GLOBAL CLIMATE CHANGE AND CHANGE IN DISEASES DISTRIBUTION (original) (raw)

**GLOBAL CLIMATE CHANGE AND CHANGE IN DISEASES DISTRIBUTION**

**BY**

**DANEP, GODFREY SUNDAY**

**FEBRUARY, 2017**

**Abstract**

*Climate change is expected to have a colossal effect on human health, including on the burden and distribution of many infectious diseases. Climate change, also called global warming, refers to the rise in average surface temperatures on Earth. The infectious diseases that will be most affected by climate change include those that are spread by insect vectors and by contaminated water. The burden of adverse health effects due to these infectious diseases will fall primarily on developing countries, while it is the developed countries that are primarily responsible for climate change. It is up to governments and individuals to take the lead in halting climate change, and we must increase our understanding of the ecology of infectious diseases in order to protect vulnerable populations.*

**INTRODUCTION**

Climate change, also called global warming, refers to the rise in average surface temperatures on Earth. An overwhelming scientific consensus maintains that climate change is due primarily to the human use of fossil fuels, which releases carbon dioxide and other greenhouse gases into the air. The gases trap heat within the atmosphere, which can have a range of effects on ecosystems, including rising sea levels, severe weather events, and droughts that render landscapes more susceptible to wildfires (Environmental Protection Agency, 2010).

Shuman (2011) observed that it has long been known that infectious diseases are indigenous to one or another part of the globe and can be spread. As far as we know, global climate change was not responsible for spread of these diseases in the past. More likely they spread as a result of human social and behavioral change. Nevertheless, spread of a very special set of diseases is apt to occur with climate change. These are diseases transmitted by arthropods - mosquitoes, sand flies, midges, and ticks—and other diseases transmitted from animals to people, which we call zoonoses. Climate change may also affect diseases spread by snails or by water, such as schistosomiasis and cholera, because changes in rainfall will have an impact on flow of rivers and levels of lakes; melting of polar ice may raise the sea level and inundate coastal and delta regions (Shope, 1992).

According to Lafferty (2009), the infections that will spread with climate change have some commonalities. They are focal, and their distribution is limited by the ecology of their reservoir, be it arthropod, snail, or water. They usually have a two- or three-host life cycle, meaning that in addition to infecting people, they infect a vector and frequently also a wild vertebrate animal host. Either the vector or the host, or both, are the reservoir. The range of the reservoir is delineated by temperature and sometimes water. In order to survive global climate change (and some of these infectious agents will not survive) the agents will need to have reservoirs that will survive; they will probably survive by moving in a polar direction, north in the Northern Hemisphere, in order to find a temperature range that is ecologically permissive. If the agent and reservoir are successful in the newly warmer climate, the agent can be expected to multiply more rapidly, and if the reservoir is an arthropod or snail, it too will develop more rapidly (it may also have a shorter life). It will be obvious to the reader, that the reservoir must survive the change, the agent must be able to move if the reservoir is translocated, and the reservoir must be able to adapt to conditions in the new ecologic zone.

Among the diseases that have been predicted to be more severe or move into more populated areas of North America are the mosquito-borne viral diseases dengue, St. Louis encephalitis, and yellow fever; the sand fly-borne protozoal disease leishmaniasis; the water-associated disease cholera; and the bat-borne vampire bat rabies (Lafferty, 2009; WHO, 2010).

In Nigeria for instance, The Minister of State for Environment, Usman Jubril, who was a panelist on a Nigeria Television Authority (NTA) programme, said: “The effects of climate change are felt at every sight of the country. Rising global temperatures would have a catastrophic effect on human health and patterns of infection would change, with insect-borne diseases such as malaria and dengue fever spreading more easily” (The Guardian, 2016). He further asserts that there are some infections that occur in season, so naturally if there is a change in season or climate there will have to be changes in the type of infections and in the manner that there were originally known to occur.” According to a new report by the World Health Organisation (WHO) WHO (2010), severe drought, flooding, heavy rains and temperature rises are all known effects of El Niño that can lead to food insecurity and malnutrition, disease outbreaks, acute water shortages, and disruption of health services.

