#18,285
The concern whenever we see spillover of an avian-adapted virus to mammals - and particularly when it involves long chains of infections - is the potential for host adaptations to emerge (as demonstrated by the classic serial passage experiment shown above).
In July of 2023, while we were watching an outbreak of HPAI H5N1 in cats in Poland, we were also seeing a similar outbreak in South Korea, where cats at two different animal shelters tested positive for the virus.
At the time of these two outbreaks, reports of outbreaks in domestic cats were uncommon. We'd only seen a handful of sporadic HPAI H5 feline infections in the United States (see NVDC Report: 2 Domestic Cats Infected With HPAI H5N1), and in Europe (see WOAH: France Reports Cat Infected With Avian H5N1).
Since then, of course, we've seen dozens of additional infections, many involving severe neurological manifestations (see USDA Adds 16 Additional Cats To Mammals with HPAI H5N1 List (n=53)).
Last December, in Emerg. Microbes & Inf.: Characterization of HPAI A (H5N1) Viruses isolated from Cats in South Korea, 2023, a letter from researchers in South Korea classified this virus as a new genotype (South Korea genotype III), and identified a number of mammalian adaptions (most notably D701N in PB2).
Yesterday the CDC's EID Journal published another report on this outbreak, which in addition to the previously reported D701N, also reports finding an isolate with E627K. They write:
We identified amino acid substitutions related to mammal adaptation in both YS/2023 and GA/2023 viruses.
In both viruses, we found mutations S123P, S133A, and T156A (H5 numbering), which enhance binding affinity of the HA protein to α2,6-sialic acid on the host cell surface and contribute to increased mammal receptor tropism (20; J. Yang et al., unpub. data, External Link).Notably, both isolates produced fatal illness in mice and ferrets, with ferrets displaying neurological manifestations. Additionally, infected ferrets demonstrated mammal-to-mammal contact transmission.In addition, in the polymerase basic 2 (PB2) gene segment, we identified mutations encoding D701N in YS/2023 and E627K in GA/2023; both substitutions are mammal-adapting mutations known to increase polymerase activity and virulence in mammals (Table 2) (21–23). However, mutations associated with antiviral drug resistance, such as H274Y in NA and S31N in the matrix protein, were not detected (21,24).
Due to its length and technical nature, I've only posted some excerpts. Follow the link to read the full report. I'll have a postscript after the break.
Research
Pathogenicity of Highly Pathogenic Avian Influenza A(H5N1) Viruses Isolated from Cats in Mice and Ferrets, South Korea, 2023
Il-Hwan Kim1, Jeong-Hyun Nam1, Chi-Kyeong Kim, Yong Jun Choi, Hyeokjin Lee, Bo Min An, Nam-Joo Lee, Hyoseon Jeong, Su-Yeon Lee, Sang-Gu Yeo, Eun-Kyoung Lee, Youn-Jeong Lee, Jee Eun Rhee, Sang Won Lee, Youngmee Jee, and Eun-Jin Kim
Abstract
The prevalence of highly pathogenic avian influenza (HPAI) A(H5N1) viruses has increased in wild birds and poultry worldwide, and concomitant outbreaks in mammals have occurred. During 2023, outbreaks of HPAI H5N1 virus infections were reported in cats in South Korea.
The H5N1 clade 2.3.4.4b viruses isolated from 2 cats harbored mutations in the polymerase basic protein 2 gene encoding single amino acid substitutions E627K or D701N, which are associated with virus adaptation in mammals.
Hence, we analyzed the pathogenicity and transmission of the cat-derived H5N1 viruses in other mammals. Both isolates caused fatal infections in mice and ferrets. We observed contact infections between ferrets, confirming the viruses had high pathogenicity and transmission in mammals. Most HPAI H5N1 virus infections in humans have occurred through direct contact with poultry or a contaminated environment. Therefore, One Health surveillance of mammals, wild birds, and poultry is needed to prevent potential zoonotic threats.
