Co-occurrence of viruses and mosquitoes at the vectors' optimal climate range: An underestimated risk to temperate regions?

PLoS Negl Trop Dis. 2017 Jun 15;11(6):e0005604. doi: 10.1371/journal.pntd.0005604. eCollection 2017 Jun.

Abstract

Mosquito-borne viruses have been estimated to cause over 100 million cases of human disease annually. Many methodologies have been developed to help identify areas most at risk from transmission of these viruses. However, generally, these methodologies focus predominantly on the effects of climate on either the vectors or the pathogens they spread, and do not consider the dynamic interaction between the optimal conditions for both vector and virus. Here, we use a new approach that considers the complex interplay between the optimal temperature for virus transmission, and the optimal climate for the mosquito vectors. Using published geolocated data we identified temperature and rainfall ranges in which a number of mosquito vectors have been observed to co-occur with West Nile virus, dengue virus or chikungunya virus. We then investigated whether the optimal climate for co-occurrence of vector and virus varies between "warmer" and "cooler" adapted vectors for the same virus. We found that different mosquito vectors co-occur with the same virus at different temperatures, despite significant overlap in vector temperature ranges. Specifically, we found that co-occurrence correlates with the optimal climatic conditions for the respective vector; cooler-adapted mosquitoes tend to co-occur with the same virus in cooler conditions than their warmer-adapted counterparts. We conclude that mosquitoes appear to be most able to transmit virus in the mosquitoes' optimal climate range, and hypothesise that this may be due to proportionally over-extended vector longevity, and other increased fitness attributes, within this optimal range. These results suggest that the threat posed by vector-competent mosquito species indigenous to temperate regions may have been underestimated, whilst the threat arising from invasive tropical vectors moving to cooler temperate regions may be overestimated.

MeSH terms

  • Animals
  • Chikungunya Fever / transmission
  • Chikungunya Fever / virology
  • Chikungunya virus / isolation & purification*
  • Climate*
  • Dengue Virus / isolation & purification*
  • Disease Transmission, Infectious*
  • Ecosystem
  • Flavivirus Infections / transmission
  • Flavivirus Infections / virology
  • Mosquito Vectors / growth & development*
  • Risk Assessment
  • West Nile virus / isolation & purification*

Grants and funding

This research was supported by grants from the Biotechnology and Biological Sciences Research Council (‘Vector competence of British mosquitoes to flaviviruses’; http://www.bbsrc.ac.uk/) and the National Institute of Health Research Health Protection Research Unit in Emerging and Zoonotic Infections, vector theme (http://www.nihr.ac.uk/funding/health-protection-research-units.htm). The research was funded in part by the National Institute for Health Research Health Protection Research Unit (NIHR HPRU) in Emerging and Zoonotic Infections at the University of Liverpool, in partnership with Public Health England (PHE), and the Liverpool School of Tropical Medicine (LSTM). The views expressed are those of the authors and not necessarily those of the NHS, the NIHR, the Department of Health or Public Health England. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.