Back from the 50th Leman Conference - Where to Start?
Time away to see family, old friends and gain so much new knowledge and perspective
The annual Minnesota Allen D. Leman Swine Conference has been a part of my professional life since soon after my graduation from veterinary school in 1976. Al Leman was my hero - plain-spoken, incisive and always probing. I’ll never forget him chewing out the entire industry for taking so long to establish PRRS virus as the etiology for “Mystery Pig Disease” way back in about 1985 or so after we collectively struggled in the dark blaming “Encephalomyocarditis (EMC) Virus and a few other suspects for a debilitating respiratory and reproductive “syndrome” suddenly striking the swine industry.
I would love to hear his comments today regarding our collective inability to nail down the route(s) of transmission, minimal infective dose, and pathogenesis of H5N1 2.3.4.4b B3.13 in cattle 7 months after determining the causative agent. He would be appalled that we still have failed to place this virus into pigs, despite direct (unpublished) evidence that a closely related turkey vulture H5N1 2.3.4.4b strain infects pigs, transmits on to other pigs, AND causes encephalitic symptoms. Releasing this work has been delayed despite (likely) 4 positive H5 HI titers found in a little over 4000 non-targeted feral swine samples tested to date in an ARS-sponsored feral swine surveillance project. I will cover more information on H5N1 and swine research in another column soon. ARS has stated that they plan to infect pigs with the dairy clade in the lab in October. Let’s hope we don’t have feral pigs or domestic pigs naturally infected in California or elsewhere in the meantime…
To be fair the National Animal Disease Center in Ames, IA, where this BSL-3 swine work will be done, has been swamped with H5 dairy cattle work in their limited BSL-3 space. However, I do have to question why more cattle and ruminant studies have not been “farmed out” to qualifying research institutions and shared with the broader research community to speed answers in all species. Even non-BSL-3 researchers could certainly be conducting field projects and serological profiling studies if provided requests for proposals and funding by USDA. Research capacity must both be expanded and prioritized.
The final morning of the conference featured a general session topic led by Drs. Marie Culhane, Carol Cardona, and Montse Torremorell entitled “Everything, Everywhere, All Influenza”. The presentation was a broad perspective, from poultry to swine, to the latest dairy issues; however, it started with a broad history of just where the current H5 saga began in the mid- 1990’s, how it travelled through backyard poultry in SE Asia, into wild birds, and then onward to its eventual worldwide spread with the widespread mammalian adaptation that we see today.
Again, the presentation is much too broad for a single blog; however, Dr. Cardona presented one slide that captured a topic worth reviewing today as we contemplate where we are headed with dairy-spillover H5 in the face of its ongoing threat to the poultry industry and public health. From a regulatory and notification standpoint, we have chosen to handle H5 in cattle and potentially other livestock species differently than has been the default process in poultry:
The poultry process developed out of necessity; HPAI kills birds and producers need to know the levels of risk from their neighbors. Producers quickly realized that transparency was necessary if they were infected, if they were to expect the same transparency from their neighbors should the opposite hold true.
We now have an uneven playing field. Dairy producers essentially are not penalized for non-disclosure of an internal infection with the same virus. Milk sales continue, so losses are limited to the economic costs of the disease outbreak with no regulatory penalties for non-reporting at this point.
The strains on this “shared ecosystem” are rapidly coming to a head in California, where one poultry flock has already been infected and many more are likely to follow as the H5 viral load builds in the valleys in both dairy cattle herds and wildlife populations in contact with them. People are another possible common source of infection, whether directly, or via fomite transfer. Public health authorities have been “primed” to conduct surveillance in farm worker and poultry depopulation crews, making human case detection more likely as cases continue. I again personally heard first-hand reports of worker conjunctivitis on an affected dairy farm in the mid-west where willful lack of follow-up by local public health officials prevented official human testing for zoonotic infection. We cannot doubt that this virus is quite infectious in the conjunctiva for people, making ongoing contact worrisome.
In summary, this combination of poultry economic risk, human susceptibility, and wildlife spread (including feral swine, the “mixing species”) will not allow H5N1 in dairy cattle to just fade away into blissful silent endemicity with little or no testing. The virus will not disappear, a sterilizing vaccine is not on the near horizon, and evidence indicates the virus will either ebb and flow in previously affected herds or may reinfect any herds that happen to clear infection.
H5N1 may have points of vulnerability to slow within or between herd transmission, but we can’t address them until we understand it. Good clinicians with today’s diagnostic tools will quickly clarify this process, if they can live on a few farms from the start of infection. Much of this can’t be replicated in a BSL-3 lab. We need experts on naive farms as bulk tank samples first go positive to watch as cows first become infected, as well as to monitor other stock on the farm simultaneously. Is the virus in the air or dust, on fomites, in the water troughs, insects, rodents, or where? What are early clinical signs? When do nasal swabs, urine, blood, and milk first go positive? When do fevers appear and rumens slow? What percentage of cows become viremic, develop mastitis?
Understanding infection can eventually lead to fewer cases and lower virus loads. In the mean-time stakeholders will increasingly demand testing, sequencing and transparency one way or another to remain in the dairy business. It’s the price of living in a “shared ecosystem.”
John