#17,899
For the second time in just over a week we are learning of a recent H1N1v swine variant infection. Last week the ECDC reported on an H1N1v infection in Spain in an adult male worker at a pig farm, and overnight the WHO has posted a DON report on the latest case from the state of State of Paraná in Brazil.
While most swine variant infections are generally mild, and are seen in people with recent close contact with pigs, that isn't always the case.
Two of her contacts (both of whom tested negative for the virus) did have contact with pigs, however. Her exposure remains unknown.
Most years, we see a few dozen swine variant infections reported around the globe, primarily from the United States, Canada, Brazil, Western Europe, and recently from Taiwan. Given the limited amount of testing and surveillance around the world, these are thought to be significant under-counts.
Last November the UK reported their first laboratory-confirmed swine variant H1N2v infection (see UKHSA Identifies 1st H1N2v (Swine Variant) Infection In the UK), which raised alarm bells and set off an immediate public health investigation.
Three weeks ago the ECDC's journal Eurosurveillance published a Rapid Communications on this event, which describes 1 laboratory confirmed - and two probable - infections that were detected by the UK's epidemiological investigation.
Although swine variant viruses are generally not efficiently transmitted between humans (until, as we saw in the H1N1 pandemic of 2009, they suddenly are) some limited human-to-human transmission does appear to occur.
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 Moderate
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
In 2021 the CDC ranked a Chinese Swine-variant EA H1N1 `G4' as having the highest pandemic potential of any flu virus on their list (see EID Journal: Zoonotic Threat of G4 Genotype Eurasian Avian-Like Swine Influenza A(H1N1) Viruses, China, 2020).
But most of the swine-Influenza A viruses (swIAV) that circulate around the world do so under the radar.
Today's update from the WHO describes a adult male (with underlying medical conditions) who lives alone in the city of Toledo in Paraná, Brazil - with no history of contact with pigs - who was briefly hospitalized with flu-like illness in mid-December, but who has since recovered.
Of note, sequencing shows the virus shares 99% similarity with an H1N1v virus previously detected in a human case from the city of Toledo-Paraná in October 2022, and shared some genetic segments with other swine variant (H1 & H3) viruses detected in the region.
Excerpts from the full report follow:
Influenza A (H1N1) variant virus - Brazil
7 February 2024
Situation at a Glance
On 16 January 2024, Brazil notified the World Health Organization (WHO) of a laboratory-confirmed human infection with swine-origin influenza A(H1N1) variant (v) virus, in the municipality of Toledo, State of Paraná. The patient, who had underlying medical conditions, developed symptoms and was hospitalized on 16 December 2023. He had no history of exposure to pigs and has fully recovered. From the epidemiological investigation, no close contacts were identified. This is the first human infection caused by an influenza A(H1N1)v virus reported in Brazil in 2024, and the ninth case of a human infection with a swine variant virus reported in the state of Paraná, Brazil, since 2015. 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. The likelihood of community-level spread among humans and/or international disease spread through humans is considered low. 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.Description of the Situation
On 16 January 2024, the Brazil National Focal Point (NFP) for International Health Regulations (IHR), notified the World Health Organization of a human infection with a swine-origin influenza A(H1N1)v virus.
The patient is an adult male, with underlying medical conditions, who resides in the municipality of Toledo, in the State of Paraná. The man, who lives alone, had no history of exposure to pigs or to any ill individuals. From the epidemiological investigation, no close contacts were identified.
The patient first developed symptoms on 12 December 2023, including fever, headache, fatigue and cough, and sought medical assistance on 16 December 2023, when he was hospitalized. He did not receive antiviral treatment but fully recovered on 18 December 2023, when he was discharged from the hospital.
A sample was sent on 19 December 2023 to the Central Public Health Laboratory of the State of Paraná for analysis of influenza and SARS-CoV-2. The sample was subtyped as influenza A/H1 virus by real-time polymerase chain reaction (RT-PCR). On 11 January 2024, the sample was sent for confirmation to the National Influenza Center (NIC), National Reference Laboratory for respiratory viruses of FIOCRUZ, Rio de Janeiro, where on 15 January 2024, influenza A (H1N1) variant virus was confirmed.
According to the sequencing results, the virus shares 99% similarity with the A/Paraná/ 20675/2022 (A/H1N1pdm09-like) virus previously detected in a human case from the city of Toledo-Paraná in October 2022. The segments PB2, PB1, PA, NA, and MP corresponded to the virus A/Paraná/10835/2021 (A/H1N1pdm09-like) also reported in the city of Toledo, and the NP and NS segments corresponded to the virus A/Paraná/44706/2022 (A/H3N2v) reported in the city of Santa Helena, also in the state of Paraná. On 1 February 2024, the NIC sent the sample to the US Centers for Disease Control and Prevention (US CDC) Influenza Division – a WHO Collaborating Centre (CC) for Surveillance, Epidemiology, and Control of Influenza – for further characterization.
These laboratory findings might indicate ongoing spread of the virus in the animal population and exposure of the human population in the state of Paraná. Community transmission in humans has not been identified.(SNIP)
WHO Risk Assessment
This is the first human infection with an influenza A(H1N1)v virus reported in Brazil in 2024. The patient had no history of exposure to pigs or any ill individuals. Based on currently available information, this represents a sporadic case 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 never been identified. Current evidence suggests that these viruses have not acquired the ability to sustain 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 infection with influenza viruses that normally circulate in pigs, but they can reduce severity.
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 assessment will be reviewed should further epidemiological or virological information become available.
While we've been understandably focused on avian H5Nx viruses the past few months, swine-origin influenza viruses constitute a plausible pandemic threat, are very much worthy of our attention.
