APHIS: Recommendations for (HPAI) H5N1 in Livestock For State Animal Health Officials, Accredited Veterinarians and Producers

Credit USDA

#17,987

It's been just over 10 days since we learned that a widespread illness reported in dairy cattle in northern Texas since January was, in fact, HPAI H5N1 (see USDA Statement on HPAI In Dairy Cattle in Texas & Kansas Herds). 

Although experimental infection of cattle with avian flu had been demonstrated in 2008, cattle were thought to be relatively immune to influenza A, and unlikely hosts for H5N1. As a result, it took several weeks before influenza testing was done. 

While investigations are ongoing, there are early, worrisome signs that cow-to-cow transmission of the virus may be occurring, and at least 6 states (Texas, Kansas, New Mexico, Michigan, Idaho & Ohio) have reported cases.  Additionally, at least 3 dead cats and birds recovered from affected dairy farms have tested positive for the virus. 

While the risk to the public is still considered low, 4 days ago the state of Texas announced the first (mild) human infection in a dairy worker (see  Texas DSHS Health Alert: 1st Human Case of H5N1 Influenza In Texas). 

Since then we've seen a flurry of technical documents and guidance issued by the USDA and the CDC, including:

USDA: Testing Recommendations Of Influenza A In Cattle

CDC Statement & Risk Assessment On The Texas H5N1 Case

The USDA/APHIS Unveils HPAI in Livestock Website

CDC: Interim Recommendations for Prevention, Monitoring, and Public Health Investigations Of HPAI H5N1 In Animals

While it isn't clear how much of a risk all of this poses, we are clearly in uncharted territory.  We've no idea how long H5N1 has been circulating in cattle, or how widespread it may be.  With the report of HPAI infected goats in Minnesota in late March, the possibility of spillover into other livestock - including swine - must be considered. 

Testing takes time, and uses (finite) laboratory resources, and right now the emphasis is on testing symptomatic dairy cows .  While it would certainly be helpful if we could cast a wider net, the logistics are daunting. 

• There are roughly 9 million dairy cows in the United States, add in all cattle and calves and that number jumps to 90 million.  

• The U.S. raises about 100 million pigs, on nearly 60,000 farms.  There are also an estimated 9 million feral hogs in the United States.

• There are more than 2.5 million goats in the U.S., and there may well be other susceptible species (e.g. sheep, camelids, etc.). 

We've neither the time, nor the lab capacity, to test more than a tiny percentage of U.S. livestock. And even if we could, it would only provide a snapshot of a brief point in time. There is also a strong possibility that HPAI H5 has quietly made inroads into cattle or pigs in other countries around the globe. 

While we will certainly learn more over time, the emphasis right now is on limiting the damage, even if we can't see the full extent of the threat. And that means increasing farm biosecurity, minimizing the movement of cattle, improving the safety of farm workers (PPEs, vaccines, etc.), and increased surveillance of both livestock and farm workers.

While far from ideal, it may be our only option at this time. To that end, APHIS (the Animal and Plant Health Inspection Service of the USDA) published a 4-page set of guidance this week for State Health Officials, Veterinarians, and Producers. 

I've reproduced the first page below, follow the link to read it in its entirety.  I'll have a postscript after you return. 

There is much debate over just how big of a deal all of this is.  With the dearth of information at present, it is fair to say no one really knows.  The jump to cattle - and apparent cow-to-cow transmission - is a clear escalation of the threat, but it isn't necessarily a prelude to a pandemic.  

Yes, it does provide the virus with more opportunities to adapt to mammalian species, and a better chance of spilling back into humans than - say - from infected sea lions or skunks in the wild.  

But it isn't nearly as alarming as finding it spreading in pigs (or mink), which already carry a wide array of influenza A viruses and offer much better potential for reassortment. 

 

That, of course, could still happen. Hopefully, increased testing of swine is in the works, particularly for exhibition pigs (see EID Journal: Shortening Duration of Swine Exhibitions to Reduce Risk for Zoonotic Transmission of Influenza A Virus), which have sparked small outbreaks of swine variant virus infections in the past. 

While some of the `worst-case scenarios' being bandied about online, or in the tabloids, are probably overblown (see Revisiting the H5N1 CFR (Case Fatality Rate) Debate), anything over a 1% fatality rate would be devastating. 

Whether it is caused by HPAI H5, or some other novel subtype (e.g. H5N6, H3N8, H9N2, etc.) - another influenza pandemic is inevitable.  And if it turns out to be severe, we'd better be bettered prepared to deal with it than we were with COVID.