Post by Nadica (She/Her) on Jul 28, 2024 1:47:40 GMT
Influenza A(H5N1) 2.3.4.4b B3.13: US cattle outbreak update - Published July 17, 2024
Full PDF available at link
Overview
The UK Health Security Agency (UKHSA) is working with the Animal and Plant Health Agency
(APHA), the Department for Environment, Food and Rural Affairs (Defra), Food Standards
Agency (FSA), and the public health agencies of the 4 nations to monitor the risk to human
health from emerging influenza viruses.
A previous assessment of this situation was published in May 2024.
Current evidence review
1. Animal outbreak
There is ongoing transmission of influenza A(H5N1) in the US, primarily through dairy cattle but
with multispecies involvement including poultry, wild birds, other mammals (cats, rodents, wild
mammals) and humans (1, 2). There is high uncertainty regarding the trajectory of the outbreak
and there is no apparent reduction in transmission in response to the biosecurity measures that
have been introduced to date. There is ongoing debate about whether the current outbreak
should be described as sustained transmission given that transmission is likely to be facilitated
by animal farming activities (3). However, given that this is a permanent context, the majority of
the group considered this outbreak as sustained transmission with the associated risks.
The available genomic data show a single expanding clade, genotype B3.13, consistent with
ongoing transmission through dairy cattle and spillover into other mammals and birds.
2. Human cases
There is evidence of zoonotic transmission (human cases acquired from animals). There is
likely to be under-ascertainment of mild zoonotic cases (4). There have been ten human cases
detected associated with the current US outbreak, 4 in dairy workers at separate farms and 6 in
poultry workers exposed during a single depopulation event at which a large number of workers
were symptomatic (1). Environmental factors may have contributed to increased viral exposure
at this site (5). Human case genomes where available are within the cattle outbreak clade
although the first human case in Texas is distinct (3). The sequence from this case
(EPI_ISL_19027114) does contain the HA L131Q and T211I mutations present in all B3.13
sequences, but not contain the PB2 M631L, PA K497R or the NA N71S mutations observed in
the main cattle outbreak clade. It contains PB2 E627K and D441N mutations, K142E in PA, and
S7L and Q40R in NS1 that are not observed in other B3.13 sequences. The ongoing cattle outbreak in dairy cattle with spillover to poultry farms means that there could
be large numbers of human exposures and increased opportunity for zoonotic cases. However,
there are insufficient data to assess whether the rate of zoonotic infection is unusually high.
Full PDF available at link
Overview
The UK Health Security Agency (UKHSA) is working with the Animal and Plant Health Agency
(APHA), the Department for Environment, Food and Rural Affairs (Defra), Food Standards
Agency (FSA), and the public health agencies of the 4 nations to monitor the risk to human
health from emerging influenza viruses.
A previous assessment of this situation was published in May 2024.
Current evidence review
1. Animal outbreak
There is ongoing transmission of influenza A(H5N1) in the US, primarily through dairy cattle but
with multispecies involvement including poultry, wild birds, other mammals (cats, rodents, wild
mammals) and humans (1, 2). There is high uncertainty regarding the trajectory of the outbreak
and there is no apparent reduction in transmission in response to the biosecurity measures that
have been introduced to date. There is ongoing debate about whether the current outbreak
should be described as sustained transmission given that transmission is likely to be facilitated
by animal farming activities (3). However, given that this is a permanent context, the majority of
the group considered this outbreak as sustained transmission with the associated risks.
The available genomic data show a single expanding clade, genotype B3.13, consistent with
ongoing transmission through dairy cattle and spillover into other mammals and birds.
2. Human cases
There is evidence of zoonotic transmission (human cases acquired from animals). There is
likely to be under-ascertainment of mild zoonotic cases (4). There have been ten human cases
detected associated with the current US outbreak, 4 in dairy workers at separate farms and 6 in
poultry workers exposed during a single depopulation event at which a large number of workers
were symptomatic (1). Environmental factors may have contributed to increased viral exposure
at this site (5). Human case genomes where available are within the cattle outbreak clade
although the first human case in Texas is distinct (3). The sequence from this case
(EPI_ISL_19027114) does contain the HA L131Q and T211I mutations present in all B3.13
sequences, but not contain the PB2 M631L, PA K497R or the NA N71S mutations observed in
the main cattle outbreak clade. It contains PB2 E627K and D441N mutations, K142E in PA, and
S7L and Q40R in NS1 that are not observed in other B3.13 sequences. The ongoing cattle outbreak in dairy cattle with spillover to poultry farms means that there could
be large numbers of human exposures and increased opportunity for zoonotic cases. However,
there are insufficient data to assess whether the rate of zoonotic infection is unusually high.