Culex pipiens distribution in Tunisia: Identification of suitable areas through Random Forest and MaxEnt approaches.

BACKGROUND: Tunisia has experienced several West Nile virus (WNV) outbreaks since 1997. Yet, there is limited information on the spatial distribution of the main WNV mosquito vector Culex pipiens suitability at the national level. OBJECTIVES: In the present study, our aim was to predict and evaluate the potential and current distribution of Cx. pipiens in Tunisia. METHODS: To this end, two species distribution models were used, i.e. MaxEnt and Random Forest. Occurrence records for Cx. pipiens were obtained from adult and larvae sampled in Tunisia from 2014 to 2017. Climatic and human factors were used as predictors to model the Cx. pipiens geographical distribution. Mean decrease accuracy and mean decrease Gini indices were calculated to evaluate the importance of the impact of different environmental and human variables on the probability distribution of Cx. pipiens. RESULTS: Suitable habitats were mainly distributed next to oases, in the north and eastern part of the country. The most important predictor was the population density in both models. The study found out that the governorates of Monastir, Nabeul, Manouba, Ariana, Bizerte, Gabes, Medenine and Kairouan are at highest epidemic risk. CONCLUSIONS: The potential distribution of Cx. pipiens coincides geographically with the observed distribution of the disease in humans in Tunisia. Our study has the potential for driving control effort in the fight against West Nile vector in Tunisia.

Role of eco-climatic factors in the distribution of bluetongue in endemic areas in Tunisia.

Background: Bluetongue (BT) is an important infectious, non-contagious, OIE-listed viral disease of domestic and wild ruminants. The disease is transmitted among susceptible animals by a few species of an insect vector in the genus Culicoides. Recently, during the fall of 2020 (September and October), a Bluetongue virus-4 epizootic marked the epidemiological situation in several delegations of Tunisia with clinical cases recorded in sheep and cattle. Aim: Determine the eco-climatic variables most likely associated with delegations reporting BT cases. Methods: A logistic regression model (LRM) was used to examine which eco-climatic variables were most likely associated with delegations reporting BT cases. Results: Based on the LRM, our findings demonstrated that the key factors contributing significantly to BT cases' distribution among delegations in Tunisia included day land surface temperatures (DLST), night land surface temperatures (NLST) and normalized difference vegetation index (NDVI). A positive correlation between sheep distribution and rainfall amounts was demonstrated. Statistical analysis focusing on the most affected delegations during the BT epidemic (the Sahel and the Centre of Tunisia) demonstrated that the epidemic situation seems to be a consequence of the combination of the following environmental parameters: NDVI with values ranging between 0.16 and 0.2, moderate rainfall 2-4-fold above the normal (10-50 mm) and DLST values between 32°C and 34°C in September. Conclusion: These findings suggest and develop a robust and efficient early warning surveillance program in risk areas based on eco-climatic risk factors.

Detection of enzootic circulation of a new strain of West Nile virus lineage 1 in sentinel chickens in the north of Tunisia.

Tunisia has experienced various West Nile disease outbreaks. Notwithstanding the serological and molecular confirmations in humans, horses and birds, the human surveillance system can still be improved. Three sentinel chicken flocks were placed in different Tunisian endemic regions and followed up from September 2016 to January 2017. A total of 422 sera from Sejnene (north of Tunisia), 392 from Moknine (east coast of Tunisia) and 386 from Tozeur (south of Tunisia) were tested for West Nile-specific antibodies and viral RNA. The WNV elisa positive rate in sentinel chickens in Sejnene was 10.7% (95% CI: 5.08-21.52). No positive samples were detected in Moknine. In Tozeur, the overall serological elisa positive rate during the study period was 9.8% (95% CI:4.35-21.03). West Nile virus nucleic acid was detected in two chickens in Sejnene.Phylogenetic analysis of one of the detected partial NS3 gene sequences showed that recent Tunisian WNV strain belong to WNV lineage 1 and is closely related to Italian strains detected in mosquitoes in 2016 and in a sparrow hawk in 2017. This report showed the circulation, first molecular detection and sequencing of WNV lineage 1 in chickens in the north of Tunisia and highlights the use of poultry as a surveillance tool to detect WNV transmission in a peri-domestic area.

West Nile disease in Tunisia: an overview of 60 years.

West Nile virus (WNV) is an arthropod borne virus of public health importance. The virus is a member of the genus Flavivirus and belongs to the Japanese encephalitis virus (JEV) antigenic complex under the Flaviviridae family. The WNV is continuously spreading across Tunisia especially in the coastal and Southern area of the country. The first human West Nile disease (WND) epidemic in Tunisia occurred in 1997, since then, the quantity and the extension of spillover effects increased constantly. However, the existing knowledge of factors triggering such events continues to be rather poor. The last epidemic WNV human meningitis and meningoencephalitis recorded in 2012, with 86 cases and 6 deaths, confirmed the failure of the current system in predicting new cases. This review, based on analysis of scientific papers published between 1970 and 2015, summarises the state of knowledge on WNV in Tunisia and highlights the existing knowledge and research gaps that need to be addressed.