ENVIRONMENTAL CHANGE ANDVECTOR-BORNE DISEASEBy Dr Nik Nor Ronaidi bin Nik Mahdi
SCENARIOS OF GLOBAL CHANGE Global change refers to the complex of environmental changes that is occurring around the world as a result of human activities. Environmental change issues: 1. Atmospheric composition 2. Climate change 3. Urbanization 4. Land use and biodiversity loss 5. Industrial and agricultural pollution 6. Trade and travel
ASSESSMENT OF IMPACTS TO VBD Vulnerability: a measure of the potential impacts of a given change, taking into account the adaptive capacity that is available to the affected community to respond to that change. Exposure: A change in the geographical distribution of a VBD will affect the exposure of naive hosts to that disease. Such a change can come about from the movement of either a vector or pathogen to a new environment through trade, human movement, or natural means. Sensitivity: the degree to which a system responds to an external perturbation, (eg: change of temperature) The sensitivity of a human population to a change in exposure depends on the immune status of the population.
ATMOSPHERIC COMPOSITION The Earth’s surface is kept warm by greenhouse gases, (water vapor, CO2, methane, NO, and some industrial gases like CFC). Concentrations of these gases is rising as a result of the anthropogenic activities: burning of fossil fuels for power and transport →↑CO2 Livestock and leakage from coal beds →↑methane. ↑CO2 →reduce the water loss through transpiration and act as a fertilizer in plants. Indirect impact to VBD: ↑CO2 → plants produce more foliage (provide more favorable microclimates for insect vectors) + plant growth seasons will be extended (effectively increasing the duration of favorable microclimates) + larger plants (provide more humid shelter for insect vectors and pathogens) higher water table and soil moisture content →↑ in the frequency of pools of open water that provide suitable habitat for mosquito breeding.
CLIMATE CHANGE What is the different between weather and climate? Weather is the continuously changing condition of the atmosphere, usually considered on a time scale that extends from minutes to weeks. Climate is the average state of the lower atmosphere, and the associated characteristics of the underlying land or water, in a particular region, usually spanning at least several years. A statistical analysis to separate solar and anthropogenic influences implied that 60% of the warming in the last 140 years was due to human activity (Beer et al, 2000)
CLIMATE CHANGE The increasing temperatures will intensify the hydrological (rainfall and evaporation) cycle, leading to an increased frequency and intensity of extreme weather events such as storms, floods, and droughts. It is estimated that average global temperatures will have risen by 1.0–3.5 oC by 2100, increasing the likelihood of many vector-borne diseases (Watson RT et al, 1998).
CLIMATE CHANGE Mosquito species (e.g: Anopheles gambiae complex, A. funestus, A. darlingi, Culex quinquefasciatus and Aedes aegypti) are sensitive to temperature changes: larvae mature faster in higher temperature → greater capacity to produce more offspring adult female mosquitoes digest blood faster and feed more frequently in warmer climate → increasing transmission intensity. malarial parasites complete extrinsic incubation faster within the female mosquito as temperature rises → increasing the proportion of infective vectors Increased precipitation may increase the number and quality of breeding sites for vectors (e.g: mosquitoes) and the density of vegetation, increasing the availability of resting sites.
URBANIZATION Critical factors: Drainage and water supplies Poverty → no necessary infrastructure for the safe storage and distribution of water and drainage of wastewater (provide safe place for vector breeding)
LAND USE AND BIODIVERSITY Agricultural activities↑ due to population growth: ↑ needs for deforestation and water storage, supply, and distribution for human consumption and irrigation These developments affects the opportunities available for breeding by vectors of diseases. With changes in land use comes fragmentation of habitats, loss of biodiversity and alteration of existing vector-host-parasite relationships Deforestation: May increase the breeding of sun-loving Anopheles vectors of malaria in Africa May reduce the incidence of lymphatic filariasis by exposed the mosquito breeding sites to sunlight in Indonesia
INDUSTRIAL AND AGRICULTURALPOLLUTION Endocrine-disrupting chemicals (EDCs): mimic or disrupt the activity of hormones, especially estrogen and thyroid hormones, in humans and animals include alkyl phenols, dioxins, organochlorine pesticides, phthalates, polychlorinated biphenyls, polybrominated diphenyl ethers, and synthetic pyrethroids found in plastics, herbicides, and pesticides that are distributed widely around the world. The side effects of these chemicals could reduce options for human adaptation to vector-borne diseases either by degrading immune responses or by withdrawal of vector control products from the market.
TRADE AND TRAVEL One million people are reported to travel internationally each day, and one million people travel from developed to developing countries (and vice versa) each week (Garret L, 1996). International trade in merchandise has increased three- to fourfold over the period from 1980 to 2000, with most of the increase occurring in Asia, where there was a fivefold increase in the value of exports (World Trade Organization) These movements has the potential to spread disease pathogens and their vectors over long distances.
MALAYSIA’S EXPERIENCE Filariasis: Wuchereria bancrofti and Brugia malayi main species of parasites in Malaysia are the periodic and subperiodic strains of Brugia malayi Periodicity refers to the habit of the microfilaria, migrating to peripheral blood at certain distinct times of the day. Periodic → night; Subperiodic → partially nocturnal and are also found in peripheral circulation throughout the 24 h cycle This synchronization of the parasite cycle to the circadian rhythm is an evolutionary adaptation to the biting behavior of the predominant vector Periodic B. malayi vectors (Anopheles campestris mosquitoes, Mansonia uniformis and M. Annulifera) adapt well to the rice fields and their associated irrigation canals, ditches and drains in the coastal plains of northern Peninsular Malaysia.
