Transmission of Human Respiratory Syncytial Virus in the Immunocompromised Ferret Model

Abstract

Human respiratory syncytial virus (HRSV) causes substantial morbidity and mortality in vulnerable patients, such as the very young, the elderly, and immunocompromised individuals of any age. Nosocomial transmission of HRSV remains a serious challenge in hospital settings, with intervention strategies largely limited to infection control measures, including isolation of cases, high standards of hand hygiene, cohort nursing, and use of personal protective equipment. No vaccines against HRSV are currently available, and treatment options are largely supportive care and expensive monoclonal antibody or antiviral therapy. The limitations of current animal models for HRSV infection impede the development of new preventive and therapeutic agents, and the assessment of their potential for limiting HRSV transmission, in particular in nosocomial settings. Here, we demonstrate the efficient transmission of HRSV from immunocompromised ferrets to both immunocompromised and immunocompetent contact ferrets, with pathological findings reproducing HRSV pathology in humans. The immunocompromised ferret-HRSV model represents a novel tool for the evaluation of intervention strategies against nosocomial transmission of HRSV.

Keywords: animal model; contact; ferret; immunocompromised; respiratory syncytial virus; transmission.

Figure 1

Schematics overview of the experimental design; ferret groups are lettered (A–F); red ferrets are immunocompromised ferrets; black ferrets are immunocompetent ferrets; contact ferrets (group C–F) are placed in the same cages as donor ferrets (group A,B) on day 5 post-inoculation (dpi); all ferrets are euthanized at 13 dpi. Days of collection of nose swabs, throat swabs, broncho-alveolar lavages (BAL), and respiratory tract samples are indicated with dark squares; samples used for viral sequencing are indicated with patterns.

Figure 2

HRSV RNA concentrations and viral titers in the throat and nose swabs of donor ferrets; (a) HRSV concentration in the throat swabs (plain line) and nose swabs (dashed line) of group A ferrets inoculated intra-tracheally (I.T); (b) HRSV viral titers in the throat swabs (plain line) and nose swabs (dashed line) of group A ferrets inoculated intra-tracheally (I.T); (c) HRSV concentration in the throat swabs (plain line) and nose swabs (dashed line) of group B ferrets inoculated intra-nasally (I.N); (d) HRSV viral titers in the throat swabs (plain line) and nose swabs (dashed line) of group B ferrets inoculated intra-nasally (I.N); each line represents a single ferret; for (a,c): quantification limit of qPCR data is indicated by a dotted line, and non-quantifiable Ct values were assigned the value 1.3 log10 vp/mL.

Figure 3

Average RNA concentrations and viral titers in the throat and nose swabs of group A to F ferrets, expressed as areas under the curve (AUC); (a) AUC RNA concentration; (b) AUC viral titers; significant differences are marked with asterisks (* p ≤ 0.05 and ** p ≤ 0.01); error bars indicate standard deviations.

Figure 4

Photomicrographs of intranasally HRSV-inoculated immunocompromised donor ferret (animal #3) inflamed mucosa of the nasal turbinates at 13 dpi (a,b) and of immunocompromised contact ferret (animal #10) tracheal mucosa following productive HRSV transmission at 8 days post-exposure (c,d). (a) RSV-infected epithelial cells may develop bright eosinophilic viral inclusion bodies (arrows) and may form syncytial multinucleated cells (H&E-stain); (b) Serial slide shows HRSV-antigen expression faintly of the cytoplasmic inclusion bodies (arrows) enclosed by a corona of multiple nuclei, and markedly of the outer cellular membranes and cilia of RSV-infected nasal epithelial cells as red-brown staining (Immunoperoxidase, hematoxylin-counterstain); (c) The mucosa is markedly inflamed with infiltrated neutrophils and covered with layer of exudate (asterisk); multinucleated epithelial syncytial cells containing bright eosinophilic viral inclusion bodies (arrows) are present within RSV-infected tracheal epithelial cells (H&E-stain); (d) Serial slide shows HRSV-antigen expression faintly of the cytoplasmic inclusion bodies (arrows) and markedly of the apical side and cilia of RSV-infected tracheal epithelial cells as red-brown staining (Immunoperoxidase, hematoxylin-counterstain). Original magnifications 400×.