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Significance of eco-climatic factors in the distribution of bluetongue in endemic areas in Tunisia
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  • Thameur Ben Hassine,
  • Soufien Sghaier,
  • Sarah Thabet,
  • Heni Haj Ammar,
  • Salah hammami
Thameur Ben Hassine
General Directorate of Veterinary Services

Corresponding Author:[email protected]

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Soufien Sghaier
Veterinary Research Institute of Tunisia (IRVT), 20 Rue Jebel Lakhdar, Tunis 1006
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Sarah Thabet
National School of Veterinary Medicine of Sidi Thabet
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Heni Haj Ammar
General Directorate of Veterinary Services, 30 Rue Alain Savary 1002 Tunis
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Salah hammami
National School of Veterinary Medicine of Sidi Thabet
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Abstract

Bluetongue (BT) is an OIE-listed disease of ruminants caused by a Bluetongue virus (BTV) of the Orbivirus genus within the family Reoviridae and transmitted by biting midges of the genus Culicoides. BTV circulation has been described in North African countries and many BTV emergences in Europe were related to the wind-driven dissemination of infected midges from those countries. During the fall of 2020 (September and October), an epizootic of BT linked to BTV4 marked the epidemiological situation in several delegations of Tunisia with clinical cases recorded in sheep and cattle. Eco-climatic variables are known to influence the Culicoides presence and abundance and, therefore, the probability of occurrence of BT. A logistic regression model (LRM) was used to examine which eco-climatic variables were most likely associated with delegations reported BT cases. Eco-climatic variables included: Normalized Difference Vegetation Index (NDVI), Day Land Surface Temperature (DLST), Night Land Surface Temperature (NLST), precipitation, elevation, cattle and sheep distribution. Our findings, based on the LRM, demonstrate that the key factors that contributed significantly to BT cases distribution among delegations in Tunisia included DLST and NDVI. 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 0.16-0.3, moderate rainfall 2-4-fold above the normal (10-50 mm) and DLST values between 32 and 34°C.