El Niño is a warming of the central to eastern tropical Pacific Ocean, which affects rainfall patterns and temperatures in many parts of the world but most intensely in the tropical regions of Africa, Asia-Pacific, and Latin America, which are particularly vulnerable to natural hazards. Typically, some places receive much more rain than normal while others receive much less.

The health implications are usually more intense in developing countries with fewer capacities to reduce the health consequences. The current El Niño from 2015 to 2016 is predicted to be the worst in recent years, and comparable to the El Niño in 1997-1998, which had major health consequences worldwide. In Eastern Africa, as a result of the El Niño in 1997-1998, WHO found that rainfall patterns were unusually heavy and led to serious flooding and major outbreaks of malaria, cholera and Rift Valley Fever.

Based on the latest UN figures, the report estimates 60 million people will be impacted by El Niño this year with many suffering health consequences.

An Associate Director of the Center for Health and the Global Environment, Harvard University, Dr. Aaron Bernstein said: “All pathogens viruses, bacteria, fungi and parasites are temperature-sensitive. Furthermore, they have differences in how they reproduce and they infect people and other animals based on the temperature they are living at” Similar to mosquitoes, rodents are highly adaptable. They will respond readily to disturbances in the environment brought about by climate change. Rodents reproduce fast (up to seventeen litters a year). They eat whatever humans’ eat, and thrive on contaminated water and food. Rodents are vectors for a variety of deadly diseases.

They multiply in temperate regions following mild wet winters, act as reservoirs for various diseases. Certain rodent-borne diseases are associated with flooding, including leptospirosis, tularemia and viral hemorrhagic disease (Lassa fever).

Malaria killed 627,000 in 2012 alone. According to the Intergovernmental Panel on Climate Change (IPCC), climate change will be associated with longer transmission seasons for malaria in some regions of Africa and an extension of the disease’s geographic range. As temperatures warm, the *Plasmodium* parasite in the mosquito that causes malaria reproduces faster and the vector (the organism that transmits a disease), i.e. the mosquito, takes blood meals more often. Rain and humidity also provide favorable conditions for young mosquitoes to develop and adult mosquitoes to survive (WHO, 2010).

This seminar will illustrate how these diseases may spread, and it will suggest how some other diseases of Africa and Asia may extend their geographic range and cause more serious human illness than currently encountered.

**IMPACT OF CLIMATE CHANGES IN DISEASES DISTRIBUTION**

**General impact of climatic conditions on infectious diseases**

Before humans understood that microorganisms caused epidemic diseases, they knew that these diseases were intimately related to climate. From the above assertions, we now have an understanding as to why epidemics of infectious diseases are strongly tied to climate. For those infectious diseases transmitted by insect vectors, we know that vectors are more active at higher temperatures (Lafferty, 2009). Tropical species of mosquitoes such as *Anopheles* require temperatures above 16 °C to complete their life cycles, and malaria parasites are able to develop more rapidly within mosquitoes at higher temperatures (>20 °C). In the case of malaria due to *Plasmodium falciparum*, one mosquito can infect 200 individuals if temperature conditions are ideal, allowing for rapid spread of the disease. Vector-borne diseases such as malaria are also thought of as water-borne diseases, since mosquitoes typically thrive in aquatic habitats, where they lay their eggs in water-filled containers. Thus, epidemics of malaria and dengue fever tend to occur annually during rainy seasons in the tropics and inter-annually after weather events such as those associated with El Niño-Southern Oscillation (the warm phase in the atmospheric temperature oscillation over the tropical Pacific Ocean) (Patz, 2005).

