Multinodular Pulmonary Fibrosis Research Articles

Clinical findings and outcome predictors for multinodular pulmonary fibrosis in horses: 46 cases (2009-2019).

Prognostic indicators for equine multinodular pulmonary fibrosis (EMPF), an interstitial fibrosing lung disease, are poorly described. Describe diagnostic findings and outcome predictors for EMPF. Forty-six adult horses with EMPF. Retrospective multicenter case series from 2009 to 2019. Radiographic (n = 27) and ultrasonographic studies (n = 19) from EMPF horses and bronchoalveolar lavage fluid (BALF) cytology from 6 EMPF and 13 asthma cases were independently reviewed and blinded to diagnosis and outcome. Associations between predictor variables and survival were assessed by predictor screening followed by Fisher's exact and Wilcoxon rank sum tests. Primary clinical findings were weight loss (36/46, 78%), increased respiratory effort (33/46, 72%), tachypnea (32/46, 70%), and fever (18/46, 39%). Macrophage atypia was seen in more EMPF than asthmatic horse BALF (67% vs. 8%; P = .02). Equine herpesvirus 5 (EHV-5) was detected in 24 of 30 (80%) and hyperfibrinogenemia in 25 of 28 (89%) cases. Twenty-seven of 46 horses (59%) and 11 of 45 (24%) survived to discharge and to 3 months, respectively. Three-month survival was associated with lower median (range) respiratory rates (30 [24-36] vs. 41 [30-60] breaths per minute; P = .04), and higher BALF lymphocyte:neutrophil ratios (4.7 [1.4-22] vs. 0.47 [0.11-1.9]; P = .01) and blood lymphocyte counts (1.25 [0.93-2.55] vs. 0.90 [0.70-1.24] × 109/L; P = .03). Imaging findings, EHV-5 detection, and corticosteroid treatment were not associated with survival. Fever is not a sensitive clinical sign of EMPF. Diagnostic testing should be pursued for horses with increased respiratory rate and effort and weight loss. The prognosis for EMPF horses is poor. Corticosteroid treatment does not improve 3-month survival.

Genomic diversity and natural recombination of equid gammaherpesvirus 5 isolates

BackgroundEquid gammaherpesvirus 5 (EHV5) is closely related to equid gammaherpesvirus 2 (EHV2). Detection of EHV5 is frequent in horse populations worldwide, but it is often without a clear and significant clinical impact. Infection in horses can often present as subclinical disease; however, it has been associated with respiratory disease, including equine multinodular pulmonary fibrosis (EMPF). Genetic heterogeneity within small regions of the EHV5 glycoprotein B (gB) sequences have been reported and multiple genotypes of this virus have been identified within individual horses, but full genome sequence data for these viruses is limited. The primary focus of this study was to assess the genomic diversity and natural recombination among EHV5 isolates. ResultsThe genome size of EHV5 prototype strain and the five EHV5 isolates cultured for this study, including four isolates from the same horse, ranged from 181,929 to 183,428 base pairs (bp), with the sizes of terminal repeat regions varying from 0 to 10 bp. The nucleotide sequence identity between the six EHV5 genomes ranged from 95.5 to 99.1%, and the estimated average nucleotide diversity between isolates was 1%. Individual genes displayed varying levels of nucleotide diversity that ranged from 0 to 19%. The analysis of nonsynonymous substitution (Ka > 0.025) revealed high diversity in eight genes. Genome analysis using RDP4 and SplitsTree programs detected evidence of past recombination events between EHV5 isolates. ConclusionGenomic diversity and recombination hotspots were identified among EHV5 strains. Recombination can drive genetic diversity, particularly in viruses that have a low rate of nucleotide substitutions. Therefore, the results from this study suggest that recombination is an important contributing factor to EHV5 genomic diversity. The findings from this study provide additional insights into the genetic heterogeneity of the EHV5 genome.

Association of equine gammaherpesvirus-5 with facial lymphohistiocytic interface dermatitis in seven adult horses from the United States.

