Sheep pulmonary adenomatosis: characterization of two pathological forms associated with jaagsiekte retrovirus

Retroviral coinfection (Jaagsiekte and Maedi-Visna viruses) in sheep with pulmonary tumors in Transylvania (Romania): retrospective study on 82 cases

Ovine pulmonary adenocarcinoma (OPA) is an important viral-induced neoplasia in sheep caused by exogenous Jaagsiekte sheep retrovirus (exJSRV). Coinfection of exJSRV and Maedi-Visna virus (MVV) is reported in OPA cases, but its worldwide distribution and significance on lung pathology is not yet completely understood. This study aimed to investigate the MVV coinfection rate in 82 exJSRV-related OPA cases, and their pathological effects on lung parenchyma in slaughtered sheep in Transylvania (Romania). On gross examination, classical form of OPA was identified in 92.7%; no changes consisting with MVV interstitial pneumonia were identified in the included cases. The most common histological type of OPA was acinar (58.5%) and the myxoid growths were found in 18 cases. The exJSRV and MMV coinfection rate in examined sheep was 47.6% (39/82). The assessment of perineoplastic areas from coinfected animals, revealed interstitial lymphoplasmacytic infiltrates in all cases, lymphoid hyperplasia in 60.6% cases (20/33) and fibromuscular hyperplasia in 63.7% (21/33). This is the first report providing new data on distribution of OPA coexisting with MVV infection in slaughtered sheep in Romania. We consider that the OPA and MVV coinfection may play an important role on the severity of ovine chronic pulmonary diseases and further studies are needed to confirm this hypothesis.

Pathological Spectrum of Ovine Pulmonary Adenocarcinoma in Small Ruminants: A Focus on the Mixed Form

Ovine pulmonary adenocarcinoma (OPA) is a contagious respiratory tumor of small ruminants, manifesting in chronic weight loss and respiratory failure. Infection with the betaretrovirus jaagsiekte sheep retrovirus (JSRV) is the cause of OPA. Here, we describe the gross and microscopic features of twenty-six sheep and one goat with naturally occurring JSRV-associated OPA. All the animals included in this study had pulmonary lesions morphologically consistent with OPA, but the majority of the observed lesions demonstrated features of both the classical and the atypical form of OPA, and were, therefore, classified grossly as mixed. The gross lesions were located mainly in the cranial pulmonary lobes, were multifocal to coalescing, variable in number and size, flat to slightly raised, firm, and white to grey. Histologically, the cases were classified according to the predominant architectural patterns as lepidic, papillary, acinar, or mixed; the mixed histological pattern was the most prevalent. The aim of this study was to describe the gross and microscopic spectrum of OPA in naturally infected small ruminants from Spain. The mixed form of OPA is less commonly reported, and can be confused with other concurrent pulmonary pathologies (such as BALT hyperplasia in SRLV-associated pneumonia or lungworm granulomas).

Exogenous Jaagsiekte Sheep Retrovirus type 2 (exJSRV2) related to ovine pulmonary adenocarcinoma (OPA) in Romania: prevalence, anatomical forms, pathological description, immunophenotyping and virus identification

BACKGROUND

Ovine pulmonary adenocarcinoma (OPA) is a neoplastic disease caused by exogenous Jaagsiekte Sheep Retrovirus (exJSRV). The prevalence of JSRV-related OPA in Eastern European countries, including Romania is unknown. We aimed to investigate: the prevalence and morphological features of OPA (classical and atypical forms) in the Transylvania region (Romania), the immunophenotype of the pulmonary tumors and their relationships with exJSRV infection. A total of 2693 adult ewes slaughtered between 2017 and 2019 in two private slaughterhouses from Transylvania region (Romania) was evaluated. Lung tumors were subsequently assessed by cytology, histology, immunocytochemistry, immunohistochemistry, electron microscopy and DNA testing.

