Natural infection of filarioid nematodes in mosquitoes: An approach to neglected disease xenosurveillance and prevention in intercontinental human transit areas in Darién.

BACKGROUND

Filarioid nematodes are significant vector-borne parasites affecting both humans and animals. Despite their importance, their distribution, ecological dynamics, and health implications remain poorly characterized in the Neotropics. This knowledge gap is particularly critical in high-risk areas like the Darién, a vital migratory corridor connecting the diverse ecosystems of South and Central America, where unregulated migration intersects with complex ecological and social dynamics, creating optimal conditions for the emergence and spread of filarial infections.

METHODOLOGY/PRINCIPAL FINDINGS: Ethics approval: This project was approved by the Bioethics Research Committee of Institute, Gorgas Memorial Institute for Health Studies (Approval Number: 073/CBI/ICGES/21). Mosquito sampling was conducted across four high-mobility localities in Darién Province, Panama (Metetí, San Vicente, El Real de Santa María, and Lajas Blancas), during five collection periods, yielding 2,331 specimens representing 57 species and 10 genera. The highest species richness was recorded in El Real (S = 39) and Metetí (S = 38). In an entomological surveillance conducted in Darién, Panama, mosquitoes were collected and molecularly screened for filarial DNA, revealing widespread parasite circulation with 29 out of 57 mosquito species found positive. Infection rates calculated for individual mosquitoes showed an overall rate of 12.0% (MLE of 18.7 per 1,000 in pools), exhibiting significant geographical heterogeneity and notably elevated rates in Uranotaenia species. Positive samples underwent COX1 gene sequencing and BLAST analysis, identifying a diverse range of filarial species, including Dirofilaria sp. 'hongkongensis', Brugia malayi, Onchocerca skrjabini, Setaria cervi, Onchocerca lienalis, Dirofilaria repens, and Wuchereria bancrofti; among these, six unique samples were identified with high confidence. The majority of positive mosquitoes (75.6%) were unfed, suggesting they had not recently blood-fed from a host.

CONCLUSIONS/SIGNIFICANCE: Our findings demonstrate the significant and widespread circulation of filarial parasites across diverse mosquito species in Darién, Panama. The identification of a broad range of filarial species, notably including Brugia-like species, highlights the complex dynamic of filarial parasite circulation in this region. The consistently elevated infection rates in Uranotaenia species, among others, underscore their potential critical role as vectors. This study provides essential entomological data, emphasizing the urgent need for continuous surveillance and targeted public health interventions to mitigate filarial transmission risks.