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.

Mediastinal Ectopic Thyroid Carcinoma and Concurrent Multinodular Pulmonary Fibrosis in a Horse

A 30-year-old Standardbred gelding was referred for chronic pleural effusion. Thoracic ultrasound revealed marked bilateral pleural effusion and a large heterogeneous mass within the cranial mediastinum, which extended from the right 5th to the 11th intercostal space. Subsequently, on thoracic radiographs, the cranial mediastinal mass was confirmed, and a nodular interstitial pattern was identified in the lungs. Because of progressive clinical deterioration of the patient, the owners elected humane euthanasia and necropsy was performed. The mediastinal mass was consistent with an ectopic thyroid carcinoma, and the pulmonary nodules represented equine multinodular pulmonary fibrosis (EMPF). This case report describes a type of mediastinal tumor not previously described in horses. Moreover, it shows the need of including EMPF as a possible differential diagnosis for a nodular interstitial pulmonary pattern in conjunction with a mediastinal or other masses.

Effect of valacyclovir on EHV-5 viral kinetics in horses with equine multinodular pulmonary fibrosis

BACKGROUND

Equine herpesvirus-5 is commonly isolated from the lungs of horses with EMPF, suggesting an etiological link. Valacyclovir is used empirically to treat EMPF; however, no data is available concerning its impact on EHV-5 viral kinetics.

OBJECTIVES

To determine the effect of oral administration of valacyclovir on EHV-5 viral load measured by qPCR in blood, nasal secretions (NS) and BALF in horses with EMPF.

ANIMALS

Six horses diagnosed with EMPF.

METHODS

A prospective clinical trial was performed. Horses received 10 days of PO administered valacyclovir (loading dose 30 mg/kg, maintenance dose 20 mg/kg). Blood, NS, and BALF were collected for EHV-5 viral kinetics analyses during treatment. Blood and NS were collected every other day. BALF was collected on day 0 and day 10.

RESULTS

There was no statistical difference in median EHV-5 viral load between day 0 and day 10 for all samples tested. In blood median EHV-5 viral load was 7676 (range 575-39 781) on day 0 and 6822 (range 1136-18 635) glycoprotein B (gB) gene copies per million cells on day 10. For NS median EHV-5 viral load was 2.944 × 10⁶ (range 184 691-3.394 × 10⁹ ) on day 0 and 8.803 × 10⁶ (range 251 186-9.868 × 10⁸ ) gB gene copies per million cells on day 10. For BALF median EHV-5 viral load was 59,842 (range 61-315 655) on day 0 and 185 083 (range 3562-542 417) gB gene copies per million cells on day 10.

CONCLUSIONS AND CLINICAL IMPORTANCE

Valacyclovir might not be an effective short-term antiviral treatment but efficacy in treatment of EMPF is unknown.

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

REASONS FOR PERFORMING STUDY

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.

OBJECTIVES

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.

STUDY DESIGN

Prospective study.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Update on interstitial pneumonia

Interstitial pneumonias encompass a wide variety of acute and chronic respiratory diseases and include the specific diseases equine multinodular pulmonary fibrosis and acute lung injury and acute respiratory distress. These diseases have been diagnosed in all age groups of horses, and numerous agents have been identified as potential causes of interstitial pneumonia. Despite the varied causes, interstitial pneumonia is uniformly recognized by the severity of respiratory disease and often poor clinical outcome. This article reviews the causal agents that have been associated with the development of interstitial pneumonia in horses. Pathophysiology, clinical diagnosis, and treatment options are discussed.