RESULTS

Out of 2693 examined sheep, 34 had OPA (1.26% prevalence). The diaphragmatic lobes were the most affected. Grossly, the classical OPA was identified in 88.24% of investigated cases and the atypical OPA in 11.76% that included solitary myxomatous nodules. Histopathology results confirmed the presence of OPA in all suspected cases, which were classified into acinar and papillary types. Myxoid growths (MGs) were diagnosed in 6 classical OPA cases and in 2 cases of atypical form. Lung adenocarcinoma was positive for MCK and TTF-1, and MGs showed immunoreaction for Vimentin, Desmin and SMA; Ki67 expression of classical OPA was higher than atypical OPA and MGs. JSRV-MA was identified by IHC (94.11%) in both epithelial and mesenchymal cells of OPA. Immunocytochemistry and electron microscopy also confirmed the JSRV within the neoplastic cells. ExJSRV was identified by PCR in 97.05% of analyzed samples. Phylogenetic analysis revealed the presence of the exJSRV type 2 (MT809678.1) in Romanian sheep affected by lung cancer and showed a high similarity with the UK strain (AF105220.1).

CONCLUSIONS

In this study, we confirmed for the first time in Romania the presence of exJSRV in naturally occurring OPA in sheep. Additionally, we described the first report of atypical OPA in Romania, and to the best of our knowledge, in Eastern Europe. Finally, we showed that MGs have a myofibroblastic origin.

Diagnosis and prevalence of ovine pulmonary adenocarcinoma in lung tissues of naturally infected farm sheep

AIM

This study was aimed to detect ovine pulmonary adenocarcinoma (OPA) in sheep flocks affected with pulmonary disorders at organized farm.

MATERIALS AND METHODS

A total of 75 sheep died naturally were thoroughly examined for the lesions of OPA during necropsy. Tissue sections from affected portion of the lungs from each animal were collected aseptically and divided into two parts; one each for polymerase chain reaction (PCR) and another for histopathology.

RESULTS

On PCR examination of lung tissues, six sheep (8%) were found to be positive for JSRV. Two of them were 3-6 months of age and did not show clinical signs/gross lesions of OPA. Four adult sheep positive on PCR revealed characteristic lesions of OPA on gross and histopathological examination.

CONCLUSION

In the absence of known specific antibody response to the infection with JSRV, there is no diagnostic serological test available. The PCR assay employed in this study on lung tissues, using primers based on the U3 region of the viral long terminal repeat for JSRV would be helpful in the screening of preclinical and clinical cases of OPA in sheep.

Expression of p53 protein, Jaagsiekte sheep retrovirus matrix protein, and surfactant protein in the lungs of sheep with pulmonary adenomatosis

Ovine pulmonary adenocarcinoma (OPA) is a naturally occurring cancer in sheep that is caused by the Jaagsiekte sheep retrovirus (JSRV). Because the pathologic and epidemiologic features of OPA are similar to those of bronchoalveolar carcinoma in humans, OPA is considered a useful animal model for pulmonary carcinogenesis. In this study, 3,512 lungs from various breeds of sheep were collected and macroscopically examined. OPA was identified in 30 sheep, and samples of these animals were further examined by histologic, immunohistochemical (p53 protein, surfactant protein A [SP-A], proliferating cell nuclear antigen [PCNA], JSRV matrix protein [MA]), and PCR methods. Papillary or acinar adenocarcinomas were detected microscopically in the affected areas. Immunoreactivity for p53 PAb240 was detected in 13 sheep, whereas p53 DO-1 was not detected in any of the OPA animals. PCNA immunoreactivity was recorded in 27 animals. SP-A and JSRV MA protein was immunopositive in all 30. JSRV proviral DNA was detected by PCR analysis in all of the lung samples collected from OPA animals. In addition, the pulmonary SP-A levels were increased in tumor cells. The results of this study suggest that PCNA and p53 protein expression may be useful indicators in monitoring malignancy of pulmonary tumors.

