#18,418
Hooded cranes are regarded (and often referred to as) `National Treasures’ in Japan, which is why roughly 15 years ago - in 2010 & 2011 - we saw a near panic among officials when 5 Hooded Cranes Tested Positive For H5N1 at the migration grounds at Izumi.
Around 10,000 endangered Hooded cranes, 3,000 white-naped cranes, and thousands of more common birds arrive from Siberia and China each year to overwinter in the Izumi Plain, making The Izumi Crane Observation Center a popular destination for birdwatchers from around the globe.
As we discussed in 2011's Japan’s Bird Flu Dilemma, there are limited options available to officials when a potentially deadly HPAI virus strikes a rare, and protected species of birds. Complicating matters, Kagoshima Prefecture is also a major poultry producing region of Japan, which may allow for cross-contamination between livestock and wild birds.
Yesterday the CDC's EID Journal published a review of the impact of HPAI H5 infection at the Izumi preserve in 2022-2023, which finds limited evidence of cross-contamination between local poultry and migratory birds, evidence of respiratory transmission of the virus (as opposed to transmission via infected feces), and a lack of `herd immunity' among the endangered crane population.
Due to its length, I've only posted the abstract and highlights. Follow the link to read it in its entirety. I'll have a bit more after you return.
Research
Highly Pathogenic Avian Influenza A(H5N1) Outbreak in Endangered Cranes, Izumi Plain, Japan, 2022–23
Mana Esaki1, Kosuke Okuya1, Kaori Tokorozaki, Yuko Haraguchi, Taichi Hasegawa, and Makoto Ozawa
Abstract
During the 2022–23 winter season, >1,500 endangered cranes, including hooded crane (Grus monacha) and white-naped crane (Grus vipio), were found debilitated or dead in the Izumi Plain, Japan. Most of the cranes, particularly those collected in November, were infected with highly pathogenic avian influenza (HPAI) H5N1 viruses; virus shedding was higher from the trachea than from the cloaca.
The isolation rate from the cranes’ roost water was not markedly higher than that of previous seasons, suggesting that the viruses might be more effectively transmitted among cranes via the respiratory route than through feces. Most wild bird–derived H5N1 isolates were phylogenetically distinct from viruses isolated on nearby chicken farms, indicating limited relationship between the wild bird and chicken isolates. Serologic analyses suggested that herd immunity had little effect on outbreak subsidence. This study deepens our understanding of the circumstances surrounding the unexpected HPAI outbreaks among these endangered cranes.
(SNIP)
Discussion
We report a large HPAI outbreak among endangered cranes. In total, 1,504 debilitated or dead endangered cranes were collected during the 2022–23 winter season in the Izumi Plain, Japan (Figure 1, panel A). We confirmed that most of the debilitated or dead cranes, particularly those collected in November (95.7%), were infected with H5N1 viruses (Figure 1, panel B).
In wild ducks, LPAI viruses mainly replicate in the intestine and are thus shed in the feces (5,6). Environmental water contaminated with the feces of wild ducks has been effectively used for AIV surveillance in the Izumi Plain since 2012 (10,11,13,14,18,29). During the 2022–23 winter season, we isolated 24 HPAI H5N1 virus strains from the roost water of cranes (Appendix Table 3). Despite the large outbreak of HPAI H5N1 among endangered cranes, the number of water HPAI isolates during the 2022–23 winter season was not markedly higher than that in previous seasons (Figure 4).In addition, the gene copy numbers of HPAIVs in tracheal swabs from the infected cranes were higher than those in cloacal swabs (Figure 3), indicating high virus shedding in the respiratory tracts. Overall, these findings suggest that HPAI H5N1 circulating among the endangered cranes during the 2022–23 season might have been transmitted more efficiently via the respiratory route rather than through environmental water.
(SNIP)
In conclusion, HPAI H5N1 viruses caused large-scale mortality of endangered cranes, including hooded cranes and white-naped cranes, in the Izumi Plain of Japan during the 2022–23 winter season. Our findings suggest that H5N1 circulated mainly via the respiratory route, but not the environmental waterborne route, among the endangered cranes. Most of the HPAIVs circulating in wild birds were genetically distant from those isolated from chicken farms. In addition, the endangered crane populations have not developed herd immunity against H5N1. Our study provides new insights into understanding the circumstances surrounding HPAI H5N1 outbreaks among endangered cranes and could help in their conservation.
Ms. Esaki is a PhD candidate at Joint Graduate School of Veterinary Medicine, Kagoshima University, Kagoshima, Japan. Her primary research focuses on the molecular diagnosis and epidemiology of avian influenza viruses.
We've known for nearly 2 decades that HPAI viruses are more likely to turn up in tracheal swabs of birds than LPAI viruses (which are primarily shed in feces), although both may be shed by either route. The following FAO guidance from the late 2000s explains.
TRACHEAL AND CLOACAL SWABS
Swabs taken from the cloaca (vent) or trachea can be used for viral cultures or reverse transcription polymerase chain reaction (RT-PCR) to test for the presence of many viral pathogens, including AI viruses. While non-pathogenic AI viruses replicate primarily in the avian intestinal tract, recent strains of H5N1 HPAI viruses have been detected both from cloacal and tracheal/oropharyngeal samples.Research has revealed that, unlike other AI viruses, the H5N1 HPAI subtype replicates to higher levels and for longer periods in the respiratory tract compared to the gastrointestinal tract (Sturm-Ramirez et al. 2004, Hulse-Postet al. 2005). Furthermore, after experimental exposure, higher concentrations of the virus have been found in tracheal samples than in cloacal samples on any given day. Therefore, tracheal and cloacal swabs are currently the preferred samples for H5N1 surveillance in wild birds.
Since lab results can vary depending upon the bird species, and the subtype/pathogenicity of the virus, the advice is to swab both ends of the bird. It will be interesting to see if this observed increased transmission of HPAI via the respiratory route in Hooded Cranes is an aberration, or a trend.
Notably, even after years of repeated incursions of HPAI H5 viruses, researchers determined ` . . . endangered crane populations have not developed herd immunity against H5N1'. A finding that should give pause to the notion of `letting the virus run its course' through poultry in order to acquire immunity.
As an aside, those with good memories may also recall that Izumi was also the site of a study we first looked at in 2023 - and again in 2024 (see Sci Repts: Blowflies As Potential Vectors Of Avian Influenza) - which tested blowflies captured at this national wildlife reserve for signs of HPAI H5 (and found it).
The authors wrote:
Our observations suggest C. nigribarbis may acquire the HPAI virus from deceased wild birds directly or from fecal materials from infected birds, highlighting the need to add blowflies as a target of HPAI vector control.
Not only are we still learning about the capabilities of HPAI H5, it continues to evolve and potentially expand its abilities. All of which makes recent cutbacks in research on this - and other emerging infectious diseases - penny wise and pound foolish.
