How Climate Changes Are Impacting Infectious Diseases

Everywhere you look—on land, in the sky, or under the sea—things are heating up! Scientific studies reveal that Earth’s average temperature has climbed by roughly two degrees Fahrenheit (one degree Celsius) since 1850, with the warming rate more than tripling since 1982. Global sea levels have also risen around eight inches (20 cm) over the past century, with the pace nearly doubling in the last 20 years. Multiple governmental and non-governmental organizations have documented that this rapid environmental shift is triggering extreme weather events, impacting ecosystems worldwide (e.g., the Intergovernmental Panel on Climate Change¹).

Earth’s smallest residents are also feeling the impact, particularly the adaptable pathogens that are extending their range, increasing their activity, and interacting with new hosts more rapidly in this changing world. The combination of climate change and pathogen expansion could be fueling a surge in infectious diseases. GEN consulted experts from academia and the biopharma industry to gather insights on the situation and explore potential solutions.

Vector-borne diseases

Vectors such as mosquitoes, ticks, and fleas carry pathogens. Bites from such arthropods may lead to vector-borne diseases that include Lyme disease, West Nile virus infection, Zika, dengue fever, and malaria. Indeed, the U.S. has witnessed a doubling of arthropod-related diseases (approximately one million cases) between 2001–2023, according to the U.S. Centers for Disease Control and Prevention (CDC).²

Climate changes are creating an ideal environment for arthropod expansion. For example, shorter, milder winters coupled with longer summers and wetter conditions are enhancing the survival of ticks such as the disease-carrying Ixodes, also known as deer ticks or black-legged ticks. Further, these conditions are not only promoting an expansion of their habitats, but also those of host species that the ticks need for survival (e.g., deer, rodents, birds).

“In the U.S., Lyme disease is the most commonly reported vector-borne illness, with an estimated 476,000 cases reported each year,” reports Julie Skinner, PhD, vice president, Bacterial Vaccines, Pfizer Vaccine Research and Development. “Lyme disease represents a major public health threat with no preventive vaccine currently available. If left untreated, the disease can disseminate and cause serious complications affecting the joints, the heart, or the nervous system.”

Skinner adds that the medical need for vaccination against Lyme disease is steadily increasing as the geographic footprint of the disease widens, due in part to climate change that impacts tick activity. Several vaccines are currently in development to treat Lyme disease, including at Pfizer.

Skinner elaborates, “Our Lyme disease vaccine candidate, VLA15, in a partnership with Valneva, is currently the most advanced Lyme disease vaccine candidate in clinical development. This investigational multivalent protein subunit vaccine uses an established mechanism of action for a Lyme disease vaccine that targets the outer surface protein A (OspA) of Borrelia burgdorferi, the bacterium that causes Lyme disease. It covers the six most common OspA serotypes that cause human disease and are prevalent in North America and Europe.”

The company is conducting a Phase III trial (VALOR), initiated in August 2022, to evaluate the efficacy, safety, lot consistency, and immunogenicity of the vaccine in participants aged five years and older. Skinner indicates that upon successful completion of the trials, Pfizer could potentially submit a Biologics License Application to the U.S. FDA and the Marketing Authorization Application to the European Medicines Agency (EMA) in 2026.

Toolbox against malaria

Another climate change-induced threat is the potential spread of malaria, a disease transmitted through the bite of Anopheles mosquitoes carrying specific Plasmodium species. The World Health Organization (WHO) estimates that approximately 263 million malaria cases occurred globally in 2023 in 83 malaria-endemic countries.³ While local U.S. cases of malaria had not been reported since 2003, recently several cases unrelated to travel have been identified in Florida and Texas, according to the CDC.

“Changing climate conditions are altering mosquito habitats by increasing humidity and temperature in previously unaffected areas, expanding the geographical reach of malaria transmission,” advises Thomas Breuer, MD, chief global health officer, GSK. He continues, “This makes it more difficult to predict and manage outbreaks, requiring adaptive strategies and continuous monitoring to effectively combat the spread of the disease. This also highlights the urgent need to strengthen health systems to maintain routine health services and prevent surges in malaria cases.”