Advances in the study of transmissible respiratory tumours in small ruminants

Sheep and goats are widely infected by oncogenic retroviruses, namely Jaagsiekte Sheep RetroVirus (JSRV) and Enzootic Nasal Tumour Virus (ENTV). Under field conditions, these viruses induce transformation of differentiated epithelial cells in the lungs for Jaagsiekte Sheep RetroVirus or the nasal cavities for Enzootic Nasal Tumour Virus. As in other vertebrates, a family of endogenous retroviruses named endogenous Jaagsiekte Sheep RetroVirus (enJSRV) and closely related to exogenous Jaagsiekte Sheep RetroVirus is present in domestic and wild small ruminants. Interestingly, Jaagsiekte Sheep RetroVirus and Enzootic Nasal Tumour Virus are able to promote cell transformation, leading to cancer through their envelope glycoproteins. In vitro, it has been demonstrated that the envelope is able to deregulate some of the important signaling pathways that control cell proliferation. The role of the retroviral envelope in cell transformation has attracted considerable attention in the past years, but it appears to be highly dependent of the nature and origin of the cells used. Aside from its health impact in animals, it has been reported for many years that the Jaagsiekte Sheep RetroVirus-induced lung cancer is analogous to a rare, peculiar form of lung adenocarcinoma in humans, namely lepidic pulmonary adenocarcinoma. The implication of a retrovirus related to Jaagsiekte Sheep RetroVirus is still controversial and under investigation, but the identification of an infectious agent associated with the development of lepidic pulmonary adenocarcinomas might help us to understand cancer development. This review explores the mechanisms of induction of respiratory cancers in small ruminants and the possible link between retrovirus and lepidic pulmonary adenocarcinomas in humans.

Diagnostic pathology in microbial diseases of sheep or goats

Post-mortem examination is a key step in the diagnostic process of infectious diseases in sheep and goats. Diagnostic pathology deals with identification and study of lesions, at the same time providing also significant clues regarding pathogenesis of the diseases. This article reviews the salient pathological findings associated with the most significant infectious diseases of sheep and goats present in countries where small ruminants are a relevant agricultural industry. Lesions are reviewed according to the different organ systems where they occur. Emphasis has been given in the description of the salient lesional patterns than can be identified in each organ and which can be of help in the differential diagnosis of the lesions caused by bacteria, viruses, fungi or prions. Finally, a review of the usefulness of ancillary tests that may be used on various tissue samples for performing an aetiological diagnosis, is included; the application of various techniques, from immunohistochemistry to molecular biology-based tests, is described.

Ovine pulmonary adenocarcinoma in slaughtered sheep: a pathological and polymerase chain reaction study

Ovine pulmonary adenocarcinoma (OPA) is a contagious tumour in sheep caused by jaagsiekte sheep retrovirus (JSRV). This tumour originates from the pneumocyte type II and Clara cells and grossly appears as hard, prominent nodules in different lobes. The clinical signs of the disease are similar to those of other chronic respiratory diseases and are not pathogonomic. Therefore, post mortem examinations and histopathological studies are the most reliable ways to diagnose OPA, particularly subclinical cases of this neoplasm. In this study, out of 1000 sheep lungs grossly inspected, 50 animals were suspected of OPA. The suspected lungs as well as 25 apparently normal lungs were examined by histopathological and PCR methods. The proviral DNA was detected in 1/25 apparently normal lungs and 8/50 of the suspected lungs and subsequently confirmed by histopathological studies. The PCR-positive lung samples from five sheep revealed lesions of 'atypical' OPA and those from three sheep showed the 'classic' form of the disease. The tumours were multifocal and the masses were distributed throughout the cranioventral and diaphragmatic lung lobes. The stroma of the tumours in the atypical cases was more severely affected with inflammatory cell infiltration and connective tissue proliferation. The histopathological characteristics of maedi including hyperplasia of the perivascular and peribronchiolar lymphoid cells, interstitial lymphoplasmacytic infiltration and smooth muscle hyperplasia were also associated with OPA, especially the atypical form of this adenocarcinoma. Atypical OPA was more prevalent than the classic form. Geographic and climatic conditions, duration of exposure to the virus and the immune status of individual animals might be responsible for the differences between the two pathological entities of OPA.

