People celebrate the arrival of summer every year, but it comes with a downside: an annual population explosion of disease-carrying ticks and mosquitoes. Recent findings from the Centers for Disease Control and Prevention reveal a staggering threefold increase in reported cases of what we broadly term “vector-borne diseases”—or illnesses transmitted to humans by mosquitoes, lice, ticks and the like—between 2004 and 2016 in the United States. Making matters worse, nine new pathogens emerged for the first time in the U.S. during this same period.
What has spurred such a dramatic uptick (no pun intended)? While multiple factors are involved, the influence of climate change cannot be overlooked.
CLIMATE CHANGE AND DISEASE
Since vectors are cold-blooded, changes in temperature alter both the biology and population dynamics of mosquitos and ticks, which in turn impacts their development rates, feeding patterns and reproductive cycles. When temperatures rise, the time between generations of mosquitoes shortens. What’s more, earlier and extended periods of warm weather may prolong the time during which vector populations are able to thrive. (On the flip side, extremely hot temperatures coupled with drier conditions in some areas can have a negative impact on vector populations.)
Disease pathogens are also influenced by weather patterns. For example, the virus that causes dengue fever goes through the developmental stages in the mosquito more rapidly when temperatures are warmer. That means the time it takes from when a mosquito bites an infected person and can pass on the virus is much quicker.
Spring is arriving earlier each year, meaning mosquito and tick populations will grow active earlier along with it. As warm seasons extend, the opportunity for introducing pathogens increases. These conditions, coupled with other human-induced changes, influence risk. For example, cutting away forested areas for suburban development has been identified as a significant contributor to the expansion of Lyme disease in New England.
The precise contribution of climate change to current and future increases in vector-borne diseases within the U.S. is not well-established. Changes in land-use, diagnostics, travel, and importation of goods, combined with flawed data sets, make it difficult to isolate its impact. And some argue that social factors such as indoor lifestyles and good infrastructure (including air conditioning and window screens) will buffer people from the influence climate change might have on vector-borne diseases. What is clear, however, is that these climate-sensitive diseases have a high potential to be influenced by changing weather patterns.
BETTER SURVEILLANCE NEEDED
We urgently need resources to enhance vector and disease surveillance and to improve our capacity to respond, especially given the uncertainty around how a changing climate may influence the spread of vectors and vector-borne diseases. For diseases transmitted between animal hosts and vectors, like West Nile virus and Lyme disease, monitoring vector populations and non-human hosts may provide an early warning signal to trigger public health responses.
On the other hand, for diseases passed almost exclusively between humans and vectors, such as dengue, virus levels in mosquito populations often coincide with transmission already occurring in humans. Therefore, monitoring mosquito abundance and enhancing our ability to detect human cases is critical.
COMMUNITY ENGAGEMENT IS KEY
Prevention goes hand in glove with detection. While often a secondary public health concern, vector-borne disease prevention efforts made headlines with the spread of the Zika virus in 2015, when it was reported that the virus could have devastating consequences for pregnant women and their babies. However, for many mosquito-borne illnesses threatening the U.S. there is not an effective vaccine or treatment, so the need for better vector-control methods is urgent.
How can communities work together to solve this problem? Part of the answer must include better public education to help people recognize the symptoms of vector-borne diseases. Increased community engagement is also necessary in order to help better understand the specific needs and abilities of that community in regard to public health and vector-control programs.
Some areas are experimenting with new technologies to intensify traditional control efforts. For example, Harris County worked with Project Premonition to test robotic traps for mosquitoes that can remotely determine the species by wing movement. Lee County, Florida, is using drones to control nuisance mosquitoes in hard to reach mangrove areas.
Nearby, 20,000 male mosquitoes infected with a naturally occurring bacteria, Wolbachia, were released in the Florida Keys in 2017—an area that experienced a dengue outbreak in 2009. When males infected with Wolbachia mate with female mosquitoes, the bacteria affect the eggs so that they will not hatch, resulting in a reduced or eliminated mosquito population.
While these new technologies hold significant promise, communities must be engaged before investments are made to determine if there is public support. Drones flying over neighborhoods, releases of Wolbachia-infected or genetically modified mosquitoes, all have the potential to draw concern from residents. Experts and public health officials are quickly learning that the biggest roadblock to introducing new control measures can be rooted within the very communities they are intended to help.
This became evident when the Florida Keys Mosquito Control District wanted to introduce genetically modified male mosquitoes after that 2009 outbreak. Despite a near-decade–long process of obtaining government approvals and engaging the community through town halls, referendums, and educational sessions no release has been conducted, in large part due to community opposition.
Many people were—and still are—opposed to anything that is genetically modified, even though the result would be the same as the Wolbachia bacteria–infected mosquitos: reducing the population through sterilization.
As with most advances, some communities will have the resources to take advantage of these new technologies and some will not. The good news is that there are ways to mitigate risk of infection that anyone can take. Eliminating habitats for mosquitoes and ticks in private and public areas is critical. Any standing water is a hazard as it can create a breeding ground for mosquitoes. Public health officials recommend that every week residents empty and scrub, turn over, cover, or throw out items that hold water—such as tires, buckets, planters, toys, pools, birdbaths, flowerpots or trash containers.
Many people may not realize that some mosquitoes—like the one that transmits Zika—can even lay eggs in containers inside the home, so it is important to check flower vases and containers. And, of course, contact with mosquitoes can be reduced by wearing repellent or longer clothing and screening doors and windows.
Unfortunately, not all people have the resources to adhere to these standard public health recommendations. Making home repairs and purchasing repellent on a regular basis may be out of reach for some of the most vulnerable populations. Therefore, identifying key barriers to the implementation of prevention tactics is a critical gap in current public health recommendations.
Engaging the whole community is critical. After all, it’s entirely possible that while you are on top of these recommended chores, your neighbor may not be. In past surveys we have conducted in Key West and Tucson, we’ve noted that of the people who reported a reason for not being able to remove standing water, one in 10 indicated they were physically unable to do so. Assisting neighbors in removing or treating standing water will aid in the protection and health of the entire community.
It’s crucial that public officials open a conversation with community members to ensure they are knowledge partners every step of the way, to provide a forum for discussion and to assuage concerns about the newest technologies, to ensure communities know what is necessary to make sure mosquitoes aren’t welcome, and to assist the community members who need help with upkeep in their own yards. Organizing entire communities to understand the risk—and then react to it—is the only way to start to address this increasing threat to health.