A comparative analysis of the 2007 and 2017 Italian chikungunya outbreaks and implication for public health response

Abstract

Chikungunya virus (CHIKV) is a mosquito-borne infection that is emerging in temperate areas of Europe, following the expansion of one of its vector species, Aedes albopictus. Although CHIKV fever is a self-limiting disease, with a clinical syndrome often resolving within few days, it can also cause severe sequelae, including chronic polyarthralgia lasting up to 5 years. Additionally, CHIKV outbreaks may limit blood bank donations, adding economic burden on the health system. Public health authorities in Europe need to increase their preparedness against this emerging threat. Two large CHIKV outbreaks occurred in Italy in 2007 and 2017, with hundreds of cases and significant geographical spread. The aim of this paper is to review and compare the 2 Italian outbreaks in terms of available estimates of key epidemiological features, patient clinical presentation, virus and immunological characteristics, and public health response. Recommendations for public health and future directions for research are also discussed and highlighted. Key results Both outbreaks started in small towns, but cases were also detected in nearby larger cities where transmission was limited to small clusters. The time spans between the first and the last symptom onsets were similar between the 2 outbreaks, and the delay from the symptom onset of the index case and the first case notified was considerable. Comparable infection and transmission rates were observed in laboratory. The basic reproductive number (R 0) was estimated in the range of 1.8-6 (2007) and 1.5-2.6 (2017). Clinical characteristics were similar between outbreaks, and no acute complications were reported, though a higher frequency of ocular symptoms, myalgia, and rash was observed in 2017. Very little is known about the immune mediator profile of CHIKV-infected patients during the 2 outbreaks. Regarding public health responses, after the 2007 outbreak, the Italian Ministry of Health PLOS NEGLECTED TROPICAL DISEASES

Spatial modes for transmission of chikungunya virus during a large chikungunya outbreak in Italy: a modeling analysis

“…These results support previous research suggesting the need for improving preparedness towards earlier detection and response [24,25], which can be achieved by increasing the awareness of physicians and health personnel with respect to the transmission risks and clinical manifestations of arboviral diseases [18,26]. Although the specificity of Anzio as a summer holiday destination and its proximity to a large metropolitan city likely inflated the probability of local transmission and exportation (for example compared to the 2007 outbreak in Emilia Romagna, Italy [27,28]), it is not unlikely to observe similar patterns in future outbreaks: many touristic destinations in temperate areas are towns with low human population density and great suitability for mosquito populations and therefore with a high risk of arboviral transmission. The larger-than-expected role of human mobility and the partial effectiveness of reactive interventions [29] call for the implementation of preventive vector control activities targeting all municipalities at risk of autochthonous transmission that are adjacent to affected areas.…”

ZanzaMapp: A Scalable Citizen Science Tool to Monitor Perception of Mosquito Abundance and Nuisance in Italy and Beyond

“…In late spring/summer 2017 (in the absence of a specific promotion of ZanzaMapp in the media), new users were <100/week until mid of September, when their rapidly increased up to 811 in the second week of October. This is likely to be associated to the Chikungunya virus outbreak, which caused almost 500 infected cases in Lazio in September–October 2017 [ 4 ] and which was largely covered by the media, creating serious concern in the population: This created the opportunity to promote again ZanzaMapp in TV and newspaper interviews. In 2018, when no advertisement was carried out, new users were <50/week.…”

“…A linear association is observed between ZanzaMapp records and population densities at log10 scale (where a 10-fold increase in population density correspond in a 19.7 increase in the number of records; Figure S3), confirming the expectation that the highest number of records would come from highly populated areas. The majority of records are from the Lazio Region (19.6%, 45.2%, and 34.2% in 2016 (total = 25,578), 2017 (total = 6187) and 2018 (total = 3134), respectively), reflecting the location of most of the people involved in the studies, Rome, and, in 2017, the increased interest in the app elicited by the chikungunya outbreak in the region [4]. Overall, results suggest a high success of ZanzaMapp in attracting potential users (as shown by the high numbers of new users following major TV promotion events) and a limited one in eliciting long-lasting commitment.…”

“…In temperate regions, however, mosquitoes are mostly perceived as a nuisance, in spite of the fact that mosquito-borne viruses, such as the West Nile virus, are endemic in several European and North American Countries. Moreover, the colonization of these regions by invasive species (typically belonging to the genus Aedes ), ongoing since the eighties, has led to several cases of autochthonous transmission of exotic arboviruses such as dengue in Europe and USA [ 1 , 2 ], Zika in the USA [ 3 ], and to two chikungunya outbreaks with hundred human infections in Italy [ 4 ]. Differently from mosquito control interventions aimed at preventing disease transmission in tropical areas, interventions for nuisance (and risk of pathogen transmission) reduction purposes in temperate regions are rarely organized at country/regional level and largely implemented by private pest control companies appointed either by municipalities to treat public areas or by citizen to treat private ones.…”

Spatio-Temporal Distribution of Aedes Albopictus and Culex Pipiens along an Urban-Natural Gradient in the Ventotene Island, Italy

“…However, even if the transmission route of the pathogen via the mosquito vector is known, the ability of the public health authorities and scientific community to forecast and understand the risks of transmission remains still limited [5]. Indeed, it remains yet to be fully understood whether the mechanisms and conditions that caused the extraordinary increase in West Nile virus cases in Europe during 2018 [6,7] and triggered the chikungunya outbreak in 2017 [8] were exceptional or potentially forecastable. Among other variables, the spatial distribution and seasonality of vectors, as well as their interconnections with hosts, are critical factors that can greatly impact the risk of transmission [9].Therefore, it is essential to understand how these species are distributed across the landscape and what natural and anthropogenic factors influence their spatial distribution.…”