PEST & VECTORS MANAGEMENT

Aedes Index

Prepared by:

Khairul NizamMCHSc (Environmental Health)

School of Environmental HealthVictoria International College

OBJECTIVES

• Understand the indices used to monitor the density level of Aedes.

• To calculate the Aedes index, Container index, Breteau index.

• To interpret the Aedes index, Container index, Breteau index.

• Understand the method use to monitor the adult Aedes.

• Three indices are commonly used to record Ae. aegypti and Ae. albopictus density levels:

1.The House (premises) Index (HI) or Aedes Index:▫Percentage of houses or premises positive for Aedes larvae

2.Container Index (CI):▫ percentage of water−holding containers positive for Aedes

larvae.

3.Breteau Index (BI):▫number of positive containers per 100 houses in a specific

location.

The House (premises) Index (HI) or Aedes Index:

Container Index (CI):

No. of houses positive Aedes larvaeNo. of houses inspected

X 100HI =

No. of positive containersNo. of containers inspected

X 100CI =

Breteau Index (BI):

No. of positive containersNo. of houses inspected

X 100BI =

• The emergence of adult mosquito population can be estimated by the pupal count i.e., by counting all pupae found in each container.

• Pupal Index (PI):▫The number of pupae per 100 houses.

No. of pupae_________ No. of houses inspected

X 100PI =

• Among the above three indices, the House Index (HI) has been widely used to calculate the presence and distribution of Aedes populations in a given locality.

• However, the HI does not take into consideration the number of positive containers per house.

• Similarly, the Container Index (CI) only provides information on the proportion of water-holding containers that are positive.

• On the other hand, the Breteau Index (BI) establishes a relationship between positive containers and number of houses.

• Hence, the BI is considered the most useful single index for estimating Aedes density in a location.

• The BI and HI are commonly used for the determination of priority (risk) areas for control measures.

• Generally, a HI greater than 5% and/or a BI greater than 20 for any locality is an indication that the locality is dengue-sensitive.

• For epidemiological purposes, the HI is extremely important and indicates potential spread of virus through an area once an infected case becomes established.

• Adult landing/biting rate: ▫Aedes mosquito can be collected on a human bait and

landing rate /bait /hour is calculated. ▫The mosquitoes thus collected can be used for the virus

isolations.

Indices High risk of transmission

Low risk of transmission

House index > 10% < 1%

Breteau index > 50 < 5

Landing/Biting rate > 2 per man hour < 0.2 per man hour

Methodology of surveillance

• The survey should be carried out in a given locality by searching breeding of Aedes mosquitoes in different water containers lying in domestic or peri-domestic situations in an area.

• All types of water container should be thoroughly checked for Aedes breeding with the help of torch light and if found positive some of the larvae may be picked up for the confirmation of Aedes larvae.

• Adult Aedes mosquitoes can be collected on human bait. The worker can collect mosquitoes from his own body (exposed legs) or that of his helper.

• The collection should be carried out between 9.00 and 11.00 hrs. The males should not be counted while calculating the landing/Biting rate.

ADULT SURVEY

Oviposition traps• “Ovitraps” provide a sensitive and economical method for

detecting the presence of Ae. aegypti and Ae. albopictus in situations where the Aedes density is low and general larval surveys produce unsatisfactory results (e.g. when the Breteau Index is < 5).

• The standard ovitrap is a wide-mouthed glass jar of approximately 250 ml which is painted black on the outside to attract the Aedes females to oviposit.

• A piece of hardboard or a wooden paddle is placed diagonally inside the glass as an oviposition substrate.

• The jar is partially filled with clean water to provide the right ovipositing medium for the female mosquito.

• Such jars in the absence of ovipaddles can have white towelling strips placed inside attached by paper clips.

• Generally, the ovitraps have proven useful for the early detection of new Aedes infestations in areas where the Aedes mosquitos have not been established previously.

• They are extensively used for surveillance at international ports of entry, (airports and seaports) which, according to international sanitary codes, should be maintained free of vector breeding.

• Ovitraps can also be used to assess Aedes population fluctuation over a long-term period especially in epidemiological studies of dengue infection.

• Surveys of adult mosquitos are more time consuming (labour intensive) and the results are less satisfying than larval surveys.

•Material/equipments required for Dengue surveillance: 1. Torch light2. Larval laddle 3. Pippettes 4. Test tubes 5. Aspirator tubes6. Photo tray white 7. Polythene bags 8. Rubber bands

9. Cotton 10.Lint cloth11.Entomological pins 12.Stage mount tubes 13.Petri dish 14.Small mosquito15.cages 16.Dry battery cells

Thank You

REFERENCES

• WHO. 2006. Guideline for prevention and control of dengue.

• WHO. 1995. Guidelines for dengue surveillance and mosquito control, 1995.