SARS-CoV-2 ORF8 accessory protein is a virulence factor.

IMPORTANCE: The relevance of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) ORF8 in the pathogenesis of COVID-19 is unclear. Virus natural isolates with deletions in ORF8 were associated with wild milder disease, suggesting that ORF8 might contribute to SARS-CoV-2 virulence. This manuscript shows that ORF8 is involved in inflammation and in the activation of macrophages in two experimental systems: humanized K18-hACE2 transgenic mice and organoid-derived human airway cells. These results identify ORF8 protein as a potential target for COVID-19 therapies.

Investigation into the Pathology of Idiopathic Systemic Amyloidosis in Four Captive Badgers (Meles meles).

Systemic idiopathic amyloidosis was described in four captive badgers (Meles meles). Two animals (B1 and B2) were not enrolled in any trial, while animals B3 and B4 took part in a vaccine efficacy study and had been challenged with Mycobacterium bovis. A full set of tissues was collected and processed routinely for histopathological, immunohistochemical and ultrastructural studies. Splenomegaly was found in three out of four animals. Histopathological evaluation revealed congophilic, permanganate-resistant systemic amyloid deposits in the tissues of all badgers. Animals B2 and B4 displayed a marked granulomatous response to amyloid within the spleen. Animals B1 and B2 also displayed clinicopathological findings suggestive of chronic kidney disease. Ultrastructural examination identified peculiar star-shaped arrays of amyloid. Immunohistochemical studies were unrewarding. Systemic amyloidosis should be considered among the differentials of wasting in captive badgers.

African swine fever: A re-emerging viral disease threatening the global pig industry.

African swine fever (ASF) recently has spread beyond sub-Saharan Africa to the Trans-Caucasus region, parts of the Russian Federation and Eastern Europe. In this new epidemiological scenario, the disease has similarities, but also important differences, compared to the situation in Africa, including the substantial involvement of wild boar. A better understanding of this new situation will enable better control and prevent further spread of disease. In this article, these different scenarios are compared, and recent information on the pathogenesis of ASF virus strains, the immune response to infection and prospects for developing vaccines is presented. Knowledge gaps and the prospects for future control are discussed.

Comparative analysis of cellular immune responses and cytokine levels in sheep experimentally infected with bluetongue virus serotype 1 and 8.

Protective immunity in sheep with bluetongue virus (BTV) infection as well as the role of BTV-induced cytokines during immune response remains unclear. Understanding the basis immunological mechanisms in sheep experimentally infected with serotypes 1 and 8 (BTV-1 and -8) was the aim of this study. A time-course study was carried out in order to evaluate cell-mediated immune response and serum concentrations of cytokines (IL-1ß, TNFα, IL-12, IFNγ, IL-4 and IL-10) with inflammatory and immunological functions. Depletion of T cell subsets (mainly CD4(+), γδ and CD25(+)) together with the absence of cytokines (IFNγ and IL-12) involved in the regulation of cell-mediated antiviral immunity at the first stage of the disease suggested that both BTV-1 and BTV-8 might impair host's capability against primary infections which would favor viral replication and spreading. However, cellular immune response and cytokines elicited an immune response in sheep that efficiently reduced viremia in the final stage of the experiment. Recovery of T cell subsets (CD4(+) and CD25(+)) together with a significant increase of CD8(+) T lymphocytes in both infected groups were observed in parallel with the decrease of viremia. Additionally, the recovery of CD4(+) T lymphocytes together with the significant increase of IL-4 serum levels at the final stage of the experiment might contribute to humoral immune response activation and neutralizing antibodies production against BTV previously described in the course of this experiment. These results suggested that both cellular and humoral immune response may contribute to protective immunity against BTV-1 and BTV-8 in sheep. The possible role played by IL-10 and CD25(+) cells in controlling inflammatory and immune response in the final stage of the experiment has also been suggested.

Effects of Preinfection With Bovine Viral Diarrhea Virus on Immune Cells From the Lungs of Calves Inoculated With Bovine Herpesvirus 1.1.

