Filaria Antibody (IgG4)

The filaria IgG4 assay may be helpful in the diagnosis of infections with major filaria parasites, including Wuchereria brancrofti, Brugia malayi, Onchocerca volvulus, and Dirofilaria immitis. Because cross-reactivity may occur in infections with other nematodes, identification of parasites in blood or other body fluid remains the definitive means of diagnosis [2]. A negative result on this test does not rule out chronic filarial infection.

W bancrofti and B malayi cause lymphatic filariasis, a disease transmitted by mosquitoes and characterized by swollen lymph nodes, shaking chills, body aches, fever, and edema in the extremities and genitals [1]. Lymphatic filariasis is common in tropical and subtropical regions of Africa, Asia, and South America. Most cases in the United States are seen among immigrants or visitors from endemic countries and, sometimes, individuals who travel from the United States to endemic countries [1,2].

O volvulus is transmitted to humans through bites of black flies in Africa, Latin America, and the Middle East. The infection mostly affects skin, lymph nodes, and eyes. Severe ocular lesions can lead to blindness known as "river blindness" [2,3].

D immitis, also known as dog heartworms, infects dogs, wild canids, and humans through mosquito bites worldwide, including in North America. Infected humans are usually symptomatic. Occasionally, dying adult worms in pulmonary arteries cause nonspecific symptoms such as coughing, low-grade fever, and chest pain [2,4].

Generally, clinicians order this test when individuals from regions endemic for filariasis present with symptoms consistent with the infection. Early diagnosis of disease at the subclinical level may decrease the risk of complications [1,2].

The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.

References
1. National Organization of Rare Diseases. Filariasis. Accessed September 21, 2021. https://rarediseases.org/rare-diseases/filariasis/
2. Carroll KC, et al. Manual of Clinical Microbiology. 12th ed. ASM Press; 2019. Accessed September 21, 2021. https://www.clinmicronow.org/doi/full/10.1128/9781683670438.MCM.ch147_1
3. Center for Disease Control and Prevention. Onchocerciasis. Accessed September 21, 2021. https://www.cdc.gov/dpdx/onchocerciasis/
4. Center for Disease Control and Prevention. Dirofilariasis. Accessed September 21, 2021. https://www.cdc.gov/parasites/dirofilariasis/

Methodology: Immunoassay (IA)