Climate change has resulted in negative impacts on different sectors of human life. The primary cause of global warming remains to be human activities that are responsible for the emission of greenhouse gasses. Currently, climate change is linked to the increased northward bound mobilization of tropical and subtropical disease causing vectors. The illnesses that occurred only in tropical and subtropical areas are now becoming endemic in North America that did not have the right ecological support for neglected tropical disease (NTD) causing vectors. This research seeks to establish the role of human actions in climate change that further leads to the northward spread of health complications from NTDs. The study uses the case study of Leishmaniasis, which is one of the NTDs that has become endemic in North America. An in-depth literature review of scholarly articles is conducted to establish the effect of climate change on the incidence of Leishmaniasis in North America. The research reveals that Leishmaniasis, one of the NTDs, has spread in North America as a result of global warming, which has been induced by human activities such as deforestation and industrial gas emissions. Therefore, there is the need for reduction in deforestation and limitation of industrial gas emission to slow climate change and mitigate effects on public health.
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Keywords: Leishmaniasis, neglected tropical diseases, climate change
Climate Change and Disease
Climate change continuesto be one of the primary challenges today. Modifications in atmospheric conditions result in negative impacts on human health. Global warming has led to the incidence of neglected tropical diseases (NTD) in the areas that did not encounter these diseases before. North America is one of the parts of the world that did not experience the occurrence of NTDs previously. Nowadays, there are some NTDs that have become common in North America. These NTDs include Chagas, Leishmaniasis, Toxocariasis, Strongyloidiasis Cysticercosis, Toxoplasmosis and Giardiasis among others. Leishmaniasis is one of the most dominant NTDs in North America. This illness used to be endemic in South America, and it is transmitted by species of the sand fly. Leishmania is the protozoa transmitted by the sand fly that causes Leishmaniasis. The parasites are often injected into the human blood through the bite of the sand fly. Then the parasites settle in macrophages of the human body where they multiply and grow to colonize other body cells and tissues. The body immune response to this infection involves the production of oxygen and nitrogen species, neutrophils and monocytes. Moreover, this disease is associated with tropical and subtropical temperatures. Environmental factors such as rainfall, vegetative index and land surface temperature affect the habitat of sand flies. Therefore, this disease appeared in North America because of the climate change. Hence, human activities remain the primary cause of global warming. However, these activities should be minimized to slow climate change at both national and individual levels. Thus, there is a northward movement of tropical and subtropical disease causing vectors as a result of climate change caused by human activities, which ought to be regulated to decelerate the process of global warming.
Neglected Tropical Diseases that Have Become Endemic to North America
North America has seen an increasing epidemiology of neglected tropical diseases (NTD). Chagas and Leishmaniasis remain the leading NTDS that have high incidence in North America (Hunter, 2014). Both illnesses are caused by protozoan parasites. However, they have different pathologies and symptoms that reflect their distribution and impact. Moreover, an increasing occurrence of Helminthic infections that fall under NTDs has been evident. These infections include Toxocariasis, which is caused by a cat roundworm. Toxocariasis has affected a total of 2.8 million people in the North American region (Haruno, 2013). Another helminthic disease is Cysticercosis, which is caused by a pork tapeworm Taenia Solium. Besides, this disorder is more common among immigrant populations in North America (Haruno, 2013). One more NTD that is spread in North America is Strongyloidiasis, which is caused by a threadworm. Toxoplasmosis caused by Toxoplasma Gondii has also become endemic in North America. Over 60 million individuals in North America are believed to carry the Toxoplasma parasite (Haruno, 2013). Nonetheless, these people are asymptomatic and only display mild flu-like symptoms as a result of immune response mediation. In addition, Giardiasis, which is also parasitic, has been diagnosed in certain North American countries such as Guatemala, Haiti, Jamaica and the Bahamas (Greer, Ng, & Fisman, 2008). Therefore, these diseases constitute the NTDs that have been established as endemic in North America.
Leishmaniasis is one of the NTDs that have become endemic in North America being common in South America before. This ailment is caused by protozoa of the genus Leishmania. The vectors that transmit the disease causing protozoa are different species of the sand fly insects. Leishmaniasis was more spread in tropic and subtropic countries. Its occurrence in North America was first established in 2009 (Hunter, 2014). Moreover, this illness is associated with tropical climate and especially warm rainforest environments. As an NTD, it has also been prevalent among poor populations. The expansion of the geographic range of sand flies has been connected with climate and environmental changes. Leishmaniasis was more common in South American countries such as Argentina, Peru, Venezuela, Colombia and Ecuador (Salom?n, Quintana, Mastr?ngelo, & Fern?ndez, 2012). Therefore, Leishmaniasis is one of the endemic NTDs in North America transmitted by an insect vector that has been widespread in South America.
