outbreak of bluetongue disease in zel sheep flocks in mazandaran province, iran

Background: bluetongue (bt) is a significant arthropod-borne viral disease affecting sheep, with varying clinical manifestations depending on the strain of the virus, the host breed, their immune status, and environmental conditions. while endemic in iran, few studies have focused on outbreaks, particularly in native breeds. objectives: this study aims to provide comprehensive data on the clinical presentation, post-mortem findings, and molecular diagnosis of a bt outbreak in zel sheep flocks in mazandaran province, iran, to better understand the virus’s impact and precognition.methods: during the 2018 outbreak, clinical and post-mortem evaluations were conducted on 12 flocks (1800 sheep). samples, including blood and tissue from both live and dead sheep, were collected and analyzed using reverse transcription polymerase chain reaction (rt-pcr) and nested pcr to confirm bt virus (btv) presence. results: clinical, necropsy observations, and molecular analysis confirmed btv infection in both live and dead sheep. the morbidity rate was approximately 13.33%, with a mortality rate of 2.11% across the entire population and 15.83% among the infected sheep. the most common clinical signs observed were high fever (80%), swelling and edema of the lips and face (96.25%), and redness of the buccal and nasal mucosa (87.5%). nasal discharge and frothy, blood-stained salivation were present in 15% of the infected sheep, while tongue erosion and ulcers affected 22.9%. necropsies revealed 100% mucosal lesions, hemorrhagic pulmonary artery lesions in 81.6%, and systemic congestion of major organs in 50% of cases. serous effusions were found in 42%, indicating severe systemic involvement in the dead sheep. these findings align with reports from other regions experiencing btv outbreaks and suggest that climatic conditions and vector proliferation contributed to the spread of the disease.conclusion: this study reaffirms the enzootic nature of bt in iran and stresses the critical role of clinical, necropsy, and molecular diagnostics in managing bt outbreaks. to minimize future outbreaks and economic losses from btv’s effects on sheep health in the regions, adopting preventive measures such as vaccination programs, serotype monitoring, enhanced surveillance, vector control, and regulation of livestock movement is recommended.