Ineffective elimination of vectors of disease
Vector control in many rural settings is one of the great challenges of public health. Although methods for preventing the spread of vector-borne diseases have been known for many years, far from being eradicated they are on the increase. A number of the vectors have become more resistant to the chemicals used to combat them, control programmes have not been maintained, and environmental changes have produced new breeding sites for the intermediate hosts. Urban settlement without adequate water supply and sanitation, flooding of land behind dams, new forms of rubbish capable of holding water, social disruption leading to migration and new agricultural practices are examples of changes which have given these diseases and their vectors opportunities to spread.