Microfilaremic loiasis is associated with T cell hyporesponsiveness against SARS-CoV-2

Loiasis is a chronic filarial infection endemic to Central and West Africa. Although long considered benign, increasing evidence links loiasis to substantial morbidity and mortality. The infection is associated with immune modulation, including Th2-skewed responses and elevated regulatory cytokines. Clinically, loiasis is classified as microfilaremic (presence of circulating microfilariae) or amicrofilaremic ("occult") disease, the latter defined by a history of eyeworm migration without detectable microfilaremia. This study investigated how chronic L. loa infection influences antibody and T cell responses to SARS-CoV-2 following natural infection.

Between 2022 and 2024, this cross-sectional study was done in rural and periurban villages of the Ngounié and Moyen-Ogooué provinces of Gabon. Study procedures included diagnostics for loiasis and immunological assays. Microfilaremia was confirmed by stained blood smear microscopy, and occult disease was identified using the Rapid Assessment Procedure for Loiasis. SARS-CoV-2-specific IgG responses to spike and nucleocapsid proteins were measured by ELISA, and IFN-γ responses to spike antigen were assessed using an interferon-gamma release assay.

Overall, 192 participants were categorized as microfilaremic (n = 43), occult loiasis (n = 59), or without evidence of active loiasis (n = 90). IFN-γ responses were reduced in microfilaremic individuals compared with other participants (p = 0.031), whereas IgG responses did not differ. Subsequent analysis across the three groups confirmed that IFN-γ responses were lower in microfilaremic compared with occult participants (p = 0.012).

These findings suggest that microfilaremic loiasis may impair proinflammatory T cell responses to viral antigens, highlighting the need for further research into the broader immunological effects of Loa loa infection in endemic populations.