Figure 1.1 Impact of climate change on health. Source: WHO (2010)

On the other hand, epidemics of the mosquito-borne West Nile virus infection can occur during times of drought. This happens because mosquitoes and birds—the primary hosts of the virus—are brought into close proximity at scarce water sources, enhancing transmission of the disease between mosquitoes and birds (and thus to humans) (Pachauri, et al, 2007). In addition, natural predators of mosquitoes are greatly reduced during times of drought as wetlands dry up.

Like vector-borne diseases, waterborne diseases are also strongly impacted by climate, particularly the effect of climate on the hydrologic cycle. During times of drought, water scarcity results in poor sanitation and exposure of much of the population to potentially contaminated water. For example, an epidemic of cholera occurred in late 2009 in northern Kenya after a severe drought, with over 4700 cases reported in one month, including 119 deaths (Gettleman, 2010). The mainstay of treatment for diarrheal disease such as cholera is rehydration, which further exacerbates the situation due to the lack of adequate potable water available for this purpose.

Excess rainfall and flooding, like drought, can also contribute to epidemics of water-borne infectious diseases, in this case due to poor sanitation resulting from run-off from overwhelmed sewage lines or contamination of water by livestock. An example is the 1993 outbreak of diarrheal disease due to *Cryptosporidium* in Milwaukee, Wisconsin after heavy spring rains (WHO, 2010). In this outbreak, there were over 403 000 reported cases, demonstrating how widespread diarrheal disease can become when community water sources become contaminated.

In Nigeria, a study by the United States Embassy in 2011 revealed an estimated 100 million malaria cases with over 300,000 deaths per year; the research has shown that malaria thrives in the hot and humid areas where the Anopheles mosquito can live. As the climate warms, the territory where the mosquito and the malaria parasite will be able to live will likely expand, putting more people at risk. Already dengue fever, another mosquito-borne tropical disease, has re-established itself in the Florida Keys, where it was wiped out decades ago. Furthermore, heavy rain and warm temperatures have helped the mosquitoes carrying Zika thrive (WHO, 2010; Usikalu, 2009).

**Current impact of climate change on infectious diseases**

We currently know more about the effect of climate change on the distribution of disease that affect animals and plants and its infectious diseases. In general, species ranges have shifted away from the poles and the equator and toward higher altitudes. However, these changes cannot be attributed entirely to climate change, as habitat destruction played an important role as well. At the same time, it is difficult to determine what impact climate change has had thus far on the distribution of infectious diseases, as many other factors play a role as well. Important examples of such factors include extensive travel and migration of human populations, drug and pesticide resistance, urbanization and increased population density, and availability of health services (Lafferty, 2009).

Despite our fairly limited knowledge, there are some widely cited examples demonstrating that climate change has indeed resulted in the introduction of certain infectious diseases into previously unaffected areas. One such example is the spread of malaria beginning in the 1950s into highland regions of East Africa where this disease previously did not exist (Lindsay et al, 1998). This occurred in the setting of much warmer and wetter weather than usual, although deforestation was also occurring at the same time, which may have contributed somewhat to the warming trend.

During the same time as the expansion of malaria into the African highlands, there was a sharp reduction in the prevalence of malaria in the Sahel, an arid region of West Africa which was experiencing a particularly severe drought (Faye, 1996). In the case of malaria in the highlands of Africa, this geographic range shift resulted in high morbidity and mortality due to introduction of the disease into a largely non-immune population (Faye, 1996).