Equine herpesvirus-5 (EHV-5) is commonly found in healthy asymptomatic horses worldwide. Although a cause-and-effect relationship has not been thoroughly determined, this virus has been associated with several disease conditions including equine multinodular pulmonary fibrosis (EMPF) and 1 case of interface dermatitis. The authors searched the New York State Animal Health Diagnostic Center database for cases of equine interface dermatitis between 2007 and 2022. Ten cases were identified and scrutinized for viral inclusion bodies which were present in 5 of 10 cases. Two similar cases with interface dermatitis and viral inclusion bodies, which were not part of a retrospective search, were from the Oregon Veterinary Diagnostic Laboratory. The authors describe a total of 7 horses with dermatitis characterized by crusted, alopecic, non-pruritic, non-painful, irregular to annular areas over the face, most commonly the muzzle, for up to several years duration. Histologically, there was a CD3+ T lymphocyte-dominated lymphohistiocytic interface dermatitis with hydropic degeneration, apoptotic keratinocytes, and pigmentary incontinence. Keratinocytes within the upper stratum spinosum and stratum granulosum had glassy pale basophilic intranuclear inclusion bodies consistent with herpesvirus. The presence of EHV-5 was confirmed by quantitative polymerase chain reaction (qPCR) and in situ hybridization in 7 horses and by electron microscopy in 1 horse. One horse later developed EMPF and was euthanized. EHV-5 was not detected with qPCR from 5 control horses and 5 horses with interface dermatitis without histologic evidence of viral inclusion bodies. These are the first cases of facial interface dermatitis associated with EHV-5 reported in the United States.

Equine multinodular pulmonary fibrosis and presumed corticosteroid‐induced side effects in a horse

SummaryEquine multinodular pulmonary fibrosis (EMPF) associated with herpesvirus‐5 infection (EHV‐5), is a severe, fibrosing interstitial lung disease of horses. Most common reported clinical signs are pyrexia, weight loss, depression, respiratory distress with tachypnoea and cough. Multiple tissue tropism of the EHV‐5 has been suggested. Treatment with valacyclovir and corticosteroids has been reported to be successful in a few cases, but the disease is usually associated with a poor prognosis because of progressive impairment of respiratory function. Corticosteroid administration can carry potential side effects, such as hypothalamic–pituitary–adrenal axis suppression, laminitis and increased susceptibility to infections. This report described a case of an 11‐year‐old gelding diagnosed with EMPF. The horse was treated with valacyclovir and corticosteroids and, after a transient initial improvement, showed a rapid deterioration of clinical signs and multiple complications, including severe bacterial dermatitis, liver damage and pleural effusion of unknown origin. A polymerase chain reaction (PCR) assay of liver biopsy sample was positive for EHV‐5, confirming the virus' multiple tissue tropism. A role of corticosteroids in exacerbating the disease progression and the increasing susceptibility to infections was strongly suspected.

Multiplex real-time PCR for the detection and differentiation of equid gammaherpesvirus 2 and 5

Equid gammaherpesvirus 2 (EHV-2) and 5 (EHV-5) are widely distributed in the equines. Although their pathogenic potential is not yet fully understood, they appear to play a role in disease patterns like equine multinodular pulmonary fibrosis. In this study, a multiplex real-time PCR (rtPCR) was designed to detect DNA of the glycoprotein H (EHV-2) and E11 gene (EHV-5). Analytical specificity was determined by testing DNA of other herpesviruses by SYBR Green rtPCR and melting curve analysis, as well as Sanger sequencing of positive field samples. Analytical sensitivity was assessed by standard curve generation of serial plasmid dilutions containing the respective target gene. Melting curves and BLAST analysis of the sequences indicated specific detection of the viruses. The lower limit of detection of the singleplex rtPCR was 40 and 29 DNA copies per reaction for EHV-2 and EHV-5, respectively. Comparison of the Ct values of a selection of positive field samples showed only minimal differences between the singleplex and the multiplex assay. The here described multiplex rtPCR protocol allows sensitive and specific detection of EHV-2 and EHV-5. It represents a convenient and rapid tool for future studies to investigate the clinical relevance of EHV-2 and EHV-5 in more detail.

