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| Credit CDC |
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In February of 2018 China Reported the first human infection with A novel H7N4 virus, which resulted in a 3-week hospitalization for a 68 year old woman in Jiangsu Province for severe pneumonia.
Eight days later, in WHO: Genetic Characteristics Of Avian H7N4, we learned this AI virus was a purely avian LPAI H7 strain - distinct from A(H7N9) - although it carried the PB2 637K marker associated with mammalian adaptation.Since then, no new human infections have been reported, but in March of this year it was announced by the OIE that Multiple Outbreaks Of LPAI H7N4 In Cambodian Poultry occurred roughly two months after the China outbreak.
Two outbreaks of genetically similar novel viruses, roughly 2,700 km apart (see map below), reveal just how quickly a new avian lineage can take hold and spread, and remind us that the recent lull in China's avian flu activity may not hold forever.
Today we have a research letter, published in the EID Journal, that clarifies some details on the Chinese case, and establishes that the Cambodian virus detections are similar to the Chinese virus.
I've only posted the abstract, and some excerpts from the report, so follow the link to read it in its entirety.
Volume 25, Number 10—October 2019
Research Letter
Dhanasekaran Vijaykrishna, Yi-Mo Deng, Miguel L. Grau, Matthew Kay, Annika Suttie, Paul F. Horwood, Wantanee Kalpravidh, Filip Claes, Kristina Osbjer, Phillipe Dussart, Ian G. Barr, and Erik A. Karlsson
Abstract
Active surveillance in high-risk sites in Cambodia has identified multiple low-pathogenicity influenza A(H7) viruses, mainly in ducks. None fall within the A/Anhui/1/2013(H7N9) lineage; however, some A(H7) viruses from 2018 show temporal and phylogenetic similarity to the H7N4 virus that caused a nonfatal infection in Jiangsu Province, China, in December 2017.
Avian influenza virus (AIV) subtype A(H7) is of concern because it has been a leading cause of zoonotic infections over the past 2 decades (1). The A/Anhui/1/2013-lineage A(H7N9) viruses, a leading cause of zoonotic infections in Asia since 2013, have not been detected in the Greater Mekong Subregion, but independent H7 lineages, including H7N3, H7N7, and H7Nx, have been detected occasionally in Cambodia since 2009 (2–4).
H7N3 virus was detected from a duck mortality event in Kampong Thom during January 2017 (2), and H7N7 virus was detected in a live-bird market (LBM) in Takeo in September 2017 (4). Furthermore, highly pathogenic avian influenza (HPAI) A(H5N1) and low-pathogenicity avian influenza (LPAI) A(H9N2) are endemic in Cambodia (5); 59 poultry outbreaks of AIV and 56 human HPAI A(H5N1) cases have occurred since 2006.
Although the exact ecologic links are unknown, serologic studies suggest that AIVs of multiple subtypes are frequently introduced into poultry in Cambodia, possibly through cross-border trade or through wild birds (2,6,7).
In December 2017, a 68-year-old woman in Jiangsu, China, who had underlying medical conditions was infected by an LPAI influenza A(H7N4) virus, which led to severe pneumonia and intensive care unit admission, but she recovered and left the hospital after 21 days (8,9).
Genetically similar H7N4 viruses were subsequently detected in contact chickens (9,10) and aquatic poultry in Jiangsu (GISAID, https://www.gisaid.orgExternal Link), substantiating that the infection was zoonotic and raising concerns of endemicity of H7N4 in the region.
Because of the antigenic differences between the A/Jiangsu/1/2018-like A(H7N4) virus and other H7 lineages (10), including A/Anhui/1/2013(H7N9) lineage, this newly detected H7N4 virus has been proposed as a vaccine candidate for pandemic preparedness (10).
Beginning in February 2018, 2 months after the H7N4 case in China, this virus was detected in ducks in Cambodia; the frequency of detection increased in March and April (4). Therefore, because of the novelty of the strain and the association with human infection, we sought to understand the genomic diversity of H7 viruses in Cambodia.
(SNIP)
Our results show that H7N4 is a newly developing virus lineage that originated from divergent avian lineages within the Eurasian AIV gene pool. The dispersed genetic origins from locations in Europe and central Asia and the similarity of the Cambodia and Jiangsu H7N4 samples indicates that the H7N4 virus was generated in aquatic birds, likely just before their first detection.
Detection of H7N4 in LBMs in Cambodia in such a short span of time at such a large spatial distance highlights the risk and potential for rapid spread of AIV lineages throughout the region. The ability to infect a human subject, the continual reassortment and antigenic evolution of this lineage, and the endemicity of numerous LPAI and HPAI viruses may further increase the risk for zoonotic infections and warrants vigilant, active surveillance in wild birds and poultry in the region.
Dr. Vijaykrishna is an evolutionary biologist based at the Biomedicine Discovery Institute in Melbourne, working closely with staff and students at IPC and World Health Organization Collaborating Centre, Melbourne. His primary research interests are in using disease surveillance and comparative genomics to track and solve problems in clinical and veterinary virology.