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Molecular Mechanisms Associated with Leishmaniasis
Leishmania are among the most resilient obligate intracellular protozoa hosted by sandflies of the genus Phlebotomus. Figure 1 shows a Phlebotomus sand fly. The protozoa survive the harsh digestive system of sand flies where they also proliferate intracellularly through deactivating the macrophage before it penetrates into the human body. When one of Leishmania-carrying sand flies bite people. The sand fly injects small numbers of parasites into the human blood. The parasites are taken up rapidly by the mononuclear blood cells. The injected parasites are in the promastigote stage, (Rossi & Fasel, 2017). After the bite, the parasites enter the amastogote stage where they multiply and increasingly affect other body cells and tissues. These parasites often seek macrophage cells to colonize thereby reducing one’s immunity. Successful infection of Leishmania results from the alteration of signaling events in the host cell. This alteration is caused by the multiplying presence of parasites in the cells. The signal alteration then leads to increased production of autoinhibitory molecules, namely TGF-beta. Additionally, this alteration triggers a decreased induction of cytokines such as IL12 hence weakening protective immunity, (Cunningham, 2012). Further, Nitric oxide production is also inhibited. Besides, the resultant defective expression of the major histocompatibility complex (MHC) genes significantly reduces subsequent T cell activation mediated by macrophages that in turn conduces abnormal immune responses (Rossi & Fasel, 2017). Figure 2 shows the molecular mechanism and pathway of Leshmania from the Phlebotomus sand fly bite to the eventual Leishmaniasis symptomps.
Human Innate and Adaptive Immune Response to Leshmaniasis
Leshmania is one of the protozoa that develops its strength from evading and modulating the immune system. After penetrating into the human blood Leshmania rushes to locate host cells that they can colonize. These parasites in most cases settle in the macrophages. The latter exhibit a human innate response a few hours after the infection. The macrophages produce reactive oxygen and nitrogen species as an anti-leishmania response. This production is targeted at killing pathogens that are invasive. The process is tightly regulated to ensure that the host cell is not damaged. Additionally, the process involves several body enzymes and gets activated by phagocytosis. The NADPH oxidase 2 (NOX2) and inducible nitric oxide synthase (iNOS) are the two primary producers of reactive specie in macrophages (Rossi & Fasel, 2017). Another innate response is the mechanism aimed at trapping the Lshmania by the neutrophils, which are rapidly recruited to the infection site. The neutrophils produce ‘neutrophil extracellular traps’ (NETs), which are a network of extracellular fibrils composed of Deoxyribonucleic acid with antimicrobial proteins. These proteins include elastase, histones and toxic granules. One more innate human response incorporates the production of inflammatory monocytes through platelet activation. These monocytes are recruited at the infection site, and this process depends on chemokine (C-C motif) ligand 2 (Rossi & Fasel, 2017). However, the production of monocytes has not proven effecting in preventing the multiplication of the leshmania parasites (Cunningham, 2012). The only established human adaptive response is the production of granzyme B. The latter is a helpful protease found in natural killer cells (NK cells), cytotoxic lymphocytes (CTLs), and cytotoxic T cells. This protease contributes to mediating apoptosis in targeted cell and also stimulates the release of Cytokine. According to da Silva Santos et al, (2013), the production of granzyme B after occurrence of Leishmaniasis helps an individual to becomes more immune to subsequent infection. Therefore, granzyme B production is an adaptive immune response to Leishmaniasis.
Environmental Factors Associated with Infection by Leishmaniasis
Some environmental factors that affect the infection with Leishmaniasis are crucial in the given analysis. The reason for this is that the disease causing protozoa Leishmania and the vector, which are specific species of sandflies, require particular environments. Land surface temperature is one of the environmental factors associated with the infection by Leishmaniasis, as sandflies thrive in tropical and sub-tropical temperatures. Temperature and humidity levels impact the survival of sand flies and development speed at different stages of its life cycle. “Forest fragmentations, climatic variables, vegetation indices and land surface temperature are important candidate predictors for vector-borne diseases such as leishmaniasi” (Oryan & Akbari, 2016). The other environmental factors are the vegetation index and rainfall. Reduced vegetation has been associated with increased distribution of sandflies. Abdullah, Dewan, Shogib, Rahman and Hossain (2017) state that “… elevation, rainfall, temperature, and forest cover were found to be associated with the distribution of sand flies in France”. Hence, vegetation cover, land surface temperature and humidity levels are the environmental factors that contribute to the infection by Lesishmaniasis.
