of mammal species affected worldwide by H5N1
#17,907
After making a brief appearance in Hong Kong in 1997, HPAI H5N1 went to ground for 5 years, only to resurface in 2003 and begin its slow spread out of Southeast Asia and into Europe, the Middle East and Africa.For most of the next dozen years it was primarily a disease of gallinaceous birds (chickens, turkeys, quail, etc.), with occasional (and often fatal) spillovers into humans.
While some scattered mammalian infections were reported - particularly among zoo animals fed infected chicken (see Fatal H5N1 Infection In Tigers By Different Reassortant Viruses - China) - mammalian infections were only rarely reported (see HPAI H5: Catch As Cats Can).
In 2014 a new clade of HPAI H5 emerged in South Korea (clade 2.3.4.4) which spread rapidly to Europe, and for the first time, to North America where it sparked a major epizootic (see map below).
The virus was not, however, well adapted for long-term carriage by migratory birds, and it disappeared completely over the summer of 2015 (see PNAS: The Enigma Of Disappearing HPAI H5 In North American Migratory Waterfowl).
But the following summer H5N8 underwent a reassortment event in Russia/China that increased its ability to be carried by migratory birds (see EID Journal: Reassorted HPAI H5N8 Clade 2.3.4.4. - Germany 2016) and allowed it to spark the first of several major epizootics in Europe.
As a result, H5N1 has since spread from Europe/Asia to both North and South America, and has been detected in both the Arctic and Antarctic regions for the first time. Even more ominously, HPAI H5N1 continues to expand its host range in both terrestrial and marine mammals.
Even if that never happens, the impact on our shared ecosystem - and the loss of tens of millions of birds and hundreds of thousands of mammals - is enormous and growing.
Today we've got an early release from the EID journal that compares the impact of the HPAI H5 virus between its earlier waves of infection (2003–2019) and its current (2020-2023) presentation. This is a lengthy and detailed report, so I've only posted some highlights.
Follow the link to read it in its entirety. I'll have a brief postscript after the break.
Synopsis
Recent Changes in Patterns of Mammal Infection with Highly Pathogenic Avian Influenza A(H5N1) Virus Worldwide
Pablo I. Plaza, Víctor Gamarra-Toledo, Juan Rodríguez Euguí, and Sergio A. Lambertucci
Abstract
We reviewed information about mammals naturally infected by highly pathogenic avian influenza A virus subtype H5N1 during 2 periods: the current panzootic (2020–2023) and previous waves of infection (2003–2019). In the current panzootic, 26 countries have reported >48 mammal species infected by H5N1 virus; in some cases, the virus has affected thousands of individual animals. The geographic area and the number of species affected by the current event are considerably larger than in previous waves of infection. The most plausible source of mammal infection in both periods appears to be close contact with infected birds, including their ingestion.
Some studies, especially in the current panzootic, suggest that mammal-to-mammal transmission might be responsible for some infections; some mutations found could help this avian pathogen replicate in mammals. H5N1 virus may be changing and adapting to infect mammals. Continuous surveillance is essential to mitigate the risk for a global pandemic.
Since last century, highly pathogenic avian influenza (HPAI) viruses have caused diverse waves of infection (1). However, the ongoing panzootic event (2020–2023) caused by HPAI A(H5N1) virus could become one of the most important in terms of economic losses, geographic areas affected, and numbers of species and individual animals infected (1–4). This pathogen appears to be emerging in several regions of the world (e.g., South America); it has caused death in domestic and wild birds but also in mammals (2,5,6). This trend is of great concern because it may indicate a change in the dynamics of this pathogen (i.e., an increase in their range of hosts and the severity of the disease) (3).
H5N1 has affected several mammal species since 2003 (6,7), thus raising concern because H5N1 mammalian adaptation could represent a risk not only for diverse wild mammals but also for human health (8–10). Unfortunately, information about this topic, especially related to the current panzootic (2020–2023), is disperse and available often only in gray literature (e.g., databases and official government websites). This fact complicates access and evaluation for many stakeholders working on the front lines (e.g., wildlife managers, conservationists, and public health authorities at regional and local levels).
For this article, we compiled and analyzed information from scientific literature about mammal species, including humans, naturally affected by the current panzootic event and compared those findings with the outcomes of previous waves of H5N1 infection. We focus particularly on the species infected, their habitat, phylogeny, and trophic level, and the sources of infection, virus mutations, clinical signs, and necropsy findings associated with this virus. We also address potential risks for biodiversity and human health.