In 2002, the World Health Organization (WHO) released data from a statistical model regarding the impact of climate change on human health as of the year 2000 (WHO, 2010). The aspects of climate change considered in the model included direct effects of heat and cold, drought and famine, population displacement due to natural disasters or resource shortages, breakdown of health infrastructure in natural disasters, and conflict over scarce resources. The health outcomes examined were diarrheal disease, vector-borne disease (specifically, malaria), malnutrition, and injury due to natural disasters. Outcomes were measured in disability-adjusted life years (DALY)—a commonly used measure which includes years of life lost and years of life lived with disability.

| **Table 1:** Global health outcomes due to climate change as of the year 2000, expressed in Disability-Adjusted Life Years (DALYs).9 |
| | **Total DALYs (1000s)** | **DALYs/million population** | |
| Africa | 1894 | 3071.5 |
| Southeast Asia | 2572 | 1703.5 |
| Eastern Mediterranean | 768 | 1586.5 |
| Latin America and Caribbean | 121 | 188.5 |
| Western Pacific | 169 | 111.4 |
| Developed countries | 8 | 8.9 |
| Source: Shuman (2011) | |

What is readily apparent from these data is that developing regions of the world have been dramatically affected by climate change in comparison with developed countries. This stands in stark contrast with CO_{2} emissions, which are accounted for almost entirely by developed countries such as the US and countries with rapidly developing economies such as China and India. According to the most recent data from the United Nations (UN) Millennium Development Goals in 2006, developing regions (excluding China and India) produced just 6.2 billion tons (about 22%) of the global total of 28.7 billion tons of CO_{2} emissions (United Nation, 2009).

**Future impact of climate change on infectious diseases**

The 2002 WHO report also used a statistical model to estimate the global burden of disease that will occur in the future as a result of climate change (WHO, 2010).

According to the model, by 2030, there will be 10% more diarrheal disease than if climate change did not occur, which will primarily impact the health of young children. If global temperatures increase by 2–3 °C, as they are expected to, it is estimated that the population at risk for malaria will increase by 3%–5%, which means that millions of additional people would likely develop malaria each year. Others have developed models as well in an attempt to predict the future impact of climate change on infectious diseases.

However, the authors were careful to state that being at risk for getting a disease does not necessarily translate into getting the disease, and that further modeling studies are needed to estimate what the actual impact on human health will be. Developing early warning systems for vector-borne diseases is more difficult because accounting for the unique biology of the vector adds another layer of complexity. However, there is significant interest in developing such early warning systems. For example, models for early warning systems for dengue fever have now been developed in Thailand and Puerto Rico, where robust surveillance data is available (Lafferty, 2009). While many models for early warning systems have been developed, the systems themselves are not widely used at this point. As noted previously regarding the impact of climate change on infectious diseases, the development of truly useful early warning systems is affected by difficulty measuring the impact of non-climatic factors (*e.g.*, migration, population immunity) on susceptibilities of different populations to disease.

In summary, for decades, greenhouse gases, such as carbon dioxide have been increasing in the atmosphere. Its impacts varies in different ways, including:

1. Rapid changes in global temperature: Increased greenhouse gases and the greenhouse effect has contributed to an overall warming of the Earth’s climate, leading to a global warming (even though some regions may experience cooling, or wetter weather, while the temperature of the planet on average would rise).
2. Extreme Weather Patterns: Most scientists believe that **the warming of the climate will lead to** more extreme weather patterns such as:

• More hurricanes and drought;
• Longer spells of dry heat or intense rain (depending on where you are in the world);
• Scientists have pointed out that Northern Europe could be severely affected with *colder* weather if climate change continues, as the arctic begins to melt and send fresher waters further south. It would effectively cut off the Gulf Stream that brings warmth from the Gulf of Mexico, keeping countries such as Britain warmer than expected;
• In South Asia, the Himalayan glaciers could retreat causing water scarcity in the long run.

