Influenza C virus infection in rats

Area of Science:

• Virology
• Immunology
• Infectious Diseases

Background:

• Influenza C virus infections in humans are common but poorly understood.
• Animal models are crucial for studying influenza virus pathogenesis and immune responses.

Purpose of the Study:

• To investigate influenza C virus replication, clinical signs, and immune responses in a rat model.
• To determine the impact of inoculum size and prior infection on virus shedding and antibody production.

Main Methods:

• Intranasal inoculation of Wistar King A/Hkm (WKA/Hkm) strain rats with influenza C virus (Ann Arbor/1/50 strain).
• Monitoring for clinical symptoms, virus recovery from nasal homogenates, and serum hemagglutination-inhibiting (HI) and neutralizing antibody titers.
• Assessing virus shedding and antibody response following primary infection and reinfection at different time points.

Main Results:

• Influenza C virus replicated in rat nasal passages, inducing hemagglutination-inhibiting (HI) and neutralizing antibodies, despite the absence of overt clinical illness.
• High-dose (10^6.2 and 10^3.2 PFU) infections resulted in virus recovery from days 1-10 and detectable HI antibodies by day 10.
• Low-dose (10^1.2 PFU) infections led to prolonged virus shedding up to day 20 without detectable serum HI antibodies.
• Virus recovery was largely unaffected by rat sex, age, or strain, with a minor exception of slower growth in the LE strain.
• Rats reinfected 7 weeks after a high-dose primary infection showed no virus shedding, but reinfection 50-55 weeks later resulted in low-titer virus production.
• Rats with a prior low-dose infection shed virus upon challenge 7 weeks later.

Conclusions:

• Rats can serve as a model for studying influenza C virus infection, exhibiting nasal replication and antibody responses.
• Inoculum size significantly influences the duration of virus shedding and the development of detectable serum antibodies.
• The study demonstrates the potential for repeated influenza C virus infections in rats, mirroring patterns observed in human infections under specific conditions.