COVID-19 is just the beginning: Climate change is bringing a lot more diseases with it

When Salon reached out to Dr. Jeff Harvey about climate change and pandemics, the special professor of biological conservation and advocacy at the Free University in Amsterdam warned of "various insect-transmitted pathogens found on tropical ecosystems such as malaria, dengue fever, leishmaniasis etc." The reason is simple: Many of the climate change conditions that will kill humans in droves are positively heavenly for mosquitoes, such as the increased heat and constant movements of large animal populations.

 

The first of the mosquito-diseases listed by Harvey, malaria, is described by the Centers for Disease Control and Prevention (CDC) as causing "high fevers, shaking chills, and flu-like illness." This mosquito-borne ailment is carried by parasites like Plasmodium falciparum, P. vivax, P. ovale, P. malariae, P. knowlesi and the especially fatal P. falciparum. The World Health Organization (WHO) estimates that 627,000 people died of malaria infections in 2020 out of 241 million clinically confirmed infections.

Like malaria, dengue fever is transmitted by mosquitoes and can be be quite harmful to human beings. To be clear, the WHO reassures the public that dengue fever usually is asymptomatic, and when it does lead to symptoms these are often mild such as rashes, headaches, body aches, nausea and fevers. Yet when dengue fever is severe, patients may suffer symptoms like persistent vomiting, severe abdominal pain, bloody vomit and stools, persistent thirst and overall bodily weakness. The CDC estimates that currently there are roughly 400 million people each year who are infected with dengue, although only around 100 million will become sick and approximately 21,000 each year will die.

Leishmaniasis is not transmitted by mosquitoes, but rather by sand flies that are on average about one-fourth the size of a mosquito. Between 900,000 and 1.6 million people are infected with this disease every year according to the Pan American Health Organization, and of that number 20,000 to 30,000 will die. The most common form of the disease, as well as the least dangerous, is cutaneous leishmaniasis, which causes sores that if untreated can turn into ulcers, which are often in turn covered by scabs or crusts. These are occasionally painful, but usually not. By contrast, visceral leishmaniasis infects several internal organs (bone marrow, liver and spleen being most common among them) and can be fatal.

"Climate change will exacerbate the ecological risk of human exposure to leishmaniasis in areas north of the present range of the disease in the United States (particularly the east-central part of the country) and possibly even in parts of south-central Canada," researchers wrote in a 2010 peer-reviewed study on the disease.

Dr. Sadie Jane Ryan is an associate professor of medical geography at the University of Florida, with a joint appointment in Geography and the Emerging Pathogens Institute (EPI). Speaking to Salon by email, Ryan also listed malaria and dengue as diseases that will become more common due to climate change because of mosquitoes. She also mentioned the zika virus, which is similarly mosquito-borne. Thankfully the zika virus is usually very mild, with symptoms like fever, headaches, muscle pain, joint pain and rashes. Yet the zika virus is associated with problems during and after pregnancies; according to the New England Journal of Medicine, "the mortality rate was 52.6 deaths per 1000 person-years among live-born children with congenital Zika syndrome, as compared with 5.6 deaths per 1000 person-years among those without the syndrome."

"Tick-borne diseases are less straightforwardly climate-driven, as a lot of their ecology is mediated by landscape factors and their hosts," Ryan told Salon, "but that is all on the move with climate change too, and is reflected in studies of climate and tick borne diseases."

 

Whether we're talking about ugly diseases like babesiosis and anaplasmosis or the most notorious tick-borne disease, Lyme disease, ticks are not going to hesitate to move as the climate gets warmer, and to carry their assorted pathogens with them. Ticks prefer air temperatures greater than 6°C but less than 7°C, a humidity rate is above 85%, and — like mosquitoes — to be in close proximity to large number of blood-delivering hosts. As an article from the scientific journal eLife explained at the time, this is part of a larger trend of pests flourishing as the Earth warms. "While climate adaptation has typically been studied in the context of conservation biology, population genetics theory suggests that evolutionary adaptation is most likely for short-lived species with high population growth rates — properties of many pest, pathogen, and vector species," the authors explained.

The cholera epidemic of 1817 to 1824 is one of the most infamous in world history, claiming millions of lives throughout Asia and scarring many with this disease's terrible symptoms. Cholera sufferers will experience severe diarrhea with very watery stools, as well as vomiting and leg cramps. According to UNICEF, roughly 4 million cholera cases exist globally from year to year with as many as 143,000 deaths — a disproportionately large number of them being children under the age of 5.

 

"Waterborne or contaminant-associated diseases such as cholera are also quite well-studied and projected to shift distribution (spread) with climate change – mostly due to ocean warming, but also with the impending increases in flooding events and surface water shifts," Ryan wrote to Salon. Even worse, cholera has many horrible relatives. "I think that people should be aware of the potential for climate to shift the risk of vibrio infections," Ryan explained. "We tend to think of cholera when we talk about vibrio species, but several related species cause a range of human diseases with symptoms from GI upset, to 'flesh eating' – necrotizing tissues – to rapid onset mortality with cholera, when it is the toxin positive form."

Even when literal pathogens do not afflict humans, that hardly means there won't be climate change-related pandemics. A wealth of studies already show that people are experiencing mental health issues related to climate change: Anxiety, insomnia and depression. Given that the vast majority of climate change is being caused by the super-rich (despite their claims to the contrary), it makes sense that people would feel frustrated, powerless and hopeless as a result of the Earth's controllable — yet stubbornly uncontrolled — warming.

 

Of course, this mental stress will also impact our bodies.

 

"Less immediately obvious to some people are the non-ID diseases, the mental health burdens that increase with global heating, with displacement due to climate, and increased stress, which exacerbates vulnerability to a suite of diseases, via immune suppression," Ryan wrote to Salon.