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Histopathological, serological, molecular and electron microscopy detection of Maedi-Visna infection in sheep population in the West of Iran.

Background
Maedi-Visna (MV) is a progressive lymphoproliferative viral disease that affects multiple organs of small ruminants, including sheep and goats. The disease occurs primarily in the lung tissue and causes interstitial pneumonia.


Aims
The aim of present study was to investigate the prevalence of ovine MV infection in Iranian sheep population through macroscopic, histopathological, serological, and molecular assays, as well as transmission electron microscopy (TEM).


Methods
Lung and blood samples of one-hundred female sheep (≤ 2 years old) referred to the Kermanshah slaughterhouse with respiratory symptoms were collected for histopathological and molecular evaluations. Corresponding serum samples were also collected for serological examination.


Results
Histopathological study showed the Maedi-like pulmonary lesions in 85% of the affected lungs, which included the interstitial pneumonia, smooth muscle hypertrophy of alveolar septa and around the blood vessels, interstitial lymphoplasmacytic infiltration and lymphofollicular hyperplasia. Specific antibodies against MV virus were detected in 7% of serum samples. Long terminal repeat (LTR) region of MV provirus was amplified in three (3%) DNA samples, extracted from the suspected lungs. Sequencing analysis of polymerase chain reaction (PCR)-positive samples confirmed the presence of MV provirus in the genome. No amplification was observed, neither in the DNA samples extracted from the blood samples of suspected sheep nor the control group. Transmission electron microscopy also confirmed the presence of MV virions inside the cytoplasmic membrane of MV-infected macrophages.


Conclusion
Although histopathology can provide a preliminary estimation of Maedi in populations, definitive diagnosis of the disease needs to be approved by more sensitive techniques such as serological examinations and molecular analysis.