Thus, the expansion of rice cultivation in the broad alluvial plains of the states of Kedah, Perlis, Penang and Perak, resulted in increased prevalence of periodic brugian filariasis in the 1960s and 70s (Cheong, 1983). However, Malaysia’s successful malaria control program, which curtailed breeding of Anopheline mosquitoes, have resolved the periodic B. Malayi endemic by the early 1990s. Subperiodic B. malayi adapts to a different ecosystem. Its vectors (Mansonia bonneae, M. dives, M. uniformis and M. Indiana) breed in riverine swampforest ecotypes → These habitats are often inaccessible to mosquito larviciding, making these vectors particularly difficult to control. In addition, subperiodic B. malayi is a zoonosis, with several species of leaf monkeys (Presbytis spp.) and domestoc cats acting as natural hosts.→rubber cultivation intrudes into the foraging range of reservoir hosts (monkeys) which harbor subperiodic B. malayi. However, as Malaysia industrializes, the changes in land use patterns resulted in a gradual decrease in disease rates.
Dengue: The ecology of dengue in Malaysia was dramatically altered by the rapid pace of urbanization that occurred from the mid– 1970s onwards. Vectors: Aedes aegypti and A. Albopictus A. aegypti is well adapted as an urban, domestic, anthropophilic mosquito, breeding in artificial containers where relatively clean clear water is retained. A. albopictus was originally a sylvatic/rural mosquito, breeding in outdoor natural water-retaining habitats such as tree holes and leaf axils of some plant species including banana plants and various types of palm. A variety of other human activities contribute to breeding of Aedes Agricultural refuse of plantation cash crops such as cocoa and coconuts produces water-filled pods and shells which provide Aedes breeding niches → outbreak in cocoa pods in Serian, Sarawak.
The construction industry has also become an important source of Aedes vectors, since many breeding habitats are present in flooded basement parking lots, lift shafts, foundation pits and balconies during the active phase of construction. During the economic downturn in 1997/1998, numerous abandoned construction sites in Penang became such a serious source of breeding sites for aedes (Lim, Foong, Abu-Hassan, & Kwa, 2000).
FRAMEWORK FOR DESIGNINGADAPTATION OPTIONS Adaptation is the process by which the potential impacts are reduced by applying a range of management options Management of VBD: 1) Vector control chemical, biological, trapping, and environmental management techniques 2) Targeting the pathogens Chemotherapy Vaccines Successful control of VBD depends on three capacities: 1. effective surveillance to provide feedback on progress 2. community ownership of the new measures 3. a viable public health infrastructure to deliver the services
ADAPTIVE RESPONSE OPTIONS1. Legislative: Many policy changes could be implemented to adapt the impacts of VBD under global change They involve legislation or administrative actions to respond to changes in distributions of vectors, diseases, and human hosts. The measures include changes of: monitoring, case detection, diagnosis and reporting, public information and education, knowledge capture and management using information technologies such as remote sensing and mapping with geographical information systems climate forecasting computer modeling quarantine surveillance early-warning systems mass vaccination programs.
Efforts to eradicate malaria with insecticides failed in many regions due to the withdrawal of DDT, the development of resistance to the pesticides, or the reintroduction of the mosquitoes from other areas.1. Behavioral: personal behavioral responses include avoidance of exposure to vectors by staying indoors at dawn and dusk and wearing protective clothing.2. Engineering: Habitat modification, insect screens, bednets, biological control, pesticides, and repellents Targeting of pathogens with drugs or vaccines also provides options to reduce transmission and to reduce symptoms. A range of chemical, biological, trapping, and environmental management techniques are available for the control of disease vectors Biological control of mosquito populations by using natural enemies is a well-established practice and is based mostly on predatory fish
The incidence of JE in East Asia has been greatly reduced by a combination of mass vaccination of children, improved living conditions, reduced use of water with new rice cultivars, and rehousing and relocation of piggeries to prevent mosquito feeding and reduce contact with human populations.
THREATS TO SUSTAINABILITY OFADAPTATION OPTIONS Resistance Drugs and pesticides E.g: Resistance to permethrin and deltramethrin in Anophales gambiae in West Africa. The international spread of multiple drug-resistant malaria organisms in Southeast Asia Human safety and nontarget effects of vector control For example, efforts to control Aedes aegypti with organophosphorus insecticide led to three poisonings and reduced cholinesterase levels in 53 out of 2,391 people sampled from the local population in southern Brazil
Community health and public health infrastructure The capability of a society to adapt to global change depends also on the human resources and operational public health system. So that developing countries have far fewer options available to them than do developed countries Adaptive capacity of different social groups.
REFERENCES Robert W. Sutherst (2004), Global Change and Human Vulnerability to Vector-Borne diseases, Clinical Microbiology Review 17(1):136-173i B. H. Kwa (2006), Environmental change, development and vectorborne disease: Malaysia’s experience with filariasis, scrub typhus and dengue. Environ Dev Sustain 10:209–217b W. J. Tabachnick (2009), Challenges in predicting climate and environmental effects on vector-borne disease episystems in a changing world. The Journal of Experimental Biology 213, 946-954m WHO (2010), Global Environmental Change. http://www.who.int/globalchange/environment/en / accessed on 25th July 2010.