The distribution of immune cells in the lungs of classical and atypical ovine pulmonary adenocarcinoma

Ovine pulmonary adenocarcinoma (OPA) is a contagious tumour caused by infection of sheep with Jaagsiekte sheep retrovirus. Two forms of OPA have been identified, classical and atypical, which can be distinguished clinically and pathologically. Most notably classical OPA is progressive until death, while atypical OPA remains subclinical. In the present study the local immune responses in the lungs of cases of atypical OPA were compared with those from classical cases by immunohistochemistry using a panel of mouse anti-sheep mAbs. Distinct differences in the distribution of immune cell subsets in the two forms of OPA were observed. In particular there was an intratumoural influx of T cell subsets and MHC Class II expression on the tumour cells in atypical OPA, neither of which was seen in classical OPA. It is possible that these differences may contribute, at least in part, to determining the progressive course of classical OPA compared with the subclinical nature of atypical OPA.

Surveillance of Jaagsiekte sheep retrovirus in sheep in Hokkaido, the northern island of Japan

Surveillance of jaagsiekte sheep retrovirus (JSRV) infection was performed by polymerase chain reaction (PCR) of blood DNA samples collected from 40 sheep and goats in 10 different flocks in Hokkaido, the northern island of Japan. No exogenous (oncogenic) JSRV sequence was detected by PCR in these samples, while the ovine endogenous retrovirus sequence was successfully amplified in all samples. Our paper is the first demonstration of JSRV surveillance in Japan and shows no evidence of oncogenic JSRV infection in sheep and goats in Hokkaido.

Immunohistochemical and histopathological findings of ovine pulmonary adenocarcinoma (Jaagsiekte) in Egyptian sheep

Ovine pulmonary adenocarcinoma (OPA) is a naturally occurring retrovirus-induced transmissible lung cancer in sheep. Lungs and associated (bronchial and mediastinal) lymph nodes of seven sheep with OPA were examined. Lungs had few multifocal consolidated slightly elevated gray to white masses ranging from 0.5 to 3 cm in diameter. Histopathologically, these masses appeared as well-differentiated acinar adenocarcinoma with little evidence of anaplasia. The acini composed of well-differentiated cuboidal to low columnar epithelium with clear or vacuolated cytoplasm and low mitotic index. No metastases were observed in the bronchial and mediastinal lymph nodes of any animal. The presence of Jaagsiekte sheep retrovirus (JSRV) was demonstrated in the lungs by immunohistochemistry. JSRV protein was detected in all tumor epithelial cells, histologically normal alveolar type II cells, and few bronchiolar epithelial cells, alveolar macrophages, lymphocytes, and plasma cells. This study is the first to confirm the presence of natural OPA in Egypt.

Immunohistochemical detection of pulmonary surfactant proteins and retroviral antigens in the lungs of sheep with pulmonary adenomatosis

The lungs and mediastinal and bronchial lymph nodes from 26 sheep with ovine pulmonary adenomatosis (OPA) were examined. Microscopically, the tumour was disseminated throughout the lungs and displayed acinar or papillary growth. The neoplastic cells were cuboidal or columnar with clear cytoplasm and a low mitotic rate. Retrovirus antigen (Jaagsiekte Sheep Retrovirus Capsid Protein, JSRV CA) was demonstrated in the cytoplasm of tumour cells in the lung and lymph nodes by immunohistochemistry. The neoplastic cells had more diffuse and intense expression of pulmonary surfactant protein-A (SP-A) compared with the expression of SP-B or SP-C. SP-A and SP-B expression was localized to the apical cytoplasm of the neoplastic cells, whereas SP-C was most strongly expressed in the perinuclear area of the tumour cells. In the lungs of two sheep, low numbers of tumour cells expressed Clara cell secretory protein (CCSP). The nuclei of the neoplastic epithelial cells and of the germinal centre lymphocytes within the peribronchiolar lymphoid tissue expressed the proliferating cell nuclear antigen (PCNA). CD3(+) T lymphocytes infiltrated the pulmonary tissue and surrounded the neoplastic foci. The results of this study demonstrate that JSRV continues to replicate in neoplastic cells after they have been transformed, and that the neoplastic cells produce pulmonary surfactant proteins. A local T-cell response occurs within affected lungs.

