Climate change interferes, directly and indirectly, with a wide variety of diseases by acting as a multiplying force for the diffusion of infectious diseases. Global warming promotes the spread of insects that behave as vectors, transmitting the pathogen. In addition, temperature changes can facilitate or inhibit the proliferation of bacterial or parasitic species.
“We are not facing an Andromeda Strain that will wipe everybody out on the planet” said Daniel Brooks, referring to the 1971 science fiction film about a deadly pathogen. “There will be a lot of localised outbreaks putting pressure on medical and veterinary health systems.”
In the last decade, there has been a substantial global increase in the capacity of A.Aegypti and A.Albopictus mosquitoes to transmit the Dengue virus.
Likewise, mainly due to the rise in temperatures and the degree of salinity of marine waters, the risk of transmission of cholera has also increased. The same can be said of malaria, whose transmission increased about 20% over the last 60 years. Malaria is perhaps the most transmissible disease that has been studied with climate change, and there is evidence of its spread (but also contraction) outside the areas where it is endemic.
The mortality estimates for climate-related diseases, calculated by the Global Burden of Disease Study (2015), show how climate change affects not only the transmission of infectious diseases but also others within certain geographical areas and demographic profiles. For example, the mortality from melanoma, pathogenetically associated with exposure to ultraviolet rays, has sharply increased in Europe, America and the Western Pacific countries. A researcher team from Columbia University and the Harvard School of Public Health also analysed the link between flu strains, migratory routes of wild birds and the abnormal weather conditions due to the impact of man on nature. In the article, published in Proceedings of the National Academy of Sciences, the scientists verified that each pandemic was associated with phenomena attributable to “El Niño”, a series of changes in normal climatic conditions identified periodically in the Pacific Ocean. This happened before the pandemics of 1918, 1957, 1968 and 2009.
Studying the ocean temperatures recorded in the equatorial Pacific before the four pandemics, American researchers found that, in all four cases, they were lower than usual, according to a phase of the periodic climatic oscillation known as ENSO (the El Niño-Southern Oscillation). But how does this cause a change in the patterns of spreading flu strains? When such climatic conditions occur, the migrations, stopping times and contact opportunities that wild birds have with other migratory species or domestic animals are modified. These alterations support the transmission of viruses and phenomena of genetic reassortment, a mechanism that stimulates the development of variants and consequently the appearance of potentially lethal flu strains. It means that, if climate change takes on higher intensity, localised outbreaks, such as Ebola, could become the norm rather than the exception. This escalation in unexpected places will put a strain on the ability of doctors and health professionals to deal with them.
Last December, The Lancet published a report dedicated to climate change and health. “The Lancet Countdown,” is the result of the collaboration of the leading experts in the field of climate science, ecology, geography, economics, energy, nutrition, political and social sciences and medicine from various academic institutions, the United Nations and multiple intergovernmental agencies from five continents. According to the report, because of global warming, the most vulnerable subgroups of the population, the elderly, those with cardiovascular disease, diabetes, chronic respiratory diseases and those living in urban areas, are exposed to higher risks in all regions of the world. Europe and the eastern Mediterranean show a higher vulnerability than Africa and south-east Asia. This is probably related to the older population living in the urban areas of those regions.
Similarly, the dossier published in Proceedings of the American Thoracic Society by an international team of pulmonologists and paediatricians, supports a connection between the modification of the world climate and the increase in the incidence of many diseases, primarily respiratory asthma, but also of cardiovascular nature. Examples of pathologies present in places that until a few years ago were substantially immune emerge from the dossier. One among these is the case of mould spores typical of Central America, which are now also found in Canada, where they have given rise to relevant allergic phenomena.
Dr. Kent Pinkerton, professor of paediatrics at the University of California at Davis, claims that there are some vector-borne diseases caused by some types of parasites or organisms whose range has expanded owing to the effects of climate change. People will become increasingly sensitive to the impact of global climate change, especially infants and young children, people with asthma or chronic obstructive pulmonary disease (COPD), and the elderly, who have compromised immune systems.
Several studies on climate change, carried out over the last 25 years, have shown a marked increase in the frequency of floods and extreme temperatures. Climate change will result in an annual increase of 1.4 billion cases of drought and 2 billion flood cases by the end of the century. If it is easy to think of the direct consequences of this phenomenon on people’s health, it is less obvious to associate it with indirect, but equally important, risks that can affect humans. In fact, climate change is associated with a sharp decline in food security – ease of access, quantity and quality – , leading to malnutrition, as food production is threatened by adverse weather conditions that should become increasingly frequent and devastating.
The Lancet report explains that climate-related risks are so strong that they can overcome the food benefits of new agricultural production technologies and poverty reduction. Despite a reduction in the prevalence and absolute values of malnutrition compared to recent decades, in past years, there has been a turnaround in this trend. Not only agriculture but also fishing and marine breeding are threatened: between 2003 and 2015 there was an increase in the average temperature of marine waters in 16 of the 21 basins analysed, resulting in coral bleaching due to thermal stress and an annual reduction of the amount of fish caught.
Every inhabitant of the earth should have access to sufficient good quality, uncontaminated and non-stagnant water. We know this is not the case. By 2025 about half of the world’s population will live in conditions of extreme water scarcity, and the quality of water is declining in many parts of the world. Approximately 50% of the wet areas have been lost, along with their characteristic flora and fauna, while at the same time 70% of the available reserves are used for irrigation.
There is a robust component of social inequity, not only for the obvious consideration that those who do not have access to good quality water are the poorest but also because the richer ones are responsible for colossal squandering. Think of golf courses irrigation in very arid areas such as Kuwait or Qatar. Apart from the diseases directly linked to the scarcity of good quality water, drought is itself a cause of various diseases. In large areas of China, where drought is becoming an acute problem, airborne diseases are more likely to spread. This effect is combined with the increase of particulate pollution in urban areas; while in rural areas sand storms are more severe due to soil erosion.
Although prolonged drought remains one of the most important causes of malnutrition and early mortality, in some geographical areas such as South America and Africa, natural disasters are becoming increasingly important. According to The Lancet, 15% of deaths related to natural disasters are caused directly by excessive rainfall. This is not including potentially serious long-term consequences such as depression, mental illness and infectious diseases.
It is important to note that the change in the distribution of transmissible diseases as a result of climate change is not a phenomenon that will only affect low-income countries, although these will be the most affected.
The time has come to gain greater awareness of the fact climate change is one of the main enemies for individual and public health.