Dose-dependent immune modulation in arboviral coinfections among febrile patients.
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BACKGROUND: Arboviruses pose substantial diagnostic and public health challenges in tropical regions where multiple pathogens co-circulate. Nigeria, with diverse ecological zones and limited surveillance infrastructure, represents a critical nexus for arboviral transmission, yet comprehensive data on seroprevalence, coinfection dynamics, immune modulation, and viral genetic diversity remain scarce. METHODS: We conducted cross-sectional surveillance across three Nigerian ecological zones from January 2019 to December 2023. Sera from 871 participants were tested for IgG and IgM antibodies to dengue virus (DENV), chikungunya virus (CHIKV), Zika virus (ZIKV), yellow fever virus (YFV), West Nile virus (WNV), and Rift Valley fever virus (RVFV) using immunoblot assays. A stratified subset (n=300) underwent cytokine profiling for interleukin-6 (IL-6), tumour necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ), and interleukin-10 (IL-10). IgM-positive samples underwent RT-PCR confirmation with genotype assignment through sequence comparison against GenBank reference strains. RESULTS: Overall IgM seropositivity indicating recent infection was 86.8% (756/871), with DENV most prevalent (59.6%; 95% CI: 56.3-62.8%), followed by CHIKV (49.4%), YFV (48.3%), ZIKV (19.7%), WNV (3.4%), and RVFV (2.3%). Coinfection with two or more arboviruses was detected in 61.2% (533/871) of participants. Seropositivity was highest in the tropical rainforest zone (94.2%) compared with Guinea savanna (84.5%) and Sudan savanna (80.4%; χ²=31.8, p<0.001). Cytokine profiling revealed significantly elevated concentrations of IL-6, TNF-α, IFN-γ, and IL-10 in dual and triple infections compared with mono-infections (all p<0.001), demonstrating dose-dependent immune modulation. All four DENV serotypes were identified, with DENV-2 predominating (59.9%). Molecular characterisation confirmed circulation of CHIKV East/Central/South African genotype (82.1%), DENV-2 Cosmopolitan genotype, and both African (71.2%) and Asian (28.8%) ZIKV lineages, with study sequences showing >99% nucleotide identity to established reference strains. CONCLUSIONS: These findings reveal extraordinarily high levels of arboviral infection and coinfection across Nigerian ecological zones. The dose-dependent cytokine elevation in coinfections suggests distinct immunopathological mechanisms. These data underscore the urgent need for multiplex diagnostics, genotype-specific monitoring, and climate-informed vector control strategies.