This document summarizes a study on dengue transmission and risk factors in Dhaka, Bangladesh. Key findings include: - Dengue virus types 1-4 circulate in Dhaka and are transmitted between humans by the Aedes aegypti mosquito. - Entomological surveys found high Aedes larval indices, with over 80% of households testing positive for larvae. Breteau indices were over 40. - Serosurveys found over 80% of residents tested positive for dengue IgG antibodies, indicating high exposure rates. - The most common larval habitats were water storage containers like tanks, buckets and drums. Habitat types varied by socioeconomic status. - Knowledge of

1. Dengue Transmission and Risk Factors in Dhaka, Bangladesh
Parnali Dhar Chowdhury1, C. Emdad Haque1, Robbin Lindsay2, Abdullah Brooks3,4, Michael A Drebot2
1Natural
Resources Institute, University of Manitoba
Microbiology Laboratory, Public Health Agency Canada
3John Hopkins University, USA, and 4 icddr,b Bangladesh
2 National
GRF Davos One Health Summit 2013
17-20 November, 2013; Davos, Switzerland

2. Areas of risk for dengue disease
Dengue viruses 1- 4 can cause DF / DHF
Person  Aedes mosquito  Person
A. aegypti

3. Estimated population at risk of dengue fever under
“standard” climate change scenario: 1990, 2085
1990
2085
Decreased mosquito abatement
Increased urbanization, etc.
.
Source. Hales S et al. Lancet (online) 6 August 2002. http://image.thelancet.com/extras/01art11175web.pdf

4. •
Dhaka, the capital of Bangladesh, 16th
Largest city (15.4 million population in
2012) of the world
• Estimated to grow to about 20 million
(2020), making it the world’s third
largest city
• Population growth =~7%
 Insert map of Bangladesh and
Location of Dhaka
• Attracts some 300-400 thousand new
migrants/year
Source:http://www.google.com/imgres

5. Dengue Trends in Dhaka:
Facts from Reality
Dhaka : Total number of reported dengue cases by year
(n = 22,705).
 Asymptomatic nature of dengue
(known as Dhaka fever) since 1964
 First major outbreak in 2000 with
5,551 hospitalized cases (93 deaths)
 Short term (2000-2008) trend reveals
short cyclical pattern – reasons
are unknown
Dhaka: Total number of reported dengue cases, by month,
2000-2008 (n = 22,705)
 Limited knowledge of dengue
vector distribution and density,
disease risk perception, and
circulating serotypes

nearly all viruses isolated were DENV-3
(Rahman et al. 2002; Wagatsuma et al. 2004; Podder
et al. 2006; Islam et al. 2006)

co-circulation of DENV3 with DENV 2 & 4
(Aziz et al. 2002)
Source: (Karim et al. 2012)

6. First Outbreak in 2000
Panic situation
• People
• Professional
• Media
• Posters –Blood
Test… labs.
• Blaming!!
BANGALI A, Mannan Dr.

7. Questions and Objectives about Dengue in Dhaka
Ecological / Entomological / Virological / Socialogical-Economic Factors for Dengue
What are the distribution of
Aedes mosquitoes and
whether Aedes density vary
with different socio-economic
statuses (SES)?
What are the seroprevalence
of DENV and how it is
correlated with Aedes
abundance?
How human Knowledge,
Attitudes, and Practices (KAP)
at the individual and
household levels are involved
in enhancing or reducing
vector habitat?
Objectives:

To delineate vector distribution by
examining Aedes larva and pupa
breeding spaces in houses

To conduct household level
serosurvey in the same household

To map risk perception and analyze
KAP regarding dengue disease

8. Methodology
• Multi-stage, multi-level study
design for entomological
survey of dengue vector
distribution
• Focus group discussions
(FGDs) and key informant
interviews (KIIs) for risk
perception analysis
• Guiding Principles:
2
1. Representative samples of
the City of Dhaka
2. Socio-economic variability
among the wards considered
3. Gender perspectives
considered in FGDs and KIIs

9. Differences among Socio-economic Statuses: Some Selected Images

10. An Outline of Findings and Analysis
Vector ecology and distribution during 2011 and 2012
Container analysis (mosquito breeding and larval
development) and water-use pattern at household level
Serosurvey result of pre- and post-monsoon 2012
Risk perception of dengue disease and its vector

11. Overview of Entomological Survey
MONSOON 2011
MONSOON 2012
TOTAL LARVAE
COLLECTED
2587
3644
Ae. aegypti
2128 (84%)
Ae. albopictus
344 (13%)
2811
(77.1%)
634(17.4%)
Other Sp.
3%
61 (1.7%)
TOTAL PUPAE
COLLECETED
339
1129
Survey
Time
House
Index
Container Breteau
Index
Index
PUPAE/100
HOUSES
MONSOON
2011
27.74%
32.84%
52.39%
36.02
MONSOON
2012
24.17%
31%
44.17%
169.9
Total Household Visited
(target=1200) :
842 (2011)
834 (2012)
Overwhelming majority
of households have been
found to be infested with
Aedes aegypti
Calculation of Stegomyia
Indices are quite high for
vector surveillance in both
years

