Climate change and infectious diseases

The World Health Organization and United Nations Environment Programme established the Intergovernmental Panel on Climate Change (IPCC) in 1988 because there was little knowledge about health issues caused by global climate change.[2] Intergovernmental Panel on Climate Change has presented three assessment reports. IPCC First Assessment Report, IPCC Second Assessment Report and IPCC Third Assessment Report wrote about climate change, potential health risks caused by climate change and early evidence of actual health impacts.[2] IPPC and other policy-related assessments at the regional and national levels stimulated scientific studies to understand the climate-health relationships.[2]

A noticeable effect of the global climate change is the increase of temperature. In 1895, the record-keeping of temperature in the U.S began and it has increased by 1.3 °F to 1.9 °F.[3]^:26 This is because the concentrations of greenhouse gases increase.[4] Based on this information the annual average U.S temperatures are expected to increase by 3 °F to 10 °F having direct effects on human health.[4] The extreme temperatures (hot and/or cold) affect the body by compromising its ability to regulate its internal temperature and by worsening chronic conditions such as cardiovascular and respiratory diseases.[4] Respiratory diseases also worsen by the air quality. Air quality becomes poor because of climate change, which produces higher concentrations of CO2, higher temperatures and changes in precipitation.[5] Climate change affects the growing season and the pollen because the start or duration of the growing season becomes extended, and the quantity, the allergenicity and the spatial distribution of pollen increase.[5] Climate change affects vector-borne diseases by affecting the survival, distribution and behavior of vectors such as mosquitoes, ticks and rodents.[3]^:29 The viruses, bacteria and protozoa are carried by these vectors transferring it from carrier to another.[6] Vector and pathogen can adapt to the climate fluctuations by shifting and expanding their geographic ranges, which can alter the rate of new cases of disease depending on vector-host interaction, host immunity and pathogen evolution.[7] This means that climate change affects infectious diseases by impacting their length of the transmission season and their geographical range.[8] Vector-borne diseases are a concern because they have played a significant role in human history by determining the rise and fall of civilizations.[8] This is why the World Health Organization considers climate change as one of the greatest threats to human health.[8]

There are many viruses that coincide with climate change. Dengue being one of many is a virus that can be transmitted by Aedes Aegypti mosquitoes and was first isolated in 1943 by scientists Ren Kimura and Susumu. Dengue is deadly and has affected people all over the world, especially for those who live in warmer climates. The symptoms in mild cases are vomiting, rash, high fever (40 °C/104 °F), joint pain, eye pain, and in severe cases (fever 38 °C/100 °F) death.[9] Dengue is a mosquito-borne virus. There are higher peaks of mosquitoes during raining season. From the end of the industrial revolution to our present day, the levels of carbon dioxide have risen from 280 parts per million to 412 parts per million within the last 150 years.[10] The Worlds Health Organization (WHO) has reported an increase from a thousand to one million for the number of confirmed cases and countries between 1955 and 2007.[9] Coincidentally, due to the climate change, a greenhouse barrier has formed in the earth’s atmosphere, composed of gases such as nitrous oxide, methane, and carbon dioxide.[10] The greenhouse gases trap sun rays that should be reflected back out into the universe, thereby causing the Earth's temperature to elevate.[10] The increasing temperatures mostly affect countries that are closer to water since water can absorb a lot of energy from the sun and can release it in the form of vaporization. As the evaporated water condenses, the amount of condensation increases and the likelihood of precipitation increases as well. As a result, climate change causes higher raining seasons, temperature, and humidity. These conditions are favorable for Aedes aegypti mosquito population since these conditions form habitats that are accessible for laying eggs and spreading the transmission of dengue virus to people.