1. super-storms: Mentioned further above was the concern that more hurricanes could result. The link used was from the environmental organization WWF, written back in 1999. In August/September 2004 a wave of severe hurricanes left many Caribbean islands and parts of South Eastern United States devastated. In the Caribbean many lives were lost and there was immense damage to entire cities. In the U.S. many lives were lost as well, some of the most expensive damage resulted from the successive hurricanes
2. Ecosystem Impacts: With global warming on the increase and species’ habitats on the decrease, the chances for various ecosystems to adapt naturally are diminishing. Many studies have pointed out that the rates of extinction of animal and plant species, and the temperature changes around the world since the industrial revolution, have been significantly different to normal expectations.
3. Rising Sea Levels: Water expands when heated, and sea levels are expected to rise due to climate change. Rising sea levels will also result as the polar caps begin to melt. Rising sea levels will impact many coastlines, and a large mass of humanity lives near the coasts or by major rivers. Analysis by the World Wildlife Fund has found that many cities are unprepared for climate change effects such as rising sea levels.
4. Increasing ocean acidification: the basic chemistry of ocean acidification is well understood. These are the 3 main concepts:

1. More CO2 in the atmosphere means more CO2 in the ocean;
2. Atmospheric CO2 is dissolved in the ocean, which becomes more acidic; and
3. The resulting changes in the chemistry of the oceans disrupts the ability of plants and animals in the sea to make shells and skeletons of calcium carbonate, while dissolving shells already formed.

1. Increase in Pests and Disease: An increase in pests and disease is also feared. A report in the journal *Science* in June 2002 described the alarming increase in the outbreaks and epidemics of diseases throughout the land and ocean based wildlife due to climate changes.
2. Failing Agricultural Output; Increase in World Hunger: The *Guardian* summarizes a United Nations warning that, one in six countries in the world face food shortages this year because of severe droughts that could become semi-permanent under climate change. Drought and desertification are starting to spread and intensify in some parts of the world already.
3. Agriculture and livelihoods are already being affected: Failing agriculture in the future have long been predicted. While warm weather can often be good for some crops, hotter than average temperatures for the *entire* season is often not good for plants. This would affect at least half the world’s population that either live in the region or rely on food coming from that region.

**PROPOSED SOLUTIONS**

**Preventing further climate change**

The primary method for preventing climate change from impacting human health is to stop climate change altogether. While some degree of climate change has already occurred, the idea is to reduce greenhouse gas emissions to the point where this phenomenon is considerably slowed. The Intergovernmental Panel on Climate Change has determined that a 50% reduction in greenhouse gas emissions (compared with 1990 levels) by 2050 will be necessary to stabilize the global temperature increase at 2–2.4 °C compared with preindustrial times. Some international efforts to reduce emissions have already been put in place. The Kyoto Protocol, which was developed in 1997 by the UN Framework Convention on Climate Change, has now been ratified by 187 nations (but most notably not by the US) and was put into effect in 2005 (UN, 2009). Under the protocol, 37 developed countries have agreed to reduce their collective greenhouse gas emissions by 5.2% compared with 1990 levels by 2012. This can be accomplished using a variety of mechanisms including emissions trading, where countries can trade credits for greenhouse gas emissions.

More recently, the UN Climate Change Conference took place in Copenhagen in late 2009 to establish a framework for tackling climate change beyond 2012, when the Kyoto Protocol expires. The European Union put forth the most ambitious proposal, which would require developed countries to reduce CO_{2} emissions by 30% (15%–30% for developing countries) below 1990 levels by 2020. This would be accomplished by emissions trading, development of new emissions standards for cars, promoting energy efficiency among the residential sector, investment in renewable energy sources (rather than fossil fuels), reduction in deforestation, and advancement of technologies to capture and store carbon from the atmosphere. However, the meeting ended without passage of a binding resolution. Instead, several countries (including the US) developed a nonbinding agreement to halt the global temperature increase to 2 °C, with no mention of targets for emissions. One of the major issues at the conference was the responsibility of developed countries to assist developing countries (including China and India) in reducing emissions.