PCR examination of bronchoalveolar lavage samples is a useful tool in pre-clinical diagnosis of ovine pulmonary adenocarcinoma (Jaagsiekte)

Ovine pulmonary adenocarcinoma (OPA) is a contagious lung tumour of sheep caused by Jaagsiekte sheep retrovirus (JSRV). The disease is a particular problem in flocks in many parts of the world. The aim of the study was to assess screening methods for individual animals as a prelude to future eradication trials. Results of histological examination were used as the standard to evaluate the relative sensitivity and specificity of an established heminested polymerase chain reaction (PCR) test for JSRV proviral DNA from blood and bronchoalveolar lavage (BAL) samples. PCR results from tissue samples are included as control data. PCR testing of blood samples was found to have an estimated sensitivity of only 10% (95% confidence interval (CI) 3-20) while the sensitivity of the PCR test on BAL samples was 89% (CI 79-96) in comparison to the results of histological examination. We conclude that PCR testing of BAL samples is an effective confirmatory test for sheep with suspected clinical OPA. It is also a useful tool for the pre-clinical identification of individual infected sheep within an infected flock and therefore may prove beneficial in future control or eradication programmes.

Jaagsiekte Sheep Retrovirus (JSRV): from virus to lung cancer in sheep

Jaagsiekte Sheep Retrovirus (JSRV) is a betaretrovirus infecting sheep. This virus is responsible for a pulmonary adenocarcinoma, by transformation of epithelial cells from the bronchioli and alveoli. This animal cancer is similar to human bronchioloalveolar cancer (BAC), a specific form of human lung cancer for which a viral aetiology has not yet been identified. JSRV interacts with target cells through the membrane receptor Hyal2. The JSRV genome is simple and contains no recognised oncogene. It is now well established that the viral envelope protein is oncogenic by itself, via the cytoplasmic domain of the transmembrane glycoprotein and some domains of the surface glycoprotein. Activation of the PI3K/Akt and MAPK pathways participates in the envelope-induced transformation. Tumour development is associated with telomerase activation. This review will focus on the induction of cancer by JSRV.

Lung cancer induced in mice by the envelope protein of jaagsiekte sheep retrovirus (JSRV) closely resembles lung cancer in sheep infected with JSRV

Background

Jaagsiekte sheep retrovirus (JSRV) causes a lethal lung cancer in sheep and goats. Expression of the JSRV envelope (Env) protein in mouse lung, by using a replication-defective adeno-associated virus type 6 (AAV6) vector, induces tumors resembling those seen in sheep. However, the mouse and sheep tumors have not been carefully compared to determine if Env expression alone in mice can account for the disease features observed in sheep, or whether additional aspects of virus replication in sheep are important, such as oncogene activation following retrovirus integration into the host cell genome.

Results

We have generated mouse monoclonal antibodies (Mab) against JSRV Env and have used these to study mouse and sheep lung tumor histology. These Mab detect Env expression in tumors in sheep infected with JSRV from around the world with high sensitivity and specificity. Mouse and sheep tumors consisted mainly of well-differentiated adenomatous foci with little histological evidence of anaplasia, but at long times after vector exposure some mouse tumors did have a more malignant appearance typical of adenocarcinoma. In addition to epithelial cell tumors, lungs of three of 29 sheep examined contained fibroblastic cell masses that expressed Env and appeared to be separate neoplasms. The Mab also stained nasal adenocarcinoma tissue from one United States sheep, which we show was due to expression of Env from ovine enzootic nasal tumor virus (ENTV), a virus closely related to JSRV. Systemic administration of the AAV6 vector encoding JSRV Env to mice produced numerous hepatocellular tumors, and some hemangiomas and hemangiosarcomas, showing that the Env protein can induce tumors in multiple cell types.