Recent advancements in our understanding of equid gammaherpesvirus infections.

Equid gammaherpesviruses are ubiquitous and widespread in the equine population. Despite their frequent detection, their contribution to immune system modulation and the pathogenesis of several diseases remains unclear. Genetic variability and the combination of equid gammaherpesvirus strains a horse is infected with might be clinically significant. Initial gammaherpesvirus infection occurs in foals peripartum with latency then established in peripheral blood mononuclear cells. A novel EHV-5 study suggests that following inhalation equid gammaherpesviruses might obtain direct access to T and B lymphocytes via the tonsillar crypts to establish latency. EHV-5 is associated with equine multinodular pulmonary fibrosis, however, unlike with EHV-2 there is currently minimal evidence for its role in milder cases of respiratory disease and poor performance. Transmission is presumed to be via the upper respiratory tract with periodic reactivation of the latent virus in adult horses. Stress of transport has been identified as a risk factor for reactivation and shedding of equine gammaherpesviruses. There is currently a lack of evidence for the effectiveness of antiviral drugs in the treatment of equine gammaherpesvirus infections.

Equine multinodular pulmonary fibrosis in a Thoroughbred with pituitary pars intermedia dysfunction

Equine multinodular pulmonary fibrosis in a Thoroughbred with pituitary pars intermedia dysfunction

Systematic review of the putative role of herpesviruses in pulmonary fibrosis in horses and humans

SummaryBackgroundEquine multinodular pulmonary fibrosis (EMPF) and human idiopathic pulmonary fibrosis (IPF) have been compared due to their pathological similarities, poorly understood pathogenesis, poor response to therapy and high fatality rate. IPF lacks an adequate animal model for experimental investigation.ObjectivesAssess EMPF as a putative candidate to investigate the clinical importance of gammaherpesviruses (γ‐HVs) and their role in lung fibrosis, aetiological potential or involvement as cofactors for disease occurrence.Study designQuantitative systematic review.MethodsDatabases were searched, following a PRISMA protocol to identify relevant publications based on predetermined criteria. The articles were examined through a data extraction form designed for this review; bias, evidence and overall strength of the articles were assessed. Statistical analysis was performed on the extracted data to prove repeatability, quantify evidence and determine the significance of studies that did not include statistics.ResultsSixteen relevant publications were identified, and gaps and patterns were recognised. Virus detection within the pulmonary parenchyma and a close association within alveolar epithelial cells highlighted herpesvirus involvement in pulmonary fibrosis in both species.Main limitationsA limited number of articles matched the inclusion criteria, and raw data and the statistical analyses details were incomplete; the authors’ background in veterinary medicine may have resulted in inclusion bias.ConclusionsThis systematic review demonstrates that more research on both EMPF and IPF is required, with a methodical approach to characterise the relationship between γ‐HVs and lung cells. Similarities in the pathogenesis and clinical manifestations of EMPF and IPF support the use of EMPF as a model to study IPF and better understand the putative role that γ‐HVs, and that genetic and epigenetic factors might play in lung fibrosis. Such research could improve our approach to therapy of pulmonary fibrosis in both species.

Prognostic indicators and long‐term survival in 14 horses with equine multinodular pulmonary fibrosis

