Disease-carrying mosquito species tied to deforestation

Two University of Florida infectious disease experts have found deforestation not only destroys beneficial habitats and renders the land less fertile, it also allows disease-carrying mosquitoes to multiply.

An analysis of published data on deforestation and mosquitoes found that deforested tropical regions held more potentially harmful mosquito species than pristine tropical forests.

“Converting pristine tropical forests into areas for agriculture or other uses creates a habitat for the mosquitoes that transmit human diseases,” said Nathan Burkett-Cadena, Ph.D., an assistant professor of entomology at UF’s Florida Medical Entomology Laboratory and the lead author of the study.

After comparing data from multiple studies of deforestation and viral diseases, the analysis found a strong correlation between deforestation in tropical habitats and an overall higher concentration of mosquitoes capable of carrying human pathogens within those habitats.

Burkett-Cadena created the methodology used to analyze findings from the studies the researchers pulled from a biomedical research database.

In an earlier study, Amy Vittor, M.D., Ph.D., an assistant professor of medicine in the UF College of Medicine’s division of infectious diseases and global medicine, found the number of mosquitos carrying malaria was significantly higher in deforested regions of the Amazon.

This analysis, however, took vectors of viral diseases into account. Data from 17 studies were considered with the main criterion being that each study had to incorporate findings on mosquitoes in deforested and forested sites from around the world.

The authors found 56.5 percent of the mosquito species in deforested areas were confirmed vectors of human disease. In contrast, of the species occurring in forested areas, only 27.5 percent were vectors. Furthermore, mosquito species capable of carrying multiple human pathogens all favored deforested habitats.These included Aedes aegypti, the mosquito that transmits the dengue, West Nile, yellow fever and Zika viruses.

“While there are mosquitoes everywhere, more mosquitoes tend to be vectors of disease in deforested areas,” said Amy Vittor, who is also a member of UF’s Emerging Pathogens Institute. Vittor and Burkett-Cadena were co-authors of the study.

In addition to the data on viral diseases like West Nile and Zika, the article, published in the September issue of Basic and Applied Ecology, shows that deforested areas have higher concentrations of the vectors for malaria and lymphatic filariasis.

The authors speculate that this trend is due to evolutionary processes driving pathogens and their vectors to adapt to human landscapes. Since humans tend to be more concentrated in these areas, those species that prefer humans may experience selective pressure to adapt to the ecological changes.

Deforested areas are both warmer and drier than similar pristine forests, and studies of Anopheles gambiae, which transmits malaria, have shown that increased larval heat tolerance may have allowed this species of mosquito to widen its range beyond tropical rainforests around the same time early humans were converting central African rainforests into savannah.

Vittor hopes this study will provide a bird’s-eye view of the relationship between deforestation and disease.

“The last couple of decades have seen an increase in efforts looking into the association between deforestation and specific diseases,” Vittor said. “Here we’re taking a global view, comparing the distribution of mosquito species capable of carrying disease in deforested and forested areas in the tropics.”

For more information, read the full article in Basic and Applied Ecology: https://doi.org/10.1016/j.baae.2017.09.012