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While human infection with HPAI H5N1 is still believed to be rare, it is plausible that some (likely small) number of cases have gone unrecognized here in the United States - and in other countries - which has led to calls for clinicians to adopt a heightened index of suspicion for avian flu (see ECDC Call For Increased Vigilance Against Avian Flu).
As we've discussed previously, tomorrow (July 16th) the CDC will hold a COCA call for clinicians and healthcare centers on HPAI H5N1.
Even though Canada has yet to report any cases, today the CMAJ (Canadian Medical Association Journal) published a brief review for clinicians on identifying and treating potential H5N1 infections in humans.
First the review, after which I'll have a brief postscript.Highly pathogenic avian influenza A (H5N1) virus
Robert Kozak, Isaac I. Bogoch and Samira Mubareka
CMAJ July 15, 2024 196 (25) E878; DOI: https://doi.org/10.1503/cmaj.240697
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Highly pathogenic avian influenza (HPAI) H5N1 virus is spread globally by wild birds
The circulating H5N1 clade (2.3.4.4b) has caused outbreaks on poultry farms and among backyard flocks, and die-offs among wild birds. Infections in mammals, including cattle and humans, triggered by viral spillover from birds highlights the potential for a pandemic, but the mechanisms of transmission are not fully known.1,2 Evidence exists of viral reassortment and mammalian adaptation,3 resulting in increased risk of transmission and disease among mammals.
As of June 12, 2024, no reported human cases of H5N1 have been acquired in Canada
Nearly 900 human cases of H5N1 have been reported globally since 2003, with a case fatality rate of 52%.4 The clinical presentation may vary from mild to severe influenza. Dairy workers in the United States who recently became infected presented with hemorrhagic conjunctivitis.2
Clinicians should ask about animal exposures in people presenting with influenza-like illness, conjunctivitis or, less commonly, meningoencephalitis
People with substantial exposure to livestock or wildlife may be at risk for infection. Currently, the risk to the general population is low, with no evidence of sustained person-to-person transmission.3
Conventional laboratory-based testing may identify H5N1 HPAI as influenza A virus
Confirmatory testing is conducted at a provincial or national reference laboratory for suspected infections, which underscores the need to identify patients with exposure histories as soon as possible.4 Nasopharyngeal and conjunctival swabs, if the patient has eye symptoms, should be collected, and public health should be informed of cases under investigation.
No vaccine currently exists for human use in Canada
Oseltamivir is the recommended antiviral for treatment and prophylaxis of HPAI infection. Oseltamivir should be administered as soon as possible to a person with a suspected infection, or after close contact with a confirmed case of HPAI.5
Footnotes
Competing interests: Robert Kozak reports receiving government or academic grants from the Canadian Institutes of Health Research (CIHR) and the University of Toronto. Dr. Kozak also reports serving as a member of the executive board of the Canadian College of Microbiology from 2019 to the present, and as scientific planning chair of the Canadian Association of Clinical Microbiology and Infectious Diseases. Samira Mubareka reports receiving support from the CIHR — Public Health Agency of Canada Applied Public Health Chair in Pandemic and Health Emergency Prevention, Preparedness, Response and Recovery. Isaac Bogoch reports receiving grants from CIHR for HIV prevention and screening for neglected tropical diseases, and consulting fees from the Weapons Threat Reduction Program at Global Affairs Canada.
This article has been peer reviewed.Received June 12, 2024.
This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY-NC-ND 4.0) licence, which permits use, distribution and reproduction in any medium, provided that the original publication is properly cited, the use is noncommercial (i.e., research or educational use), and no modifications or adaptations are made. See: https://creativecommons.org/licenses/by-nc-nd/4.0/
While only 4 cattle-linked human H5N1 infections have been reported in the United States (and over the weekend 5 new poultry-linked cases), it is widely believed - based on anecdotal reports of sick dairy workers that were never tested - that some cases have likely been missed over the past few months.
Three weeks ago the ECDC published Enhanced Influenza Surveillance to Detect Avian Influenza Virus Infections in the EU/EEA During the Inter-Seasonal Period which cautioned:
Sentinel surveillance systems are important for the monitoring of respiratory viruses in the EU/EEA, but these systems are not designed and are not sufficiently sensitive to identify a newly emerging virus such as avian influenza in the general population early enough for the purpose of implementing control mOseltamivir is the recommended antiviral for treatment and prophylaxis of HPAI infection. Oseltamivir should be administered as soon as possible to a person with a suspected infection, or after close contact with a confirmed case of HPAI.5easures in a timely way.
All of which makes encouraging a heightened awareness on the part of clinicians and healthcare facilities both prudent and timely.
