Identification of Suitable Areas for West Nile Virus Circulation in Tunisia

Abstract

West Nile virus (WNV) is a mosquito-transmitted Flavivirus belonging to the Japanese encephalitis antigenic complex of the Flaviviridae family. It is transmitted primarily by the bite of infected mosquitoes, particularly Culex spp. and Aedes/Ochlerotatus spp., which acquire the virus by feeding on viraemic birds. Humans, horses and other mammals are regarded as incidental or dead-end hosts. In the last decades, an increasing number of cases of WNV infection in horses and humans have been notified in the Mediterranean basin. In Tunisia, human cases of WNV-related meningoencephalitis were detected in 1997, 2003, 2007, 2010, 2011 and 2012. Based on the analysis of climatic and environmental conditions found in the locations where human cases have been reported in 2012, the aim of this study was to identify similar areas in Tunisia potentially at risk of disease occurrence. Data related to 85 neuroinvasive West Nile fever (WNF) human cases were georeferenced and a set of environmental and climatic variables (wetlands and humid areas, normalized difference vegetation index (NDVI), temperatures and elevation, migratory bird settlements) were used in the analysis. Areas, ecologically similar to those where human cases were detected, were identified using the Mahalanobis distance statistic. A leave-one-out cross-validation was performed to validate the sensitivity of the model, and 78 of 85 points were correctly classified.

Evidence of exposure of laughing doves (Spilopelia senegalensis) to West Nile and Usutu viruses in southern Tunisian oases

“…Indeed, we found that doves inhabiting littoral oases were more exposed to flaviviruses compared with those in inland oases. This finding is consistent with our expectation and also with the findings of previous studies on the spatial distribution of flaviviruses in the Mediterranean basin and Tunisia [10,47]. In southern Tunisia, the inland areas experience higher temperatures and evaporation rates in comparison with the coast.…”

“…Our results showed a significant effect of dove age on the prevalence of total anti-flavivirus antibodies. The occurrence probability of anti-flavivirus antibodies was four times higher in adult doves compared with young ones, which is consistent with other investigations of mosquito-borne flaviviruses [10,38]. As the host gets older, the exposure time to mosquito bites, and hence virus infection, increases.…”

“…Although most human infections with WNV are clinically silent, some WNVinfected patients develop neuroinvasive disease that can manifest as meningitis, encephalitis and/or myelitis. In Tunisia, WNV has been associated with three major West Nile outbreaks in humans: in 1997 (173 cases, with eight deaths), in 2003 (21 cases and three deaths) and in 2012 (86 cases and 12 deaths) [6][7][8][9][10][11]. USUV was discovered in South Africa in 1959, and since then has been detected in several other African and European countries [1].…”

Integrated Early Warning Surveillance: Achilles′ Heel of One Health?

“…From January 2019, using scientific references [10,20,21,26,37] and grey literature [38][39][40], we identified possible indicators for highlighting vulnerabilities of MLS countries to the selected arboviral diseases. A set (from four to six) of potential indicators were identified for each pathogen and sector involved in arbovirus surveillance (entomology, human health, and, in the case of zoonotic pathogens, animal health).…”

“…In fact, the identification of early warning indicators in association with rapid implementation of prevention and control measures could reduce the severity of arbovirus epidemics [18,19]. Ad hoc indicators can also highlight the vulnerability of countries or specific zones to the introduction and spread of arbovirus infections, thus providing precious information to prevent the occurrence of outbreaks and epidemics [20,21].…”