GLOBAL climate change is caused by the accumulation of "green-house" gases in the lower atmosphere. The concentration of these gases is increasing mainly due to conversion of fossil fuel and deforestation. For example, individuals are responsible for about 40 percent of emissions in the UK, with energy use in homes, driving and air travel the biggest sources.
The temperature of the earth is escalating dangerously. As a result, the ice-caps and glaciers in the polar regions are melting, submerging low-lying coastal lands, including that of Bangladesh. The viruses and microbes that were inactive and buried under freezing ice, are now starting to wake up as optimum temperature for their activities is coming back. They are invading human and animal bodies. Human settlers are occupying and destroying forests, disturbing the flora and fauna including the vectors, viruses and microbes. Reciprocally, the viruses are also finding new hosts in humans and animals, causing illness.
Occurrence of drought in erstwhile rainy areas is causing water crisis. Man and crops are facing disaster for this. The Human Development Report 2007/2008 of UNDP shows that climate change is not just a future scenario. Increased exposure to droughts, floods and storms is already destroying opportunity and reinforcing inequality.
Climate-related increases in sea surface temperature and sea level can lead to higher incidence of water-borne infectious and toxin-related illnesses. Climate stress on agriculture causes malnutrition. Increased flux of ultraviolet radiation will cause alterations in the human immune system, thus increasing vulnerability to infections.
Climate change may increase the risk of some infectious diseases, particularly those that appear in warm areas and are spread by mosquitoes and other insects, like malaria, dengue fever, yellow fever and encephalitis. Disease transmission is directly affected by climate change by removing the vector's habitat, increasing reproductive and biting rates, and shortening the disease incubation period.
Vector-borne diseases are very sensitive to temperature, humidity and rainfall. Climate change may alter the distribution of important vectors species, and that may increase the outbreak of diseases into new areas.
Disease surveillance facilities in Bangladesh
The Institute of Epidemiology, Disease Control & Research (IEDCR) is an important public health institute of Bangladesh. The main activities of IEDCR include disease surveillance as well as entomological surveillance, and disease outbreak investigation.
Due to climate change, the pattern of distribution and duration of existing disease may be changed. On the other hand, new types of illnesses might emerge. An effective surveillance system is needed to monitor all these changes.
At present, nine types of disease surveillance systems are in operation. IEDCR conducts 7 of them: Priority Communicable Disease Surveillance, Outbreak Related Emergency Surveillance, Institutional Disease Surveillance, Sentinel Surveillance, Nipah Surveillance, Acute Meningo-Encephalitis Surveillance and Hospital-based Influenza Surveillance.
Two other types are conducted by other institutions. Expanded Program for Immunisation (EPI) conducts surveillance for EPI diseases, Medical Information System (MIS) conducts routine disease surveillance for disease profile.
Besides these formal surveillance activities, the Directorate General of Health Services (DGHS) and Director (Disease Control) receive reports of illness having public health importance from all over the country. Data are also received from existing programs, e.g., Malaria Eradication Program, Kala-azar Control Program, Tuberculosis Control Program, HIV/AIDS Surveillance Program, Filariasis Control Program etc.
Recently, IEDCR has taken an initiative to build a coordinated mechanism for all the surveillance activities and data collection, and analysis and reporting of illnesses of public health importance.
Impact of climatic change on vector-borne disease
Malaria: Over the last 10 to 15 years, the prevalence and geographic distribution of malaria worldwide has increased slowly but steadily. Its recent worldwide increase is due mainly to mosquito resistance to insecticide, breakdown of control efforts, migration of vectors and irrigation.
However, its spread is also related to environment. Agriculture extension and road building have created better habitats for vector mosquitoes. With gradual increase in global temperature since the last ice age (8-9.5° C) transmission of malaria has migrated from Africa to Southern Europe.
Dengue fever: Specific experiment has been conducted on the effect of temperature on the ability of Aedes aegypti to transmit DEN-2 virus. The pattern of temperature and vector efficiency parallels the climatic pattern of Dengue Haemorrhagic Fever (DHF) outbreak in Bangkok, Thailand where the case rate rise in hot season (80°-30° C) and decrease during the cool season (25°-28° C).
Vector-borne disease control strategies in changed climatic condition
Both disease and vector surveillance, and treatment and control of vectors should be part of a comprehensive public health policy that promotes co-operation among researchers, medical clinicians and government staff at local, regional and international level.
Researchers and policy makers should consider modern technology as a means for collecting information about vector-borne diseases, developing effective control strategies and setting appropriate priorities. Four types of surveillance should be conducted to track vector-borne diseases,
-Recording human cases
-Determining the distribution and infectivity of vectors
-Monitoring a broad range of non-human vertebrates reservoir species
-Following the weather patterns to help predict vector distribution. Monitoring climatic parameters provide sufficient information to forecast the population of key vector
Basic research both in the field and laboratory should be taken to examine the disease agent's ability to adapt to changing climatic condition to allow prediction of which pathogen might migrate and their potential destination. Information about the parameters limiting vectors are equally important.
Control measures can be targeted at several different aspects of the life cycle of vector. Vaccination for animals and humans are aimed at preventing the proliferation of pathogens and pesticides, and breeding place management will reduce or eliminate the vectors. Immigration policies and custom inspections may limit pathogen and vector entrance. Drug treatment may limit future transmission of diseases.
Satellite-based remote sensing of ecologic conditions, geographic information system (GIS) analytic techniques, inexpensive computational power, and molecular techniques to track the geographic distribution and transport of specific pathogens are some of the rapid advances in science which are used in developed countries for disease epidemiology and surveillance. They enable the public health scientists to analyse the evolution and distribution of microbes, and their relationship to different environments. It may contribute to quantify the disease impacts of climatic and environmental changes.
Epidemic disease control mostly relies on surveillance, followed by a rapid response. Climate forecasts and environmental observations could be used to identify high-risk locations for disease outbreaks. Operational early warning systems are not yet possible for our limited knowledge of climate-disease relation and limited climate forecasting capabilities. But establishing this goal will help to develop analytic, observational, and computational capacities.
Climate forecasts should be co-ordinated with meteorologic, ecologic, and epidemiologic surveillance systems. Together, this information could be used to identify risky locations and could be a wake-up call as surveillance data confirm earlier projections. Early warning systems of disease should also include vulnerability and risk analysis, response plans, and effective risk communication.
The lack of high-quality epidemiologic data for most diseases is a serious obstacle to improve our understanding of climate and disease linkages. These data are necessary to establish a baseline against which one can detect unusual changes, and develop and validate models. A concerted effort should be made to collect long-term, area specific disease surveillance data, along with the appropriate set of meteorologic and ecologic observations.
Centralised, electronic databases should be developed to facilitate rapid, standardised reporting and sharing of epidemiologic data among researchers. If an effective, modern and co-ordinated surveillance system could be built, then it will be possible to rapidly identify any outbreak of existing or emerging disease, known or unknown disease in any locality. Then it will be possible to take appropriate measures for prevention and control of those illnesses of public health importance.
Prof. Mahmudur Rahman, PhD is Director, Institute of Epidemiology Disease Control and Research (IEDCR).
Dr. M. Mushtuq Husain PhD is Senior Scientific Officer, Dept of Medical Social Science, IEDCR.
Nuzhat Naseen Bano is Scientific Officer, Dept of Medical Entomology, IEDCR.