What is Dengue and how Dengue spreads?
Dengue is an outbreak prone seasonal viral disease, transmitted through bites of
female adult Aedes mosquitoes.
2. How does the Aedes mosquito look like?
These are small blackish mosquitoes with white
stripes on abdomen & legs.
These are also called tiger mosquitoes.
3. How many species of Aedes mosquitoes are involved in Dengue transmission?
Aedes aegypti & Aedes albopictus
4. Where Aedes mosquitoes breed?
Aedes mosquitoes breed in stagnant water within and around houses.
Aedes mosquitoes are container breeder viz., cement tanks, overhead tanks,
underground tanks, tyres, desert coolers, pitchers, discarded containers, junk
materials, potholes, rooftop, window parapet, ornamental fountain, lucky bamboo
pot, money plant bottle etc, in which water stagnates for more than a week.
Frequently asked Questions (FAQ)
Dengue
5. Does the Aedes breed in dirty polluted water & drains?
No, they breed only in clean water.
6. Can Aedes lay egg in stagnant water like in overhead tank etc.?
Yes.
7. What are the risk factors?
Dengue is associated with water supply, sanitation and solid waste management.
The risk of dengue has shown an increase in recent years due to rapid
urbanization, life style changes, industrialization and deficient water supply areas
leading to improper water storage practices.
8. How long eggs of Aedes takes to become adult Mosquito?
Dengue vector takes one week to become adult from egg.
9. What are the different stages of Dengue Mosquito in life cycles?
Egg, larva, pupa, adult.
Eggs are laid in water.
Larval and pupal stages are aquatic.
Adult mosquitoes are only terrestrial/ aerial
10. What is the average life span of an adult Aedes?
The life span for adult mosquitoes is around three weeks.
11. Where does Dengue vector rest?
Dengue vector mosquitoes rest in indoor houses mainly in corners under
furniture, beds, shelves, almirah and dark clothing hanging inside.
12. When does Dengue vector bite?
Dengue vector mosquitoes bite during day time usually in morning (8-10 am) &
afternoon (3-5 pm) hours.3
13. What are the preferred host for Aedes mosquitoes?
Human being
14. How long Dengue vector can go for feeding / breeding / egg lying (Flight range)?
Usually adult female of Aedes aegypti is limited within 100 meters (Source WHO
Regional Publication SEARO No 29 –Prevention and Control of Dengue and DHF
Comprehensive Guidelines Page 51)
15. Does mosquito has preference for site on host during bite?
Yes – Legs, Hand, Face, Neck, Ears. However mosquito can bite any exposed body
parts.
16. What are the Vector control methods?
Vector control/management includes:
Environmental management for Source Reduction
Biological Control: Larvivorous fish viz., Gambusia and Guppy are recommended for
control of Ae. aegypti in large water bodies or large water containers.
Chemical control
o Larval control
Temephos as chemical larvicide
Diflubenzuron and Pyreproxifen as Insect Growth Regulator
o Adult control
Pyrethrum space spray is used in indoor situations as space spray
Malathion fogging is used outdoor using insecticide Malathion technical
Cyphenothrin 5% EC- another molecule is also recommended in the
programme for fogging which can be used both for indoor and outdoor fogging.
Personal protection
Protective clothing
Repellents as household insecticide products, namely, mosquito coils, mats
etc
Aerosols against mosquitoes
Insecticide treated mosquito nets or long lasting insecticidal nets (LLIN) to
protect infants and night workers while sleeping in daytime.4
Legislation
o Civic byelaws: Under this act fine/punishment is imparted, if breeding is
detected. These measures are being enforced in major Corporations.
o Building Construction Regulation Act: Building byelaws should be made for
appropriate overhead / underground tanks, mosquito proof buildings,
designs of sunshades, porticos, etc for not allowing stagnation of water vis-
à-vis breeding of mosquitoes.
In Mumbai, prior to any construction activity, the owners/builders deposit a fee
for controlling mosquitogenic conditions at site by the Municipal Corporation.
Builders should be held responsible for creating breeding potential and
penalized.
17. What is fogging?
Fogging is the insecticidal spray in air to kill adult mosquitoes. Fog is an aerosol
spray with droplets of diameter below 50 microns.
18. How fogging is done?
Fogging is done with the help of hand operated or vehicle mounted fogging
machines
Two methods are used viz., Thermal fogging and ULV (Ultra Low Volume)
fogging
19. What chemicals are used in fogging and how it is done?
Pyrethrum extract 2%, Malathion technical and Cyphenothrin 5% EC. Pyrethrum
is plant product
a. Pyrethrum space spray is used in indoor situations as space spray
Commercial formulation of 2% pyrethrum extract (a plant product) is available
It is diluted with kerosene in the ratio of one part of 2% pyrethrum extract with
19 parts of kerosene (volume/volume).
One litre of 2% pyrethrum extract is diluted by kerosene into 20 litres to make
0.1% pyrethrum formulation (‘ready-to-spray’ formulation).
After dilution, pyrethrum extract is sprayed with Flit pump or hand operated
fogging machine fitted with micro-discharge nozzle @ 30-60 ml/1000 cu. ft
b. Malathion fogging is used outdoor using insecticide Malathion technical
Thermal fogging is commonly used with diesel. The technique is based on the
principle that insecticide is vaporized, which condenses to form a fine cloud of5
droplets on contact with cooler air when it comes out of the machine. The
insecticide is vaporized at a very high temperature inside the machine. Once
the fog comes out of the machine, it tends to spread in different directions by
mixing with wind. It is visible and psychologically more acceptable but poses
traffic hazards by reduced visibility.
