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Increasing Incidence of Bovine Influenza-H5N1 Raises Questions


With the 12h state reporting bovine influenza-H5N1, and with almost 100 confirmed herds as of June18th, USDA is faced with a problem of transparency.  Daily updates of incident cases on websites should be achievable.  Release of isolates for genome sequencing is essential with participation by WHO influenza reference laboratories in the U.S. and in Europe. Simply beating the drum of improving biosecurity pays lip service to the emerging problem.


It is fortunate that heat treatment inactivates the virus in fluid milk so pasteurized milk and dairy products should be safe to consume.  The question of transmissibility to human contacts appears to be extremely limited at present but it will be critical to continually monitor for mutations that may facilitate infection of human respiratory tissue.  At the present time all three identified patients who contracted H5N1 infection demonstrated conjunctivitis (with only one displaying mild upper respiratory signs).  This is due to the fact that conjunctival tissue along with bovine mammary glands contains sialic receptors to both avian and mammalian strains of H5N1.


States reporting bovine influenza H5N1

In a ProMED posting moderator JH questions whether the USDA will initiate surveillance of beef cattle in feed-lots to establish whether infection has entered these herds.  JH opined “Given the geographic coverage of the USDA map, odds are not in our favor that beef cattle haven’t been infected.  Until a few months ago spill-over of H5N1 into bovines was reviewed as unlikely even though infection with several influenza A variants have occurred on a limited basis previously in cattle.  Even cow-calf operations may be at risk, given that their water may be contaminated by free-living birds excreting H5N1 virus, known to survive for prolonged periods in water containing organic matter. 


Is the reluctance to establish a limited testing problem based on the presumption that it is best  not to turn over rocks unless one knows what might be under them?  Assay of muscle tissue from culled dairy cows subjected to antemortem condemnation has yielded H5N1 virus.  The implications for asymptomatic infection of beef cattle are self-evident.  Fortunately it has been shown that heat treatment adequate to kill foodborne bacteria infection inactivates H5N1 virus.


At the present time the CDC is calling for all milk from herds with cases of bovine influenza-H5N1 to be withheld from market. This recommendation is based on prudence, notwithstanding the effectiveness of pasteurization. If this policy were to be implemented there would be absolutely no voluntary reporting of cases and a call for federal indemnification. Steve Naig, the Iowa Commissioner of Agriculture has called for Federal compensation for herd operators to cover losses. A proportion of affected dairy cows have either died from H5N2 infection or have been culled as a result of chronic low lactation with unsalable milk.