Vector control methods
In this step, we will look at the key methods for controlling the population of the sand fly, the vector of the Leishmania parasite. Measures will vary from area to area and will be dependent upon the habits of the mammalian hosts and of the vector[1-3]. A pre-control survey should be conducted to establish which methods will be most effective.
Control is achieved by breaking transmission of the parasite or by isolation of the human host from its life cycle (see Step 3.2). It is important to focus on the location-specific ‘risk factors’ for VL that are related to vector contact, for example:
Proximity of humans to sand fly breeding sites (termite hills, cow sheds, rodent burrows, Balanite trees, Red acacia etc,)
Housing conditions (thatched huts with cracked mud walls) that provide resting sites and enable house entry
General deterioration around houses (rubble, collapsed houses, organic waste
Consideration of all these factors should lead to a tailor-made strategy of Integrated Vector Management for a specific setting.
Reduce man-fly contact by:
- Bed net (fine mesh netting)
- Screening of windows
- Protective clothing: long-sleeved shirts, and trousers, socks
- Application of insect repellents
- Avoiding outdoor activities when sand flies are most active (usually dusk to dawn)
Use insecticides that target the sand fly
- Long-lasting insecticidal nets (LLINs) specifically ones appropriate for sand fly prevention.
- Use of indoor residual spraying (IRS)- for indoor biting species
- Spraying outer surfaces of shelters, crevices/cracks of stone walls, and other potentially outdoor resting sites
- Selective outdoor residual spraying may prove effective (e.g. on tree trunks, and termite hills)
- Impregnation and spraying of clothing, windows/privacy screens etc with permethrin or pyrethrum may be effective
Breeding site management
The principle of environmental management is to make it unsuitable for the vector to live and reproduce. Therefore, the target areas for environmental management should be the domestic animal shelters built close to human dwellings, the lack of good hygienic conditions in the peridomicile and the proximity of small wooded areas.
- Clearing away the rubble of broken down houses.
- Plastering breeding places.
“Alternative” vector control methods
- Alternative vector control technologies have been proposed. For example, plastering of walls and floors using mud and lime plaster was associated with a decrease in P. argentipes indoor density compared to controls in a pilot study in India. However, this and other environmental management (EVM) methods need further evaluation.
- Mechanical destruction of animal/sand fly burrows.
- Not well studied and difficult to conclude, some showed undesirable results.
Treatment or elimination of Animal Reservoir (Zoonoses only)
- Control of animal reservoirs, e.g. wild rodents, feral dogs and other mammalian hosts
- Screening and treatment of domestic dogs
- Impregnated dog collars are used in some parts of the world
Health Education on
- The transmission pattern of the disease
- The signs and symptoms of the disease
- The need to report early (at the first signs of illness) to a health facility
- The elimination of rubbish heaps and other sand fly breeding places (location appropriate)
- The need for consistent use of ITNs and other personal protection measures
Key questions to consider when determining the suitability of control strategies
- Has the vector been identified?
- Is the transmission cycle anthroponotic, zoonotic or a mixture of both?
- If zoonotic is the reservoir known?
- Where does transmission occur?
- At what time of day are people being exposed to sand fly bites?
- Is transmission seasonal or year-round?
- Does the infrastructure support organised, sustainable control measures?
- Are at risk communities willing to participate in control measures?
- What methods are available and are there practical, legal, environmental or cultural constraints on their use?
The next 3 steps will go into more detail on the practicalities of using insecticides and impregnated bed nets to control sand flies. Dr Vijay Kumar will talk about the Indian experience (Step 3.7) followed by articles on spraying (Step 3.8) and bed nets (Step 3.9)
© London School of Hygiene and Tropical Medicine 2018