Table of Contents
Introduction to Climate change
Climate change is considered as a major pressing issue facing the world currently. Evidently, weather episodes are clearly deviating, ocean levels are peaking and level of greenhouse gas emission is unprecedented compared with the pre-industrial years (EEA, 200). The IPCC has forecasted world mean temperature rise of 1.5-5.8 °C throughout twenty first century. Severe weather events like heat waves, intense downpour and water shortage facing the world now can be credited to the significant rise in temperature (IPCC, 2001). In the quest to counteract the undesirable outcomes temperature change brings, the world’s response for sustainable development poses a major challenge for humans (Weng et al., 2013; Yang et al., 2013).
Variations in atmospheric conditions greatly affect the global south than the global north. This accounts for the narrow temperature distinction experience in the global south in comparison with the temperate regions. And thus hit strongly by adverse temperature fluctuations. This downside is generally aggravated by unobstructed urbanization, notably, the parallel interaction between informal settlements and structured layouts. The uniqueness of tropical climate poses bigger vulnerability of humans to various health-related issues. Tropical countries are believed to emit the smallest amount of greenhouse gases (GHG), however they are most at risk of climate change impacts (Patz et al., 2007).
Again, the Mediterranean region is earmarked as of a major hotspot for temperature changes and is responding critically to the trends of global warming (Gualdi et al., 2013). The Mediterranean experiences a warming episode with high magnitude of warmth and reduced rainfall. Vector-borne disease is believed to have resurfaced and also the incidence is probably going to extend during this era of global temperature change coupled with the densely inhabited Mediterranean setting (Reiter, 2001).
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Climate change within the context of the Sustainable development goals
Climate change poses monumental danger to the event of sustainable surroundings and its substantial impacts greatly affect the underprivileged and vulnerable. It’s additionally eminent to require forceful solutions to oppose global climate change and its impacts to considerably attain all the sustainable Development Goals (SDGs). Climate action could be many-sided with damaging effects endangering the achievement of the other sustainable development goals. Non-fulfillment to imperative measures can cause global climate change the potential to retrogress the headway already created for the global success and tranquility.
Global climate change has horrific health implications. These accounts to the hike in infectious and non-communicable diseases. Battling global climate change can guarantee the quality of life of humans. Achieving climate action will not solely alleviate negative result of global climate change but however, provide a safer planet for future generations. Taking climate action will also prevent food scarcity and guarantee nobody goes hungry and safeguard communities from severe weather events. Climate action may also create additional benefits for households and large-scale industries as they currently account for fewer gas emissions. This will also create avenue for more jobs to help alleviate people from poverty (WHO, 2017).
Desisting from the use of fossil fuels and exploitation resources will scale back the negative impacts of our unsustainable actions. Through climate action, we will foster peaceful, unbiased and inclusive societies. Also, good governance of natural resources will reinforce peace building and safeguard access to basic human needs in areas where resource deficiency contribute to instability hitherto. Climate action creates avenue to handle world challenges through building new formidable partnerships. This opportunity also provides equal platform for consultants on global climate change and sustainable development to establish synergies and improve conflict resolution and also harness opportunities. On the contrary, if climate actions measures are not rigorously planned, there may be resultant negative effect that could be detrimental (UNFCC, 2019).
We often dialogue that sustainable Development Goals will solely be maintained if good health is maintain, which again depends on effective vector management which has connections with other goals. Enterprising advances are being enforced by completely different sectors required for the management and eradication of VBDs; specifically those championing healthy environments (Pruss-Ustun et al. 2016).
Vector borne disease
Vector-borne diseases are infections circulated by insects like mosquitoes, ticks and different arthropods or little invertebrate like snails or crustaceans. Vectors act as main mode of infection transmission from one host to a different and successively form an essential stage within the transmission cycle. Two main types of VBD transmission that can occur are; Anthroponotic infections or human-vector-human transmissions, where humans are the sole reservoir of the disease. And, zoonotic infections or animal-vector-human transmission, where animals are the main reservoir of the infection and humans are classified as spillovers and do not usually account for the disease transmission cycle.
The type of transmission of a vector borne disease has implications on their control strategies. Anthroponotic infections can be eradicated if all human sicknesses are treated, whereas zoonotic diseases are far more tedious to control since all animal reservoirs of the disease would need to be treated (Hill et al., 2006). The bulk of the risk groups reside in developing countries located in the global south. With reference to the World health organization, the amount of annual deaths due to vector-borne diseases currently stands over 700,000, with about 4 billion people at risk of infection (WHO, 2017).
However, several diseases are under-reported, particularly those that are rarely fatal like Onchocerciasis and Lymphatic filariasis (Hill et al., 2005). Climate change may destroy the ecosystem, which in the long-term accounts for the emanation of vectors and pathogens in the new ecological environment (McMichael and Ranmuthugala, 2013).
