First evaluation of antibody responses to Culex quinquefasciatus salivary antigens as a serological biomarker of human exposure to Culex bites: A pilot study in Côte d'Ivoire

Abstract

Background: Culex mosquitoes are vectors for a variety of pathogens of public health concern. New indicators of exposure to Culex bites are needed to evaluate the risk of transmission of associated pathogens and to assess the efficacy of vector control strategies. An alternative to entomological indices is the serological measure of antibodies specific to mosquito salivary antigens. This study investigated whether the human IgG response to both the salivary gland extract and the 30 kDa salivary protein of Culex quinquefasciatus may represent a proxy of human exposure to Culex bites.

Methodology/principal findings: A multidisciplinary survey was conducted with children aged 1 to 14 years living in neighborhoods with varying exposure to Culex quinquefasciatus in the city of Bouaké, Côte d'Ivoire. Children living in sites with high exposure to Cx quinquefasciatus had a significantly higher IgG response to both salivary antigens compared with children living in the control site where only very few Culex were recorded. Moreover, children from any Culex-high exposed sites had significantly higher IgG responses only to the salivary gland extract compared with children from the control village, whereas no difference was noted in the anti-30 kDa IgG response. No significant differences were noted in the specific IgG responses between age and gender. Sites and the use of a bed net were associated with the level of IgG response to the salivary gland extract and to the 30 kDa antigen, respectively.

Conclusions/significance: These findings suggest that the IgG response to Culex salivary gland extracts is suitable as proxy of exposure; however, the specificity to the Culex genus needs further investigation. The lower antigenicity of the 30 kDa recombinant protein represents a limitation to its use. The high specificity of this protein to the Culex genus makes it an attractive candidate and other specific antibody responses might be more relevant as a biomarker of exposure. These epidemiological observations may form a starting point for additional work on developing serological biomarkers of Culex exposure.

Fig 1. Map of study areas in the city of Bouaké, Côte d’Ivoire.

Different study sites are hatched. Map source: https://www.openstreetmap.org/export#map=12/7.6821/-5.0039.

Fig 2. Alignment of arthropod protein orthologs of the 30 kDa protein from Cx. quinquefasciatus.

Species, accession numbers, percentage of protein coverage (cov), percentage of identical amino acid residues (pid) and amino acid positions are indicated. Residues identical to the reference sequence of Culex quinquefasciatus are highlighted in different colors according to the amino acid properties. For each species the protein homolog producing the best score was selected for the alignment.

Fig 3. IgG responses to Cx. quinquefasciatus SGE and the 30 kDa recombinant protein in the four study sites.

Each dot represents an individual and box plots indicate the median value, 25th and 75th percentile IgG response (ΔOD) against SGE (A) and the 30 kDa (B). The number of processed sera is indicated below (n). Significant p-values are indicated above the plots.

Fig 4. IgG responses to Cx. quinquefasciatus SGE and the 30 kDa recombinant protein according to level of exposure of sites.

Each dot represents the an individual and the box plots indicate the median value, 25th and 75th percentile IgG response (ΔOD) against SGE (A) and the 30 kDa (B). The number of processed sera is indicated below (n). Significant p-values are indicated above the plots.

Fig 5. Correlation between IgG specific response to Cx. quinquefasciatus SGE and the 30 kDa recombinant protein.

Scatter plot analysis of IgG responses to both salivary antigens is presented, and the ΔOD values among the 223 children are reported.