Breuer reports that GSK is developing a new, second-generation malaria vaccine candidate that will hopefully improve protection for children against the deadliest form of malaria, Plasmodium falciparum. “This work will build on the first-generation vaccines by adding a new antigen that works at a different stage of the life cycle of the malaria parasite. If successful, the program will deliver a new combined blood- and liver-stage vaccine against malaria for endemic countries in the hope of improving protection.”

According to Breuer, innovative approaches are crucial to get ahead of the increasing incidence of malaria. “Malaria vaccines are part of the international community’s ‘toolbox’ for fighting malaria, alongside other interventions such as seasonal chemoprevention, indoor residual spraying, and bed nets.”

Spores galore

Fungi represent a diverse group of organisms that inhabit a wide range of environments and fulfill various ecological roles. However, of the approximately one million known fungi species, about 300 can infect people. “One of the barriers we have to fungal infection is our body temperature,” says George R. Thompson III, MD, professor, department of internal medicine, division of infectious diseases and the department of medical microbiology and immunology, University of California Davis School of Medicine. “Most fungi cannot grow in our warmer body temperature. The problem is that some of these fungi that can grow just below 90 degrees Fahrenheit are becoming more accustomed to warmer climate temperatures. This means their peak growing temperature is also increasing, allowing them to potentially cause infection in mammals.”

Thompson points out that Candida may be an example of this. “Candida is a group of yeast, the most well-known of which is C. albicans, that causes primarily mucosal infections. However, infection in hospital patients can cause invasion and sepsis, resulting in 35-40% mortality. Additionally, in the early 2000s there appeared another species, C. auris, that was found in a Japanese patient’s ear. But over the next decade, we saw something very unusual—the independent emergence of C. auris at three regions around the world, so they weren’t clonal or genetically related. Thus, C. auris is emerging as a significant treatment-resistant global pathogen.”⁴

Even though pathogens in the environment outnumber humans and exposure will eventually create resistance, Thompson believes there is cause for hope. “Not only have the CDC and NIH been very proactive in supporting research studies, but also our understanding of immunology has skyrocketed over the past ten years. I think we will be able to leverage these advances to provide immunotherapy for nontraditional pathogens. We hear the term precision medicine, and we are just at the beginning of that age to offer it for infectious diseases.”

Fungal therapeutics

“Valley fever is now well documented as spreading due to the climate,” states John Rex, MD, CMO, F2G. This fungal disease, also known as coccidioidomycosis, is caused by inhalation of Coccidioides spores. According to the CDC, at least 10,000 to 20,000 cases are reported yearly. However, since initial symptoms can resemble the flu, it is likely underreported.

Rex notes, “Because they can produce invasive infections, fungi such as Aspergillus and Coccidioides can cause devastating and lifelong illnesses. While infections are increasing, current treatments are not consistently effective, especially for Coccidioides.”

F2G is aiming at new fungal therapeutics. Rex disclosed, “We have discovered and developed an entirely new class of antifungal agents called orotomides that are small molecule inhibitors of a critical enzyme in pyrimidine biosynthesis, dihydroorotate dehydrogenase (DHODH). Pyrimidines are essential for the synthesis of DNA, RNA, and protein. All living beings have this enzyme, but all do not have the same version.”

Rex says company scientists screened a combinatorial chemical library of over 300,000 small molecule chemicals and identified an initial hit from which olorofim was ultimately derived. “The inhibitory concentration (IC50) of olorofim is 2000-fold different than the human version, so it very rapidly shuts down fungal growth and then causes fungal death without inhibiting human DHODH. It is formulated to be taken as a pill twice a day and has been shown in clinical studies to be reliably absorbed with predictable drug interactions.”

The company has completed a Phase II study of about 200 patients with results to be published soon in Lancet Infectious Diseases. “This study had approximately 20% of patients with Valley fever, 50% with aspergillosis, and the remaining 30% had a mixture of very rare fungal infections. Based on data from the Phase II study, we are currently in Phase III utilizing olorofim as a therapy for invasive aspergillosis. We are also planning a Phase III study for disseminated Valley fever as well as developing olorofim for pediatric and inhaled uses.”

