Blood-feeding arthropods, like mosquitoes, insects and ticks, are increasingly sharing their environments with humans due to the climate, with chronic results.
Every organism on earth is experiencing climate change’s consequences. But for those that rely on having close proximity to humans to spread diseases, there has perhaps never been a better time to be alive. To fend them off humans will need to improve global data sharing.
The COVID-19 pandemic brought front and centre the consequences zoonotic diseases can have for our global society — loss of life, long term health complications, supply chain disruptions, school disruptions, and a loss of societal connectivity. Zoonotic disease, or rather, diseases transmitted from animals to humans, is responsible for nearly 60 percent of emerging infectious diseases globally.
Within the United States, the zoonotic diseases from blood-feeding arthropods, like mosquitoes and other insects, pose the most serious threat to public health. Ticks in particular are now increasingly overlapping with humans and other wild animals due to climate redistribution, with 95 percent of zoonotic vector-borne diseases reported in the US being tick-related.
Ten new tick-borne diseases that pose a risk to humans have been identified since 1984 alone. They are technically challenging to diagnose, especially in resource-strapped areas, and can cause severe, chronic health problems that require expensive long-term care if left undetected.
Climate change and urban expansion are increasing zoonotic disease risk in human populations. Animals are shifting where they live to find food and suitable habitats in a phenomenon known as climate redistribution. As a result, we are now increasingly sharing space with new animal neighbours. Similarly, animals are also interacting with each other in ways that are not native to their ecosystems. This creates even more opportunities for zoonotic diseases to find new pathways into human populations.
SARS-CoV-2, the virus that causes COVID-19 disease, likely evolved in bats before being transferred to humans. Ebola, another zoonotic disease outbreak in the last decade, first evolved in an unknown animal, though likely bats or primates, before infecting humans.
Our individual and societal risk of tick-borne zoonotic diseases are only increasing as humans continue to use land in new ways, such as in urban and rural development and outdoor recreation. This narrows the barrier between urban and wild spaces and places ticks and humans in greater contact. As temperatures warm across the US, tick habitats have also expanded northward and southward into cooler climates. Altered seasonal weather patterns have allowed them to be more active throughout the entire year, instead of primarily during the warmer summer months.
Climate change has also altered the timing and land use of migratory mammalian species like deer, foxes, and elk. With ticks residing in new habitats and becoming increasingly active, they can use these species as food and transportation to continue their expansion and potentially introduce diseases into new areas along the way. Ultimately, this dynamic exchange between tick and animal distributions and the availability of more suitable tick habitats increases the risk and prevalence of tick-borne diseases in humans, livestock, and wildlife.
For example, from 2016 to 2017 there was a 46 percent increase in Spotted Fever Rickettsiosis cases across the US and a 250-300 percent increase in Lyme disease prevalence in Northeastern and North Central states.
There are several potential policy options to address these risks, but the central focus should be implementing robust surveillance, reporting, and research systems on a global level. While monitoring, tracking, and preventing tick-borne diseases pose serious challenges, leveraging insights from research into zoonotic diseases across the globe shows how we can better adapt to and increase resilience.
There are three core options to combat tick-borne diseases: Enhancing international monitoring and communication via intergovernmental agencies such as the World Health Organization and United Nations; increasing and integrating tick surveillance into pre-existing local wildlife agencies; and promoting community resiliency against tick-borne diseases with public health education campaigns. While there are diverse pros and cons to each of these policy options, one stands out to have a global effect.
While it is unlikely to completely mitigate the risks of tick-borne zoonotic disease, the improvement of international monitoring and response efforts to manage this risk can be improved. The most effective, feasible, and likely of these strategies that can have an immediate impact is by tapping into existing programs offered by various international organisations including the UN’s Environment Program.
Like other fields of scientific progress, increasing the amount and availability of data in this area will increase the efficacy of existing programs and provide new opportunities for collaboration. This requires increased buy-in from governmental and non-governmental organisations alike, both financially and scientifically.
Public health officials’ involvement is vital before and during outbreaks. Wildlife and agricultural managers, community leaders, and public health officials also play an important role in managing and responding to zoonotic disease risks across animal species, not just in ticks.
Without wildlife and agricultural officials working and monitoring the tick presence in, and health of, animal populations, outbreaks could go undetected. They can also help provide education to the public on how to avoid tick-borne diseases,
It’s important to recognise the nuance and elevated risk climate change and our land use behaviour creates. Ticks aren’t the only piece in this puzzle. Animals are shifting their habitats, interacting with unfamiliar animals and humans in new ways. All of these factors combine to create new potential for zoonotic disease transmissions. A global problem that will require a global response.
This article is based on Philson et al. 2021: https://doi.org/10.38126/JSPG190109
Conner S. Philson is a Ph.D. Candidate in Ecology and Evolutionary Biology at UCLA and a Graduate Fellow at the Rocky Mountain Biological Laboratory.
William M. Ota is a Ph.D. Candidate in Evolution, Ecology, and Organismal Biology at the University of California Riverside.
Dr. Lyndsey Gray, PhD MPSH is an infectious disease epidemiologist, microbiologist, and global health expert currently working as the Science Diplomacy Chair at the National Science Policy Network.
Lindsey Pedroncelli is a Ph.D. Candidate in Microbiology and Plant Pathology at the University of California Riverside.
The authors declare no conflict of interest.
Editors Note: Conner S. Philson, UCLA