SummaryThere is limited information on long‐term follow‐up and prognostic indicators for horses diagnosed with equine multinodular pulmonary fibrosis (EMPF). The objectives of this study were to describe the signalment, clinicopathological data, radiographic and ultrasonographic findings, equine herpesvirus‐5 viral loads, clinical outcomes, and pathologic lesions associated with EMPF. Medical records from 2008 to 2016 were reviewed for this retrospective case series of 14 horses diagnosed with equine multinodular pulmonary fibrosis on lung histopathology. Independent variables associated with survival to hospital discharge (short‐term survival) were determined using Chi‐square or Fisher’s exact test. Odds ratios and 95% confidence intervals were calculated when applicable. Short‐term survival was 57%, with only 14% of cases surviving longer than 6 months after discharge. The odds of short‐term survival were higher in horses administered corticosteroids (OR = 0.029, 95% CI 0.002‐0.615; P = 0.026). Severity of thoracic radiographic changes and equine herpesvirus‐5 viral loads measured by quantitative PCR in the lung on presentation were not associated with survival time. Severity of thoracic radiographic changes was also not correlated to equine herpesvirus‐5 viral loads in the lung ante‐mortem. Equine multinodular pulmonary fibrosis has a poor prognosis for survival, with horses frequently displaying severe radiographic and histopathological changes at the time of diagnosis. Treatment with systemic corticosteroids reduced the odds of short‐term mortality.

Two Cases of Equine Multinodular Pulmonary Fibrosis in Japan

Equine multinodular pulmonary fibrosis (EMPF) is a recently described form of interstitial pneumonia associated with equine herpesvirus type 5 (EHV-5). This disease has been reported in North and South America, Europe and Oceania but not, to our knowledge, in horses in Japan. We diagnosed EMPF in two Thoroughbred horses in Japan on the basis of gross and histopathological findings. In both cases, significant gross lesions, restricted to the lungs, consisted of numerous firm and coalescing nodules widely distributed throughout the lung. The nodules were <3cm in diameter and pale white to tan in colour. Microscopically, they showed severe interstitial fibrosis and infiltration of macrophages, neutrophils, lymphocytes and a few eosinophils. The residual alveoli were lined by cuboidal epithelial cells (type II pneumocytes) and filled with many macrophages, which rarely displayed oval eosinophilic to amphophilic intranuclear inclusion bodies. Polymerase chain reaction and sequence analyses identified the glycoprotein H gene of EHV-5, and in-situ hybridization detected EHV-5 in the alveolar macrophages in the lesions. In one case, electron microscopy revealed herpesvirus-like particlesand EHV-5 was isolated from pulmonary lesions.

Unravelling the first key steps in equine herpesvirus type 5 (EHV5) pathogenesis using ex vivo and in vitro equine models

Equine herpesvirus type 5 (EHV5) is a ubiquitous, yet obscure pathogen in the horse population and is commonly associated with fatal equine multinodular pulmonary fibrosis (EMPF). To date, little is known about the precise pathogenesis of EHV5. Here, we evaluated the dynamics of EHV5 infection in representative ex vivo and in vitro equine models, using immunofluorescence staining and virus titration. EHV5 was unable to infect epithelial cells lining the mucosa of nasal and tracheal explants. Similarly, primary equine respiratory epithelial cells (EREC) were not susceptible to EHV5 following inoculation at the apical or basolateral surfaces. Upon direct delivery of EHV5 particles to lung explants, few EHV5-positive cell clusters were observed at 72 hours post-inoculation (hpi). These EHV5-positive cells were identified as cytokeratin-positive alveolar cells. Next, we examined the potential of EHV5 to infect three distinct equine PBMC populations (CD172a+ monocytes, CD3+ T lymphocytes and Ig light chain+ B lymphocytes). Monocytes did not support EHV5 replication. In contrast, up to 10% of inoculated equine T and B lymphocytes synthetized intracellular viral antigens 24 hpi and 72 hpi, respectively. Still, the production of mature virus particles was hampered, as we did not observe an increase in extracellular virus titer. After reaching a peak, the percentage of infected T and B lymphocytes decayed, which was partly due to the onset of apoptosis, but not necrosis. Based on these findings, we propose a model for EHV5 pathogenesis in the horse. Uncovering EHV5 pathogenesis is the corner step to finally contain or even eradicate the virus.