There are many ways, where nations have come together in order to combat Dengue. For example, many scientists from Cuba and the United States have done advanced collaboration to expedite the progress of the mosquito-borne virus, dengue. Despite cultural differences, these two nations have set aside political conflicts in order to exchange vital information and ideas between scientists and the public. They launch the Havana symposium, which allowed Cuba and the U.S to discuss ways of controlling the virus and the transmission of dengue to the people. Together, they have done research on the properties of insecticides and mosquito repellents that are derived from plants and the effect of these properties on living cells.[11] This information has been vital for finding ways to prevent Dengue transmission. One example is Dengvaxia, which is a vaccine available for Dengue prevention. However, it is only recommended for people who were already exposed to the Dengue virus infection. Still, there are other forms of preventing the spread of Dengue. Another form of prevention is using insect repellents, avoiding moisture build-up indoors and outdoors, and wearing protective clothing can prevent the spread of Dengue. A step-by-step tutorial for prevention and protection against the spread of Dengue is available online.

There are other organizations that are preventing climate change and the spread of new viruses. For example, The Intergovernmental Panel on Climate Change (IPPC) provides scientific evaluations based on climate change impact, adaption and alleviation options, and future risks. The information from IPPC is the most reliable source when it comes to climate change. IPPC reports are used as a foundation for policymaking. The United Nations Environment Programme (UNEP) and World Meteorological Organization (WMO) are other organizations that work toward mitigating climate change.[12] UNEP works on seven different areas of climate change and is the leading international environmental authority. In addition, the seven areas that UNEP mainly focuses on are climate change, managing ecosystems, natural disasters and conflicts, environmental policies, chemicals, and wastes, monitor the financial output of environmental conditions, and the study of many environmental conditions. This organization is known for mitigating environmental conditions and trends at a global, regional, and national level. Also, they have created programs that help to fight against climate change such as REDD+ program (Reducing emissions from deforestation and forest degradation), Climate and Clean Air Coalition (Climate and Clean Air Coalition to Reduce Short-Lived Climate Pollutants), and Climate Technology Centre and Network. WMO specifically monitors weather, climate, and water. WMO dedicates their time to bring international awareness and cooperation, pertaining to the earth’s atmosphere. This organization focuses on reducing the risk of disasters and provides vital information about meteorological, climatological, hydrological, and oceanographic activities. In 2014, a global foundational fund known as the Green Climate Fund was created.[13] This fund focuses on underdeveloped countries, islands, and many African states, which have been affected the most due to climate change. Another fund is the Climate Investment Funds, which supports economies that are trying to minimize the use of carbon in order to prevent climate change. There are also support groups that are fighting for environmental causes. 350.org is a support group that fights against fossil fuel industries and the mining in various parts of Brazil.[14] Another organization is the C40 Cities Climate Leadership Group, which is trying to develop solutions to reduce greenhouse gas emissions and climate change.[15]

The war of microorganisms against mankind is one that's been ongoing for centuries. Microorganisms have been around long before the existence of humans. At one point or another, we have all had the flu or a cold; this is caused by viruses. Ebola is one of the deadliest viruses, starting out as a small outbreak and eventually turning into a major global issue. The average case fatality rate of the Ebola virus is approximately 40% and to date, there have been more than 28,600 cases with 11,310 deaths.[16] Recent studies are holding climate change liable for the uptick in Ebola. Many researchers are linking deforestation to the disease, observing that change in the landscape increases wildlife contact with humans.[17] Ebola virus is typically found in animals of the wild and can be transmitted from these animals to humans when exposed to infected bodily fluids.[16] The virus can also be transmitted from another human when in direct contact with the virus hosts blood, vomit, or feces. Seasonal droughts alongside strong winds, thunderstorms, heat waves, floods, landslides, and a change in rainfall patterns also impact the wildlife migration. These conditions pull them away from their natural environment and closer to human proximity.[18] One example of an Ebola outbreak caused by climate change or a shift in nature was seen during the drought of Central Africa. This ultimately amplified food insecurity leading West African communities to eat animals such as bats who were infected with the virus.[17]

