Effectiveness and economic assessment of routine larviciding for prevention of chikungunya and dengue in temperate urban settings in Europe

Abstract

In the last decades, several European countries where arboviral infections are not endemic have faced outbreaks of diseases such as chikungunya and dengue, initially introduced by infectious travellers from tropical endemic areas and then spread locally via mosquito bites. To keep in check the epidemiological risk, interventions targeted to control vector abundance can be implemented by local authorities. We assessed the epidemiological effectiveness and economic costs and benefits of routine larviciding in European towns with temperate climate, using a mathematical model of Aedes albopictus populations and viral transmission, calibrated on entomological surveillance data collected from ten municipalities in Northern Italy during 2014 and 2015.We found that routine larviciding of public catch basins can limit both the risk of autochthonous transmission and the size of potential epidemics. Ideal larvicide interventions should be timed in such a way to cover the month of July. Optimally timed larviciding can reduce locally transmitted cases of chikungunya by 20% - 33% for a single application (dengue: 18-22%) and up to 43% - 65% if treatment is repeated four times throughout the season (dengue: 31-51%). In larger municipalities (>35,000 inhabitants), the cost of comprehensive larviciding over the whole urban area overcomes potential health benefits related to preventing cases of disease, suggesting the adoption of more localized interventions. Small/medium sized towns with high mosquito abundance will likely have a positive cost-benefit balance. Involvement of private citizens in routine larviciding activities further reduces transmission risks but with disproportionate costs of intervention. International travels and the incidence of mosquito-borne diseases are increasing worldwide, exposing a growing number of European citizens to higher risks of potential outbreaks. Results from this study may support the planning and timing of interventions aimed to reduce the probability of autochthonous transmission as well as the nuisance for local populations living in temperate areas of Europe.

Fig 1. Epidemiological predictions in the absence of control interventions.

Probability of local transmission of chikungunya (CHIKV) and dengue (DENV), disaggregated by outbreak size, in the 10 study locations during the mosquito seasons.

Fig 2. Effectiveness of larviciding in reducing the expected number of secondary CHIKV infections.

Distribution across all sites and both years, disaggregated by coverage value (lighter colour: 30%; darker colour: 50%), intervention timing (starting date every 15 days between May 1^st and September 1^st) and effort level (i.e., number of larvicide applications with monthly frequency (from 1 to 4). Grey bars: optimal starting date; shaded area: duration of intervention.

Fig 3. Estimated effectiveness of optimally timed interventions for different coverages (30% and 50%) and effort level (0–4), disaggregated by site and year.

Fig 4. Probability of highest net health benefit according to the number of larvicide treatments, disaggregated by year, coverage and study site.

Fig 5. Probability of highest net health benefit for a single larvicide application according to the type of intervention (none vs. public vs. public and private), by year, coverage (30 and 50% for public intervention; 60 and 75% for both public and private intervention) and study site.