Conclusion

Lung cancers induced by JSRV infection in sheep and by JSRV Env expression in mice have similar histologic features and are primarily characterized by adenomatous proliferation of peripheral lung epithelial cells. Thus it is unnecessary to invoke a role for insertional mutagenesis, gene activation, viral replication, or expression of other viral gene products in sheep lung tumorigenesis, although these processes may play a role in other clinically less important sequelae of JSRV infection such as metastasis observed with variable frequency in sheep.

An influx of macrophages is the predominant local immune response in ovine pulmonary adenocarcinoma

Infection with a retrovirus, Jaagsiekte sheep retrovirus (JSRV), causes ovine pulmonary adenocarcinoma (OPA). The excess production of surfactant proteins by alveolar tumour cells results in increased production of pulmonary fluid, which is characteristically expelled through the nostrils of affected sheep. The immune response to JSRV and the tumour is poorly understood: no JSRV-specific circulating antibodies or T cells have been detected to date. The aim of the present study was to obtain phenotypic evidence for a local immune response in OPA lungs. Specific-pathogen free lambs were infected intratracheally with JSRV. When clinical signs of OPA were apparent, the lungs were removed at necropsy and immunohistochemistry (IHC) was performed on lung sections using a panel of mouse anti-sheep mAbs. No influx of dendritic cells, B cells, CD4, CD8 or gammadelta T cells was seen in the neoplastic nodules or in their periphery. MHC Class II-positive cells were found intratumourally, peritumourally and in the surrounding alveolar lumina. In the tumours, many of these cells were shown to be fibroblasts and the remainder were likely to be mature macrophages. In the alveolar lumen, the MHC Class II-positive cells were CD14-positive and expressed high levels of IFN-gamma. They appeared to be immature monocytes or macrophages which then differentiated to become CD14-negative as they reached the periphery of the tumours. A high level of MHC Class I expression was detected on a range of cells in the OPA lungs but the tumour nodules themselves contained no MHC Class I-positive cells. On the basis of these findings, it is proposed that the lack of an effective immune response in OPA could result from a mechanism of peripheral tolerance in which the activity of the invading macrophages is suppressed by the local environment, possibly as a consequence of the inhibitory properties of the surfactant proteins.

Infection of lung epithelial cells and induction of pulmonary adenocarcinoma is not the most common outcome of naturally occurring JSRV infection during the commercial lifespan of sheep

Jaagsiekte sheep retrovirus (JSRV) is the causative agent of ovine pulmonary adenocarcinoma (OPA). In this study, we followed over a 31-month period the natural transmission of JSRV in adult sheep and in their offspring. We established groups derived from flocks with either a high or low incidence of OPA and monitored virus transmission, clinical disease and macroscopic/microscopic lung lesions at necropsy. Results obtained show that (i) JSRV infection can occur perinatally or in the first few months of life in lambs and in adult sheep; (ii) only a minority of JSRV-infected animals develop clinical disease during their commercial lifespan; and (iii) JSRV is more readily detectable in peripheral blood leucocytes and lymphoid organs than in the lungs. These data support a model of opportunistic JSRV infection and tumorigenic conversion of type II pneumocytes/Clara cells in the lungs, while lymphoreticular cells serve as the principal virus reservoir.