In ULV, no diluent is used and hence the technique is more cost-effective
than thermal fogging but it does not generate a visible fog.
Cyphenothrin 5% EC- another molecule is also recommended in the
programme for fogging which can be used both for indoor and outdoor
fogging.
For indoor fogging, the dose is 0.5 mg a.i per sq.mt.(20 ml in 1 litres
Kerosine Oil)
For outdoor, the dose is 3.5 g a.i per hectare (7 ml in 1 litres diesel).
20. What time fogging should be done?
Early Morning & Evening (Dusk) Period depending on wind velocity
21. How effective fogging is?
Fogging kills the mosquitoes coming in contact with fog. It is not recommended as
routine vector control measure. Fogging should be last option due to limitations:
o Temporary stay of fog in environment with no residual effect
o Effect primarily on adult mosquitoes coming in contact of fog
o Repeated application needed
o Effect on vectors dependent on climatic factors like wind velocity and its
direction, humidity, temperature etc.
o Speed of the movement of fogger carrying vehicle or spray men
o Dispersal of fog
o Quality of fogging equipment
o High costs
o Mosquito rests indoor, outdoor fog hardly reach indoor
22. Does fogging has any harmful effect ?
People with respiratory problem may feel discomfort exposed to fogging.6
23. Duration of protection by repellent etc. ?
Usually short duration as it has no residual efficacy.
24. Are repellents, coils, mats, house hold spray safe and what precautions to be taken?
Usually these are safe as dosages are to repel mosquito and dosage are fixed
according to body weight.
Persons having allergy to these repellents should avoid its use.
In case of allergy/discomfort, the doors and windows may be open for some time
to dilute its effect.
25. Any role of Neem, lemon grass in controlling mosquitoes?
DEET (N,N-diethylmetatoluamide) blocks a mosquito's ability to find people
who've applied it. This is applied with a 10% to 30% concentration on skin.
Higher concentration of DEET may provide longer protection (about 8 hrs). The
10% concentration protects for about two hours. DEET may be used on adults,
children, and infants older than 2 months of age.
Picaridin is also one repellant comparable to DEET at similar concentrations.
Oil of lemon & eucalyptus may offer protection that's comparable to low
concentrations of DEET. These are not recommended for children less than 3
years.
Others. Shorter acting repellents that may offer limited protection generally
contain plant-based oils such as oil of geranium, cedar, lemon grass, soy or
citronella.
26. What is attractant?
Substance attract mosquito for feeding or egg lying.
Carbon Di Oxide (CO2 ) is known attractant and is also used in many trap devices.7
27. Whether kerosene or other oils can be used for mosquito control, if yes how and
it's mechanism?
These oils have ability to spread and thus make a thin film on water surface
which creates a barrier for respiration and larvae are killed due to suffocation.
28. What are the anti-larvals, its availability, frequency and doses used in
programme?
Temephos 50% EC is recommended at a dose of 1 ppm. Its 2.5 c.c. is mixed in
10 Lit of potable water and it is sprayed @ 20 c.c. per sq. meter surface area or
200 Litres per hectare of ready to use solution at weekly interval. Anti larval
measures with Temephos granules may be applied fortnightly.
Diflubenzuron 25% WP is an Insect Growth Regulator (IGR) and its
recommended dose is 25 gm a.i. per hectare in clean water and 50 gm a.i. per
hectare in polluted water at weekly interval
Pyreproxifen 0.5% GR is an Insect Growth Regulator (IGR) and its recommended
dose is 2 kg a.i per hectare in clean water and 4 Kg a.i. per hectare in polluted
water at 3 weekly interval.
29. What is the maximum penalty for creating mosquitogenic conditions?
It varies from state to state viz. in Delhi it is up to Rs. 500/-, Mumbai Rs 200-500
and for builders Rs 2000-10000, Karnataka Rs. 200-500, and Chennai up to 500/-
.
30. What individuals have to do for Aedes control?
Protecting from mosquito bites
Long – sleeved clothing and mosquito repellents.
Window & door screening and
Using mosquito nets (insecticide-treated nets/LLIN)
Using household insecticides aerosols, mosquito coils or other insecticide
vaporizer.8
31. What is current update on new tools?
a. GM (Genetically modified Mosquito) – (Male sterile mosquitoes are released in
environment so as to mate with wild females and produce sterile eggs). It is still in
experimental stage
b. Wolbachia (Bio-control agent) - is a symbiont bacteria and reduces average life
span of mosquitoes. But it has not been used in any programme beyond
experimental stage.
32. What are the parameters used for larval breeding?
Four indices that are commonly used to monitor Ae aegypti infection levels are:
o House index (Hl): percentage of houses infected with larvae and/or
pupae
HI = Number of houses infected
Number of houses inspected X100
o Container Index (Cl): percentage of water holding containers infected
with larvae or pupae.
Cl = Number of positive containers
Number of containers inspected X100
o Breteau Index (Bl): number of positive containers per 100 houses
inspected
Bl: Number of positive containers
Number of houses inspected X100
o Pupae Index (Pl): number of pupae per 100 houses
Pl = Number of pupae
Number of houses inspected X1009
33. What are important messages for Dengue prevention?
Covering all water holding containers & tanks with tight lids
Emptying, cleaning by scrubbing and drying water coolers at least once a week
before refilling.
Disposing & destroying all unused containers, junk materials, tyres, coconuts shells
etc.
Wearing full sleeved clothing, using mosquito nets (day time) & repellan
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