Consideration of disease burden, it is eminent to also evaluate the morbidity it causes. Disability adjusted life years (DALYs) are one measure that is often used to assess the burden of diseases associated with vectors. “One DALY is defined as one lost year of healthy life and is a measurement of the gap between the current health of a population and an ideal situation where everyone lives to old age in full health” (Prieto et al., 2003). The geographical distribution of VBDs is largely reflective of the geographical distribution of both vectors and their reservoir hosts. Many vectors are unable to regulate their own internal temperature and are therefore highly dependent on climate for their survival and development (Heinrich, 1981).
Grassl (2011) confirmed a positive correlation between regional patterns of climate and specific health outcomes among the people residing in such areas.
Evidence for climate change has been controversial, as we need to rule out, or account for, the effect of climate-independent factors before ascribing climate as a determinant of observed changes in vector-borne diseases. Trend analysis has been nagged by the scarcity of health records and many confounding factors too. Some studies have developed innovative ways to provide some evidence on the effects of climate change on human health. The latest IPCC report has stated with medium confidence that proof exists showing associate adjusted distribution of some communicable disease vectors (IPCC, 20012).
Vector borne disease dynamics
Vector borne diseases can in a way be classified as an entire ecosystem, which elements such as the vectors-pathogens-hosts relationship, joined to unique optimal environmental conditions (Caminade et al., 2016). The variations in temperature and precipitation pose a huge impact in the spread of vector borne diseases. The definitive hosts are also influenced by climatic variations in lieu of displacing chunk populations due to famine or heavy downpour (Patt et al., 2010). Interaction of three factors must exist for a disease to manifest. These are the risk population, vector and the disease pathogen. In endemic areas, elements necessary for survival and replication must appear to be suitable for both vectors and pathogens. However, in eradicating VBDs, other factors such as improved health care services and vector control measures play vital role.
The conditions needed for survival and replication must appear to be suitable for both vectors and pathogens in areas considered to be endemic. However, other factors such as improved health care services and vector control measures play vital role in the eradication of VBDs. Indirect impacts posed by changes in livelihood conditions due to climate effect could also affect the nutritional status of individuals, thereby potentially increasing their susceptibility to disease.
Climate versus Weather effects
Climate can be defined as the mean weather condition at a specific locality studied for a long time, while weather is the daily atmospheric conditions at a given location. Weather will tend to fluctuate on daily basis while climate is the long-term average of shifts in a location (IPCC). With respect to vector borne diseases, climate acts to limit the spectrum of these diseases by limiting the geographical range of favorable habitat for vector and pathogen survival. In other words, climate determines what regions can potentially support one disease or another with reference to the physiological requirements of the vector, reservoir host and pathogen.
For example, the range of endemic malaria was believed to be limited in high altitudes by the temperature threshold requirements of the mosquito host. However, recent changes in climate have begun to shift these thresholds to high altitude and can be contributing to a high incidence of endemic malaria in Kenyan highlands. Conversely, weather will affect the timing and intensity of a disease outbreak. For example, increased droughts followed by bursts of intense precipitation have been linked with mosquito-borne disease outbreaks, such as dengue, in countries like India and Bangladesh. (Epstein, 2001; Patz, 2002).
Environmental determinants of Human diseases.
Environmental determinants of health are generally the external elements that can be linked to variation of the health status of humans. For example: An individual’s genotype may reveal their susceptibility or resistance to a particular disease. The tendency to acquire ones basic needs may in turn affect an individual’s immunity to infection. Malnutrition may acerbate one’s ability to carry out daily tasks and make a living. Social relationships may also influence access to resources, such as transport to health care facilities whereas socio-economic policies may also ascertain the access to health care services. All these are contributing factors to personal and public health. Climate, independently, is a contributing factor to health and variations in climate are prospective to have adverse end results on human health. According to the Intergovernmental Panel on Climate Change (IPCC), climate change poses deleterious effects to humans. Changing weather episodes indirectly affect the quality of water and food content. While institutions revolt to circumvent climate change effects, this will impact resources available for communities to mitigate climate change effects.
Direct effects of Climate change on Vector borne diseases
Climate has the potential to increase the abundance of both animal reservoirs and vectors (Greerer et al., 2008). There are evidences of this occurrence with regards to Lyme disease in North America (Ogden et al., 2006), malaria in the Kenyan Highlands (Pascual et al. 2006), and bluetongue in Europe (Purse et al., 2006).
Also, climate change may also prolong the length of the transmission cycles of diseases. Notable example is West Nile virus, which has recently appeared in North America, has escalated the mosquito cycle and that of the reservoir hosts (Campbell et al. 2015). There is highest risk of infection for Humans late in the summer when mosquito population densities are considered to be the highest (Harvell et al., 2002).
Other seasons have the propensity to increase the transmission season of the disease, thereby adjusting the risk of human infection earlier in the warm season. Again, climate could also increase the probability of successful introduction of vectors and reservoir hosts. For example, the global spread of Aedes albopictus, which has been linked to the sale of used-lorry tires. This same phenomenon was related to outbreak o Chikungunya virus outbreak in Bangladesh (Campbell et al. 201). Importation of a reservoir host was believed to be associated with the epidemic of West Nile Virus in the Northern America dating back in the late 1990s (Lanciotti et al., 1999). As mentioned previously, climate change effects leading to new cases of animal diseases are likely to extend the risk of human disease as well.
