CREDIT CDC
#17,498
Although avian H5 currently tops our list of zoonotic influenzas of greatest concern, swine-variant viruses (H1N1v, H1N2v & H3N2v) remain a low-key perennial threat - both here in North America - and around the world.
A few recent blogs include:
EID Journal: Long-term Epidemiology and Evolution of Swine Influenza Viruses, Vietnam
Taiwan CDC Reports 3rd H1N2v Case
FluView Week 43: Flu Still Climbing & A Novel (H3N2v) Infection In New Mexico
Seven years ago, in EID Journal: Influenza A Viruses of Human Origin in Swine, Brazil, we looked at the rising threat of swine variant viruses in South America.
Since then we've looked at several swine variant cases reported from Brazil, including 2016's EID Journal: Characterization of a Novel Human Influenza A(H1N2) Virus Variant, Brazil and WHO: Overview & Risk Assessment On Novel H1N2v Virus Detected In Paraná, Brazil (Dec. 2020).
Late yesterday the WHO published a report and risk assessment on a recent fatal infection in Paraná, Brazil of a 42 y.o. woman (with underlying conditions) with a swine variant H1N1v virus. The woman lived near a swine farm, but had no direct contact with pigs.
While severe and/or fatal infections with swine variant viruses are rare, we have seen them reported previously (see J. Virology: Analysis Of A Swine Variant H1N1 Virus Associated With A Fatal Outcome). And while most people contract these viruses from direct contact with pigs, limited human-to-human spread has been reported.
Last fall, in EID Journal: Severe Human Case of Zoonotic Infection with Swine-Origin Influenza A Virus A/H1pdm09N1av-like, Denmark, 2021, we looked at another case in a woman who lived near - but had no direct contact - with a swine farm.
For now the WHO considers this to be a sporadic case, and the risk of further spread is considered low. Some excerpts from the WHO risk analysis follows, after which I'll have a brief postscript.
Influenza A(H1N1) variant virus - Brazil
16 June 2023
Situation at a glance
On 7 June 2023, Brazil notified the World Health Organization (WHO) of a fatal laboratory-confirmed human case of infection with a swine-origin influenza A(H1N1) variant (v) virus in the inner state of Paraná.
Sporadic human cases of influenza A(H1N1)v have been reported previously, including from Brazil. According to the International Health Regulations (IHR) 2005, a human infection caused by a novel influenza A virus subtype is an event that has the potential for high public health impact and must be notified to the WHO.
Based on the information currently available, WHO considers this a sporadic case, and there is no evidence of person-to-person transmission of this event. The likelihood of community-level spread among humans and/or international disease spread through humans is low.
Description of the case
On 7 June 2023, the Brazil IHR National Focal Point (NFP) notified WHO of a fatal human infection caused by a swine-origin influenza A(H1N1)v virus detected by the National Influenza Centre (NIC), Oswaldo Cruz Foundation, Rio de Janeiro.
The patient was a 42-year-old woman with underlying medical conditions who lived near a swine farm. She developed fever, headache, sore throat, and abdominal pain on 1 May 2023 and was hospitalized on 3 May with a severe acute respiratory infection. On 4 May, the patient was admitted to the Intensive Care Unit (ICU) and she passed away on 5 May.
Ongoing investigations reported that the patient did not have any direct contact with pigs, however, two of her close contacts worked at the swine farm. The two contacts did not develop respiratory disease and tested negative for influenza. To date, no human-to-human transmission associated with this case has been identified.
During hospitalization, a nasopharyngeal swab sample was collected from the patient for influenza and SARS-CoV-2 testing, as part of regular respiratory virus surveillance activities. Real-time Polymerase Chain Reaction (RT-PCR) was conducted at the State of Paraná Central Public Health Laboratory, where the sample was subtyped as an influenza A/H1 virus. The sample also tested positive for a swine influenza A virus marker by RT-PCR.
The specimen was forwarded to the National Influenza Centre Oswaldo Cruz Foundation, in Rio de Janeiro, where further complementary analyses and genomic sequencing were performed. Samples received at the NIC on 25 May were confirmed to be an influenza A(H1N1)v virus by sequence analysis on 30 May. The recovered genome has a high identity (99%) with the haemagglutinin (HA) of other Influenza A(H1N1)v viruses previously detected in the municipality of Toledo state of Paraná in 2022. In addition, it has 96% identity with the HA of viruses collected from pigs in Brazil in 2015.
On 8 June, after the Brazilian Ministry of Health (MoH) notified WHO under the IHR, the NIC started the process to send the patient's samples to the WHO Collaborating Centre at the United States Centers for Disease Control and Prevention (US CDC) for further characterization.
