Abstract
Insect saliva induces significant antibody responses associated with the intensity of exposure to bites and the risk of disease in humans. Several salivary biomarkers have been characterized to determine exposure intensity to Old World Anopheles mosquito species. However, new tools are needed to quantify the intensity of human exposure to Anopheles bites and understand the risk of malaria in low-transmission areas in the Americas. To address this need, we conducted proteomic and bioinformatic analyses of immunogenic candidate proteins present in the saliva of uninfected Anopheles albimanus from two separate colonies—one originating from Central America (STECLA strain) and one originating from South America (Cartagena strain). A ~65 kDa band was identified by IgG antibodies in serum samples from healthy volunteers living in a malaria endemic area in Colombia, and a total of five peptides were designed from the sequences of two immunogenic candidate proteins that were shared by both strains. ELISA-based testing of human IgG antibody levels against the peptides revealed that the transferrin-derived peptides, TRANS-P1, TRANS-P2 and a salivary peroxidase peptide (PEROX-P3) were able to distinguish between malaria-infected and uninfected groups. Interestingly, IgG antibody levels against PEROX-P3 were significantly lower in people that have never experienced malaria, suggesting that it may be a good marker for mosquito bite exposure in naïve populations such as travelers and deployed military personnel. In addition, the strength of the differences in the IgG levels against the peptides varied according to location, suggesting that the peptides may able to detect differences in intensities of bite exposure according to the mosquito population density. Thus, the An. albimanus salivary peptides TRANS-P1, TRANS-P2, and PEROX-P3 are promising biomarkers that could be exploited in a quantitative immunoassay for determination of human-vector contact and calculation of disease risk.
Highlights
In spite of a significant decrease in malaria cases over the past decade, malaria is still an important public health concern in the Americas
When comparing immunoglobulin G (IgG) antibody levels and malaria infection status, we found that samples with active malaria infection had significantly higher antibody levels than the controls for all the peptides, with the exception of the IgG levels against PEROX-P1 in Turbo (p = 0.7614) and PEROX-P2 in El Bagre (p = 0.5343) (Figure 4)
Our results showed no significant differences in IgG levels among the control groups for TRANS-P1 and TRANS-P2 (Figure 5)
Summary
In spite of a significant decrease in malaria cases over the past decade, malaria is still an important public health concern in the Americas. Plasmodium falciparum accounts for ~25% of infections, with the majority of cases reported due to infections with P. vivax (~74.1%) [1] (WHO, 2018). In Colombia, malaria exhibits unstable epidemic/endemic patterns characterized by differing intensities and segregation between regions [2,3]. This diversity in malaria transmission is favored by the variety of geographic regions with differing climates and abundance variety of anopheline vectors [4]. An. albimanus, An. Darlingi, and An. nuñeztovari are the vectors considered responsible for the majority of malaria transmission in Colombia [5,6,7]. As in the rest of the continent, most malaria cases in Colombia are caused by P. vivax (70%). Along the Pacific coast, P. falciparum is predominant and is associated with the largely Afro-Colombian communities with many Duffy-negative individuals [2]
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