Home page  |  About this library  |  Help  |  Clear       English  |  French  |  Spanish  
Expand Document
Expand Chapter
Full TOC
to previous section to next section

close this bookGuidelines for Dengue Surveillance and Mosquito Control, 1995 (WHO, WHO/WPRO; 1995; 112 pages)
View the documentFOREWORD
open this folder and view contents1. INTRODUCTION
open this folder and view contents3. SURVEILLANCE - VECTOR SURVEYS
open this folder and view contents4. CONTROL: ENVIRONMENTAL MANAGEMENT
open this folder and view contents5. CONTROL: CHEMICAL AND BIOLOGICAL METHODS
open this folder and view contents6. CONTROL: PERSONAL PROTECTION
open this folder and view contents7. CONTROL: SPACE SPRAY APPLICATIONS
open this folder and view contents8. COMMUNITY BASED ACTION
open this folder and view contents9. LEGISLATION
open this folder and view contents10. MANAGING OUTBREAKS
close this folderANNEXES
View the documentAnnex 1 - Laboratory and clinical diagnosis of dengue fever
View the documentAnnex 2 - Larval survey summary form showing house, container and Breteau indices for Ae. aegypti
View the documentAnnex 3 - Example of notification of dengue fever/dengue haemorrhagic fever by phone and written communication
View the documentAnnex 4 - Quantities of 1% Temephos (Abate) sand granules required to treat different size water containers to kill mosquito larvae
View the documentAnnex 5 - Procedure for treating mosquito nets and curtains
View the documentAnnex 6 - Names and addresses of suppliers of vector control equipment, insecticides and other control materials
View the documentAnnex 7 - Procedure, timing and frequency of thermal fogging and ULV space spray operations
View the documentAnnex 8 - Preparation of spray solutions to kill adult mosquitos during DHF outbreaks
View the documentAnnex 9 - Sample order form, backed by law enforcement, for distribution to house occupants to eliminate Aedes larvae
View the documentAnnex 10 - Procedures for collection of Aedes larvae with enforced legislation
View the documentAnnex 11 - Health education posters on DHF vector control
View the documentAnnex 12 - Safety measures for insecticide use
View the documentAnnex 13 - Selected references
View the documentBACK COVER

Annex 7 - Procedure, timing and frequency of thermal fogging and ULV space spray operations

Basic steps

The following steps are followed in carrying out the space spraying of a designated area.

a. The street maps of the area to be sprayed must be studied carefully before. the spraying operation begins.

b. The area covered should be at least 300 metres within the radius of the house where the dengue case was located.

c. Residents should be warned in advance before the operations so that food is covered, fires extinguished, and pets are moved out together with the occupants.

d. Ensure proper traffic control when conducting outdoor thermal fogging since it can pose a traffic hazard to motorists and pedestrians.

e. The most essential information about the operation area is the wind direction. Spraying should always be done from downwind to upwind, i.e. going against the direction of the wind.

Vehicle-mounted spraying


a. Doors and windows of houses and buildings in the area to be sprayed should be opened.

b. The vehicle is driven at a steady speed of 6-8 km/hr (3.5-4.5 mile/hr) along the streets. Spray production should be turned off when the vehicle is stationary.

c. Always spray downwind to upwind. If possible, drive the vehicle at right angles to the wind direction.

In areas where streets run parallel as well as perpendicular to the wind direction, spraying is only done when the vehicle travels upwind in road parallel to tile wind direction.

d. In areas with wide streets with houses and buildings far from the roadside, the spray head should point at an angle to the left side of the vehicle (in countries where driving is on the left side of the road). The vehicle should also be driven close to the edge of the road.


e. In areas where the roads are narrow, with houses close to the roadside, the spray head should be pointed directly towards the back of the vehicle.

f. In dead-end roads, the spraying is done only when the vehicle is coming out of the dead-end, not while going in.

g. The spray head should be pointed at a 45° angle to the horizontal to achieve maximum throw of the droplets.


h. Vector mortality downwind increases as more streets are sprayed upwind in relation to the target area.

Portable thermal fogging


a. Thermal fogging with portable thermal foggers is done from house to house, always fogging from downwind to upwind.

b. All windows and doors should be shut for half an hour after the fogging to ensure good penetration of the fog and maximum destruction of the target mosquitos.

c. In single storey houses, fogging can be done from the front door or through an open window without having to enter every room of the house. All bedroom doors should be left open to allow dispersal of the fog throughout the house.

d. In multi-storey buildings, fogging is carried out from upper floors to the ground floor, and from the back of the building to the front. This ensures that the operator has good visibility along his spraying path.

e. When fogging outdoors, it is important to direct the fog at all possible mosquito resting sites, including hedges, covered drains, bushes, and tree-shaded areas.

f. The most effective type of thermal fog for mosquito control is a medium/dry fog, i.e., it should just moisten the hand when the hand is passed quickly through the fog at a distance of about 2.5-3.0 metres in front of the fog tube. Adjust the fog setting so that oily deposits on the floor and furniture are reduced.

