The principal method by which these diseases are controlled is through vector control. Nowadays, vector control programmes rely on insecticide-based control, often deployed as a monotherapy. However, with the rising threat from insecticide-resistant vectors and global environmental change, there is a need to incorporate more vector control interventions to eliminate these diseases.
Vector control aims to limit the transmission of pathogens by reducing or eliminating human contact with the vector. This purpose is well-served when there is high host diversity and low density.
Human activities influence the incidence of VBDs of all kinds. We are currently living in the Anthropocene era, which is driven by human influence and ushers in a growing number of direct and indirect challenges for the health and prosperity of people. We know that many epidemics have occurred in disturbed areas, where forests have been removed and land has been used for agriculture or urban living. This has convinced medical entomologists that VBD problems rarely exist in undisturbed areas of the world. That is true even in tropical rainforests.
The logical reason is that the undisturbed tropical forests have high biodiversity and low host density. When these lands get transformed into agricultural or urban, biodiversity decreases and host density (humans) increases. This combination increases disease transmission – which is against the purpose of vector control.
Vector control aims to limit the transmission of pathogens by reducing or eliminating human contact with the vector. This purpose is well-served when there is high host diversity and low density.
So, then, are we ready to offer disease vectors a buffet (animals and birds) and not a one-dish (humans) for blood feeding? The answer clearly lies in environmental management.
Medical entomologists and environmentalists must play an expanded role in alerting public officials to the dangers of VBDs and help plan mega projects such as housing developments, seasonal wetlands and water redistribution projects.
Planting trees is one of the best ways of facing this challenge, as a single tree can attract and support hundreds of different species. That is just one stroke of a paintbrush on a bigger canvas, as urban plantation drives can develop livable and sustainable communities. It promotes health and social wellbeing and cleans the environment.
Before insecticides, VBD control generally relied on understanding local vector behaviour and tailored environmental control. It is agreed among vector control experts that one needs to have a thorough knowledge of breeding places and habits of a disease vector to apply the most suitable control methods to the situation – by keeping in mind that the goal of environmental management is ‘source reduction’ and considering that initiatives such as the provision of adequate water supply and construction of sub-soil drainage systems have shown positive results in past. It starts from the level of a unit, focusing on small steps of housing improvement, such as the use of doors and window screens, and moving upwards to the community level by improving sanitation to eliminating breeding sites of vectors. Demolition and removal of uninhabited buildings from the localities close to habitations may also prove beneficial. A lot needs to be done in rural areas as well, starting from regular resurfacing of mud walls to removing organic waste to discourage vector breeding.
Many success stories of preventing VBD problems by managing the environment were reported before the World War II. However, the general lack of planning, insufficient resources, and complexity of the problem has limited the effectiveness of environmental management. Another reason for lack of attention to environmental management is the spectacular success of synthetic chemical pesticides after WWII. It has resulted in a de-emphasis in environmental management techniques.
Although the problems of vector resistance to insecticides, concerns about their safety, and environmental impact of chemical pesticides has renewed interest in integrating all available control methods, including environmental management, into comprehensive vector and disease management schemes, yet there is an urgent need to invest in political will and return to locally tailored vector control that draws on an entire toolbox of interventions available. Medical entomologists and environmentalists must play an expanded role in alerting public officials to the dangers of VBDs and help plan mega projects such as housing developments, seasonal wetlands and water redistribution projects.
It is time to move toward environmental and nature-based solutions. If our vector control programmes continue to rely heavily on chemical insecticides, the writing is on the wall.
The writer works at the Department of Medical Entomology and Vector Control Health Services Academy, Islamabad. He can be reached at uzair@hsa.edu.pk