Journal of Mosquito Research 2015, Vol.5, No.17, 1-10
9
Table 6 Mean House Index (HI), Container Index (CI) and Breteau Index (BI) in Nainital and Dehradun during 2010 dengue epidemics
Statistics
House Index (HI)
Container Index (CI)
Breteau Index (BI)
Nainital
Dehradun
Nainital
Dehradun
Nainital
Dehradun
Mean
32.33
28.61
25.91
17.93
124.99
77.33
Std. Deviation
6.21
7.312
7.17
3.51
74.63
11.49
Std. Error
0.56
0.6649
0.65
0.32
6.79
1.045
Lower 95% CI
16.11
12.48
10.84
8.86
28.92
42.47
Upper 95% CI
54.15
51.35
47.44
30.16
288.66
122.54
Table also shows Standard Deviation, Standard Error of Mean and 95% Confidence Interval limits for the entomological indices
We found very high entomological indices (HI, CI,
and BI) for all areas. However, it is difficult to give a
precise threshold level of entomological indices in
epidemiological context. Dengue outbreak had previously
been recorded even in very low entomological indices
in Cuba (Pelaez et al
.
2004), and Singapore (
cf
Sanchez
et al.
2006). In this present study, we found
that Dehradun (77% of cases) is more dengue prone
area than Nainital (23% cases) (Table 3). However, all
entomological indices are relatively higher in Nainital
than Dehradun (Table 6, and Figure 4). Moreover,
Mann-Whitney U nonparametric test revealed that the
observed differences of these indices (HI, CI, and BI)
between Nainital and Dehradun is not statistically
significant (p>0.05). Therefore, we hypothesize that
the epidemic intensity or severity of 2010-dengue
epidemic in Nainital and Dehradun are independent of
the rate of entomological indices. However, the layout
of housing structures differs between these two
districts; population density is higher or more
clustered in Dehradun than the Nainital, which could
also make Dehradun more dengue prone than Nainital.
There is always the possibility that other factors may
influence the relationship between entomological
indices and intensity of dengue epidemics. These
factors may be vector competence, vector bionomics
and composition, virulence of the virus, immunity
status of the population as whole or local health
authorities in reporting correct epidemic status. Some
studies have shown that entomological indices do
not seem to reliably assess dengue transmission risks
(Bang & Pant 1972; Kay et al
.
1987; Reiter & Gubler
1997; Focks et al
.
2000), other programs have used
them successfully (Pontes et al
.
2000) or continue to
recommend their use (WHO 1999).
We believe that where it is difficult to generalize the
interpretation of the threshold indices at the global
level or even country level, the threshold level of
entomological indices for an outbreak of dengue
should be set up locally at district or even city level
since all vector borne diseases are focal and local in
nature. However, entomological indices are very
useful to understand the actual man-mosquito contact,
abundance of adult mosquitoes, monitoring vector
control programs and use as a tool for forecasting
outbreak, pinpointing and mapping high-risk areas.
We observed a very high correlation between overall
HI and BI values. A high correlation and divergence of
HI and BI were also observed in West Indies
(Thongcharoen 1993), where it was also noticed that
at low rate of
Aedes
infestation, the HI and BI were
nearly the same, whereas at higher infestation rate, a
divergence between the indices was observed. Therefore,
the high correlation and divergence between HI and
BI in the present study indicated high rates of
Aedes
infestation, which may ultimately responsible for the
dengue epidemics in these areas.
Finally, Dengue/DHF is a burning health problem
throughout India, and cases and deaths were reported
from 31 states out of 35 during 2010. The results of
this study reinforce the practical importance of
entomological surveillance in measuring the risk of
dengue epidemics. Moreover, we have successfully
analyzed the epidemic characteristics of dengue/DHF,
which indicates the association of dengue with the
cultural habit of collecting rainwater due to irregular
water supply and the abundance of unmanaged water
sources due to the irregular garbage collection. Therefore,
improving these public services can improve the
dengue situation.
Acknowledgment
We are thankful to LS Chauhan, Director NCDC for
giving us the opportunity to carry out the study. We
