Effects of a Five-Year Citywide Intervention Program To Control Aedes aegypti and Prevent Dengue Outbreaks in Northern Argentina

Abstract

BackgroundDengue has propagated widely through the Americas. Most countries have not been able to maintain permanent larval mosquito control programs, and the long-term effects of control actions have rarely been documented.MethodologyThe study design was based on a before-and-after citywide assessment of Aedes aegypti larval indices and the reported incidence of dengue in Clorinda, northeastern Argentina, over 2003–2007. Interventions were mainly based on focal treatment with larvicides of every mosquito developmental site every four months (14 cycles), combined with limited source reduction efforts and ultra-low-volume insecticide spraying during emergency operations. The program conducted 120,000 house searches for mosquito developmental sites and 37,000 larvicide applications.Principal FindingsRandom-effects regression models showed that Breteau indices declined significantly in nearly all focal cycles compared to pre-intervention indices clustered by neighborhood, after allowing for lagged effects of temperature and rainfall, baseline Breteau index, and surveillance coverage. Significant heterogeneity between neighborhoods was revealed. Larval indices seldom fell to 0 shortly after interventions at the same blocks. Large water-storage containers were the most abundant and likely to be infested. The reported incidence of dengue cases declined from 10.4 per 10,000 in 2000 (by DEN-1) to 0 from 2001 to 2006, and then rose to 4.5 cases per 10,000 in 2007 (by DEN-3). In neighboring Paraguay, the reported incidence of dengue in 2007 was 30.6 times higher than that in Clorinda.ConclusionsControl interventions exerted significant impacts on larval indices but failed to keep them below target levels during every summer, achieved sustained community acceptance, most likely prevented new dengue outbreaks over 2003–2006, and limited to a large degree the 2007 outbreak. For further improvement, a shift is needed towards a multifaceted program with intensified coverage and source reduction efforts, lids or insecticide-treated covers to water-storage containers, and a broad social participation aiming at long-term sustainability.

Assessing the Relationship between Vector Indices and Dengue Transmission: A Systematic Review of the Evidence

“…In the remaining studies [20], [32], [33], [41], [42] a variety of mixed, inconclusive or weak associations were reported. Gurtler et al conducted analyses on the effect of a given intervention on mosquito indices but not on dengue cases [32].…”

Diversity of containers and buildings infested with Aedes aegypti in Puerto Iguazú, Argentina

“…For example, larvae and pupae productivity was not evaluated and stringent quantitative analysis to explore the implications of this factor in terms of larvae and pupae productivity is recommended. Closed or refused premises have also been a frequent limitation in previous studies 5 . Although during this study closed premises were visited three times, it was only possible to inspect 69% of the premises and the role of the unsurveyed premises regarding Ae.…”

“…urban studies 4,5,9,10 . In two cities in Argentina, entomological indices were higher than in Puerto Iguazú (HI: 67-76%; CI: 18-39%; BI: 127-249) 9,10 .…”

Seasonal Occurrence of Immature Mosquitoes in Swimming Pools in Buenos Aires, Argentina

“…Carbajo et al (2006) reported the ready adaptation of this vector species to urban areas. Gürtler et al (2009) andFisher &Schweigmann (2010) noted the effects of vegetation, shade conditions, improperly maintained swimming pools, and housing and waste management in areas with high human densities as factors that maintain high infestation levels of mosquito vectors, including Ae. aegypti.…”