Influence of Climate Change Associated with Leishmaniasis
The spread of Leishmaniasis to North America has been largely attributed to climate change. The vectors that cause this disease thrive in humid and tropical temperatures. The increase in temperature as a result of global warming has induced the widespread of Leishmaniasis. Rising temperatures have also led to increased humidity and rainfall in different parts of the world. Higher humidity and rainfall were previous characteristics of the areas with tropical rainforests. However, global temperature increase has triggered high humidity and rainfall even in non-tropical regions that in turn created a suitable environment for the survival of sandflies. In their research, Gonz?lez et al. (2010) indicated a strong correlation between Leishmania spread in North America to the climate change trends. Therefore, global warming has increased the incidence of Leishmaniasis.
Influence of Human Actions on Climate Change
According to the majority of scholars, human activities have been the primary cause of climate change. Most human actions that result in climate change increase the concentration of harmful gases in the atmosphere. These gases, which are referred to as the greenhouse gasses, include Carbon dioxide (CO2) Water vapor (H.2O), Nitrous oxide (N.2O), Chlorofluorocarbons (CFCs), Methane and Hydrofluorocarbons. Burning of fossil fuels and oil is one of the human activities that foster the release of carbon dioxide into the atmosphere. Carbon dioxide facilitates the formation of a thick atmospheric blanket over the earth. This layer then causes the radiation of heat back to the earth thereby increasing the temperature. Another human activity that affects climate change is manufacturing of products. Gas emission from industries is the leading source of carbon dioxide and greenhouse gasses. Currently, the production sector has grown by 52% compared to the first half of the 20th century (Calder & McKinnon, 2013). Besides, various countries compete on the thresholds of production and offer employment to their citizens through the manufacturing industry.
Furthermore, globalization has contributed to the development of international trade, which in turn significantly expanded the manufacturing scale. In 2015, 22% of greenhouse gas emissions were associated with the manufacturing industries (Hodgson, 2010). Once these greenhouse gases are released into the atmosphere, they cause a greenhouse effect. The greenhouse effect is the increased heating induced by the radiative action that results from the absorption of heat by atmospheric greenhouse gases. Therefore, gas emission from the manufacturing industry is a human activity that promotes climate change. The latter has occurred due to the fact that firstly, the emitted gasses absorb the heat that comes from the earth. This absorption led to the concentration of heat within the atmosphere hence increasing the temperatures. Secondly, the gasses exert a radiation effect, which further radiates the released heat back to the earth. This form of radiation damages the normal ventilation cycle in the atmosphere that maintains normal atmospheric temperatures; instead, it triggers the concentration of heat thereby increasing the temperatures. The third effect of greenhouse gases is their ability to raise the level of humidity in the atmosphere. Higher temperature facilitates the evaporation of liquid from the earth surface. Thus, evaporation induces high humidity that in its turn increases the rainfall, which also influences the climate. Moreover, greenhouse gasses deplete the ozone layer. The ozone layer, which is made of three oxygen molecules, is meant to regulate the permeation of sunrays to the earth. The degradation of ozone layer translates into greater emission of the Sun rays, which further increases global temperatures.
The other activity that causes climate change is deforestation. The human population is continuously growing along with the need for land space to accommodate houses and economic activities. Deforestation often affects humidity, rainfall and atmospheric concentration of carbon dioxide. Cutting down of trees often reduced humidity and rainfall. Then this trend results in higher temperature, which finally leads to extreme occurrences such as drought. Moreover, vegetation survives by absorbing carbon dioxide from the atmosphere and releasing oxygen. Therefore, the presence of vegetation decreases carbon dioxide concentration in the atmosphere, which helps with mitigating the greenhouse effect. Thus, deforestation facilitates the CO2 concentration, which in turn increases temperatures. The extensive use of fertilizers in farming also boosts the release of nitrous oxide gases into the atmosphere. Consequently, climate change is significantly promoted by human actions that enlarge the emission and concentration of greenhouse gasses in the atmosphere.