The aim of this work was to study the interstitial aggregates of immune cells observed in pulmonary parenchyma of calves preinfected with bovine viral diarrhea virus and challenged later with bovine herpesvirus 1. In addition, the intent of this research was to clarify the role of bovine viral diarrhea virus in local cell-mediated immunity and potentially in predisposing animals to bovine respiratory disease complex. Twelve Friesian calves, aged 8 to 9 months, were inoculated with noncytopathic bovine viral diarrhea virus genotype 1. Ten were subsequently challenged with bovine herpesvirus 1 and euthanized at 1, 2, 4, 7, or 14 days postinoculation. The other 2 calves were euthanized prior to the second inoculation. Another cohort of 10 calves was inoculated only with bovine herpesvirus 1 and then were euthanized at the same time points. Two calves were not inoculated with any agent and were used as negative controls. Pulmonary lesions were evaluated in all animals, while quantitative and biosynthetic changes in immune cells were concurrently examined immunohistochemically to compare coinfected calves and calves challenged only with bovine herpesvirus 1. Calves preinfected with bovine viral diarrhea virus demonstrated moderate respiratory clinical signs and histopathologic evidence of interstitial pneumonia with aggregates of mononuclear cells, which predominated at 4 days postinoculation. Furthermore, this group of animals was noted to have a suppression of interleukin-10 and associated alterations in the Th1-driven cytokine response in the lungs, as well as inhibition of the response of CD8+ and CD4+ T lymphocytes against bovine herpesvirus 1. These findings suggest that bovine viral diarrhea virus preinfection could affect the regulation of the immune response as modulated by regulatory T cells, as well as impair local cell-mediated immunity to secondary respiratory pathogens.

Bluetongue in Spain: from the first outbreak to 2012.

Outbreaks of bluetongue disease have occurred in Spain six times and have been caused by the following serotypes of bluetongue virus (BTV), in chronological order: BTV10, BTV2, BTV4, BTV1 and BTV8. Serotypes BTV1, BTV2 and BTV4 may have entered the country in Culicoides transported by wind; BTV8 via infected animal movements; and BTV10 across the Portuguese border. The evolution of each serotype has been different: BTV1, BTV4 and BTV10 spread throughout mainland Spain; BTV2 did not spread from the Balearic Islands to the Iberian Peninsula; and BTV8 has proven very poor at spreading throughout mainland Spain. The significant economic impact of the disease has led authorities to adopt control and eradication measures, which have evolved as new diagnostic tools and vaccines have become available. This review describes BTV infection in Spain, and it focuses on the clinical disease produced by each serotype, the Culicoides species which were present at what time, the origin of the virus and the control measures adopted. In the field, it has proven necessary to vaccinate livestock against each new BTV serotype as it arrived. Therefore, future eradication strategies should focus on developing polyvalent vaccines and vaccines that allow the differentiation of infected and vaccinated animals. As of 1 January 2013, the Iberian Peninsula is considered a restricted area for BTV1, and a small zone in southern Spain is a restricted area for BTV4, which includes the little BTV8 restricted area. Serotypes BTV1 and BTV4 were detected in sentinel animals in January and November and in March 2012, respectively. The last BTV8 positive animal was detected in November 2010, which implies that in the coming months, Spain may be declared free of BTV8.

Cell-mediated immune response during experimental acute infection with bovine viral diarrhoea virus: evaluation of blood parameters.

