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. 2012;6(8):e1799.
doi: 10.1371/journal.pntd.0001799. Epub 2012 Aug 28.

The interactive roles of Aedes aegypti super-production and human density in dengue transmission

Affiliations

The interactive roles of Aedes aegypti super-production and human density in dengue transmission

Harish Padmanabha et al. PLoS Negl Trop Dis. 2012.

Abstract

Background: A. aegypti production and human density may vary considerably in dengue endemic areas. Understanding how interactions between these factors influence the risk of transmission could improve the effectiveness of the allocation of vector control resources. To evaluate the combined impacts of variation in A. aegypti production and human density we integrated field data with simulation modeling.

Methodology/principal findings: Using data from seven censuses of A. aegypti pupae (2007-2009) and from demographic surveys, we developed an agent-based transmission model of the dengue transmission cycle across houses in 16 dengue-endemic urban 'patches' (1-3 city blocks each) of Armenia, Colombia. Our field data showed that 92% of pupae concentrated in only 5% of houses, defined as super-producers. Average secondary infections (R(0)) depended on infrequent, but highly explosive transmission events. These super-spreading events occurred almost exclusively when the introduced infectious person infected mosquitoes that were produced in super-productive containers. Increased human density favored R(0), and when the likelihood of human introduction of virus was incorporated into risk, a strong interaction arose between vector production and human density. Simulated intervention of super-productive containers was substantially more effective in reducing dengue risk at higher human densities.

Significance/conclusions: These results show significant interactions between human population density and the natural regulatory pattern of A. aegypti in the dynamics of dengue transmission. The large epidemiological significance of super-productive containers suggests that they have the potential to influence dengue viral adaptation to mosquitoes. Human population density plays a major role in dengue transmission, due to its potential impact on human-A. aegypti contact, both within a person's home and when visiting others. The large variation in population density within typical dengue endemic cities suggests that it should be a major consideration in dengue control policy.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Neighborhoods of study in the city of Armenia, Colombia.
Figure 2
Figure 2. Relationship between pupal abundance in highest producing container and average pupae per premise across 112 patch-surveys in Armenia.
Figure 3
Figure 3. Correlation between percent of dengue introduction iterations that generate ≥20 secondary infections and R0 (secondary infections averaged over 300 introduction trials for each of 7 pupal surveys) across 16 study patches in Armenia, Colombia.
Figure 4
Figure 4. Effects of each type of transmission event on secondary infections.
(a) Correlation between human-to-mosquito transmission (average number of infected mosquitoes per human introduction) and secondary human infections and (b) Correlation between mosquito-to-human transmission (average number of humans infected per infectious mosquito) and secondary human infections.
Figure 5
Figure 5. Pupae per container and transmission in subsequently emerged mosquitoes.
(a) Effect of pupal abundance on human-to-mosquito infection (no. subsequently emerged mosquitoes infected by introduced human infection) and mosquito-to-human infection (avg. number of. humans infected by subsequently emerged mosquitoes that became infected); (b) Effect of pupal abundance in containers that produce infected mosquitoes on avg. number of secondary infections.
Figure 6
Figure 6. Human density and transmission events (mosquito-to-human and human-to-mosquito transmission).
(a) Effects of patch-wide human density (total residents divided by houses); (b) Effects of density of residents in the house of the initial human infection (I0). Error bars are 95% CIs.
Figure 7
Figure 7. Effect of targeted elimination of pupae in houses with at least X pupae on reducing epidemic potential, compared with non-intervened levels.
Human population density is varied relative to census-observed population. Curves represent averages across the 16 study patches. Stochastic variation is greater at highest threshold control values because few patch-surveys had more than 500 pupae in a single house.

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