A PCR technique for the detection of Jaagsiekte sheep retrovirus in the blood suitable for the screening of ovine pulmonary adenocarcinoma in field conditions

Jaagsiekte sheep retrovirus found in milk macrophages but not in milk lymphocytes or mammary gland epithelia of naturally infected sheep

Jaagsiekte sheep retrovirus (JSRV) causes ovine pulmonary adenocarcinoma. JSRV can be transmitted via infected colostrum or milk, which contain somatic cells (SCs) harboring JSRV provirus. Nevertheless, the cell types involved in this form of transmission and the involvement of the mammary gland remain unknown. We separated adherent cells (macrophages and monocytes) by plastic adherence, and lymphocytes (CD4+ and CD8+ T cells, and B cells) by flow cytometry, from SCs in milk samples from 12 naturally infected, PCR blood test JSRV-positive, subclinical ewes. These cell populations were tested by PCR to detect JSRV provirus. The ewes were euthanized, and mammary gland samples were analyzed immunohistochemically to detect JSRV surface protein. We did not detect JSRV provirus in any milk lymphocyte population, but milk adherent cells were positive in 3 of 12 sheep, suggesting a potential major role of this population in the lactogenic transmission of JSRV. Immunohistochemistry did not reveal positive results in mammary epithelial cells, pointing to a lack of participation of the mammary gland in the biological cycle of JSRV and reducing the probability of excretion of free viral particles in colostrum or milk.

Neoplasia-Associated Wasting Diseases with Economic Relevance in the Sheep Industry

We review three neoplastic wasting diseases affecting sheep generally recorded under common production cycles and with epidemiological and economic relevance in sheep-rearing countries: small intestinal adenocarcinoma (SIA), ovine pulmonary adenocarcinoma (OPA) and enzootic nasal adenocarcinoma (ENA). SIA is prevalent in Australia and New Zealand but present elsewhere in the world. This neoplasia is a tubular or signet-ring adenocarcinoma mainly located in the middle or distal term of the small intestine. Predisposing factors and aetiology are not known, but genetic factors or environmental carcinogens may be involved. OPA is a contagious lung cancer caused by jaagsiekte sheep retrovirus (JSRV) and has been reported in most sheep-rearing countries, resulting in significant economic losses. The disease is clinically characterized by a chronic respiratory process as a consequence of the development of lung adenocarcinoma. Diagnosis is based on the detection of JSRV in the tumour lesion by immunohistochemistry and PCR. In vivo diagnosis may be difficult, mainly in preclinical cases. ENA is a neoplasia of glands of the nasal mucosa and is associated with enzootic nasal tumour virus 1 (ENTV-1), which is similar to JSRV. ENA enzootically occurs in many countries of the world with the exception of Australia and New Zealand. The pathology associated with this neoplasia corresponds with a space occupying lesion histologically characterized as a low-grade adenocarcinoma. The combination of PCR and immunohistochemistry for diagnosis is advised.

Ovine Pulmonary Adenocarcinoma: A Unique Model to Improve Lung Cancer Research

Lung cancer represents a major worldwide health concern; although advances in patient management have improved outcomes for some patients, overall 5-year survival rates are only around 15%. In vitro studies and mouse models are commonly used to study lung cancer and their use has increased the molecular understanding of the disease. Unfortunately, mouse models are poor predictors of clinical outcome and seldom mimic advanced stages of the human disease. Animal models that more accurately reflect human disease are required for progress to be made in improving treatment outcomes and prognosis. Similarities in pulmonary anatomy and physiology potentially make sheep better models for studying human lung function and disease. Ovine pulmonary adenocarcinoma (OPA) is a naturally occurring lung cancer that is caused by the jaagsiekte sheep retrovirus. The disease is endemic in many countries throughout the world and has several features in common with human lung adenocarcinomas, including histological classification and activation of common cellular signaling pathways. Here we discuss the in vivo and in vitro OPA models that are currently available and describe the advantages of using pre-clinical naturally occurring OPA cases as a translational animal model for human lung adenocarcinoma. The challenges and options for obtaining these OPA cases for research purposes, along with their use in developing novel techniques for the evaluation of chemotherapeutic agents or for monitoring the tumor microenvironment in response to treatment, are also discussed.

