#18,437
Last week Hawaii - which until now had never reported HPAI H5 - discovered H5 in their wastewater system, and a few days later, detected an outbreak in captive wild birds on the island of Oahu.
Over the past week the Hawaii state Department of Health has conducted an epidemiological investigation, including contact tracing and testing those who had high risk exposure to these birds.
Encouragingly, thus far they have found no evidence of human infection, although their investigation continues. Overnight (EST) they released the following statement, which discusses both their investigation and the genotype (A3) of the virus.
First their statement, then I'll return with some background on how different genotypes emerge, and how that can affect their behavior.
DOH INVESTIGATING HUMAN CONTACTS TO INFECTED H5N1 FLOCKS-NO HUMANS IN HAWAIʻI TESTED POSITIVE FOR AVIAN INFLUENZA
Posted on Nov 21, 2024 in NewsroomHONOLULU — The Hawaiʻi State Department of Health (DOH) is investigating human contacts to the flock infected with H5N1. No humans in Hawaiʻi have tested positive for avian influenza at this time.
To date, 54 individuals have been investigated for potential exposure. Of those, 34 were offered testing because of unprotected exposure (meaning without use of adequate personal protective equipment), to the infected birds within the past 10 days, or because they had developed respiratory symptoms within 10 days of contact with the birds.
Twenty-nine consented to testing, including 13 who had at least one symptom of respiratory infection and 16 who had no symptoms. All the individuals who would be considered to have very high-risk exposure to the infected birds, including prolonged direct contact with visibly sick, dying, or dead birds, consented to testing.
Testing involved collection of swabs from the nasopharynx, nose, throat, and/or conjunctiva that were tested by polymerase chain reaction (PCR) at the State Laboratories Division. Results for all 29 of those tested, including those with very high-risk exposure and/or symptoms, have come back negative for avian influenza. Two symptomatic individuals tested positive for common cold viruses. Investigation into potential exposures to individuals who interacted with ducks or geese at the Mililani Pet Fair on Nov. 2 is ongoing. At least four individuals whose only exposure was at the Mililani Pet Fair have been tested for avian influenza with all negative results. Additional investigation results will be shared as they become available.
DOH has worked with the U.S. Department of Defense to identify individuals with potential exposure. They have been tested and there are no confirmed cases.
The strain of avian influenza identified in the infected flock has been confirmed by the National Veterinary Services Laboratory as clade 2.3.4.4b, genotype A3. The A3 genotype was first identified in wild birds in Alaska in 2022. Identification of this genotype supports a theory of introduction of H5N1 to Hawaiʻi by migratory wild birds. This is a different genotype of the virus than the one that has infected dairy cows on the U.S. mainland and is also different from the genotype reported in a critically ill adolescent in British Columbia. It is unknown whether genotype A3 is likely to infect humans or other mammals.
While initial human testing results are reassuring, DOH urges the public to continue to exercise caution. Avoid close contact with wild birds, and if you encounter birds that appear sick or have died, don’t approach them. Report sick or dead birds, especially if multiple or unusual, to the Department of Agriculture (808-483-7106 during Monday to Friday from 7:45 a.m. to 4:30 p.m. or 808-837-8092 during non-business hours and holidays).
Hawaiʻi residents who recently visited or worked on a farm in another state with known or suspected H5N1 animal infections should contact the Hawaiʻi Department of Health Disease Reporting Line 808-586-4586 for a telephone risk assessment.
As we've discussed often, H5N1 is not a single viral threat, but describes a large and growing array of similar viruses all of which carry an H5 HA gene and an N1 NA gene as their surface proteins. There are other subtypes (with a different NA gene) - like H5N5 and H5N6 within the constellation of HPAI H5 viruses (see UK: HPAI H5N5 Rising) - along with numerous clades.
The H5N1 virus challenging much of the world today is clade 2.3.4.4b, but in Cambodia we've seen outbreaks from clade 2.3.2.1c, along with sporadic cases from India and Bangladesh of clade 2.3.2.1a.
As a segmented virus with 8 largely interchangeable parts, the flu virus is like a viral LEGO (TM) set which allows for the creation of new subtypes - and within each subtype - variants called genotypes.
Last fall researchers from several U.S. labs published a `snapshot' of H5N1's diversity in the United States in the months following its arrival in December of 2021. The found 3 different introductions of the virus, writing:
Unreassorted Eurasian genotypes A1 and A2 entered the Northeast Atlantic states, whereas a genetically distinct A3 genotype was detected in Alaska.
They further found that the virus rapidly reassorted with local wild bird avian influenza viruses generating six major (and numerous minor) genotypes.
Credit: Molecular detection and characterization of highly pathogenic H5N1 clade 2.3.4.4b avian influenza viruses among hunter-harvested wild birds provides evidence for three independent introductions into Alaska by Andrew M. Ramey a 1, Laura C. Scott a 1, Christina A. Ahlstrom a 1, Evan J. Buck a, Alison R. Williams b, Mia Kim Torchetti c, David E. Stallknecht d, Rebecca L. Poulson d
This reassortment process continues, and while more than 100 genotypes have been detected in North America over the past 3 years, in 2024 three new reassortments of note have emerged:
- B3.13 aka the `bovine' strain affecting dairy cattle in at least 15 states and infecting dozens of humans
- D1.1 a wild bird/poultry strain which has spilled over into > a dozen people in Washington State and a teenager in British Columbia
- D1.2 a wild bird/poultry strain which recently detected in poultry and 2 pigs in Oregon
In the 3 years prior to the emergence of these new genotypes, the United States only reported 1 H5N1 infection in a poultry culler in 2022. Since March, we've seen well over 50 human confirmed infections, and it is likely many others have gone undetected.
While we might conclude that the older A3 genotype is less likely to infect humans based on past performance, we really don't know what it is that has changed in 2024 to increase spillovers, and whether those changes could impact older genotypes.
Earlier this week we looked at the detection of the NA-S247N mutation in 3 poultry workers in Washington State - and while technically still genotype D1.1 - it is a significant variant. It is not unusual to see dozens of mutations (most of which are benign) in a single isolate.
While we can hope there is some `species barrier' (see Are Influenza Pandemic Viruses Members Of An Exclusive Club?) that will prevent H5 from ever becoming a pandemic strain, the virus has both time, and a growing array of genetic material with which to tinker.
But as we've seen so often, hope isn't much of a basis for a plan.