Epidemiology of the disease
Influenza A(H1) viruses are enzootic in swine populations in most regions of the world. When an influenza virus that normally circulates in swine is detected in a person, it is called a “variant influenza virus”. H1N1, H1N2 and H3N2 are major subtypes of swine influenza A viruses in pigs and occasionally infect humans, usually after direct or indirect exposure to pigs or contaminated environments.
Human infections with variant viruses tend to result in mild clinical illness, although some cases have been hospitalized with more severe disease and some have been fatal.
To date, sporadic human infections caused by influenza A(H1N1)v and A(H1N2)v viruses have been reported in Brazil, and there has been no evidence of sustained human-to-human transmission.
This is the first human infection caused by an influenza A(H1N1)v virus reported in 2023 in Brazil, and the third human infection reported in the state of Parana (the first was detected in 2021 and the second in 2022).
(SNIP)
WHO risk assessment
This is a sporadic case based on currently available information and further spread has not been detected.
Limited, non-sustained human-to-human transmission of variant influenza viruses has been described, although ongoing community transmission has not been identified. Current evidence suggests that these viruses have not acquired the ability of sustained transmission among humans.
There is no vaccine for Influenza A(H1N1)v infection currently licensed for use in humans. Seasonal influenza vaccines against human influenza viruses are generally not expected to protect people from influenza viruses that normally circulate in pigs, but they can reduce the likelihood of getting sick with both human and variant influenza viruses.
WHO assesses the risk of international disease spread through humans and/or community-level spread among humans posed by this event as low. The risk level will be amended if warranted by the investigations currently being conducted by national authorities.
WHO advice
Surveillance:
- This case does not change the current WHO recommendations on public health measures and surveillance of seasonal influenza.
- Due to the constantly evolving nature of influenza viruses, WHO continues to stress the importance of global surveillance to detect virological, epidemiological and clinical changes associated with circulating influenza viruses that may affect human (or animal) health and timely virus sharing for risk assessment.
- Continued vigilance is needed within affected and neighboring areas to detect infections in animals and humans. Collaboration between the animal and human health sectors is essential. As the extent of influenza viruses circulating in animals is unclear, epidemiologic and virologic surveillance and the follow-up of suspected human cases should continue systematically. Guidance on the investigation of non-seasonal influenza and other emerging acute respiratory diseases is available on the WHO website.
- Vigilance for the emergence of novel influenza viruses of pandemic potential should be maintained. WHO has developed practical guidance for integrated surveillance in the context of the cocirculation of SARS-CoV-2 and influenza viruses.
- It is critical that influenza viruses from animals or from people are fully characterized in appropriate animal or human health influenza reference laboratories. Under WHO’s Pandemic Influenza Preparedness (PIP) Framework, Member States are expected to share influenza viruses with pandemic potential on a regular and timely basis with the Global Influenza Surveillance and Response System (GISRS).
(Continue . . . )Although most swine-variant infections are mild or moderate, the CDC's IRAT (Influenza Risk Assessment Tool) lists 3 North American swine viruses as having at least some pandemic potential (2 added in 2019).
H1N2 variant [A/California/62/2018] Jul 2019 5.8 5.7 ModerateChina holds information close to the vest, but the CDC currently ranks a Chinese Swine-variant EA H1N1 `G4' as having the highest pandemic potential of any flu virus on their list. The CDC's Assessment of the Risk from swine-variant viruses reads:
H3N2 variant [A/Ohio/13/2017] Jul 2019 6.6 5.8 Moderate
H3N2 variant [A/Indiana/08/2011] Dec 2012 6.0 4.5 Moderate
Sporadic infections and even localized outbreaks among people with variant influenza viruses may occur. All influenza viruses have the capacity to change and it’s possible that variant viruses may change such that they infect people easily and spread easily from person-to-person. The Centers for Disease Control and Prevention (CDC) continues to monitor closely for variant influenza virus infections and will report cases of H3N2v and other variant influenza viruses weekly in FluView and on the case count tables on this website
Last summer, after outbreaks (related to agricultural fairs) and sporadic cases in 3 states (WV, OH, OR) the CDC released CDC HAN #00473: Variant Influenza Virus Infections: Recommendations for Identification, Treatment, and Prevention for Summer and Fall 2022.
With the summer agricultural fair season about to kick off again, the CDC advises those who are at higher risk of serious flu complications (including children under 5, adults over 65, pregnant women, and those with certain chronic medical conditions), to avoid pigs and the swine barn altogether.
Given the concurrent threat from avian H5N1, next week the CDC will hold a Webinar (Jun 20th): What Providers Need to Know about Zoonotic Influenza that will address both avian and swine variant infections.