Acute infections with bovine viral diarrhoea virus (BVDV), a major pathogen of cattle, are often asymptomatic or produce only mild clinical symptoms. However, they may play an important role in the bovine respiratory disease complex by exerting a marked immunosuppressive effect, as a result of the death of the immunocompetent cell populations involved in controlling innate and adaptive immune responses, together with a marked reduction of both cytokine expression and co-stimulatory molecule synthesis. Although experimental research and field studies have shown that acute BVDV infection enhances susceptibility to secondary infection, the precise mechanism involved in BVDV-induced immunosuppression remains unclear. The present study is aimed at measuring a range of blood parameters in a single group of fourteen calves infected with non-cytopathic BVDV-1. Focus has been put on those related to the cell-mediated immune response just as leucocyte populations and lymphocyte subpopulations, serum concentrations of cytokines (IL-1ß, TNF-α, IFN-γ, IL-12, IL-4 and IL-10) and acute phase proteins [haptoglobin, serum amyloid A (SAA), fibrinogen and albumin], as well as BVDV-specific antibodies and viremia. After non-cytopathic BVDV-1 infection, clinical signs intensity was never more than moderate coinciding with the presence of viremia and leucocyte and lymphocyte depletion. An early increase in TNF-α, IFN-γ and IL-12 levels in contrast to IL-1ß was observed in line with a raise in haptoglobin and SAA levels on the latest days of the study. As regards IL-4 levels, no evidence was found of any changes. However, a slight increase in IL-10 was observed, matching up the TNF-α decline during the acute phase response. These findings would help to increase our knowledge of the immune mechanisms involved in acute infection with non-cytopathic BVDV-1 strains, suggesting the existence of a clear tendency towards a type 1 immune response, thereby enhancing resistance against viral infections.

Comparative study of clinical courses, gross lesions, acute phase response and coagulation disorders in sheep inoculated with bluetongue virus serotype 1 and 8.

Bluetongue virus serotypes 1 (BTV-1) and 8 (BTV-8) have been described as the most prevalent in Europe during recent outbreaks displaying intense virulence, sheep being among the most severely affected livestock species. However, BTV pathogenesis is still unclear. This study sought to elucidate differences in the pathogenetic mechanisms of BTV-1 and -8 in sheep. For this purpose, a time-course study was carried out, with sequential sacrifices in order to relate pathological lesions to changes in a range of virological and serological parameters. A greater virulence of BTV-1 was probed. BTV-1 infected sheep showed a longer clinical course, with a significant increase of clinical signs and more severe gross lesions than BTV-8 infected sheep. These differences appear not to be attributable to greater virus replication, suggesting viral loads did not influence in the pathogenicity of these serotypes. While both groups displayed an early, intense antibody response, they still developed clinical signs and lesions characteristic of bluetongue, indicating a lack of correlation between antibody levels and protection against the disease. Both acute phase response (APR) and thrombocytopenia induced by BTV-1 in sheep were more intense. Furthermore, an association between acute phase proteins (APPs) concentrations and the evolution of clinical signs and gross lesions was also observed, suggesting the existence of a direct link between the pathogenicity of BTV serotypes, the severity of vascular lesions and the serum concentrations of APPs. To our knowledge, this is the first verification of a measurable APR in sheep with both experimental and naturally occurring bluetongue.

Effect of infection with BHV-1 on peripheral blood leukocytes and lymphocyte subpopulations in calves with subclinical BVD.

Bovine viral diarrhea virus (BVDV) and bovine herpesvirus-1 (BHV-1) are important cattle pathogens that induce a broad immunosuppression on cell-mediated immune response on its own participating in the bovine respiratory disease complex (BRDC). The aim of our study was to evaluate the quantitative changes in immunocompetent cells in healthy calves and calves with subclinical bovine viral diarrhea (BVD), both inoculated with BHV-1. Total leukocyte counts exhibited changes mainly in neutrophils and lymphocytes that can contribute to the BVDV immunosuppression, thus accounting for some of the intergroup differences. Monocytes did not display numerical changes in either group. Regarding lymphocyte subpopulations, even though CD4+ T lymphocytes and B cells were depleted around 4 dpi in both infected groups, the main difference observed between both groups was in CD8+ T cells which displayed an earlier depletion in BVDV inoculated calves that can promote a greater BHV-1 dissemination, thus aggravating the course of the disease.

Immunohistochemical detection of dendritic cell markers in cattle.