Back-pack aerosol spraying with ULV attachments


1. Basic points


a. Each spray squad consists of 4 spraymen and one supervisor.

b. Each sprayman sprays for 15-30 minutes and then is relieved by the next sprayman. He must not spray when tired.

c. The supervisor must keep each sprayman in his sight during actual spraying in case he falls or needs help for any reason.

d. Do not directly spray humans, birds or animals that are in front of spray nozzles less than 5 metres away.

e. Spray at full throttle. For example, a ULV Fontan nozzle tip 0.4 can deliver 25 ml of malathion per minute, and a 0.5 tip, 65 ml. The smaller tip is usually preferred unless spraymen move quickly from house to house. Some machines can run for about one hour on a full tank of petrol.


2. House spraying technique


a. Do not enter the house. House spraying means spraying in the vicinity of the house.

b. Stand 3-5 metres in front of house and spray for 10 to 15 seconds directing nozzle towards all open doors, windows and eaves. If appropriate, turn away from house and standing in the same place spray the surrounding vegetation for 10 to 15 seconds.

c. If it is not possible to stand 3 metres from the house due to closeness of houses and lack of space, spray nozzle should be directed towards house openings, narrow spaces and upwards.

d. While walking from house to house hold nozzle upwards so that particles can drift through area Do not hold nozzle towards ground.

e. Spray particles drift through the area and into houses to kill mosquitos which become irritated and fly into the particles. The settled deposits can be residual for several day to kill mosquitos resting inside houses and on vegetation not exposed to the rain.

f. This technique permits treatment of a house with insecticide ranging from 1 to 25 grams in one minute. The dosage depends on discharge rate, concentration of insecticide applied, and time it takes to spray the house. For comparison, an indoor residual house spray may require 30 minutes of spraying to deposit 300 grams of insecticide. This assumes a dosage of 2 grams per square meter to 150 square meters of sprayable surface.


3. Information to inhabitants:


a. time of spraying; for example 0630 to 1000 hours.

b. all doors and windows should be open,

c. dishes, food, fish tanks, and bird cages should be covered.

d. Stay away from open doors and windows during spraying; or temporarily leave the house and sprayed area until spraying is completed.

e. Children or adults should not follow spray squad from house to house.

Timing of application

Spraying is carried out only when the right weather conditions are present and usually only at the prescribed time. These conditions are summarized below:


Most favourable conditions

Average conditions

Unfavourable conditions


Early morning
late evening

Early to mid-morning or late afternoon, early evening

Mid-morning to mid-afternoon


Steady, between
3-13 km/hr


Medium to strong over 13 km/hr


No rain

Light showers

Heavy rain





For optimum spraying conditions please note:


a. In the early morning and late evening hours, the temperature is usually cool. Cool weather is more comfortable for workers wearing protective clothing. Also, adult Aedes mosquitos are most active at these hours.


In the middle of the day, when the temperature is high, convection currents from the ground will prevent concentration of the spray close to the ground where adult mosquitos are flying or resting, thus rendering the spray ineffective.


b. An optimum wind speed of between 3-13 hm/hr enables the spray to move slowly and steadily over the ground, allowing for maximum exposure of mosquitos to the spray. Air movements of less than 3 km/hr may result in vertical mixing, while winds greater than 13 km/hr disperse the spray too quickly.

c. In heavy rain, the spray generated loses its consistency and effectiveness. when rain is heavy, spraying should stop and the spray head of the ULV machine should be turned down to prevent water from entering the blower.

d. Spraying is permissible during light showers. Also, mosquito activity increases When the relative humidity reaches 90, especially during light showers.

Frequency of application


The commencement and frequency of spraying generally recommended is as follows:


a. Spraying is started in an area (residential houses, offices, factories, schools) as soon as possible after a DF/DHF case from that area is suspected.

b. At least one treatment should be carried out within each breeding cycle of the mosquito (seven to ten days for Aedes). Therefore, a repeat spraying is carried out within seven to ten days after the first spraying. The time the dengue virus incubates (eight to ten days) in the mosquito is also important.

Evaluation of epidemic spraying


Within two days after spraying during outbreaks, a parous rate of 10% or less, in comparison to a much higher rate before spraying, indicates that most of the mosquito population is newly emerged and incapable of transmitting the disease. This also indicates the spray was effective and greatly reduced transmission by killing the older infected mosquito population. A low parous rate after spraying can occur in the absence of a marked reduction in vector density. This can be attributed to the emergence of a new population of mosquitos which escaped the spray, a relatively low adult density before spraying and adult sampling methods which show considerable variations in density in the absence of control. An effective spray programme also should be accompanied by a reduction in hospitalized cases after the incubation of the disease in humans (about 5 to 7 days) has elapsed; The spraying should be repeated at 7 day intervals to eliminate the possibility of infected mosquitos.
to previous section to next section

Please provide your feedback   English  |  French  |  Spanish