Rise in zoonotic disease

Another significant infectious disease concern arising from climate change is zoonotic disease—illnesses that are transmitted between humans and other vertebrate animals. These diseases can be of bacterial, viral, or parasitic origin. “The effects of climate change apply for all pathogens, not only those zoonotic, but an emphasis on zoonotic diseases, is nevertheless relevant in the context of climate change because approximately 67% of all known pathogens are zoonotic and about 75% of all emerging diseases are zoonotic,” advises Emilie Andersen-Ranberg, DVM, PhD, senior veterinarian, department of veterinary clinical sciences, University of Copenhagen. She believes Arctic zoonoses are particularly concerning, as the Arctic is warming at a rate faster than the global average.

Andersen-Ranberg says that increased temperatures and precipitation patterns related to climate change are altering Arctic pathogen dispersal both geographically and by hosts. “For example, this is occurring by the introduction of pathogens into the Arctic fauna, which has otherwise been somewhat isolated because of a climatic barrier. Another example is the increased outbreaks of anthrax in the Russian Arctic occurring because of the release of anthrax spores from thawing permafrost stores.” Notably, in 2016, a large anthrax outbreak killed several thousand reindeer as well as a human.⁵

Other magnifiers of infectious diseases include increased shipping traffic. Andersen-Ranberg provides a perspective, “Shipping vessels have increasing accessibility to the Arctic due to dramatically diminishing sea ice coverage. These vessels can carry pathogens across the globe on their hull related to so-called ‘biofouling’ occurring naturally. Also, they sometimes release ballast water carried from regions far away to the Arctic Ocean. This releases organisms and a myriad of marine pathogens potentially harmful to the local Arctic marine flora and fauna.”

But Andersen-Ranberg remains hopeful and doesn’t foresee a potential zombie apocalypse of Arctic pathogens. “Coordinated efforts are needed to mitigate disease outbreaks among Arctic flora, fauna, and humans as well as to hinder outbreaks spreading from the Arctic via routes such as thawing of the ancient permafrost. With continuous warming, we cannot control or hinder all novel disease outbreaks from emerging zoonotic-based diseases, but we can build a highly important and productive early detection system internationally as well as develop well-thought-through contingency plans that include potential prophylaxis such as vaccines.”

Water-borne disease

Climate change is also exacerbating

waterborne infectious disease by altering the quality and quantity of water. For example, rising temperatures, changing weather patterns, and coastal flooding can boost the range, concentration, and proliferation of pathogens such as Vibrio species, common inhabitants of coastal waters, that can cause gastroenteritis, soft tissue infections, or lethal sepsis¹. Flooding and runoff resulting from excessive rainfall can contaminate water supplies with animal waste and harmful chemicals. Even drought can impact health by concentrating pathogens in the limited amounts of available water.⁶

Going forward

A recent report by Edelson et al. emphasizes that interdisciplinary cooperation will be essential to address the impact of climate change on infectious diseases.³ As the report summarizes, “Collaborations with veterinary, environmental, and physical sciences will be necessary to build systems to predict and adapt to short- and long-term climate change-driven health effects.”

Such a framework is gaining traction nationally and internationally as the One Health Initiative, a movement with support from organizations such as the World Health Organization (WHO) and the CDC, among others. This perspective focuses on the interconnectedness of human, animal, and environmental health. Steven J. Lawrence, MD, professor, division of infectious diseases, Washington University School of Medicine, suggests, “The One Health approach recognizes that the health of people is closely connected to the health of animals and our shared environment. Going forward, we must not only continue the surveillance of the human-animal interface but also work to arrest drivers such as preventing deforestation, regulating wildlife consumption and trade, and slowing climate change.”

References

1. www.ipcc.ch, the United Nations’ body for assessing the science related to climate change.

2. About Vector-Borne Diseases

3. World Malaria Report 2024

4. Phillips MC, LaRocque RC, Thompson GR, 3rd. Infectious Diseases in a Changing Climate. Jama. Apr 16 2024;331(15):1318-1319. doi:10.1001/jama.2023.27724.

5. Andersen-Ranberg E, Nymo IH, Jokelainen P, et al. Environmental stressors and zoonoses in the Arctic: Learning from the past to prepare for the future. Sci Total Environ. Dec 20 2024;957:176869. doi:10.1016/j.scitotenv.2024.176869.

6. Edelson PJ, Harold R, Ackelsberg J, et al. Climate Change and the Epidemiology of Infectious Diseases in the United States. Clin Infect Dis. Mar 4 2023;76(5):950-956. doi:10.1093/cid/ciac697.

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