Ovine pulmonary adenomatosis in Patagonia, Argentina

An outbreak of pulmonary adenomatosis (OPA) occurred in sheep in Patagonia, Argentina's southernmost region. On the affected farm, nine animals died over a 6-month period with pulmonary lesions of OPA. In all cases, the histology of the lungs was characterized by proliferation of cuboideal and prismatic cells lining the alveoli. Inflammatory exudates and accumulation of alveolar macrophages were marked in most cases, but in six of the cases there was no excess fluid in the airways. The presence of the Jaagsiekte retrovirus was demonstrated in the lungs by immunocytochemistry and PCR. To the best of our knowledge, this is the first report of OPA in Patagonia.

Pathology of ovine pulmonary adenocarcinoma

Clinical, gross pathology, histopathology and electron microscopy of the ovine pulmonary adenocarcinoma (OPA, jaagsiekte) either natural or experimentally induced in sheep, goat and moufflon are described. OPA is caused by an oncogenic betaretrovirus,jaagsiekte sheep retrovirus (JSRV). Most natural cases of OPA appear in animals 1-4 years old. There is no evidence of sex or breed susceptibility. Sheep affected by OPA show an afebrile respiratory illness associated with loss of weight. A very characteristic clinical sign is moist rales caused by the accumulation of fluid in the respiratory airways which is discharged from the nostrils when the head is lowered. Gross lesions are confined to the lungs but occasionally thoracic or extrathoracic structures are also affected. Two pathologic forms of OPA are currently recognized, classical and atypical. In classical forms the neoplastic lesions occurs particularly in the cranioventral parts of all lung lobes. They are diffuse or nodular, light grey or light purple in colour. On the cut surface the tumour is moist, and frothy fluid may pour from the airways on slight pressure. Atypical forms tend to be more nodular in both early and advanced tumours. They are pearly white in colour, very hard in consistency, very well demarcated from the surrounding parenchyma and their surface is dry. Histology of the lung sections reveals the presence of several foci of epithelial cell neoplastic proliferation in both alveolar or bronchiolar regions. The tumours, derived from type II pneumocytes and Clara cells, proliferate into mostly papillary but also acinar or occasionally solid growths. The tumour generally shows a benign histological pattern but intra- and extrathoracic metastases have been detected in some cases. Several considerations suggest that the tumour should be classified as an adenocarcinoma of the lung. The histology of atypical OPA is similar to that of the classical disease, with an increase in the stromal reaction accompanying the epithelial proliferations. Pathological features of OPA induced experimentally in sheep, or of OPA in goats and moufflon are similar to those described in sheep. Detailed electron microscopy of tumour material confirms that type II pneumocytes and Clara bronchiolar epithelial cells are the origin of the neoplasia. Also included in this chapter is a description of the morphology of the viral particles associated with OPA.

Natural history of JSRV in sheep

Ovine pulmonary adenocarcinoma (OPA) is a contagious lung tumour of sheep and, rarely, goats that arises from two types of secretory epithelial cell that retain their luxury function of surfactant synthesis and secretion. It is classified as a low-grade adenocarcinoma and is viewed as a good model for epithelial neoplasia because of its morphological resemblance to the human lung tumour, bronchioloalveolar adenocarcinoma. OPA is present in most of the sheep rearing areas of the globe and, in affected flocks, tumours are present in a high proportion of sheep. OPA is associated with the ovine retrovirus, jaagsiekte sheep retrovirus (JSRV), and is transmissible only with inocula that contain JSRV. All sheep contain JSRV-related endogenous viruses, but JSRV is an exogenous virus that is associated exclusively with OPA. JSRV is detected consistently in the lung fluid, tumour and lymphoid tissues of sheep affected by both natural and experimental OPA or unaffected in-contact flockmates and never in sheep from unaffected flocks with no history of the tumour. JSRV replicates principally in the epithelial tumour cells, but also establishes a disseminated infection of several lymphoid cell types, including peripheral blood leukocytes (PBLs). Longitudinal studies in flocks with endemic OPA have revealed JSRV in PBLs before the onset of clinical OPA and even in the absence of discernible lung tumour. The prevalence of JSRV infection is 40%-80%, although only 30% of sheep appear to develop OPA lesions. A unique feature of OPA is the absence of a specific humoral immune response to JSRV, despite the highly productive infection in the lungs and the disseminated lymphoid infection. This feature is associated with reduced responsiveness to some mitogens, although the phenotypic profile of the peripheral blood remains unaltered. The reduced response is an early and sustained event during infection and may indicate that the failure of infected sheep to produce specific antibodies to JSRV is a direct consequence of infection.

