The severity of epidemic and pandemic influenza outbreaks is
dictated in part by the efficiency with which the causative strain
transmits between human hosts. The mechanisms underlying influenza
virus spread are poorly understood, in part because of the
lack of a convenient animal model to study this phenomenon.
Indeed, despite extremely efficient transmission among humans
and virulence in the mouse model, we have shown that even the
1918 pandemic influenza virus does not transmit between mice.
Wetherefore evaluated the guinea pig as a model mammalian host
for influenza virus. Using the recent human isolate APanama
200799 (Pan99) (H3N2) virus, we found that guinea pigs were
highly susceptible to infection with the unadapted virus (ID50 5
plaque-forming units). Pan99 virus grew to high titers in the upper
respiratory tract and was shed in nasal washings of infected
animals. Moreover, influenza virus was transmitted from infected
guinea pigs to noninfected guinea pigs housed in the same cage,
an adjacent cage, and a cage placed 91 cm away. Our results
demonstrate that influenza virus can pass between guinea pigs by
means of droplet spread and thereby establish the suitability of the
guinea pig as a model host for influenza virus transmission studies.