H5N1/flu (other types)

The fall bird migration season is well underway, and Canada - after going more than 6 months without reporting any outbreaks of H5N1 in poultry - has reported a steep rise in outbreaks since the third week of October.  

In last 10 days of the month, the CFIA reported 11 outbreaks. 

Over the first 8 days of November, the CFIA has added 10 more outbreaks.

While it may not tell us where HPAI H5 will go in the days and weeks ahead, the events of the past 21 days have demonstrated how quickly the status quo with avian flu can change.  

On October 21st, the CDC counted 27 human H5 infections in the United States in 2024. 

Three weeks later that number is officially 46 (a gain of 19), but this doesn't include 4 cases confirmed by states (California & Washington) but not the CDC, a 2nd (strongly suspected) case in Missouri, or any of the 8 cases turned up last week by retrospective serology tests. 

Three weeks ago, both the United States and Canada had gone months without substantial outbreaks in poultry, but between them have since reported > 40 outbreaks. 

At the same time the known number of  American dairy herds infected by H5N1 has increased by 46% (from 324 to 473), across (now) 15 states.

All of that by itself would be concerning, but this doesn't begin to scratch the surface of H5 related events of the past 3 weeks. With that in mind, a mini review of 10 other H5 avian flu related events or revelations from the past 21 days.

• Starting with the oldest, on October 21st the state of Washington announced their First Presumed Human Infections with H5 (n=4), in exposed poultry cullers. We learned that this outbreak was due to a new genotype D1.1, and as of today, they are reporting 14 human cases.

• On October 24th, we got the long awaited Serology Results On Missouri H5 Patient's Contacts, which found no evidence of transmission to HCWs, but did strongly suggest a housemate was infected at the same time as the index case.  The source of these infections has yet to be identified. 

• On October 28th, in Nature: A Human Isolate of Bovine H5N1 is Transmissible and Lethal in Animal Models, we learned that the first Texas H5 isolate could be transmitted through the air between separated ferrets, that it might be capable of binding to and replicating in human respiratory tract cells, and that oseltamivir (Tamiflu) might not be as effective in treating it as Baloxivir. 

• On October 30th, the USDA Reported the 1st Detection of HPAI H5N1 in Swine (Oregon), once again with another new genotype D1.2, which had infected poultry on the same farm.  A  week later (Nov 7th) the USDA Confirmed a 2nd Pig on Oregon Farm Tested Positive.

Late on Saturday we learned that Canada had identified their first locally acquired human infection with HPAI H5 in a teenager from the Fraser Valley region.  The patient was reported to be hospitalized in the B.C. Children's Hospital, and was in intensive care. 

Today the B.C. provincial health officer - Dr. Bonnie Henry - held a lengthy news conference, and fielded questions from reporters, on the condition of this teenager, and their investigation. 

Unlike the 45+ American cases who have reported mild illness, this case is listed in critical condition and is suffering from ARDS (Acute Respiratory Distress Syndrome).  The patient - reportedly a healthy teenager - fell ill on November 2nd, with symptoms of conjunctivitis, fever and cough and was seen at a local emergency room, and sent home.

Over the next few days the patient's condition worsen, and they were admitted to B.C.'s Children's Hospital on Friday night (Nov 8th), and a presumptive test for H5 influenza came back on Saturday.  The patient was given antivirals and admitted to the I.C.U.

B.C. health officials have contacted 35-40 close contacts, and have offered them antivirals and will follow up with them for 10 days.  So far, none have shown signs of illness. 

While the investigation is ongoing, so far they've been unable to determine how this teenager was exposed.  The patient did not live on, or visit, a farm or have contact with poultry, or wild birds.  Nor did any of their known contacts. 

The patient did have contact with dogs, cats, and a reptile, but none have tested positive for influenza.  One of the dogs was reportedly symptomatic, but follow up testing has turned up nothing of value. 

While they intend to keep looking for a plausible source - as we saw with the Missouri case last August - answers may never be found. 

Complete sub-typing, and genetic sequencing will take a few days.  For now, H5N1 is strongly suspected, but earlier today WOAH reported at least one outbreak of HPAI H5N2 in a B.C. poultry farm. 

The entire press conference (about 40 minutes) is worth watching. 

While Dr. Henry continues to call this a rare event, it is obvious she takes this seriously, and she warns people to avoid contact with wild birds or sick animals, and to keep their pets away from possible exposures. 

One of the big concerns that Dr. Henry addressed is H5N1's historical disproportional impact on children, adolescents, and younger adults.  This is a topic we've addressed often, most recently last week in Preprint: Immune History Shapes Human Antibody Responses to H5N1 Influenza viruses.

While many have been reassured by the mild presentation of H5N1 in the United States over the past 6 months, this is a reminder that an H5 infection isn't always benign, and that we need to take this threat seriously.