Spontaneous squamous cell carcinoma of the tongue and multiple bronchioloalveolar carcinomas in a Virginia opossum (Didelphis virginiana)

Two primary tumours, squamous cell carcinoma of the tongue and multiple bronchioloalveolar carcinomas, were diagnosed in a Virginia opossum (Didelphis virginiana). Two oral masses were located in the right ventrolateral surface of the tongue, near the frenulum, and the lungs contained multiple, widely distributed, nodular masses. Microscopically, the oral masses were composed of invasive cords of pleomorphic, polyhedral cells, typical of squamous cells. The multiple pulmonary masses consisted of non-ciliated, cuboidal, columnar, or occasionally polyhedral cells arranged in an alveolar pattern with multifocal areas of necrosis. This is the first report of spontaneous oropharyngeal squamous cell carcinoma in the Virginia opossum. However, multiple pulmonary adenomas have been reported previously in this species, the lesions being similar to those in sheep pulmonary adenomatosis (jaagsiekte). In the present study, immunohistochemical examination of the pulmonary tumours with a rabbit polyclonal antiserum to jaagsiekte retroviral capsid protein proved negative.

Retrovirus-induced ovine pulmonary adenocarcinoma, an animal model for lung cancer

Studies on the molecular mechanisms of transformation of retrovirus-induced neoplasms in domestic and laboratory animal species have provided insights into the genetic basis of cancer. Ovine pulmonary adenocarcinoma (OPA) is a retrovirus-induced spontaneous lung tumor of sheep that has striking analogies to some forms of human adenocarcinoma. The etiologic agent of OPA, jaagsiekte sheep retrovirus (JSRV), is unique among retroviruses for having a specific tropism for the differentiated epithelial cells of the lung, and it is the only virus known to cause a naturally occurring lung adenocarcinoma. Expression of the JSRV envelope protein is sufficient to induce cell transformation in vitro, possibly via the activation of the phosphatidylinositol 3-kinase/Akt-signaling pathway mediated by the cytoplasmic tail of the transmembrane protein. The aim of this review is to draw the attention of basic and clinical scientists engaged in lung cancer research to this unique animal model, to explore the possible use of OPA as a tool to investigate the mechanisms of pulmonary carcinogenesis, and to underline the similarities between OPA and some forms of human lung adenocarcinoma. The possibility of a viral etiology for the latter will be evaluated in this review.

Jaagsiekte sheep retrovirus can be detected in the peripheral blood during the pre-clinical period of sheep pulmonary adenomatosis

Peripheral blood leukocytes (PBLs) and tissue samples from 36 sheep were examined for jaagsiekte sheep retrovirus (JSRV) by hemi-nested PCR. Animals were classified according to the status of sheep pulmonary adenomatosis (SPA), which was confirmed by pathological examination, as follows: (i) sheep with classical SPA (cSPA, n=10), (ii) sheep with atypical SPA (aSPA, n=6), (iii) non-affected sheep from SPA-affected flocks (in-contact, n=10) and (iv) non-affected sheep from SPA-free flocks (control, n=10). JSRV proviral DNA was detected in the PBLs of 10/10 cSPA, 5/6 aSPA, 4/10 in-contact and 0/10 control sheep. Lung tumours and lymphoid organs were also found to be JSRV-positive. The number of positive PCR results was greater for sheep in the cSPA group than for those in the aSPA and in-contact groups. For the first time, it is concluded that JSRV can be detected in naturally infected sheep before the onset of clinical disease and even before the development of discernible tumours.