While governments must take the lead in halting climate change, it is also our responsibility as individuals to do our part to reduce our own contributions to greenhouse gas emissions. At home, we can use more energy efficient appliances and light bulbs, properly insulate our houses, and recycle. We should drive more fuel efficient vehicles and use public transportation whenever possible

Investing in infectious diseases research and prevention efforts while reducing emissions to halt climate change is of the utmost importance, we must remember that the best case scenario would be a global temperature increase of around 2 °C. Therefore, we must also focus our efforts on mitigating the effects of climate change, including its potential impact on the global distribution of infectious diseases. In order to accomplish this, additional research is needed on the epidemiology and ecology of the infectious diseases that will likely be affected by climate change. However, these diseases typically fall under the category of “neglected diseases,” meaning that they primarily affect people living in poverty. In 2007, the National Institutes of Health (NIH) in the US spent less than one percent of its entire operating budget on research related to the neglected diseases. More recently, the Institutes launched the Therapeutics for Rare and Neglected Diseases Program, which focuses on the molecular mechanisms of neglected diseases in an attempt to develop new therapeutic options (UN, 2012).

We must fully understand the epidemiology and ecology of infectious diseases such as malaria to anticipate what effect climate change will have on their distributions, and to develop early warning systems to help populations prepare for impending epidemics. To ensure that this necessary research is being done, we must provide funding mechanisms and logistical support. The best means to accomplish this would be to incorporate research on the impact of climate change into existing infrastructures provided by large international organizations such as the WHO. For example, in 2007 the Bill and Melinda Gates Foundation, which has been a major source of funding and innovation for research and problem-solving in developing countries, announced an ambitious plan to work toward eradication of malaria (UN, 2012).

As we move forward, it is absolutely imperative that organizations such as the WHO and Gates Foundation continue their missions to treat and prevent the neglected infectious diseases as part of a multi-faceted approach at improving global health. Effective treatments and vaccines will go a long way in preventing human suffering that may occur as a result of climate change.

More so, In Nigeria, afforestation, promoting good hygiene, improving in the technology, research and development on preventing and managing climate changes and its consequences will produce immense result. Government involvement in mosquitoes treated net distribution has helped, it should be revamped. More awareness should be created instead of just academic papers. More therapeutic and vaccine should be develop to curb over spreading of the sickness.

**CONCLUSION**

Dengue, schistosomiasis, malaria and Rift Valley fever are common examples of major human diseases that can be expected to be influenced by global climate change. There are experimental vaccines for dengue and Rift Valley fever, and drugs for treatment of schistosomiasis. We can combat all three diseases with environmental sanitation and health education. In spite of these measures, we have not been successful in controlling them and we can expect local and world changes in temperature and rainfall to make their control more difficult.

Fortunately, the changes will happen gradually and if we act now, we have time to learn more about the epidemiology and ecology of the vector-borne and zoonotic diseases. We also have time to devise better control and prevention strategies. These studies will require interdisciplinary research. The trend today in graduate education and in university and government research is to specialization, and in infectious diseases the trend is to specialization at the molecular level. This trend is laudable to a point; many of our solutions will require understanding at the molecular level. However, this particular problem will also require training in more general and interdisciplinary fields including field ecology, general medicine, epidemiology, forestry and botany, entomology, climatology, microbiology and zoology to name a few.

We should aim to devise better direct intervention measures for these diseases. We also need more information about transport of agents, modes of transmission, their reservoirs, and the effect of temperature, rainfall, and other climate-related parameters on the vectors, vertebrate hosts, and the agents of disease themselves. Studies of ecology at the periphery of the ranges of the agents and their reservoirs would be especially valuable. Such information could be used to predict more accurately which of the diseases to target as threats, and which will be less likely to spread and/or become more severe.

In summary, climate change is a very real phenomenon which has already impacted the global distribution of infectious diseases. If climate change continues unabated, it is likely that the range of deadly diseases such as malaria will expand or shift, resulting in sickness and death as populations without pre-existing immunity are increasingly affected. It is our responsibility to take action now to prevent this from occurring. We must reduce greenhouse gas emissions by developing an international treaty, enacting legislation locally, develop new technology and acting responsibly as individual citizens of the world. Finally, we must continue to seek answers as to how climate change will affect our most vulnerable populations, and we must do what we can to protect them.

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