Interspecies transmission of influenza viruses, especially highly pathogenic avian H5N1, is a possible threat to global human health . Successful interspecies transmission of the avian influenza virus H3N2 to dogs and subsequent intraspecies transmission between dogs has been reported previously [1, 2]. These data suggest that avian influenza viruses can traverse interspecies (avian to mammal) transmission barriers, which in turn suggests the possibility for transmission of influenza viruses from birds to humans.
Since influenza virus was first isolated in 1933 , significant attention has been focused on elucidating its structure and genome, the immune responses it elicits, testing protective vaccines, and studying influenza epidemiology. However, information regarding the kinetics of influenza virus during an infection within an individual is limited. Human influenza infections are generally characterized by exponential growth of the virus, which peaks 2 to 3 days DPI, followed by an exponential decrease in the viral load until the virus is undetectable 6 to 8 DPI .
During influenza infection, virus shed in nasal and oropharyngeal secretions and dispersed through sneezing and coughing. Since the duration of shedding and the quantity of virus shed are important determinants of infectivity, treatment strategies for influenza should consider not just symptom reduction but also focus on reducing infectivity. The results of this study are also applicable to animal clinics that experience canine influenza cases. Veterinarians should segregate those animals suspected of carrying influenza that show a high fever (>39.5°C) and thus may spread high viral loads by nasal shedding. It has not yet been elucidated why the severity of clinical signs, especially fever, is closely related to levels of viral shedding in infected animals. This should be further studied with regard to the variability of inflammatory and immune responses in CIV-infected hosts. In similar study of viral shedding in human after infection of pandemic H1N1, viral load was maintained at a high level during the febrile period. And pandemic flu-infected patients with pneumonia had a higher viral load than those with mild lesion related with flu. The higher viral shedding load may be a reflection of disease severity, or impaired host defense mechanism, need immediate attention and treatment .
The data above show that dogs that commingle with a canine influenza infected dog shed different levels of virus in their nasal excretions. The correlation between the viral shedding and clinical signs of canine influenza H3N2 virus infection would provide important knowledge for epidemiological control and clinical management in terms of infection control strategy.