(SNIP)During July 2023, unusual deaths of cats at animal shelters occurred in the Yongsan and Gwanak Districts of Seoul, South Korea, caused by HPAI H5N1 viruses (15,16); viruses isolated from cats were obtained from each animal shelter.(SNIP)
Discussion
HPAI H5N1 outbreaks continue worldwide, posing considerable threats to humans and animals. HPAI H5N1 clade 2.3.4.4b viruses have been detected in wild birds and domestic poultry in South Korea (14). In addition, infection outbreaks in cats caused by HPAI H5N1 clade 2.3.4.4b viruses occurred in 2 animal shelters in South Korea during July 2023.
Both H5N1 viruses isolated from cats had genetic constellations similar to that of the predominant influenza virus circulating in wild birds and poultry in South Korea during 2022–2023. An investigation of the source of infection found that the cats were infected by ingesting raw duck feed contaminated with the prevalent circulating virus. The raw feed–derived viruses were genetically identical to the poultry virus; however, we found 2 mutations related to mammal adaptation (E627K and D701N) in PB2 of the isolates from cats.
Therefore, it is critical to prevent HPAI virus infections in mammals because avian-derived influenza viruses have been found to mutate after infecting mammals. We performed genetic analysis and animal model experiments to assess the potential mammal-to-mammal transmission and pathogenicity of HPAI H5N1 clade 2.3.4.4b viruses isolated from cat outbreaks in other mammals.
(SNIP)
The H5N1 PB2 substitution E627K was observed in cats in Poland, and the PB2 D701N substitution was observed in sea lions in Argentina (10,26). According to sequence data registered in GISAID, >50% of human HPAI virus isolates exhibit E627K or D701N substitutions in PB2. Those mammal-adaptive mutations are critical factors that increase replication and virulence of H5N1 viruses in cell culture and animal experiments (27–30).
Ferrets are useful animal models to study influenza virus transmission and are frequently used for influenza pathogenicity evaluation because they exhibit influenza-like symptoms after infection, including fever, malaise, anorexia, sneezing, and nasal discharge (31–33).
The H5N1 viruses isolated from cats exhibited high virus replication levels and systemic infection along with severe symptoms and high mortality rates in mice and ferrets; in addition, contact transmission among ferrets was confirmed. Therefore, it was inferred that YS/2023 and GA/2023 are highly pathogenic in mammals and are capable of mammal-to-mammal transmission.
It was also presumed that the amino acid substitutions E627K and D701N in PB2, previously associated with increased replication and virulence in mammals (29), might be responsible for the pathogenicity and transmission of H5N1 viruses in mammals. YS/2023 and the GA/2023 are genetically similar, except for the PB2 substitutions D701N in YS/2023 and E627K in GA/2023.
The GA/2023 virus with the E627K substitution showed stronger contact transmission in ferrets than the YS/2023 virus with the 701N substitution. It has been reported that the E627K substitution in PB2 of H5N1 viruses affects airborne transmission in ferrets (34). Therefore, the E627K mutation might have a greater effect on transmission of the cat-derived viruses than D701N, although this possibility requires further investigation.
(SNIP)
In conclusion, the increased pathogenicity and transmission among mammals observed in ferrets exposed to cat-derived HPAI H5N1 viruses indicate a need to conduct surveillance for H5N1 viruses in wild birds and mammals to prepare for potential zoonotic threats. A One Health surveillance approach is crucial, and sharing and integrating information, such as sequencing data, reference viruses, and experimental data, during outbreaks in birds and mammals are essential to prevent human HPAI H5N1 virus infections.
Dr. Kim is a scientific deputy director of the Division of Emerging Infectious Diseases at the Korea Disease Control and Prevention Agency (KDCA). His main research interests are infectious disease and microbiology.
For more on spillovers of HPAI into peridomestic mammals, you may wish to revisit these recent posts:
Virology: Susceptibilities & Viral Shedding of Peridomestic Wildlife Infected with Clade 2.3.4.4b HPAI Virus (H5N1)
Pathogens: Susceptibility of Synanthropic Rodents to H5N1 Subtype HPAI Viruses
Emer. Microbe & Inf.: HPAI Virus H5N1 clade 2.3.4.4b in Wild Rats in Egypt during 2023
CAHSS/Animal Health Canada: HPAI H5N1 in Cats
Preprint: Recent Bovine HPAI H5N1 Isolate is Highly Virulent for Mice, Rapidly Causing Acute Pulmonary and Neurologic Disease