Gammaherpesvirus-5 Replicates only in Pulmonary Alveolar Macrophages and is Associated with a Mac387+ Histiocytic Response in Equine Multinodular Pulmonary Fibrosis

Gammaherpesvirus-5 Replicates only in Pulmonary Alveolar Macrophages and is Associated with a Mac387+ Histiocytic Response in Equine Multinodular Pulmonary Fibrosis

Characterization of Macrophages in Equine Multinodular Pulmonary Fibrosis

Characterization of Macrophages in Equine Multinodular Pulmonary Fibrosis

Equine multinodular pulmonary fibrosis in southern Brazil: pathology and differential diagnosis

ABSTRACT: Equine multinodular pulmonary fibrosis (EMPF) diagnosed at the Laboratório Regional de Diagnóstico of Faculdade de Medicina Veterinária, Universidade Federal de Pelotas (LRD/UFPel), is described. Differential aspects of other pulmonary diseases in horses with pneumonia and interstitial fibrosis were discussed. The disease occurred in a 15-year-old equine that presented with clinical signs of respiratory distress, intermittent fever, anorexia, and dyspnea. Macroscopically, there was enlargement of the lungs with whitish, pale, firm and well-delimited nodules, approximately 7-10 cm in diameter, distributed throughout the parenchyma. Histologically, the lung nodules had alveolar spaces with walls covered by cuboidal epithelium containing macrophages, neutrophils, lymphocytes, hyperplasia of type II pneumocytes and, eventually, multinucleated giant cells. The interstitium was markedly thickened by mature fibrous connective tissue and collagen. There were intranuclear inclusion bodies in the macrophages. The PCR technique for detecting the EHV-5 DNA was positive. In a retrospective study of pneumonia cases in horses with interstitial fibrosis diagnosed in the LRD/UFPel, two animals had macroscopic and histological lesions similar to those with EMPF, but they were negative for EHV-5 in PCR. Four cases diagnosed with pneumonia and interstitial tissue fibrosis had a histological pattern that was different from that observed in the EMPF animal, thus eliminating the possibility of EMPF. It is concluded that EMPF is a sporadic disease that should be considered in cases of respiratory disease in horses. Reports of such cases are important to alert technicians about the occurrence of rare diseases in Brazil. It is also necessary to establish the true role of EHV-5 in the pathogenesis of EMPF. Cases of pulmonary fibrosis such as EMPF, in which the virus is not present, should be studied to establish whether it could be an idiopathic form of the disease.

Assessment of quantitative polymerase chain reaction for equine herpesvirus-5 in blood, nasal secretions and bronchoalveolar lavage fluid for the laboratory diagnosis of equine multinodular pulmonary fibrosis.

The ante mortem diagnosis of equine multinodular pulmonary fibrosis (EMPF) relies on histopathological results and polymerase chain reaction (PCR)-positive equine herpesvirus (EHV)-5 testing of lung tissue. Polymerase chain reaction detection of EHV-5 in bronchoalveolar lavage fluid (BALF) is commonly used to support a diagnosis of EMPF. However, the diagnostic power of EHV-5 testing on BALF and other biological samples such as blood and nasal secretions has yet to be shown to support a diagnosis of EMPF. To determine the frequency of detection and the viral loads of EHV-5 by quantitative PCR (qPCR) in blood, nasal secretions and BALF from horses confirmed with EMPF, healthy horses and horses with non-EMPF pulmonary diseases. Prospective study. The study population consisted of 70 adult horses divided into 4 groups based on a combination of clinical findings, cytology of BALF, imaging studies of the thoracic cavity and histopathology of pulmonary tissue: control group (n = 14), EMPF group (n = 11); inflammatory airway disease group (n = 32); and non-EMPF interstitial lung disease group (n = 13). For each horse, whole blood, nasal secretions and BALF were available for EHV-5 qPCR testing. Sensitivities, specificities and their respective 95% confidence intervals were calculated for viral loads from blood, nasal secretions and BALF. In addition, these measures were calculated for combined use of blood and nasal secretions. The detection of EHV-5 in BALF was strongly associated with EMPF (sensitivity 91%, specificity 98.3%). Detection of EHV-5 in blood was, independent of the viral loads, strongly associated with EMPF with a sensitivity of 91% and specificity of 83.1%. The detection of EHV-5 in nasal secretions displayed the highest sensitivity (72.7%) and specificity (83.1%) at a level of >245,890 glycoprotein B target genes/million cells to support a diagnosis of EMPF. Dually positive blood and nasal secretions at any viral loads in support of EMPF yielded a sensitivity and specificity of 90% and 89.8%, respectively. Although histopathological confirmation (lung biopsy) is considered the gold standard for EMPF diagnosis, results of qPCR testing of BALF or a combination of whole blood and nasal secretions should be regarded as clinically useful in support of this diagnosis. The latter testing may be relevant when dealing with horses in respiratory distress, for which invasive procedures such as BALF collection or lung biopsies may be detrimental to their health.