Dendritic cells (DCs) are "professional" antigen-presenting cells with a critical role in the regulation of innate and adaptive immune responses and thus have been considered of great interest in the study of a variety of infectious diseases. The objective of this investigation was to characterize the in vivo distribution of DCs in bovine tissues by using potential DC markers to establish a basis for the study of DCs in diseased tissues. Markers evaluated included MHCII, CD208, CD1b, CD205, CNA.42, and S100 protein, the latter 2 being expressed by follicular dendritic cells whose origin and role are different from the rest of hematopoietic DCs. Paraffin wax-embedded tissues from 6 healthy Friesian calves were subjected to the avidin-biotin-peroxidase method, and the most appropriate fixatives, dilutions, and antigen retrieval pretreatments were studied for each of the primary antibodies. The most significant results included the localization of CD208-positive cells not only in the T zone of lymphoid organs but also within lymphoid follicles; CD1b-positive cells were mainly found in thymus and interfollicular areas of some lymph nodes; cells stained with anti-CD205 antibody were scarce, and their location was mainly in nonlymphoid tissues; and CNA.42- and S100 protein-positive cells localized in primary lymphoid follicles and light zones of germinal centers, although showing differences in the staining pattern. Furthermore, MHCII was established as one of the most sensitive markers for any DC of hematopoietic origin. These results increase our understanding of DC immunolabeling and will help in future DC studies of both healthy and diseased tissues.

Pathology of African swine fever: the role of monocyte-macrophage.

African swine fever (ASF) is a viral hemorrhagic disease with different clinical and lesional changes depending of virulence of strains/isolates and immunological status of pigs. In acute and subacute forms of ASF, severe vascular changes are present, with hemorrhages in different organs (mainly melena, epistaxis, erythema, renal petechiaes and diffuse hemorrhages in lymph nodes), pulmonary edema, disseminate intravascular coagulation and thrombocytopenia. Lymphopenia and monocytopenia are developed during acute and subacute ASF. Lymphopenia is associated with lymphoid depletion in primary and secondary lymphoid organs, which is caused by apoptosis. All these lesions are not related to viral replication in endothelial cells or lymphocytes. Monocytes-macrophages show viral replication and cytophatic effect, including hemadsorption. The more significant changes in these cells are increased number and secretory activation (increased levels of proinflammatory cytokines) in targets organs. Proinflammatory activation is the initial cause of clinical and lesional pictures in ASF, including fever and changes in levels of acute phase proteins. Levels of IFN-ß and -γ are increased from initial phase of acute ASF. Anti-inflammatory response, represented by increased level of IL-10, is observed also, although in the final phase of acute ASF only.

Increased pathogenicity of European porcine reproductive and respiratory syndrome virus is associated with enhanced adaptive responses and viral clearance.

Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically important diseases of swine worldwide. Since its first emergence in 1987 the PRRS virus (PRRSV) has become particularly divergent with highly pathogenic strains appearing in both Europe and Asia. However, the underlying mechanisms of PRRSV pathogenesis are still unclear. This study sets out to determine the differences in pathogenesis between subtype 1 and 3 strains of European PRRSV (PRRSV-I), and compare the immune responses mounted against these strains. Piglets were infected with 3 strains of PRRSV-I: Lelystad virus, 215-06 a British field strain and SU1-bel from Belarus. Post-mortem examinations were performed at 3 and 7 days post-infection (dpi), and half of the remaining animals in each group were inoculated with an Aujeszky's disease (ADV) vaccine to investigate possible immune suppression resulting from PRRSV infection. The subtype 3 SU1-bel strain displayed greater clinical signs and lung gross pathology scores compared with the subtype 1 strains. This difference did not appear to be caused by higher virus replication, as viraemia and viral load in broncho-alveolar lavage fluid (BALF) were lower in the SU1-bel group. Infection with SU1-bel induced an enhanced adaptive immune response with greater interferon (IFN)-γ responses and an earlier PRRSV-specific antibody response. Infection with PRRSV did not affect the response to vaccination against ADV. Our results indicate that the increased clinical and pathological effect of the SU1-bel strain is more likely to be caused by an enhanced inflammatory immune response rather than higher levels of virus replication.

