Modelling Aedes albopictus dynamics and related Arbovirus outbreaks risk in central Italy

The invasive species Aedes albopictus has successfully colonized large areas of the Mediterranean basin and represents an alarming public health threat due to its potential role as competent vectors for arboviruses. Moreover, infected individuals are increasingly detected in the flow of international travelers into Europe due to the expansion of the geographic range of mosquito-borne diseases and the occurrence of significant outbreaks in endemic countries. The Public Health impact of the combination of these factors has been pointed out by the recent (2017) chikungunya outbreaks in Italy. Mathematical and statistical models can be used to interpret monitoring data and to improve our knowledge on vector and outbreak dynamics. Indeed, understanding vector population dynamics is essential to identify under which conditions the transmission risk is higher and eventually reduce the public health burden represented by mosquito-borne diseases. Estimates of vector population dynamics, autochthonous transmission risk and the impact of arbovirus transmission, both in term of number of cases or deaths, could help the planning of preventive and reactive interventions. Therefore, we analyzed the Italian 2017 chikungunya outbreak and found that the reproduction number R0 was 2.07 (95% credible interval: 1.47–2.59) and the first case importation between 21 May and 18 June 2017 with a probability of outbreak conditional to the importation event as high as 82% during the same period. We then evaluated the potential risk of yellow fever outbreaks and found between mid-July and mid-September a probability up to 31.9% of autochthonous transmission and up to 10.3% of large outbreaks. Moreover, the average probability of observing at least one death caused by yellow fever infection ranged between 7.2 and 12.5% if autochthonous transmission takes places.