Genetic variation and dynamics of infections of equid herpesvirus 5 in individual horses.

Equid herpesvirus 5 (EHV-5) is related to the human Epstein-Barr virus (human herpesvirus 4) and has frequently been observed in equine populations worldwide. EHV-5 was previously assumed to be low to non-pathogenic; however, studies have also related the virus to the severe lung disease equine multinodular pulmonary fibrosis (EMPF). Genetic information of EHV-5 is scanty: the whole genome was recently described and only limited nucleotide sequences are available. In this study, samples were taken twice 1 year apart from eight healthy horses at the same professional training yard and samples from a ninth horse that was diagnosed with EMPF with samples taken pre- and post-mortem to analyse partial glycoprotein B (gB) gene of EHV-5 by using next-generation sequencing. The analysis resulted in 27 partial gB gene sequences, 11 unique sequence types and five amino acid sequences. These sequences could be classified within four genotypes (I-IV) of the EHV-5 gB gene based on the degree of similarity of the nucleotide and amino acid sequences, and in this work horses were shown to be identified with up to three different genotypes simultaneously. The observations showed a range of interactions between EHV-5 and the host over time, where the same virus persists in some horses, whereas others have a more dynamic infection pattern including strains from different genotypes. This study provides insight into the genetic variation and dynamics of EHV-5, and highlights that further work is needed to understand the EHV-5 interaction with its host.

Identification of the first New Zealand case of equine multinodular pulmonary fibrosis

CASE HISTORY: A 10-year-old polo mare presented with a history of weight loss, poor condition and inappetance.CLINICAL FINDINGS: The mare was tachycardic, tachypnoeic and febrile. Harsh lung sounds were auscultated over all lung fields. The mare initially responded to treatment with antibiotics, anti-inflammatory drugs and bronchodilators. Throughout the course of treatment, there was a variable lymphocytosis, monocytosis and fluctuation in concentrations of fibrinogen. The mare also developed a mild anaemia, most likely due to chronic disease. Despite treatment, the mare's condition deteriorated over the following 2 months, and she was subject to euthanasia.PATHOLOGICAL FINDINGS: On post mortem examination, white to pale tan, large coalescing fibrous nodules up to 5 cm in diameter were found distributed throughout the lungs. Histopathology revealed a multifocally severe interstitial pneumonia with superimposed bronchiolar or alveolar inflammation, fibrosis, Type II pneumocyte hyperplasia and histiocytic intranuclear inclusion bodies, consistent with the findings previously reported for cases of equine multinodular pulmonary fibrosis (EMPF).DIAGNOSIS: Equine multinodular pulmonary fibrosis based on characteristic gross and histopathological findings. The diagnosis was strengthened by detection of DNA for equine herpesvirus 5 in the lung tissue.CLINICAL RELEVANCE: This report describes the first recognised case of EMPF in New Zealand. The affected horse did not respond to treatment and was subject to euthanasia. The prognosis for horses with EMPF, based on a limited number of cases worldwide, is currently considered poor.