Potential role of proinflammatory cytokines in the pathogenetic mechanisms of vascular lesions in goats naturally infected with bluetongue virus serotype 1.

In vitro studies have demonstrated that bluetongue virus (BTV)-induced vasoactive mediators could contribute to the endothelial cells dysfunction and increased vascular permeability responsible of lesions characteristic of bluetongue (BT) like oedema, haemorrhages and ischaemic necrosis in different tissues. However, few in vivo studies have been carried out to clarify the causes of these lesions. The aim of this study was to elucidate in vivo the pathogenetic mechanisms involved in the appearance of vascular lesions in different organs during BT. For this purpose, tissue samples from goats naturally infected with bluetongue virus serotype 1 (BTV-1) were taken for histopathological and immunohistochemical studies to determine the potential role of proinflammatory cytokines (tumour necrosis factor alpha, TNFα and interleukin one alpha, IL-1α) in the increased vascular permeability and their relationship with the presence of virus. Gross and histopathological examination revealed the presence of vascular damage leading to generalized oedema and haemorrhages. Immunohistochemical studies displayed that endothelial injury may have been due to the direct pathogenic effect of BTV infection on endothelial cells or may be a response to inflammatory mediators released by virus-infected endothelial cells and, possibly, other cell types such as monocytes/macrophages. These preliminary results of what appears to be the first in vivo study of tissue damage in small BT-infected ruminants suggest a direct link between the appearance of vascular changes and the presence of BTV-induced vasoactive cytokines.

Characterization of apoptosis pathways (intrinsic and extrinsic) in lymphoid tissues of calves inoculated with non-cytopathic bovine viral diarrhoea virus genotype-1.

Previous studies have shown that activation of effector caspase-3 is associated with the apoptosis of lymphocytes occurring during infection with bovine viral diarrhoea virus (BVDV); however, the regulation of the apoptosis pathways that induce cell death via activation of effector caspase-3 has not yet been clarified. The aim of this study was to examine immunohistochemically the expression of cleaved caspase (CCasp)-8 (initiator caspase of the extrinsic pathway), CCasp9 (initiator caspase of the intrinsic pathway) and Bcl-2 (an anti-apoptotic marker) in gut-associated lymphoid tissue (GALT) of the ileum from calves inoculated with a non-cytopathic strain of BVDV genotype-1. CCasp8 had similar expression to that of CCasp3. In interfollicular T-cell areas there was moderate apoptosis and evidence of moderate activation of initiator caspase-8. In B-cell follicles there was marked lymphocyte apoptosis and evidence of intense caspase-8 activation, highlighting the potentially major role of the extrinsic pathway in lymphocyte apoptosis in the GALT during BVDV infection. Additionally, there was a significant decrease in the number of CCasp9(+) cells from the start of the experiment and this was linked to inactivation of caspase-9. Therefore, the intrinsic pathway may play only a minor role in the induction of lymphocyte apoptosis. Finally, the observed overexpression of Bcl-2 protein could play a major role in protecting lymphocytes in the T-cell areas against apoptosis, while low levels of Bcl-2 expression could be associated with the follicular lymphocyte apoptosis occurring during BVDV infection.

Virus distribution and role of thymic macrophages during experimental infection with noncytopathogenic bovine viral diarrhea virus type 1.

Thymic depletion, presence of viral antigen, and changes in distribution and cytokine production of thymic macrophages were investigated in calves experimentally infected with a noncytopathogenic bovine viral diarrhea virus type (BVDV) 1 strain. Ten clinically healthy colostrum-deprived calves were used. Eight calves were inoculated with the virus and two were used as uninfected controls. Calves were sedated and euthanized in batches between 3 and 14 days postinoculation. At necropsy, thymus samples were collected for structural, immunohistochemical, and ultrastructural study and TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling). From 6 days postinoculation, the thymic cortex was multifocally depleted with increased frequency of pyknosis and karyorrhexis, suggestive of apoptosis and confirmed by the TUNEL technique. Although the onset of lymphoid depletion was coincident with the detection of viral antigen by immunohistochemistry, the number of infected lymphocytes was very low through the experiment. There was an increase in number of macrophages in cortex and medulla, accompanied by ultrastructural changes indicative of phagocyte activation, and a decrease in cells expressing tumor necrosis factor-alpha (TNF-α) and IL-1α. These results suggest that the increase in number of these cells could be related to phagocytosis of cell debris and apoptotic lymphocytes. Furthermore, the results imply that, in contrast to the situation with classical swine fever virus, the lymphocyte apoptosis resulting from bovine viral diarrhea virus infection is not mediated by TNF-α or interleukin-1 alpha (IL-1α) production by virus-infected macrophages. This is the first study that describes this decrease in the number of thymic cells expressing TNF-α and IL-1α in cattle experimentally infected with bovine viral diarrhea virus type 1.

