Quantitative measurement of influenza virus replication using consecutive bronchoalveolar lavage in the lower respiratory tract of a ferret model

Ferrets as Models for Viral Respiratory Disease

Domestic ferrets (Mustela putorius furo) have been used in biomedical research to study influenza viruses since the early 20th century. Ferrets have continued to gain importance for the study of viral respiratory disease due to their disease susceptibility and anatomic similarities to humans. Here we review features of ferret biology and management that should be considered when planning to work with this species, particularly in models of respiratory disease. We specifically discuss biosafety and husbandry, clinical and pathologic assessments, and anesthetic considerations for ferrets with respiratory disease and systemic illness. These considerations are important for animal welfare, fidelity of the model to human disease, and ensuring accuracy and reproducibility of acquired data. Finally, we briefly review the use of ferrets to study respiratory diseases by discussing their respiratory anatomy and 2 frequently studied viral respiratory diseases, influenza and coronavirus disease 2019 (COVID-19).

A Guide for the Use of the Ferret Model for Influenza Virus Infection

As influenza viruses continue to jump species barriers to cause human infection, assessments of disease severity and viral replication kinetics in vivo provide crucial information for public health professionals. The ferret model is a valuable resource for evaluating influenza virus pathogenicity; thus, understanding the most effective techniques for sample collection and usage, as well as the full spectrum of attainable data after experimental inoculation in this species, is paramount. This is especially true for scheduled necropsy of virus-infected ferrets, a standard component in evaluation of influenza virus pathogenicity, as necropsy findings can provide important information regarding disease severity and pathogenicity that is not otherwise available from the live animal. In this review, we describe the range of influenza viruses assessed in ferrets, the measures of experimental disease severity in this model, and optimal sample collection during necropsy of virus-infected ferrets. Collectively, this information is critical for assessing systemic involvement after influenza virus infection in mammals.

Complexities in Ferret Influenza Virus Pathogenesis and Transmission Models

Ferrets are widely employed to study the pathogenicity, transmissibility, and tropism of influenza viruses. However, inherent variations in inoculation methods, sampling schemes, and experimental designs are often overlooked when contextualizing or aggregating data between laboratories, leading to potential confusion or misinterpretation of results. Here, we provide a comprehensive overview of parameters to consider when planning an experiment using ferrets, collecting data from the experiment, and placing results in context with previously performed studies. This review offers information that is of particular importance for researchers in the field who rely on ferret data but do not perform the experiments themselves. Furthermore, this review highlights the breadth of experimental designs and techniques currently available to study influenza viruses in this model, underscoring the wide heterogeneity of protocols currently used for ferret studies while demonstrating the wealth of information which can benefit risk assessments of emerging influenza viruses.

Using the Ferret as an Animal Model for Investigating Influenza Antiviral Effectiveness

The concern of the emergence of a pandemic influenza virus has sparked an increased effort toward the development and testing of novel influenza antivirals. Central to this is the animal model of influenza infection, which has played an important role in understanding treatment effectiveness and the effect of antivirals on host immune responses. Among the different animal models of influenza, ferrets can be considered the most suitable for antiviral studies as they display most of the human-like symptoms following influenza infections, they can be infected with human influenza virus without prior viral adaptation and have the ability to transmit influenza virus efficiently between one another. However, an accurate assessment of the effectiveness of an antiviral treatment in ferrets is dependent on three major experimental considerations encompassing firstly, the volume and titer of virus, and the route of viral inoculation. Secondly, the route and dose of drug administration, and lastly, the different methods used to assess clinical symptoms, viral shedding kinetics and host immune responses in the ferrets. A good understanding of these areas is necessary to achieve data that can accurately inform the human use of influenza antivirals. In this review, we discuss the current progress and the challenges faced in these three major areas when using the ferret model to measure influenza antiviral effectiveness.