Differential Diagnosis for Filaria IGG4 Antibody Blood Test

Given the criteria of parasitic infections that cross-react with the Quest diagnostics Filaria IGG4 antibody blood test, are predominantly found in the USA, and present with skin sores and ulcers as a primary symptom, the following differential diagnosis is proposed:

• Single Most Likely Diagnosis

  • Leishmaniasis: This is due to its known cross-reactivity with filarial antibodies and its primary symptom of skin sores and ulcers. Leishmaniasis is caused by Leishmania parasites, transmitted by the bite of infected sandflies. Although not exclusively endemic to the USA, cases have been reported, particularly in Texas and Oklahoma.

• Other Likely Diagnoses

  • Lyme Disease: Caused by Borrelia burgdorferi, transmitted by ticks. While primarily known for its dermatological manifestation (erythema migrans), it can cause secondary skin lesions and has been reported to have some cross-reactivity with filarial antibodies in certain tests.
  • Chagas Disease: Caused by Trypanosoma cruzi, transmitted by triatomine bugs. It can cause skin lesions at the site of the bug bite and has been increasingly recognized in the southern United States. Cross-reactivity with filarial antibodies has been noted in some studies.

• Do Not Miss Diagnoses

  • Cutaneous Larva Migrans: Caused by the larvae of hookworms (Ancylostoma braziliense), typically acquired by walking barefoot on contaminated soil. It presents with a creeping eruption and can mimic other skin conditions. While not typically fatal, it can cause significant discomfort and should not be missed due to its ease of treatment.
  • Strongyloidiasis: Caused by Strongyloides stercoralis, a parasitic roundworm. It can cause skin symptoms, including a serpentine rash, and is particularly dangerous in immunocompromised patients due to the risk of hyperinfection syndrome, which can be fatal.

• Rare Diagnoses

  • Onchocerciasis (River Blindness): Caused by Onchocerca volvulus, transmitted by blackflies. While primarily associated with eye and skin lesions, it is rare in the USA, mostly seen in travelers to endemic areas. It can cross-react with filarial antibodies but is less likely given its rarity in the USA.
  • Loiasis: Caused by Loa loa, transmitted by deer flies. It can cause skin and eye lesions but is extremely rare in the USA, mostly diagnosed in travelers to West and Central Africa. Cross-reactivity with filarial antibodies has been reported, but its rarity makes it a less likely diagnosis.