Climate change is increasingly being implicated in species' range shifts throughout the world, including those of important vector and reservoir species for infectious diseases. Intergovernmental Panel on Climate Change predicted that the mean global temperature would increase by between 1.4C and 5.8C over the period 1990 to 2100. Recent investigations attribute more than 150,000 deaths per year and a global disease burden of approximately 5 million DALYs annually to climate change. It is well known that the impact of climate change is on physical and biological systems, including human health. An area that has received particular attention is the potential impact of global warming on shifts in the spatio-temporal distribution of disease vectors, and hence the frequency and transmission dynamics of vector-borne diseases. Vectors, pathogens (parasites), and hosts survive and reproduce within certain optimal climatic conditions. Changes in climate will alter the transmission of vector-borne diseases in different ways, such as changing the survival and reproduction rate of the vector and of the pathogen (parasite), as well as changing vector activities.
Public health officials often use the term tropical diseases to refer collectively to a list of infectious diseases that are found primarily in developing countries. These include malaria, schistosomiasis, dengue, trypanosomiasis, leprosy, cholera, and leishmaniasis, among others. Many of these diseases are spread by insect vectors, and all of them disproportionately affect the world's poor. Malaria is the most severe of these as stated by World Health Organization, but other diseases, less well known and sometimes described as neglected and also imposes grave burdens on people living in the tropics. The World Health Organization estimates that neglected tropical diseases affect over one billion people each year and cause about 570,000 deaths annually. For example, some 200 million people are currently infected with schistosomiasis, a parasite that is transmitted through poor sanitation. Perhaps 50 million cases of dengue occur each year, of which 500,000 lead to devastating hemorrhagic fever, with 22,000 resulting deaths. More than 1.5 billion of the world's poorest people are affected by a range of bacterial and worm based diseases including trachoma, river blindness and lymphatic filariasis. They are just some of so-called neglected tropical diseases, which are diseases of poverty. But despite the numbers they affect, and their health and social consequences, these diseases attract less than one per cent of the total health funding for the developing world.
The potential impact of global warming on the transmission of the neglected tropical diseases has received insufficient attention from researchers and different organization. Most studies on the impact of global warming on the transmission of tropical diseases have focused on malaria but very few studies have been carried out regarding the neglected tropical diseases. The Intergovernmental Panel on Climate Change (IPCC) has specially investigated the changing burdens of infectious disease that may result from climate change. One IPCC background report notes that: Climate plays a dominant role in determining the distribution and abundance of insects and tick species directly, through its effects on vector and parasite development, and indirectly through its effects on host plants and animals and land-use changes. Therefore, it is anticipated that climate change will have an effect on the geographical range and seasonal activity of vector species and, potentially, disease transmission.
Global attention to infectious disease is primarily focused on HIV/AIDS, tuberculosis and malaria; the big three, as they are called, were responsible for over five million deaths in 2007 and are responsible for 39% of all deaths attributed to infectious disease. Unfortunately, this attention has not extended to a group of parasitic and microbial diseases called the neglected tropical diseases (NTDs). These diseases are largely overlooked, due to their low mortality rate and the poverty of their sufferers. Neglected tropical diseases affect the poorest individuals. Over 70% of the affected areas have low to lower-middle income economies. They thrive under poor sanitary conditions, where clean water and food are unavailable and where insect vectors are abundant. Women, children and those geographically isolated from health care are particularly susceptible. Those in conflict-ridden areas are also particularly susceptible, due to the disruption of any health-care infrastructure. Aside from thriving in poverty, the NTDs are also said to be poverty-promoting conditions, as they reduce worker productivity and impair childhood development, and, consequently, the future earning abilities of those children. The resulting economic loss tends to worsen already impoverished conditions.
Bangladesh is highly vulnerable to climate change and its high population density. Floods and cyclones are some of the major challenges that the country faces resulting in the greatest economic and human losses to the country. Higher temperatures including more extreme weather events and sea level rise are already evident in Bangladesh. One estimate is that the average increase in temperature in Bangladesh would be 1.3C and 2.6C by the year 2030 and 2075 respectively with respect to the base year 1990. Global warming will increase the intensity of southwest monsoon, which will, in turn, bring about catastrophic ravages like floods and have far reaching consequences on health. During and after floods, the water borne diseases increase due to heavy contamination of the surface water. Thus climate change could cause floods, break-down of sanitation system, and more water and food-borne diseases like soil-transmitted helminthiasis (STH), cholera, and other diarrhoeal diseases. Bangladesh may be one of the worst hit countries of the world due to a predicted rise in sea level. The increase in salinity in underground water will affect the availability of fresh safe water. As a result, people will be more inclined to use unsafe, contaminated surface water and will contact various water borne infectious diseases like cholera and other diarrhoeal diseases and STH. Incidence of vector-borne diseases like malaria, filaria, leishmania and dengue are likely to increase as a result climate change in this region. This may increase the human contact with the vectors responsible for spread of diseases like malaria, filaria, leishmania and dengue. Though the surveillance system is very weak with gross under reporting, 13 districts of Bangladesh are known to be endemic for malaria, 34 for filariasis and 45 for visceral leishmaniasis (VL). Dengue has been detected in all six divisional headquarters of Bangladesh whereas STH affects our population throughout the country. Filariasis is a parasitic disease which is believed to have infected about 20 million people; 10 million are with various forms of disability, leaving another 70 million at risk of infection. The incidence of visceral leishmaniasis on the other hand is estimated to be about 12,000 per year with about 65 million people at risk of contracting the disease. Some reports claimed a death rate of more than 10% in patients suffering from VL. About 70000 to 80000 malaria cases and 300 to 700 death cases are reported yearly.
The impact of climate changes on neglected tropical diseases is itself neglected. There is an urgent need for researchers and organizations to investigate further the potential impact of climate changes on the transmission of neglected tropical diseases. The findings of such research are required so that populations might be able to adapt or, if necessary, migrate to overcome increased risks for transmission of neglected tropical diseases caused by climate changes.

Khalid Md. Bahauddin
Fellow (Japan), Environment; Member, Bangladesh Society of Environmental Scientist
and Bangladesh Solar Energy Society.

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