12. Most Frequent Container Types, Monsoon 2012
 8 major types of positive containers
seemed to be dominant
 These 8 containers types account for
72% of all positive containers
CONTAINER CODE:
A1=Water tank
A3=Clay pot
A4=Ceramic pot
A13=Metal bucket
A14=Plastic bucket
A19=Plastic drum (sealable)
A21=Flower tub & tray
A27=Tires
A34= Broken sports/toy parts
A38=Plastic sheets
A39=Broken plastic pots

13. Images of most frequent container types, Monsoon 2012

14. Dengue Lab Diagnostics Overview
HI
IgG ELISA
Neutralization
RT- PCR
10k
1k
100
10
1
1000
100
1
0.1
10
1
0.1
400 bp

Rn
Rn
10,000
10k
+
1k
100
10
1
0.1
0.1
Cycle
Ct

15. Serosurvey Results
Pre monsoon 2012
Post monsoon 2012
 1129 samples were collected
 1130 samples were collected
 906 (80.2%) were IgG
Positive
(3.6%) were IgM positive
Children had lower ~ 30%
seroprevalence rates
(630 paired sera and 500
replacement sera)
 924 (81.8 %) samples were
IgG positive
 Were there higher IgM
positives and children
seroconversions post
monsoon ?

16. Confirmatory Serology
+
Neutralization Assays : 1. Plaque Reduction Neutralization Test
2. Microneutralization Assay
Subset of “dengue IgG” positive patient sera tested by more specific
neutralization assays indicated that a minority of Dhaka residents
may have been exposed to Japanese Encephalitis and West Nile virus

17. Water Supply & Storing at the
Household Level
Based on entomological
survey questionnaire
Based on FGDs and KII
 I cover those water holding
 In the city of Dhaka, 94%
(n=842)households have piped
water supply with 4.6% has
reliance on deep tube-well.
 40.8% (n=842) households
(mainly from HSES & LSES) store
water for multiple reasons.
 38.4% household members
empty/clean containers on weekly
basis, whereas 59.6% empty
water more than weekly basis and
no idea of cleaning the water
holding containers.
containers which I use only for
cooking but not for other purposes
(Female respondent from MSES)
 We have no choice but to store water
everyday as we don’t have 24 hours
supply of electricity(Respondent from
LSES)
 We don’t store water in our house.
However, I have no idea whether our
housemaids are storing water or not
as they are not allowed to use our
toilets(Respondent from HSES)
HSES=High Socio-economic Status; MSES=Medium
Socio-economic Status; LSES=Low Socioeconomic Status

18. Knowledge about Dengue Vector Breeding Sites
 Respondents (n=15) do not
fully recognize breeding sites
of the dengue vector.
 Respondents associated
other “dirty” sites (i.e.,sewage
drains, waste sites) where
they found lots of larvae and
adult mosquitoes.
 There is a marked hierarchy
of people’s perceptions of
dengue vector breeding sites.
Sites outside the home were
ranked as highly probable
breeding sites, while
containers in the houses were
ranked as less likely breeding
sites.
 Dengue mosquitoes breed
everywhere.
 Dengue mosquitoes grow in
stagnant water but I never
knew about that water has to
be clean not dirty.
 I know mosquitoes those
bite, mostly breed from
outside containers and they
don’t lay eggs inside houses.
 All biting mosquitoes come
from outside to the inside of
our houses to bite us.

19. Relation of demograph,
KAP and Vector

20. Risk Perceptions of Dengue Disease and Vector
 Perception of dengue vector: its dilution with other mosquitoes
I know that dengue disease is caused by striped mosquitoes. Though
this disease is fatal, they come once a year or every two years. It is less severe when
we think of how often we are annoyed by other mosquitoes, which come daily, all the
time and everywhere
Dengue is not a problem in Dhaka, why should I worry about dengue mosquito then?
(HSES respondent)

Perception of dengue as a disease:Partial knowledge with misconception
I know dengue is caused by dengue mosquito bites but I don’t have any idea about
dengue fever or DHF
Dengue is like a mild fever, it never became severe to people in our country

21. Conclusions and Implications
 Vector and sero survey related: significant overlap ;high degree of exposure
(high degree of dengue seroprevalence, risk for 2nd exposure – >DHF)
 Differential water storage and water use patterns are profoundly
influenced by varied utility supplies and constraint in services (e.g. piped
water, electricity) to different socio-economic categories of city dwellers
 A sense of complacency about dengue disease exists across socioeconomic categories but their reasons are rooted in varied macro level
contexts
 The degree of misconception about dengue transmission is quite high,
and risk communication on dengue disease needs to be strengthened
among the community stakeholders
 Single disciplinary approach is not adequate to encompass complexities in
dengue transmission, and application of an Ecohealth approach would be
appropriate

22. Acknowledgement
Thesis Committee Personnel:
C. Emdad Haque (UM)
Michael Drebot (PHAC)
Robbin Lindsay (PHAC)
Stephane McLachlan (UM)
Institutions:
International Centre for Diarrh Disease, Bangladesh
(icddr,b)
North South University (NSU), Dhaka, Bangladesh
Population Services and Training Centre (PSTC),
Bangladesh
Public Health Agency Canada (PHAC)
Government:
Ministry of Health & Family Welfare, Govt. of Bangladesh
Funding Agencies:
IDRC-CRDI, Canada
IDRC Doctoral Research Award
Manitoba Health Research Council (MHRC)
Graduate Fellowship
University of Manitoba (UM)

23. Parnali and Robbin Lindsay
Parnali
???

24. Questions ?