An evaluation of the infectivity of milk from cows with confirmed bovine influenza-H5N1 resulted in clinical changes and systemic infection.  Studies conducted by scientists at the University of Wisconsin-Madison and Texas A&M Veterinary Medical Diagnostic Laboratory confirmed the infectivity of raw milk from dairy cows with bovine influenza-H5N1. Within one day of receiving infected milk droplets, mice demonstrated illness including lethargy.  On day 4, euthanized mice yielded H5N1virus from the nasal passages, trachea, lungs and from other organs. This study should be extended to ferrets a standard laboratory human surrogate for studies on influenza virus. Recent studies in Denmark have demonstrated that the virus can propagate in bovine mammary tissue that apparently has receptors for both mammalian and avian influenza A virus strains. 

Fortunately the circulating H5N1 strain is destroyed by pasteurization and also heating over a range of 145F for 5 to 30 minutes or 162F from 5 to 30 seconds.  The threshold of inactivation at 161.6F was 20 seconds.  A second component of the experiment demonstrated that refrigeration at 39F for as long as five weeks was inadequate to inactivate the virus that persists in milk.

The initial conclusions from the trials confirm that raw milk from affected cows is capable of infecting mice and presumably, humans.  Pasteurization inactivates the virus, eliminating risks associated with consumption of commercial milk.  Obviously, raw milk represents a potential hazard to consumers.  Refrigeration over a prolonged period does not destroy the activity of H5N1 virus in milk from infected cows.

To date, 52 herds have been confirmed with H5N1 bovine influenza in nine states.  This possibly  represents the tip of the iceberg since a survey demonstrated that 20 percent of pooled samples of commercial milk yielded RNA fragments consistent with mammary gland infection.  Retail milk sampled may have been obtained from as many as 38 states and over 140 processing plants. The high prevalence in milk sampled, together with recovery of viable H5N1 from wastewater in areas where infected herds are located presumes widespread infection.