Development of superficial lung lesions monitored on farm by serial ultrasonographic examination in sheep with lesions confirmed as ovine pulmonary adenocarcinoma at necropsy

Background

This ultrasonographic study monitored lesions involving the lung surface suspected to be the early stages of ovine pulmonary adenocarcinoma (OPA) tumours over 4 months in commercially farmed sheep. The enlargement of these lesions defined ultrasonographically, which likely represent the development of OPA tumours, have important implications for ultrasound screening schedules in veterinary management plans attempting to eliminate OPA by test-and-cull.

Results

The lungs of 58 adult Scottish Blackface sheep with ultrasonographic changes at the lung surface consistent with early OPA tumours were examined two to six times over 40 to 290 days. Lesion development, represented in early video recordings by 2–3 mm lesions involving the visceral pleural and comet tails, then a decreasing length of the hyperechoic line representing the normal visceral pleura and increasing depth of the sharply-demarcated and largely uniform hypoechoic areas into the lung parenchyma, was found in 26 of the 58 sheep. The rate at which the sonographic lesions progressed varied considerably and in 10 of 17 Group 1 sheep developed quickly from an estimated depth of 2–30 mm up to 70 mm between 60 and 120 days later. These sonographic lesions were confirmed as OPA at necropsy; histological changes of concurrent bacterial infection were detected in one of these 10 Group 1 sheep. Thirty-one sheep had sonographic changes ≤30 mm consistent with very early OPA at the first examination which had reduced or were not observed at subsequent examination. Five of these 31 sheep were necropsied, 3 had small OPA lesions while 2 had no significant pathology.

Conclusion

Lesions involving the visceral pleura, with sonographic changes consistent with previous published findings of early OPA, developed over 40–120 days to large masses in 10 of 17 Group 1 sheep with the provisional sonographic diagnosis confirmed histologically at necropsy. While it is possible that atalectic lung could have caused some of the minor sonographic changes there was no microscopic evidence of pathologies other than OPA in nine of 10 Group 1 sheep. We conclude that some small tumours progress to large tumours within 3 months questioning the assumption that OPA is a slow growing tumour in adult sheep taking several years to cause clinical disease. The findings that a proportion of small ultrasonographic lesions are not found again at subsequent scanning illustrates the challenges of interpreting small (< 1–2 cm) lesions during rapid whole flock ultrasonographic examination and we continue to recommend re-scanning suspicious sonographic changes 2 months later.

Electronic supplementary material

The online version of this article (10.1186/s13620-018-0134-0) contains supplementary material, which is available to authorized users.

Changes in blood parameters induced by experimental jaagsiekte sheep retrovirus infection

The aim of the study was to assess the changes of blood parameters in 12 three-week-old Polish Merino sheep subjected to experimental jaagsiekte sheep retrovirus (JSRV) infection.

Material and Methods: Haematological (WBC with leukocyte subpopulations: GRA, LYM, MID, and RBC, MCV, MCH, MCHC, HGB, HCT, PLT, and MPV) and biochemical blood parameters (acid/base balance, cation/anion content, and gasometry) were determined in blood samples collected one month after JSRV infection, then at four-week intervals for five consecutive months.

Results: A decrease in RBC, HCT, MCV, PLT, MPV, and LYM values in comparison with controls was found in the last month of observation. On the other hand, at the same time, an increase in HGB, MCH, MCHC, WBC, MID, and GRA indices was observed. Moreover, at the end of experiment blood gasometric indices such as pCO2, HCO3, and tCO2, and Na and K ion concentrations were higher in the affected lambs than in the healthy animals. The pH values of the challenged animals exhibited less alkaline character than in the case of controls, which was associated with a decrease in O2% saturation. However, the majority of differences between JSRV inoculated and control groups was not statistically significant.

Conclusion: The observed changes in the examined blood parameters can be considered as prodromal symptoms in the preclinical phase of adenocarcinoma development associated with JSRV infection.