(SNIP)
Potential Risks for Human Health
During 2003–2023, a total of 878 humans tested positive for the H5N1 virus, and 458 deaths were reported, indicating a lethality of ≈52% (14). During 2003–2019, most human cases came from Asia and Africa, particularly from China (n = 53), Egypt (n = 359), and Indonesia (n = 200). From 2020 through July 2023, human cases of H5N1 infection occurred in diverse countries, such as Laos (1 case), India (1 case), United Kingdom (4 cases), China (2 cases), the United States (1 case), Vietnam (1 case), Spain (2 cases), Ecuador (1 case), Chile (1 case), and Cambodia (2 cases) (14). Those recent cases resulted in >3 deaths (14). Of note, this zoonotic virus has produced human cases in new geographic areas, such as South America.
The spillover to humans has been associated with close contact between humans and infected animals, particularly poultry; this kind of contact is relatively common in some geographic regions (even close contact between dead mammals and humans, as in Peru [22]). So far, no evidence indicates human-to-human transmission, and the risk for a pandemic event still seems low (8). However, one of the most severe influenza viruses to have affected humans (i.e., Spanish influenza [1918–1919]) developed from an avian influenza virus that adapted to humans (49), a fact that should be considered when assessing the spillover risk.
Mutations in the virus found in diverse mammal species, especially in the current panzootic, are of great concern. For instance, the T271A mutation reported in minks in Spain is also present in the H1N1 that produced a pandemic in 2009 (9). Similarly, the PB2-E627K mutation found in this virus in diverse geographic areas could indicate an adaptation for replication in mammals (28,31). Moreover, some infected species, such as minks, may act as a mixing vessel for interspecies transmission between birds, mammals, and humans (9). Mutations and infections with H5N1 in potential mixing-vessel species (e.g., minks and wild and domestic pigs) should be followed closely because of the potential risk to human health.
Final Considerations
Given the magnitude of the current H5N1 panzootic, continuous surveillance is necessary to identify any increase in risk to biodiversity and human health. It is therefore essential that all affected countries share all their available information (e.g., genomic data of the H5N1 virus, species, and number of individual animals affected). We urge that all findings be shared quickly. International collaboration must be intensified to obtain rapid results; some less-developed regions have technologic and logistic barriers that hinder the production and analysis of information on the impact of this virus, and they may need help. There is a need for strong collaborative work between countries and institutions in preparation for any spillover that may lead to a mammalian panzootic or human pandemic.
It is fundamental that we rethink the interface between humans, domestic animals, and wild animals to prevent the emergence of dangerous pathogens that affect biodiversity and human health (48). Governments must assume responsibility for protecting biodiversity and human health from diseases caused by human activities, particularly diseases originating from intensive production (50), such as this H5N1 avian influenza virus. If we hope to conserve biodiversity and protect human health, we must change the way we produce our food (poultry farming, in this specific case) and how we interact with and affect wildlife.
Dr. Plaza is a veterinarian and research associate at the Conservation Biology Research Group, Ecotone Laboratory, Institute of Biodiversity and Environmental Research (INIBIOMA), National University of Comahue–National Scientific and Technical Research Council, San Carlos de Bariloche, Argentina. His primary research interests include wildlife health and epidemiology, human–wildlife interactions, and animal conservation.
While the recent changes in the behavior of HPAI H5N1 clade 2.3.4.4b are a legitimate concern, it is far from the only pandemic threat we face.
In terms of likelihood of sparking a pandemic, many researchers - including the CDC - view the swine-origin EA H1N1 `G4' virus as topping the list. Other swine viruses (H1, H2, or H3) are also believed likely to require less of an evolutionary leap to adapt to humans than an avian H5 virus.
A pretty good case case could be made for a number of other avian subtypes, including H5N6, H3N8, H6N1, H7N9, H10Nx, and even LPAI H9N2, either as a standalone virus or a reassortment with a seasonal flu virus.
And then there are the non-flu exotics, like Nipah, or MERS-CoV, or `Disease X'; the one we don't yet recognize as a threat.
The inevitability isn't that HPAI H5 will spark the next pandemic, it is that something will. And we need to be better prepared for it than we were for the last one.