Ways to Slow Climate Change
Nevertheless, climate change is inevitable, as it is a continuous phenomenon that cannot be reversed, but still the process can be slowed. Global warming cannot be reversed because human economic, social and political lives depend on some of the activities that result in climate change. The effect on climate can only be slightly reduced since human activities, especially industrial production, cannot be eliminated. However, some strategies may be introduced to alleviate the impacts of human activities on climate change. Firstly, each government should be assume responsibility for forestation. Additionally, there is a need to increase the presence of trees on the land surface. The greater number of trees will absorb carbon dioxide hence minimizing its atmospheric concentration. Trees also positively contribute to rainfall. The other means is decreasing the greenhouse gas emission in the manufacturing industry. This goal can be achieved by using alternative raw materials that do not to emit these harmful gasses in the production of the necessary product. Industrial emissions can also be cut by imposing a limit on the amount of gas emission allowed in each country (Bows, 2011). Enforcing a restriction will make manufacturers focus on finding alternative ways of production that are not harmful to the atmospheric composition.
Furthermore, the development of clean energy strategies that will replace the burning of fossil fuels, in the long run, can help to decelerate climate change. The use of natural energy sources such as the Sun to produce electricity, as well as lighting and power technologies is possible when adequately considered. Gradual adaptation of this form of energy will slowly reduce greenhouse gas emission from fossil energy sources. Increasing fuel efficiency is the other crucial way of combatting global warming. Fuel efficiency enables a vehicle to use the smallest amount of fuel to cover a particular distance thereby decreasing the gas emission that results from the use of fuel in the vehicle engines. Fuel efficiency can be increased by introducing car models that consume less fuel into the market.
Personal Contribution to Slowing Climate Change
To slow climate change, I can stop the deforestation activity in my neighborhood. This goal is possible by reporting on any form of unauthorized deforestation that I witness to the local forestry department in my town. Unfortunately, a lot of people cut down trees just because they have grown in their land without considering the consequences of the act. Therefore, it is important to inform about any person who chops down trees without authorization. In this way, I will help reduce deforestation. The other action is to purchase a vehicle that requires little fuel and to use non-gas transport system when possible and convenient. Toyota cars are made in such a way that they need half of the amount of fuel, which is necessary for a Mercedes car to cover the same distance (Bows, 2011). Further, for shorter distances, I can ride a bicycle, which does not demand fuel combustion for locomotion. I can also use energy efficiently. Conservation of energy involves switching off electronic gadgets when I am not using them, shutting down the car engine when I am in traffic or when I have parked even just for a few minutes, as well as ensuring that I do not charge any device that I do not utilize.
In conclusion, climate change caused by human activities results in the northward spread of tropical and subtropical disease causing vectors in North America, which has seen such cases of NTDs as Chagas, leishmaniasis, Toxocariasis, Strongyloidiasis Cysticercosis, Toxoplasmosis and Giardiasis among others. The climate in this region could not ecologically support habitation for the organisms that cause these illnesses. Leishmaniasis remains to be one of the most common NTDs that have become prevalent in North America. This ailment is triggered by protozoa named leishmanial, and it is transmitted by particular species of the sand fly.Once injected into the human blood stream through a sand fly bite, Leishmania settles in the macrophages and multiplies colonizing the hosting cell. The sand fly has previously been associated with tropical environments, as this vector thrives in tropical temperatures and humid conditions. Climate change, which has led to increased atmospheric temperatures and humidity, promoted the northward movement of suitable habitation for sand flies. Increased temperature is one of the primary reasons for the presence of sandflies in North America. These conditions are induced by various human activities. People have established the industries that emit greenhouse gasses thereby fostering a greenhouse effect, which in turn changes the climatic conditions. The greenhouse gases basically influence the climate through absorbing heat from the earth, radiating it back and depleting the ozone layer. Therefore, it is critical for the governments to take actions against deforestation and excessive emission of greenhouse gases as well as to introduce the utilization of clean energy sources. Personally, I can contribute by purchasing a car that consumes less fuel to reduce gas emissions that result from fuel combustion. I can also lower the energy use by conserving energy and ensuring that I switch off power supply in gadgets that I am not using. When I need to cover shorter distances cycling is the best option since it can also minimize gas emissions, as bicycles do not require fuel combustion for locomotion. Consequently, it has been established that climate change caused by human activities has led to the northward movement of tropical and subtropical disease-carrying vectors.