Human occupation, not forest structure, determines sand fly abundance in the Amazon

Area of Science:

• Ecology
• Vector-borne diseases
• Environmental science

Background:

• Phlebotomine sand flies transmit Leishmania spp., causing American cutaneous leishmaniasis (ACL) in deforested Amazonian regions.
• Landscape changes affect vector ecology and disease transmission, but the impact of forest cover, configuration, and deforestation timing is unclear.

Purpose of the Study:

• To investigate how landscape composition, configuration at various scales, and deforestation timeline influence sand fly abundance and Leishmania infection.
• Study conducted in Cruzeiro do Sul, Acre, Brazil.

Main Methods:

• Sand flies collected in 2022 and 2024 from 20 sites.
• Landscape metrics (forest cover, edge density) analyzed at 3, 5, and 7 km² scales.
• Deforestation timeline (time since forest loss) used as a proxy for human occupation duration.
• Bayesian regression models (negative binomial for abundance, binomial for infection) applied.
• Quantitative PCR and Sanger sequencing used for Leishmania infection detection.

Main Results:

• Forest cover and edge density showed no association with sand fly abundance or Leishmania infection.
• Longer deforestation timelines correlated with increased sand fly abundance, primarily due to Nyssomyia antunesi.
• No landscape variable clearly associated with Leishmania infection occurrence.

Conclusions:

• Sand fly abundance is linked to the duration of human occupation, not current forest structure, in this Amazonian frontier.
• Vector populations can persist in human-modified landscapes.
• Deforestation timeline is crucial for ACL surveillance and risk assessment.