As we approach the mid-point of the year, the Centers for Disease Control and Prevention (CDC) is updating public health professionals and clinicians about the latest status of the Highly Pathogenic Avian Influenza and its recommendations for clinicians. As part of its most recent Clinician Outreach and Communication Activity webinar, two of the CDC’s leading experts provided background on novel influenza A viruses, information on recent cases and surveillance efforts and clinical recommendations.
Influenza A is one of four types of influenza virus. And, within influenza A viruses are 18 subtypes classified based on two primary surface proteins: Hemagglutinin (H) and Neuraminidase (N). Although they can be found in a variety of animal species, from aquatic mammals to domesticated pets, waterfowl are considered the natural reservoir for influenza A viruses. Researchers have identified specific receptors found in the human upper and lower respiratory tract that enable influenza A virus binding. Pigs, wild birds and poultry share some of these key linkages.
Both the U.S. government and World Health Organization (WHO) have designated novel influenza A infections reportable to their respective organizations. CDC also supports the WHO’s Global Influenza Surveillance and Response System (GISRS).
Influenza viruses seem omnipresent with numerous distinctions delineated by scientists as subtypes and even “clades” as they continuously evolve. Even researchers describe the long and known history of influenza viruses as “complex” but top of mind at this point are H5N1 and Swine influenza A viruses that have infected humans, also known as variant influenza A viruses.
Charles (Todd) Davis, PhD, MSPH, Deputy Branch Chief for Science Influenza Division, National Center for Immunization and Respiratory Diseases at the CDC explains that in 2021 there was an uptick in H5N1 cases, specifically in North and South America, and in early 2022, outbreaks were observed in poultry farms, both commercial and domestic. He also noted that the virus has been detected in a broad range of wildlife species including domestic and marine mammals. Despite this, only one individual has tested positive thus far in the U.S. and there is ongoing monitoring and surveillance of those most exposed to H5N1 infected animals.
Tim Uyeki, MD, MPH, MPP, Chief Medical Officer, Influenza Division, National Center for Immunization and Respiratory Diseases for CDC, expanded on the current H5N1 situation, stating there have been 13 human cases globally thus far in 2022 including six cases of severe illness with two resulting in death. He also described the trends they are seeing with regards to prevalence among wildlife but pointed out that at this time there have been no reported cases of mammal-to-human transmission of avian influenza A viruses. Of note, Uyeki emphasized that there are multiple different subtypes of both Low and Highly Pathogenic Avian Influenza A virus that have infected humans and that there has been a broad range of clinical severity.
Uyeki also discussed Swine influenza A viruses that have caused sporadic human infections: H1N1v, H1N2v and H3N2v. Since 2010, there have been 439 such infections, with most (more than 300) occurring during an outbreak during 2012. Most of these were attributed to exposure to infected swine at an agricultural fair, though there was some limited, follow-on human-to-human transmission.
Both Davis and Uyeki provided comprehensive details about the specific diagnostic tests, vaccine development and other resources available for practitioners as well as prevention and treatment recommendations. Uyeki emphasized that at this time, there are no commercially available assays that can confirm or identify avian or influenza A virus. If a patient tests positive for influenza A and novel influenza A is suspected, then subtyping is needed and specimens should be sent to the CDC for identification.
What you need to know:
- Currently, studies indicate low risk for Influenza A (H5) virus transmission to the public but vigilant monitoring of exposed individuals is paramount as the virus is evolving. Kniss 2023)
- Expect sporadic novel influenza A virus infections (avian and swine-origin) in humans
- All novel influenza A viruses are of public health concern (not just Highly Pathogenic Avian Influenza A(H5N1))
- Risk Factors for Swine Influenza A Virus Infection
- Direct or indirect swine contact 4 days of illness onset
- Agricultural fair attendance 4 days of illness onset
- Risk Factors for Avian Influenza A Virus Infection
- Exposure to infected poultry
- Exposure to infected wild birds (rare)
The full webinar as well the presentation slides and secondary references can be found at: https://emergency.cdc.gov/coca/calls/2023/callinfo_062023.asp
CDC Resources
Human infections with avian influenza A viruses
Case definitions: https://www.cdc.gov/flu/avianflu/case-definitions.html
Monitoring & post-exposure antiviral prophylaxis: https://www.cdc.gov/flu/avianflu/guidance-exposed-persons.htm
Follow-up of close contacts: https://www.cdc.gov/flu/avianflu/novel-av-chemoprophylaxis-guidance.htm
Summary for clinicians: https://www.cdc.gov/flu/avianflu/clinicians-evaluating-patients.htm
Specimen collection & testing: https://www.cdc.gov/flu/avianflu/severe-potential.htm
Infection prevention and control: https://www.cdc.gov/flu/avianflu/novel-flu-infection-control.htm
Antiviral guidance: https://www.cdc.gov/flu/avianflu/novel-av-treatment-guidance.htm
Current situation: https://www.cdc.gov/flu/avianflu/avian-flu-summary.htm
CDC H5N1 Technical Report: https://www.cdc.gov/flu/avianflu/spotlights/2022-2023/h5n1-technical-report.htm
Human infections with variant influenza A viruses
Background and reporting: https://www.cdc.gov/flu/swineflu/variant.htm
Clinical guidance: https://www.cdc.gov/flu/swineflu/interim-guidance-variant-flu.htm
Figure on transmission: https://www.cdc.gov/flu/pdf/swineflu/transmission-between-pigs-people.pdf
General information: https://www.cdc.gov/flu/swineflu/index.htm
Nicole Cloutier is a Research Associate for the SPECTRE Program.