Jaagsiekte Sheep Retrovirus Can Reach Peyer's Patches and Mesenteric Lymph Nodes of Lambs Nursed by Infected Mothers

Ovine pulmonary adenocarcinoma (OPA) is a contagious lung cancer of sheep caused by jaagsiekte sheep retrovirus (JSRV). It is generally accepted that transmission by the respiratory route occurs under natural conditions. However recent studies strongly indicate that JSRV can also be transmitted to lambs perinatally via colostrum and milk (C/M). The aim of this work was to confirm that C/M can transmit JSRV infection to lambs under natural conditions and investigate the initial events associated with this transmission route. We have analyzed the presence of JSRV in C/M samples from 22 naturally infected, asymptomatic ewes throughout a lactation period, and in various tissues collected from a group of 36 of their lambs that were fed naturally. The lambs were euthanized at 12, 24, 48, and 72 hours and at 5 and 10 days after birth. We detected JSRV-provirus by PCR in the somatic C/M cells from 10/22 ewes (45.45%). The virus was also detected in 9/36 lambs (25%). JSRV-infected cells, with lymphoreticular-like morphology, were observed by immunohistochemistry (IHC) and in situ hybridization (ISH) in Peyer's patches (PP) from the small intestine of the youngest lambs and in mesenteric lymph nodes (MLN) from lambs older than 72 hours. The virus was also detected by PCR in white blood cells (WBC) in 2/36 lambs (5.5%). These results confirm colostral transmission of JSRV to lambs under natural conditions. Infected lymphoreticular cells contained in C/M appear to be involved. These cells can cross the intestinal barrier of newborn lambs, reach the MLN and enter into circulation.

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.

Assessment of transthoracic ultrasound diagnosis of ovine pulmonary adenocarcinoma in adult sheep

Ovine pulmonary adenocarcinoma (OPA), caused by Jaagsiekte sheep retrovirus (JSRV), is a disease of increasing concern in the sheep industry. There is no commercial antemortem test for OPA; therefore, an early evaluation phase study was undertaken to examine the accuracy of transthoracic ultrasound examination using a 5-6.5 MHz sector ultrasound machine widely available in veterinary practice in the UK to diagnose OPA. Restraint, preparation and examination time was restricted to five minutes per sheep to represent the cost limitations of commercial sheep farming. One hundred sheep were examined. All 41 cases identified with suspect OPA lesions during transthoracic ultrasound examination had the diagnosis confirmed at postmortem examination, while sheep without ultrasonographic changes characteristic of OPA had no gross lesions of OPA at postmortem examination. This demonstrates the specificity of transthoracic ultrasound for diagnosis of OPA. The authors propose that, in the absence of any other reliable preclinical diagnostic test, the use of transthoracic ultrasound examination should be considered for a second opinion on an initial diagnosis of OPA, for screening purchased adult flock replacements for OPA, or for screening sheep in a known OPA-affected flock. However, the authors emphasise that a negative scan cannot provide a guarantee that the animal is free of JSRV infection nor early 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.

Lung Tumor Development and Spontaneous Regression in Lambs Coinfected With Jaagsiekte Sheep Retrovirus and Ovine Lentivirus

Ovine pulmonary adenocarcinoma (OPA) is a naturally occurring and experimentally inducible lung cancer of sheep caused by Jaagsiekte sheep retrovirus (JSRV). The first aim of this study was to monitor the development of OPA with minimally invasive, real-time observations of animals experimentally infected with JSRV as well as ovine lentivirus (maedi-visna virus). Worldwide, simultaneous infection of sheep with these 2 retroviruses is a common occurrence, naturally and experimentally; consequently, the lung tumor homogenates used as inocula contained both viruses. Following inoculation, computed tomography was used to detect tumor nodules early, before the onset of clinical signs, and to monitor tumor advancement. However, not only was OPA disease progression observed, but the apparent spontaneous regression of OPA was witnessed. In fact, regression was more common than progression following JSRV inoculation of neonatal lambs. Immune responses were detected, particularly involving CD3+ T cells and the production of antibodies against JSRV that may mediate the spontaneous regression of JSRV-induced OPA. The second aim of this study was to determine whether OPA tumors harbor genetic alterations similar to those found in human lung adenocarcinoma. No mutations were found in the tyrosine kinase domain of the epidermal growth factor receptor, KRAS codons 12 and 13, or the DNA-binding domain of p53 in tumor DNA from naturally occurring and experimentally-induced OPA cases. Overall, the genetic profile combined with the disease development data provides further important characterization of OPA and describes, for the first time, spontaneous regression of OPA tumors in experimentally infected sheep.

