Climate Change May Limit Spread Of Dengue Fever

Infection with dengue virus makes mosquitoes more sensitive to warmer temperatures, as does infection with the bacterium &Wolbachia &used to control mosquito-borne viral infections. The findings suggest that global warming could limit the spread of dengue but could also limit &Wolbachia’s &ability to act as a biological control. lt;/strong>

Recent findings from &Pennsylvania State University &(PA, USA) have demonstrated the potential use of microbes in mitigating the distribution of vector-borne viral infections. The mosquito &Aeges aegypti &is the primary vector for disease-causing viruses such as dengue (DENV), Zika, chikungunya and yellow fever. Mosquitoes will be increasingly affected by the rising global mean temperatures and extreme climatic events, such as heat spikes, caused by climate change, which will impact their migration patterns and the geographic distribution of these viruses.

Ae. aegypti &breeds in human-made containers inside or near housing in urbanized settlements. The geographic range of &Ae. aegypti &is widening due to increased urbanization and climate change so dramatically that &by 2050 50% of the world’s population is predicted to live in association with &Ae. aegypti.

“Aided by increasing urbanization and climate change, this mosquito’s [Ae. Aegypti] range is expected to overlap with 50% of the world’s population by 2050, dramatically increasing the number of people who could potentially be exposed to these viruses,” commented corresponding author Elizabeth McGraw.

Endosymbiotic insect bacterium &Wolbachia pipientis &limits viral replication inside mosquitoes and is currently released globally as a biocontrol solution to prevent transmission of these deadly viruses to humans.

“Wolbachia have been shown to prevent viruses, including dengue, from replicating inside mosquitoes,” explained McGraw. “Importantly, Wolbachia are passed down to the mosquitoes’ offspring, making them a self-propagating and lower-maintenance approach to disease control in the field.”

The study, published in &PLOS Neglected Tropical Diseases, investigated the effects of rising temperature on the efficacy of &Wolbachia &biocontrol by assessing whether &Wolbachia &and DENV can affect &Ae. aegypti &sensitivity to temperature. Interestingly, the study found that the microbes had similar effects on mosquitoes, revealing that mosquitoes infected with DENV and &Wolbachia &died more quickly when exposed to extreme heat in comparison to uninfected mosquitoes.

Results demonstrated that DENV infection increased thermal knockdown time by 4.5-fold in comparison to uninfected controls, and &Wolbachia &infection by 2.5-fold. Surprisingly, in ‘doubly’ infected mosquitoes with DENV and &Wolbachia, there was no difference in thermal sensitivity compared with ‘singly’ infected mosquitoes with either agent. These findings suggest that these two agents act via a shared immune pathway mechanism within the mosquito.

The researchers explained that their work suggests DENV- and &Wolbachia-induced increases in &Ae. aegypti &thermal sensitivity may limit the geographic range of viral transmission and ability of the symbiont to be used as a biocontrol agent for other mosquito-borne viral diseases.

A potential solution to protecting &Wolbachia’s &biocontrol effects in DENV-infected mosquitoes in hotter regions would be tailoring mosquito–Wolbachia &pairings in order to artificially select combinations better suited to higher temperatures and reduced immune response prior to biocontrol release.

As climate models point to increasing frequencies of extreme temperature events, short exposures to high temperatures threaten the survival of DENV and &Wolbachia &infected mosquitoes. While this will limit the spread of dengue fever, the loss &Wolbachia &as a biological control could further the spread of other mosquito-borne diseases.

“At higher temperatures, while the virus may replicate faster, our work suggests that a corresponding reduction in mosquito thermal tolerance may act as a counterforce on mosquito survival that could help to reduce transmission and potentially human disease incidence in hotter, more climate-variable regions,” Fhallon Ware-Gilmore, lead author, commented. “Similarly, our work suggests that Wolbachia may fail to work as a biocontrol agent in hotter regions given its effect on mosquito survival.”

Source: lt;/strong>Ware-Gilmore F, Sgro CM, Xi Z &et al. &Microbes increase thermal sensitivity in the mosquito &Aedes aegypti, with the potential to change disease distributions. &PloS: Negl. Trop. Dis. lt;/em>doi:10.1371/journal.pntd.0009548 (2021) (Epub ahead of print).