other causes of the positive test result.