Pigs and earlier H5N1 isolates...
Research published overnight from Kansas State University follows earlier work from USDA ARS NADC regarding pathogenicity and transmissibility of clade 2.3.4.4b H5N1 HPAI viruses
A highly informative research paper reporting on the pathogenicity and transmissibility of a mink-derived clade 2.3.4.4b H5N1 HPAIV isolate from Spain in pigs was published overnight by a group led by Dr. Juergen Richt at Kansas State University:
This follows an earlier paper in Emerging Infectious Diseases by Dr. Bailey Arruda et al at USDA ARS NADC describing pathogenesis and transmission work in swine utilizing 4 U.S. H5N1 isolates, 2 from avian and 2 from mammalian species:
Both papers are highly technical, beyond my abilities to critically review in detail. Please read them both and share widely in the scientific community for further comments and possible collaborations.
Both research group deserve much credit for conducting difficult Select Agent research work in approved facilities in a timely manner to address critical issues facing animal agriculture. It’s ironic that a virus which is widespread in nature must be handled under strict restrictions in experimental conditions or even when shipped post-diagnosis. Fortunately, we have a few qualified agricultural laboratories staffed with excellent researchers able to conduct this important work.
Back to the subject, in summarizing and synthesizing the conclusions from the 2 papers and the underlying endemic nature of influenza in swine in general, I believe the following conclusions may apply:
No one has yet reported results with experimental inoculation of pigs (or dairy cattle for that matter) with the current dairy isolate (H5N1 2.3.4.4.b.3.13). Both these studies utilized earlier North American (Arruda) and European (Richt) isolates. H5N1 2.3.4.4b 3.13 work is or will no doubt soon be underway; however, it’s premature to state with full confidence the degree to which the current dairy virus will or will not infect and undergo onward transmission in swine. Regardless, both studies indicate that H5N1 is adapting slowly but surely towards persistence in swine and other mammals.
With any influenza pathogenesis and transmission study, the conclusions are only as valid as the current 8-gene construct of the virus and the underlying swine influenza viral ecosystem into which the H5N1 virus may be introduced. This virus will likely be introduced naturally into swine populations with endemic influenza, and early viral reassortment resulting in improved transmissibility is a possibility. Unfitness is a much greater possibility, but we’ll never see those failures. If successfully adapted, we’ll likely detect reassortments with one or more segments of the H5N1 B3.13 virus inserted into a successfully replicating new swine isolate. The odds are unknown but can and should be monitored.
Feral swine may be an under-appreciated risk. Their diet is quite opportunistic and may include mammalian and bird mortalities. Wildlife Services and other wildlife agencies are aware of this and can check sick and dead feral swine for influenza RNA and serological titers to H5N1. Producers are already utilizing herd biosecurity to minimize feral swine contact due to multiple swine disease risks. Add possible influenza transmission to that mix!
The current voluntary swine influenza surveillance process will uncover any widespread incorporation of H5N1 into the commercial swine population. It’s less likely be detected if first established in backyard herds lacking regular animal health supervision and diagnostics. Regardless, PCR testing in individual clinically ill animals will likely be a “trailing” indicator of any possible swine incursion, much as it was with the dairy infections.
Despite all the ongoing changes in an evolving pathogen that will make initial pathogenesis and transmission studies quickly out of date, the knowledge gained is a foundational base from which to build information regarding this pathogen in new species. This research capacity is critical. Remind our legislators and lobbyists the next time we see them! We cannot do One Health without a robust animal health research infrastructure.
Until next time,
John