Abstract
BackgroundIn order to characterize the complete range of lesions, especially minimal, affecting mammary gland and viral antigen distribution and target cells using immunohistochemistry in naturally Visna/maedi (VM) 84 infected sheep were studied, forty-four from flocks with clinical cases (A) and 35 randomly sampled from two abattoirs (B) together with five negative controls (C). An immunocytochemistry technique was developed and further milk samples (n = 39) were used to study viral excretion, carrier cells and the role of milk and colostrum in the transmission of the disease.ResultsAll sheep from group C and three sheep from group B were negative to VM in tissue sections by histopathology, immunohistochemistry and PCR, and also in serum using ELISA. Several degrees of CD3 + lymphocytic interstitial mastitis were observed in groups A and B: minimal (+) n = 26 sheep; moderate (++), n = 32 and severe (+++), n = 12. No differences in lesion distribution were observed between groups A and B. Viral presence was confirmed by immunohistochemistry using two different antibodies and/or PCR in every tissue with lesions while serology was negative in six sheep with lesions. Two milk samples taken from milk tanks from two flocks from group A and fourteen milk samples from 29 infected sheep from group B were positive to VM (most of them from animals with moderate and severe lesions). Positivity was only found in macrophages, even in focal and minimal lesions, while no positivity was observed in epithelial or any other cells in either tissue and milk samples.ConclusionsThis new observation of the minimal lesions described in this work increased the prevalence of VM lesions in mammary gland up to 90.9% and VM should be considered as a differential diagnosis when minimal interstitial lesions are detected. A high prevalence of VM was observed in intensive milk-producing sheep, ELISA serology did not detect as positivity all infected animals, while histology, IHC or PCR showed higher sensitivity. The cytological technique developed was very useful in milk-cell studies using hematoxylin and eosin and immunocytochemistry. Viral detection in milk samples (16/39) confirms a potential but limited role of milk/colostrum in viral transmission.
Highlights
In order to characterize the complete range of lesions, especially minimal, affecting mammary gland and viral antigen distribution and target cells using immunohistochemistry in naturally Visna/maedi (VM) 84 infected sheep were studied, forty-four from flocks with clinical cases (A) and 35 randomly sampled from two abattoirs (B) together with five negative controls (C)
No lesions were observed in six infected sheep (6/76, 7.9%) which showed no inflammatory cells in the interstitium and only a few and focal small lymphocyte aggregates were found in association with canaliculi
Serological results highlight the high prevalence of VM infection in intensive milk-producing sheep in Castilla y León (Spain), with 91.4% polymerase chain reaction (PCR) and IHC-positive sheep from abattoirs, similar to previously reported seroprevalence [9]
Summary
In order to characterize the complete range of lesions, especially minimal, affecting mammary gland and viral antigen distribution and target cells using immunohistochemistry in naturally Visna/maedi (VM) 84 infected sheep were studied, forty-four from flocks with clinical cases (A) and 35 randomly sampled from two abattoirs (B) together with five negative controls (C). Ovine Visna Maedi (VM) is caused by Visna/maedi virus (VMV), which together with caprine arthritis-encephalitis virus are small ruminant lentiviruses (SRLV) [1] It is a slow progressing disease characterized by a gradual loss of body condition due to chronic inflammation in different organs [2,3,4] consisting of interstitial pneumonia, interstitial mastitis, non-purulent meningoencephalitis with demyelination of the CNS affecting spinal cord and rarely arthritis [4,5,6]. These target cells could migrate to regional lymph nodes from where viral systemic dissemination could occur [12,13,14] or could reach the bone marrow infecting myeloid precursor cells and reaching the bloodstream [15, 16], carrying the viral DNA into blood with minimum transcription until the maturation of monocytes into macrophages in the tissue
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