#17,548
Two months ago, in UKHSA: Investigating Two Potential (Asymptomatic) H5N1 Infections In UK Farmers, we saw two probable infections with avian flu reported by the UK. Today, two more have been announced (see below).
UKHSA update on avian influenza
Latest update from the UK Health Security Agency (UKHSA) on the risk to human health from avian influenza (influenza A H5N1).
From:UK Health Security Agency Last updated 14 July 2023 — See all updates
Latest update
The UK Health Security Agency (UKHSA) has published its latest technical briefing on avian influenza.
Since the last update, published at the beginning of June, there have been 2 additional asymptomatic human detections of influenza A (H5N1) picked up through our surveillance programme of individuals with direct exposure to infected birds.
Asymptomatic detection may represent contamination of the respiratory tract or infection. Precautionary contact tracing was undertaken, but there is still no evidence of human-to-human transmission and these findings do not change the assessment of human health risk, which remains at Level 3.
There have now been a total of 4 detections through this programme, which was launched in March and aims to detect possible animal to human infections in people who are exposed to infected birds. As of 10 July 2023, 144 individuals from 8 infected premises have been tested through enhanced surveillance of poultry workers.
Dr Meera Chand, Deputy Director at UKHSA, said:
- Current evidence suggests that the avian influenza viruses we’re seeing circulating in birds around the world do not spread easily to people.
- However, we know already that the virus can spread to people following close contact with infected birds and this is why, through surveillance programmes like this one, we are monitoring people who have been exposed to learn more about these risks.
- These detections can follow contamination of the nose and throat from breathing in material from the environment, or can be due to infection. It can be difficult to distinguish these in people who have no symptoms. Following any detection, we will immediately initiate the appropriate public health response.
While the public announcement contains few details, the UK today also published a more extensive report in Investigation into the risk to human health of avian influenza (influenza A H5N1) in England: technical briefing 5 (excerpts below).
Summary
- Detections of influenza in farmed poultry continue but remain at low levels compared to the last quarter of 2022. Wild bird detections continue to be geographically dispersed across England with a strong association with gull and tern species. The joint Defra and APHA assessment states that there continues to be a high level of influenza transmission in wild birds across the UK. No additional mammals have been received for testing since the last technical briefing.
- In March 2023, asymptomatic surveillance of people exposed to avian influenza commenced. By 10 July 2023, 144 individuals from 8 infected premises have been tested, of which 4 were positive (2.7% positivity). This represents 2 additional detections since the last technical briefing. Since 2021, there have been 5 human influenza A(H5N1) detections in the UK in total, including a detection in December 2021 in a surveillance pilot.
- The 2 new detections were in individuals exposed at 2 different premises to the previously reported detections. Detections are now associated with one backyard flock (2021), and 3 infected premises (2023 surveillance programme).
- Detections in the asymptomatic surveillance study are assessed for immediate public health action based on the timing of positivity related to exposure. The first new detection is difficult to interpret due to lack of information on sample timing and may be consistent with infection or contamination of the respiratory tract. The second new detection is likely to represent contamination. Precautionary contact tracing was undertaken.
- One partial viral sequence from first of the new detections, and one full viral sequence from the second of the new detections is available, but no viral sequences from birds on the linked infected premises are available to date. Both these human detection sequences are influenza A(H5N1) clade 2.3.4.4b and consistent with the UK genotype AIV48, also known as the A/gull/France/22P015977/2022-like genotype.
- Globally, since December 2021, 15 human detections of influenza A(H5N1) have been reported officially. Twelve of these cases are from clade 2.3.4.4b. This includes the 2 new detections in England since the last technical briefing. There is no evidence of human-to-human transmission from these cases.
- International surveillance of mammals varies but continues to show spill-over into mammalian species. Since the last technical briefing, there are reports of detections of influenza A(H5N1) in cats in Poland and of a continued sea lion die-off in South America. Genomes available show changes associated with mammalian adaptation in PB2. There is no evidence confirming sustained mammalian transmission. Detailed investigations and increased numbers of genomic sequences from such outbreaks and nearby avian infections would be informative.
- There is no evidence of human-to-human transmission from any detections and recent findings do not change the assessment of human health risk, which remains at level 3 (limited mammalian transmission, low confidence) as described in the previous technical briefing (see also the qualitative assessment on influenza A(H5N1) infections in non-avian UK wildlife from the multi-agency Human Animal Infections and Risk Surveillance (HAIRS) Group).
As we've seen previously with mild and/or asymptomatic cases, it is possible that some of these cases are only nasal or throat contamination with the virus, and not an actual infection. One of these cases did report mild symptoms (Sore throat, myalgia), although it isn't clear if they were due to the virus.
So far the UK has only reported mild or asymptomatic infections, which is somewhat reassuring. But H5N1 is a multi-faceted virus, with dozens of genotypes co-circulating, each on a different evolutionary trajectory.
Simply put, what emerges in the UK isn't necessarily representative of what is circulating elsewhere in the world.
Stay tuned.