Outbreaks such as Ebola are transnational threats. Viral diseases like Ebola, have no remorse for any border or country. It's a battle that no country can face alone. Global health diplomacy helps bring together the regulation of public health, law, foreign affairs, economics, and puts the limelight on negotiations that can help build and manage policies for global environmental health. In 2014, Cuba sent 461 doctors to West Africa to help combat the outbreak of Ebola.[19] Cuba was one of the first countries that have supplied as many trained health professionals to the Ebola outbreak than any other nation. This kind of gesture helped form the start of some Ebola diplomacy between Cuba and the United States.[20] Consequently, the World Health Organization (WHO) assembled an emergency convention with many health ministers from eleven countries to reveal an alliance to help fight the Ebola epidemic.[21] The World Bank Group and the Economic Community of West African States (ECOWAS) declared aid money to help the epidemic and the World Food Programme helped distribute food for approximately one million people who were living in restricted areas.[22] Other organizations have also provided aid in an attempt to control the spread of the Ebola disease. For instance, the humanitarian aid organization Médecins Sans Frontières also known as Doctors Without Borders became the prominent organization that was responding to the crisis by having many health centers in the area. Another non-governmental organization is the Samaritan's Purse who provided direct patient care and medical aid in Liberia.[23]

In recent decades, experts began to sound the alarm that climate change could be associated with changes to the epidemiology of infectious diseases. This viewpoint focuses on a threat where there is a strong possibility that new, previously unknown infectious diseases will emerge from warmer climates as microbes adapt to higher global temperatures that can defeat our endothermy thermal barrier. Human defenses against microbial diseases rely on advanced immunity, which includes innate and adaptive arms and endothermy. This creates a thermal restriction zone for many microbes. Given that microbes can adapt to higher temperatures, there is a concern that global climate change will select for microbes with higher temperature tolerance that can defeat our immune defenses and cause new infectious diseases to emerge.

There is a specific concern about the emergence of new diseases from the fungal kingdom. Mammals are extraordinary among animals in their endothermy and homeothermy, which allows us to maintain elevated body temperature through life; but it can be defeated if the fungi were to adapt to higher temperatures and survive in the body.[24] Research has shown that fungi that are pathogenic for insects can be experimentally adapted to replicate at mammalian temperatures through cycles of progressive warming. This demonstrates that fungi are able to adapt rapidly to higher temperatures. The emergence of Candida Auris on three continents is proposed to be as a result of global warming and has raised the danger that increased warmth by itself will trigger adaptations on certain microbes to make them pathogenic for humans.[25]

If these threats materialize, medicine will need to conform to new infectious diseases for which it has no previous knowledge or experience. As seen with the recent pandemic of the novel coronavirus (COVID-19); control measures, therapeutics, and effective responses take time, where countless lives are lost in the meantime. However, if proper measures are taken today, it could increase the preparedness for confronting new infectious diseases.

Though climate change will almost certainly bring forth new infectious diseases and change the epidemiology of many existing diseases, it is important to note that humanity has successfully confronted new deadly diseases in recent years, such as SARS, coronavirus, and Ebola. Prior success is no guarantee for future success given that each new disease brings its own set of challenges as seen in with the ongoing pandemic, COVID-19. There is no proof that COVID-19 worsens or is caused by climate change, however, we’ve seen how a new infectious disease can change the way we live as humans in such a short span of time and also the number of deaths that resulted from the pandemic. The best solution against future threats is continued investment in surveillance, antimicrobial therapeutics, epidemiology, and research into mechanisms of these microbes.

The rising of new diseases and worsening of diseases due to climate change have been a wake up call for the science community. The collection of data on how climate changes over the years and how these changes are affecting health were stimulated by Science Diplomacy organizations because this information helped scientists to raise awareness about the situation nationally and internationally so action can be taken. This is shown by the actions that were taken during the malaria and dengue outbreak. However, Science Diplomacy organizations need more support from the world so a better solution can be reached to solve the climate change issue because new infectious diseases will emerge. These new infectious diseases could be the end of humanity if they are not addressed properly and on time.

• Effects of global warming on human health
• Central Epidemic Command Center
• Public health emergency of international concern