Quantification and determination of spread mechanisms of bovine viral diarrhoea virus in blood and tissues from colostrum-deprived calves during an experimental acute infection induced by a non-cytopathic genotype 1 strain.

To detect and monitor the sequential changes in virus levels, a reverse transcription quantitative real-time polymerase chain reaction assay using a TaqMan probe was carried out on frozen blood and tissues samples collected from calves experimentally infected with a non-cytopathic Bovine viral diarrhoea virus (BVDV) genotype 1 strain. Blood samples were collected among days 1-14 post-inoculation (p.i). On day 3 p.i, viral RNA was detected in blood samples from six of the eight inoculated animals. Viral RNA was detected in all remaining inoculated animals between 5 and 12 days p.i. The levels of viral RNA increased along the experiment, with a maximal peak between 6 and 9 days p.i. Analysis of virus load in tissues collected from calves euthanized on days 3, 6, 9 and 14 p.i displayed that BVDV was detected on day 3 p.i, being especially abundant in tonsils and ileocaecal valve, highlighting the role of tonsils as the main earliest viral replication sites as well as the principal source for virus spread to other lymphoid tissues and visceral organs. Coinciding with the highest viraemia levels, the highest viral loads were recorded at 9 days p.i. in tonsils, ileal lymph nodes, distal ileum and spleen, showing the main role of these secondary lymphoid organs in the pathogenic mechanisms of BVDV. However, virus levels in the liver and lung increased only towards the end of the infection. This fact could influence in the appearance of bovine respiratory diseases because of the capacity of BVDV for enhancing susceptibility to secondary infections.

Response of proinflammatory and anti-inflammatory cytokines in calves with subclinical bovine viral diarrhea challenged with bovine herpesvirus-1.

The aim of this work was to investigate the susceptibility of calves infected with bovine viral diarrhea virus (BVDV) against secondary infections. For this purpose, the profile of cytokines implicated in the immune response of calves experimentally infected with a non-cytopathic strain of BVDV type-1 and challenged with bovine herpesvirus 1.1 (BHV-1.1) was evaluated in comparison with healthy animals challenged only with BHV-1.1. The immune response was measured by serum concentrations of cytokines (IL-1ß, TNFα, IFNγ, IL-12, IL-4 and IL-10), acute phase proteins (haptoglobin, serum amyloid A and fibrinogen) and BVDV and BHV-1.1 specific antibodies. BVDV-infected calves displayed a great secretion of TNFα and reduced production of IL-10 following BHV-1 infection, leading to an exacerbation of the inflammatory response and to the development of more intense clinical symptoms and lesions than those observed in healthy animals BHV-1-inoculated. A Th1 immune response, based on IFNγ production and on the absence of significant changes in IL-4 production, was observed in both groups of BHV-1-infected calves. However, whereas the animals inoculated only with BHV-1 presented an IFNγ response from the start of the study and high expression of IL-12, the BVDV-infected calves showed a delay in the IFNγ production and low levels of IL-12. This alteration in the kinetic and magnitude of these cytokines, involved in cytotoxic mechanisms responsible for limiting the spread of secondary pathogens, facilitated the dissemination of BHV-1.1 in BVDV-infected calves.

Hepatic immune response in calves during acute subclinical infection with bovine viral diarrhoea virus type 1.