Gammaherpesviruses and Pulmonary Fibrosis

Progressive lung fibrosis in humans, typified by idiopathic pulmonary fibrosis (IPF), is a serious cause of morbidity and mortality in people. Similar diseases have been described in dogs, cats, and horses. The cause and pathogenesis of such diseases in all species is poorly understood. There is growing evidence in human medicine that IPF is a manifestation of abnormal wound repair in response to epithelial injury. Because viruses can contribute to epithelial injury, there is increasing interest in a possible role of viruses, particularly gammaherpesviruses, in the pathogenesis of pulmonary fibrosis. This review provides background information on progressive fibrosing lung disease in human and veterinary medicine and summarizes the evidence for an association between gammaherpesvirus infection and pulmonary fibrosis, especially Epstein-Barr virus in human pulmonary fibrosis, and equine herpesvirus 5 in equine multinodular pulmonary fibrosis. Data derived from experimental lung infection in mice with the gammaherpesvirus murine herpesvirus are presented, emphasizing the host and viral factors that may contribute to lung fibrosis. The experimental data are considered in the context of the pathogenesis of naturally occurring pulmonary fibrosis in humans and horses.

Identification of Equine Herpesvirus 5 in Horses with Lymphoma

Equine multinodular pulmonary fibrosis, equine herpesvirus 5 (EHV-5), and multicentric lymphoma were discovered in one patient. Review of gamma herpesvirus activity in humans revealed a propensity for lymphoproliferative disorders associated with infection. The objective was to determine the frequency of EHV-5 in lymphoma tissues and compare with the frequency found in the lymph nodes of clinically normal horses. Case control investigation of lymphoma-positive tissues and analysis via polymerase chain reaction (PCR) for EHV-5 was performed on 12 horses. Prospective collection and PCR analysis of lymph nodes (mesenteric or submandibular) for EHV-5 was performed on 21 control horses. Thirteen samples of lymphoma-positive tissues and fluid were submitted for PCR analysis for EHV-5. Of these, 67% was positive. In the control horse population, 14% was positive for EHV-5 (P = .004). Neoplastic samples positive for EHV-5 were classified as T-cell rich B-cell lymphoma (three), T-cell lymphoma (one), one was nondifferentiated, and two were not stained. Gamma herpesviruses in humans have been associated with lymphoproliferative diseases such as Kaposi sarcoma and Burkitt lymphoma. This study reveals an increased frequency of EHV-5 (gamma herpesvirus) in horses diagnosed with lymphoma compared with healthy control horses. Although the exact role this virus plays in the initiation or perpetuation of lymphoproliferative neoplasia is unknown, EHV-5 may be an etiologic agent associated with the development of some types of equine lymphoma.

Experimental Induction of Pulmonary Fibrosis in Horses with the Gammaherpesvirus Equine Herpesvirus 5

Gammaherpesviruses (γHV) are implicated in the pathogenesis of pulmonary fibrosis in humans and murine models of lung fibrosis, however there is little direct experimental evidence that such viruses induce lung fibrosis in the natural host. The equine γHV EHV 5 is associated with equine multinodular pulmonary fibrosis (EMPF), a progressive fibrosing lung disease in its natural host, the horse. Experimental reproduction of EMPF has not been attempted to date. We hypothesized that inoculation of EHV 5 isolated from cases of EMPF into the lungs of clinically normal horses would induce lung fibrosis similar to EMPF. Neutralizing antibody titers were measured in the horses before and after inoculation with EHV 5. PCR and virus isolation was used to detect EHV 5 in antemortem blood and BAL samples, and in tissues collected postmortem. Nodular pulmonary fibrosis and induction of myofibroblasts occurred in EHV 5 inoculated horses. Mean lung collagen in EHV 5 inoculated horses (80 µg/mg) was significantly increased compared to control horses (26 µg/mg) (p < 0.5), as was interstitial collagen (32.6% ± 1.2% vs 23% ± 1.4%) (mean ± SEM; p < 0.001). Virus was difficult to detect in infected horses throughout the experiment, although EHV 5 antigen was detected in the lung by immunohistochemistry. We conclude that the γHV EHV 5 can induce lung fibrosis in the horse, and hypothesize that induction of fibrosis occurs while the virus is latent within the lung. This is the first example of a γHV inducing lung fibrosis in the natural host.