Diagnostic accuracy of PCR for Jaagsiekte sheep retrovirus using field data from 125 Scottish sheep flocks

Using a representative sample of Scottish sheep comprising 125 flocks, the sensitivity and specificity of PCR for Jaagsiekte sheep retrovirus (JSRV) was estimated. By combining and adapting existing methods, the characteristics of the diagnostic test were estimated (in the absence of a gold standard reference) using repeated laboratory replicates. As the results of replicates within the same animal cannot be considered to be independent, the performance of the PCR was calculated at individual replicate level. The median diagnostic specificity of the PCR when applied to individual animals drawn from the Scottish flock was estimated to be 0.997 (95% confidence interval [CI] 0.996-0.999), whereas the median sensitivity was 0.107 (95% CI 0.077-0.152). Considering the diagnostic test as three replicates where a positive result on any one or more replicates results in a positive test, the median sensitivity increased to 0.279. Reasons for the low observed sensitivity were explored by comparing the performance of the test as a function of the concentration of target DNA using spiked positive controls with known concentrations of target DNA. The median sensitivity of the test when used with positive samples with a mean concentration of 1.0 target DNA sequence per 25μL was estimated to be 0.160, which suggests that the PCR had a high true (analytical) sensitivity and that the low observed (diagnostic) sensitivity in individual samples was due to low concentrations of target DNA in the blood of clinically healthy animals.

Colostrum and milk can transmit jaagsiekte retrovirus to lambs

Ovine pulmonary adenocarcinoma (OPA) is a contagious disease caused by jaagsiekte sheep retrovirus (JSRV). In the three studies performed, we have obtained data of the importance of colostrum/milk (C/M) in the transmission of JSRV. In the first study, a group of sheep from a flock with a long history of OPA, samples from colostrum and peripheral blood leucocytes (PBLs) were collected. Two specific PCRs (U3-LTR and env of the JSRV) were carried out. Using U3PCR 8/34 sheep were positive in colostrum whereas with envPCR 7/34 were positive. From these animals only one was positive with U3PCR in the PBLs. Evidence of the transmission of JSRV infection by C/M was obtained in two more separate studies. In the second study, PBLs from five lambs from JSRV+ ewes and two from JSRV-ewes were tested by the U3PCR. They were fed C/M by their mothers during 3 months and slaughtered 7 months after birth. Three out of five lambs from the JSRV+ sheep become PBL positive at 3-4 months old and the other two were also positive at 4-6 months of age. One lamb of the JSRV-sheep became also PBL positive at an age of 3 months. In the third study, a group of lambs from JSRV negative mothers were fed with C/M from JSRV+ sheep and housed in separate unit. For comparison, another group of the same origin and maintained in another different unit, were fed with C/M containing a JSRV virus preparation. All lambs were blood sampled monthly and JSRV infection was detected as early as 15 days and several times onwards in both groups. Control groups fed with C/M from JSRV free flock and JSRV blood test negative sheep were always negative. Together these results indicate that suckling is an important natural transmission route for JSRV.

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.

In vivo tumorigenesis by Jaagsiekte sheep retrovirus (JSRV) requires Y590 in Env TM, but not full-length orfX open reading frame

Jaagsiekte retrovirus (JSRV) causes ovine pulmonary adenocarcinoma (OPA), a transmissible lung cancer of sheep. The envelope (Env) glycoprotein protein of JSRV functions as a dominant oncoprotein in vitro and in vivo. An SH2 binding domain (YXXM) in the cytoplasmic tail of the JSRV Env is one of the main determinants of viral transformation at least in vitro. In these studies, we report the first in vivo tests of site-specific mutants of JSRV in their natural host, the sheep. We show that, in vivo, JSRV(21) with the cytoplasmic tail YXXM mutated to DXXM did not cause disease nor detectable infection, indicating that this motif is absolutely required for virus replication and possibly transformation in vivo. In contrast, mutation of the JSRV open reading frame orfX, for which no function has yet been attributed, did not alter the disease induced by JSRV(21).