Background 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). 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. Results All 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. Conclusions This 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.

Ovine visna/maedi (VM) infection is characterized by the development of chronic inflammatory lesions in different organs, mainly in the lung, mammary gland and central nervous system (CNS), with either histiocytic or lymphocytic pattern predominance being described in the CNS. To help to understand the role of host immune response in the development of these patterns, 50 naturally-infected sheep and eight non-infected sheep from intensive milk-producing flocks were studied. The histological lesion patterns in the three main target organs in each sheep were characterized. Lesion severity was determined, including minimal lesions. A histiocytic pattern was observed in 23 sheep (46%), a lymphocytic inflammatory pattern in 19 sheep (38%) and a mixed inflammatory pattern in eight sheep (16%). Forty animals showed moderate or severe lesions (80%), while 10 had minimal lesions (20%). Moderate or severe lesions affected only one target organ in 20 sheep (50%), two organs in 14 sheep (35%) and all three target organs in six sheep (15%). Infection was confirmed by immunohistochemistry (IHC) using an antibody specific for p28 of VM virus/caprine arthritis and encephalitis virus and by polymerase chain reaction (PCR) in all sheep. Minimal inflammatory lesions associated with positive IHC and PCR were observed. The results suggest that the development of a predominant inflammatory pattern in different organs within the same animal may be related to the host immune response. Minimal and focal lesions, not considered previously, should be taken into account when formulating a differential diagnosis in affected sheep.

Spanish goat encephalitis virus (SGEV) is a member of the genus Flavivirus, family Flaviviridae, and causes encephalomyelitis in goats. The aim of this study was to determine whether sheep are susceptible to experimental challenge with SGEV by two different routes. The results show that SGEV can infect sheep by both the subcutaneous and intravenous routes, resulting in neurological clinical disease with extensive and severe histological lesions in the central nervous system. Lambs challenged subcutaneously developed more severe lesions on the ipsilateral side of the brain, but the lesion morphology was similar irrespective of the route of challenge. The clinical presentation, pathogenesis, lesion morphology and distribution shows that SGEV is very similar to louping ill virus (LIV) and therefore any disease control plan must take into account any host species and SGEV vectors as potential reservoirs. Furthermore, discriminatory diagnostics need to be applied to any sheep or goat suspected of disease due to any flavivirus in areas where SGEV and LIV co-exist.

Spanish goat encephalitis virus (SGEV) is a recently described member of the genus Flavivirus belonging to the tick-borne encephalitis group of viruses, and is closely related to louping ill virus (LIV). Naturally acquired disease in goats results in severe, acute encephalitis and 100% mortality. Eighteen goats were challenged subcutaneously with SGEV; nine were vaccinated previously against LIV and nine were not. None of the vaccinated goats showed any clinical signs of disease or histological lesions, but all of the non-vaccinated goats developed pyrexia and 5/9 developed neurological clinical signs, primarily tremors in the neck and ataxia. All non-vaccinated animals developed histological lesions restricted to the central nervous system and consistent with a lymphocytic meningomyeloencephalitis. Vaccinated goats had significantly (P <0.003) greater concentrations of serum IgG and lower levels of IgM (P <0.0001) compared with unvaccinated animals. SGEV RNA levels were below detectable limits in the vaccinated goats throughout the experiment, but increased rapidly and were significantly (P <0.0001) gieater 2-10 days post challenge in the non vaccinated group. In conclusion, vaccination of goats against LIV confers highly effective protection against SGEV; this is probably mediated by IgG and prevents an increase in viral RNA load in serum such that vaccinated animals would not be an effective reservoir of the virus. (C) 2017 Elsevier Ltd. All rights reserved.

Trabajo presentado al: IV Congreso VetDoc. (Leon, 6-7 de Julio de 2017). Publicado en: Revista de Docencia Veterinaria, volumen 2(2): 151-152. ISSN: 2445-1754

The marked differences in sensitivity existing among maedi visna ELISA tests is a striking issue in the control of the disease, which so far have mainly been related to the different circulating viral strain or to the particular test used. The aim of this work is to discern whether or not the ELISA results could also be associated to different histological lesion patterns and therefore conditioned by individual immune response. Fifty infected animals and eight negative controls were used and histological, inmunohistochemical, PCR and serological studies were performed. Histological patterns were classified based on previous described immunophenotypical criteria: a lymphocytic pattern, characterized by a clear predominance of T cells, especially CD8 + T cells (n = 19), and a histiocytic pattern, with a high quantity of macrophages mixed with B cells (n = 23). A third mixed pattern characterized by a mixed inflammatory infiltration was observed (n = 8), predominantly in animals with minimal lesions with no clinical signs being observed (75%). An association between these lesion patterns and the ELISA optic density values exists (p < 0.001). Sheep with a histiocytic pattern (n = 21) showed higher titers of antibodies compared to sheep with lymphocytic pattern (n = 18), where values were much lower or even negative. Animals with histiocytic pattern are easily recognizable using the ELISA test, while sheep showing lymphocytic lesion pattern could go unnoticed in the flock as serological false negative animals, being a likely remaining source of infection. Animals with mixed patient showed mixed values, and despite showing only minimal lesions, they are also carriers of the virus and can be easily underdiagnosed.

Trabajo presentado al: XL Congreso Nacional y el XVI Congreso Internacional de la Sociedad Espanola de Ovinotecnia y Caprinotecnia. (Castellon de la Plana, Espana, 16-18 septiembre 2015).

Trabajo presentado a la XXVI Reunion de la Sociedad Espanola de Anatomia Patologica Veterinaria (Zaragoza, 18-20 Junio 2014).

1 pagina.--Trabajo presentado al: XXIX Reunion de la Sociedad Espanola de Anatomia Patologica Veterinaria. Poster 3, pag. 69. 14-16 de junio de 2017. Caceres (Espana).

5 paginas, 2 tablas.--Trabajo presentado al: XL Congreso Nacional y el XVI Congreso Internacional de la Sociedad Espanola de Ovinotecnia y Caprinotecnia. (Castellon de la Plana, Espana, 16-18 septiembre 2015).