Slide C Environmental Management for Vector Control
Each water resource development project may create its own specific vector-borne disease problems. Therefore, it requires special training, knowledge and experience to determine the potential environmental or health impacts of irrigation, drainage and flood control projects.
By properly planning and managing water resource development projects, the need for special chemical or environmental management methods for vector control later on may be avoided. If the principles of vector control measures are already included in the planning phase, and if the scheme is adequately managed and maintained, there will be no grave adverse health effects on the human population. Where water projects have created vector-borne disease problems it is important to implement the concept of integrated vector control and ensure its conscientious use in the operational phase. This concept is important in all types of water resource developmental projects. The concept of integrated vector control is given in Figure 10:
Figure 10: CONCEPT OF INTEGRATED VECTOR CONTROL
Slide C1 Concept of integrated vector control
Adapted from: Axtell, R.C. Principles of integrated pest management (IPM) in relation to mosquito control. (Mosquito News, 39:709-718; 1979)
The WHO Expert Committee on Vector Biology and Control in 1979 defined environmental management activities as follows:
Environmental management for vector control: The planning. organization, carrying out and monitoring of activities for the modification and/or manipulation of environmental factors or their interaction with man with a view to preventing or minimizing vector propagation and reducing man-vector-pathogen contact.
Slide C2 Environmental management for vector control
Environmental management for mosquito control covers a wide range of works and operations which can be further classified and defined: (Source: WHO Technical Report Series, No. 649,1980.)
a) Environmental modification: “A form of environmental management consisting of any physical transformation that is permanent or long-lasting of land, water and vegetation, aimed at preventing, eliminating or reducing the habitats of vectors without causing unduly adverse effects on the quality of the human environment.” Environmental modification includes drainage, filling, land levelling and transformation and impoundment margins. Although these works are usually of a permanent nature, proper operation and adequate maintenance are essential for their effective functioning.
Slide C3 Components of environmental management
b) Environmental manipulation: “A form of environmental management consisting of any planned recurrent activity aimed at producing temporary conditions unfavourable to breeding of vectors in their habitats.” Water salinity changes, stream flushing, regulation of the water level in reservoirs, dewatering or flooding of swamps or boggy areas, vegetation removal, shading and exposure to sunlight are examples of environmental manipulation activities.
c) Modification or manipulation of human habitation or behaviour: “A form of environmental management that reduces man - vector-pathogen contact.” Examples of this kind of approach include the siting of settlements away from vector sources, mosquito proofing of houses, personal protection and hygiene measures against vectors, provision of such installations as mechanical barriers and facilities for water supply, wastewater and excreta disposal, laundry, bathing and recreation to prevent or discourage human contact with infested waters, and zooprophylaxis, the strategic placement of cattle as a buffer between mosquito breeding places and areas of human habitation to divert vectors away from the human blood source.
Due to the different behaviour and habitats of vectors, detained specific investigations are needed to evaluate the potential risks of a water resource development project. Nevertheless two general statements may be made, as many species or larger taxonomic groups have common environmental requirements.
Slide C4 Environmental requirements of vectors
1. Many vectors require an aquatic environment, either in their immature stages (mosquitoes, blackflies) or throughout their lifecycle (snails).
2. Aquatic weeds, if not too dense, promote vector development, giving them protection from direct sunlight, natural enemies, wind and water current (except blackflies) as well as providing fodder (snails).
Basically for all environmental management measures, including the management and maintenance of irrigation, drainage, and flood control projects, the following pertinent questions may be asked:
• a are additional water bodies essential and which are the important water properties (quality, flow velocities)?
• How is the micro-climate affected (i.e., raising of humidity and average warm temperature favours vector breeding.)?
• Which aquatic weeds are involved (in addition to protection, many vectors are associated with specific weeds.)?
• What are the consequences of a project for the behaviour of the inhabitants (settlements near impoundments and irrigation channels.)?
Slide C5 Basic questionnaire for environmental management measures
It is important to understand the components of an irrigation scheme such as water catchment, impoundment, water distribution, irrigation methods, drainage and ancillary structures. They are discussed below in relation to their interactions with vector habitats.