Eight colostrum-deprived calves aged 8-12 weeks were inoculated intranasally with a non-cytopathic strain of bovine viral diarrhoea virus (BVDV) genotype-1 and the effects on the hepatic immune response were studied. Two calves were sacrificed at each of 3, 6, 9 and 14 days post-inoculation (dpi) and two uninoculated animals were used as negative controls. BVDV was detected in hepatic macrophages and monocytes from 3 to 14dpi and in Küpffer cells (KCs) from 6 to 14dpi. Increases in the numbers of MAC387(+) KCs and monocytes, but not interstitial macrophages, differentiated by morphological features, were evident in the liver following inoculation with BVDV. There was a substantial increase in the number of monocytes positive for tumour necrosis factor (TNF)-α, but only small increases in the numbers of TNF-α(+) KCs and interstitial macrophages and interleukin (IL)-6(+) monocytes, KCs and interstitial macrophages. There was an increase in the number of interstitial CD3(+) T lymphocytes in the liver, but no substantial changes in the numbers of circulating CD3(+) T lymphocytes, interstitial or circulating CD4(+) or CD8(+) T lymphocytes, or CD79αcy(+) B lymphocytes. Serum haptoglobin and serum amyloid A increased transiently at 12dpi. Upregulation of some pro-inflammatory cytokines by hepatic macrophages is evident in subclinical acute BVDV type 1 infection in calves.

Immunohistochemical detection of bluetongue virus in fixed tissue.

The VP7 structural protein is the most abundant of the major core proteins and is highly conserved in all serotypes of bluetongue virus (BTV). The aim of this study was to develop immunohistochemical techniques for the detection of BTV VP7 in Bouin's- and formalin-fixed and paraffin wax-embedded tissues from small ruminants (sheep and goats) naturally infected with BTV. Tissue samples were taken from animals in which BTV infection had been confirmed by reverse transcriptase polymerase chain reaction. Optimal results were obtained by incubation of monoclonal antibody 2E9 on samples fixed with Bouin's solution or neutral buffered formalin. Optimum antigen retrieval for Bouin's-fixed samples was by microwave heating (6 min) of tissue samples in citrate buffer (pH 6.0, 0.01 M), while for formalin-fixed samples a 30 min heating period in pH 9.0 buffer was required. In both species, BTV was mainly detected in the spleen, lymph nodes and lungs; specifically within the arteriolar and capillary endothelial cells, together with macrophages and lymphocytes. The immunohistochemical method described will be a useful tool for future research.

Morphological changes and virus distribution in the ileum of colostrum-deprived calves inoculated with non-cytopathic bovine viral diarrhoea virus genotype-1.

Eight colostrum-deprived calves were inoculated intranasally with a non-cytopathic strain of bovine viral diarrhoea virus (BVDV) genotype-1 and killed in batches of two at 3, 6, 9 and 14 days post-inoculation (dpi). Two non-inoculated animals with similar background served as controls. All infected calves developed mild pyrexia and transient leucopenia due primarily to lymphopenia. Viraemia was correlated with body temperature and inversely related to leucocyte count. Ileal Peyer's patches developed mild follicular lymphoid depletion from 3dpi. This change was accompanied by cellular fragmentation and pyknosis, characteristic of apoptosis, which was most prominent from 6dpi. Lymphocyte apoptosis was confirmed by ultrastructural examination. Stellate cells and macrophages located in the lymphoid follicles were identified as infected by virus from 3dpi and the number of these infected cells increased until 9dpi. Fewer lymphocytes expressed BVDV antigen. Macrophages had morphological features consistent with activation of secretory and phagocytic function from 3dpi. These findings suggest that BVDV is only directly responsible for the destruction of a small number of lymphocytes. Although lymphocyte infection coincided with the onset of apoptosis, the intensity of infection was disproportionate to the marked depletion of gut-associated lymphoid tissue, particularly during the early stages of this process. Characterization of the indirect pathogenic mechanisms involved in the lymphoid depletion associated with BVDV infection will require additional study.