Climate change effects on vectors
Variations in climatic conditions have strong association with the geographical setting and population differences of vectors. Thus, climate change may affect disease vectors by deranging their normal habitat and magnitude of causing infections (Wu et al., 2016). The geographical distribution of disease carrying vectors is hugely influenced by temperature changes. Persistent rise in temperature renders vectors in low-latitudinal areas to acclimatize at either mid or high-level ground regions. Vector borne diseases such as malaria, African trypanosomiasis, Lyme disease, tick-borne encephalitis, yellow fever and dengue have shown in recent studies to colonise new areas where they were formerly absent (Harvell et al., 2002). There have been increased new cases of these diseases in areas of higher above sea level, following colonization of these vectors. For example in China, as the colder periods becomes relatively brief due to rise in temperature, the intermediate host of Schistosoma japonicum, resettled in new areas where previously was considered free from this disease (Zhou et al., 2010).
However, vector allocation can be limited during temperature deviations. For example, Aedes aegypti , the mosquito host for yellow fever and dengue fever viruses (Epstein, 2001a). It is evident that A. aegypti larvae are unable to survive at temperature higher than the normal room temperature (34°C) and the adults also were unable to withstand atmospheric temperature surpassing 40°C (Christopher, 1960). As global warming crisis ensues, disease hosts such as A. aegypti may cease to be at areas where average temperature falls outside the thresholds.
Disease vectors may employ adaptation strategies to survive unfavorable climate change effects. Some arthropod vectors take refuge in areas during unfavorable temperature condition. Inference can be drawn from Jalore, India where A. aegypti mosquitoes were found in underground tanks during temperature of about 40 °C (Tyagi and Hiriyan, 2004). Similarly, evidence show a historical report of the presence of A. aegypti in Memphis, USA during winter temperature below 0°C (Reiter, 2001).
Variations in precipitation may also influence arthropod vectors. There is a strong positive correlation between rainfall and many vector-borne diseases. Some mosquito larval growth accelerates with increased rain and warmth (Hoshen and Morse, 2004). Female Anopheles mosquito is usually known to breed in clean ponds and puddles. However, prolonged droughts may restrict the size and quality of breeding sites for these mosquitoes which may in turn result in reduction in vector population and eventually decrease malaria transmission in general (Gage et al., 2008).
However, rainfall does not always favor vectors. Excessive rainfall may have adverse impact on mosquito population because excessive rainfall may destroy the breeding sites of mosquitoes (Kuhn et al., 2005). On the contrary, intense drought in wet areas may lessen the speed of water in streams and rivers. These water bodies later appear stagnant, which provide ideal breeding sites for mosquitoes (Kovats et al., 2003). Drought also allows the accumulation of decayed materials in stagnant waters, thereby providing optimum condition for Culex mosquito, which are primary carriers of West Nile Virus.
Malaria and Lyme disease are the most significant vector-borne diseases in Europe, which are transmitted by mosquitoes and ticks respectively. The evidence that climate change has intensified the risk of these diseases is weakly correlated, because of the relatively sensitive climate change observed. The impact of climate change can be attributed to population hike, alterations in agricultural procedures and changing socioeconomic conditions. However, there are still some pressing issues culpable for the increase and spread of many vector-borne diseases in many parts of Europe. Malaria was eradicated forty years ago in Italy but local transmission of Plasmodium vivax has recently been reported (Baldari et al., 1988).
The climate in Western Europe provides suitable conditions for transmission of P. vivax mainly because they can develop rapidly at lower temperatures (Boyd, 1949). The expansion of the disease to northern latitudes of Europe can be attributed to climate change (Martins, 1998). However, increasing poverty rate, the mass migration of refugees and the impoverished health care systems could account for the increase in malaria cases. In the advent of global warming, many vectors, not only malaria transmitting vectors, are likely to increase their spectrum within Europe and new emergence vectors are likely to be introduced from the tropics.
Countless of disease agents respond strongly to variations in relative humidity. Relative humidity influences the spread of malaria by affecting the movement of insects and their existence. If the average relative humidity is below 70%, the lifespan of mosquito carrying malaria parasite becomes short to circulate malaria (Pampana, 1969). When wet and warm weather are intersected by drought, the mosquito vectors harboring Lyme and West Nile disease may move into non-endemic places such as Canada and Scandinavia (Senior, 2008). Low humidity may have adverse effect on the survival of adult A. aegypti, thereby reducing dengue disease transmission (Christophers, 1960). Generally speaking, low humidity, especially when coupled with high temperature, forms unfavorable condition for ticks and fleas (e.g. forestlands), restricting the roll out of the related infectious diseases (Gage and Kosoy, 2005).
Wind also has a paired effect on arthropod vectors. Malaria cycle may be positively and negatively be affected by speed of wind. There is limit in biting opportunities for mosquitoes during strong episodes of winds, but can expand the flight distance into new location (Reid, 2000).
