ARS Influenza Research Update

June 10, 2009 — 

The USDA Agricultural Research Service's National Animal Disease Center (NADC) has released results of a study investigating whether meat, blood and tissue from pigs infected with the new 2009 H1N1 Influenza A Virus is free of infectious virus.

Researchers inoculated pigs intra-tracheally with the novel H1N1 virus and necropsied the pigs 5 days post-infection to evaluate lung lesions and viral load in the lung and tissues. Fresh samples were taken from lung, tonsil, inguinal lymph node, liver, spleen, kidney, skeletal muscle (ham), and colon contents (feces), and examined using both real time RT-PCR and virus isolation (VI) techniques, which are the most sensitive and specific tools to detect the presence of viral nucleic acid and live virus, respectively.

Results:

• Tissues outside the respiratory tract were found to be negative by VI at 5 days post infection. Only respiratory tract samples were positive by both methods (real time RT-PCR and VI).
• The inguinal lymph node from one pig and serum from two pigs were positive by real time RTPCR. However, lymph node and serum samples from all pigs were negative by VI.
• By contrast, all day 5 post infection nasal swabs and lung lavage fluids were positive by real time RT-PCR and VI, and lung tissue homogenates from all four pigs were positive by real time RT-PCR and 2/4 samples positive by VI.

Conclusion: Live 2009 A/H1N1 Influenza A Virus was only detected in the respiratory tract of infected pigs and the virus does not appear to spread and replicate in other tissues based on the day 5 post infection samples.

Next Step: A larger study will be conducted to evaluate tissues by VI and real time RT-PCR that will include additional time points (1, 3, 5, and 7 days dpi).

Additional information is available on the ARS website.