Identification of Suitable Areas for West Nile Virus Circulation in Tunisia.

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.

First detection of co-circulation of West Nile and Usutu viruses in equids in the south-west of Tunisia.

In the last fifteen years, West Nile Virus (WNV) has dramatically expanded its geographic range and is now considered the most widespread arbovirus in the world. In Tunisia, West Nile Fever (WNF) outbreaks were reported in humans in 1997, 2003 and 2012. Usutu Virus (USUV), which is a 'new' emerging Flavivirus antigenically close to WNV, has never been reported in Tunisia. A serological investigation in 284 equids was conducted in 2012 in the southern west region of the country to assess the presence and prevalence of the WNV and USUV infection. Of the 284 samples tested by competitive enzyme-linked immunoassay, 129 were positive. Of these, 120 (42.3%) had WNV-specific neutralizing antibodies. The prevalence was significantly higher in areas closer to the oasis compared with that of the surrounding arid areas. Antibody titres against USUV were also reported in 10 equids. This was the first evidence of USUV circulation in Tunisia. Data recorded by this study indicate that WNV and USUV have circulated/are circulating in the region and that there is an urgent need to adapt the current surveillance programmes to this new scenario.

[Detection of circulation of West Nile virus in equine in the north-west of Tunisia]. / Détection de la circulation de virus West Nile chez les Équidés dans le nord-ouest de la Tunisie.

Two outbreaks of West Nile Fever (FWN) were observed in the Sahel of Tunisia in 1997 and 2003. Several cases of meningitis and meningoencephalitis have been described in humans during these two outbreaks. However, no animal or clinical findings or seroconversion have been detected despite a high seroprevalence in human beings found around the affected areas. Few data are available regarding the spreading of this virus in other parts of the country. The purpose of this study was to detect a possible WNV spread in horses in some areas of Tunisia considered to be at risk for WNV but which had not been affected by previous outbreaks. A total of 133 equine blood samples were collected in six delegations from three governorates in the north-west of Tunisia. A second blood sampling was taken from animals that were tested negative after the first sampling for IgG to identify possible seroconversion. Detection of IgG was done using competitive ELISA. A significant viral spread was detected in the study area. Out of 133 samples tested for IgG during the first sampling, 36 samples were tested positive (27.1%). Two seroconversions were detected between September and October 2008 out of 84 samples tested. Statistical analysis showed a significant association between the presence of a wetland within 10 km and seroconversion. The presence of cattle seems to be a protective factor.