By Justine Dukmedjian.
It is no secret that the US has been facing its largest outbreak ever of H5N1, a strain of bird flu, since the beginning of March 2024 [1], when the bird-flu started infecting dairy cows all around the country, after first beginning to infect birds (wild birds and farm birds) in 2022.
According to the CDC (Center for Diseases Control) [2], since 2022, more than 100, 000 thousand poultry [3] in 48 states ; 10, 000 wild birds (also in 48 states) [4]; and 280 cows have been infected by H5N1 in 14 states [5]. Moreover, 6 states have reported human cases of the bird flu, bringing the total to 46 six human infections in less than twelve months. This shows quite a perceptible spike in human cases, leading the authorities to worry, especially since they think this number might be underestimated [6].
There is a strong suspicion amongst experts that the first occurrence of interhuman transmission might have happened in Missouri during the summer [7] [8]. At the end of August this year, an unidentified individual was admitted to the hospital with flu-like symptoms. They were tested positive for Influenza A, but negative to every routine seasonal subtypes of Influenza A. This triggered more extensive testing, which led to conclude that this individual was infected with H5N1 [9]. This individual had no known-exposure to poultry or dairy cows, begging the question of the source of their contamination (the Missouri health authorities are still investigating) and appeared to have possibly contaminated seven other individuals (one from his household; six health workers) [10]. Yet, after some testing, experts said that only the individual sharing a home with the patient had contracted the virus. Even though this antibodies testing can sometimes be wrong (depending on the severity of the infection and the date of the testing, a person can produce to few antibodies for tests to pick them up) experts are reasonably sure that the symptoms experienced by the health care workers after attending to the H5N1 patient aren’t linked to the bird flu [11]. A question still remains and divides experts: has the hospitalized patient contaminated the member of their household (thus making it one of the very rare cases of interhuman transmission of H5N1) or have they been contaminated by the same source [12] ?
The CDC is still currently sequencing the individual’s virus’s genome. From the little they have been to sequence yet, they do not think that the virus has acquired mutations or recombinations (“Recombination occurs when at least two viral genomes co-infect the same host cell and exchange genetic segments” [13]), allowing easier interhuman transmission [14]. This H5N1 outbreak remains extremely risky in terms of mutations, with the potential to start a pandemic. In May of this year, experts shed light on the fact that the current outbreak is due to dozens of mutations of the bird flu, some of them possibly helping it to spread more easily among species and becoming more resistant to antivirals [15]. Specialists are closely monitoring the possibility of the virus acquiring mutations to spread easily amongst mammals – and more importantly, to humans [16].
Yet, some experts are still worrying about the pandemic-potential of this H5N1 outbreak.
To give some context (and explain the sound reasoning behind this increasing worry), we’ll try to dwell upon the particularities of the H5N1 virus.
The flu viruses are divided into four types (from A to D), based on several criterias (like their propensity to mutate). Influenza A and B viruses are responsible for the seasonal flu every year during the winter. Yet, Influenza A is solely responsible for every flu-pandemic known to man. H5N1 is part of type A.
It first appeared in Hong-Kong in 1997, during an epidemic that killed six people (42 % mortality rate), aged 2 to 60 [17] [18] [19].
Originally, H5N1 was targeting specifically wild birds and poultry, being more pathogenic to the latter [20]. Yet, since the Hong Kong outbreak, it has evolved into a zoonosis, infecting sporadically people in contact with birds or cattle. Due to its belonging to the A-type and its extremely high mortality rate, H5N1 has always been closely monitored by health organizations around the world, including the WHO (the WHO has tried to manufacture a vaccine for more than two decades, with very limited success) [21]. Indeed, experts have always considered that like its “cousin” the H1N1 strand (responsible for both the 1918 and 2009 pandemics), H5N1 could mutate or recombine enough to start a pandemic by acquiring the ability to be easily transmitted between species, or, more dangerously, between people. The cases have always been sporadic, which entails preventing our immune system from learning how to defend itself against an H5N1 infection. That, added to the lack of a pre-existing vaccine and the long manufacturing processes in case of a pandemic [22] lead experts to be extremely wary of every H5N1 outbreak amongst animals. Thankfully, two antivirals seem to be effective against the H5N1 virus, and can be used as preventive measures or curative ones. Yet, they are far from being as effective as a vaccine would be [23].
Interhuman transmission of H5N1 is not unheard of. It is just extremely rare [24]. So, if the authorities were to prove that the unidentified individual from Missouri indeed did infect seven other people (making it the actual first interhuman cases in the US), it could have cataclysmic consequences, indicating that the virus has now acquired the possibility to be easily transmitted among people. Those scientists are also worried about the way health authorities – namely, the CDC and the Missouri Department of Health and Senior Services – are handling the situation. They blame the lack of information released and their tone, that they considered too optimistic for the situation. Indeed, according to those experts, retaining information and being overly optimistic about a situation that could quickly degenerate into a full-blown pandemic is not going to help health authorities among the country regain the people’s trust they lost during their handling of the Covid-19 pandemic. On the contrary, it might further damage their relationship with the people, by allowing a pandemic to happen due to another mishandling of the health situation [25]. Which raises the question: has the Covid-19 pandemic taught anything to health authorities? Especially regarding their truthfulness to the people and their ability to keep their trust in their ability to protect those placed under their responsibility?
Edited by Justine Peries.
References
[1] Mandavilli, Apoorva, “As Bird Flu Spreads, Two New Cases Diagnosed in California, October 4th 2024.
https://www.nytimes.com/2024/10/04/health/bird-flu-california-missouri.html .
Accessed October, 8th, 2024.
[2] USDA Reported H5N1 Bird Flu Detections in US Backyard and Commercial Poultry.
https://www.cdc.gov/bird-flu/situation-summary/data-map-commercial.html .
Accessed October, 8th, 2024.
[3] USDA Reported H5N1 Bird Flu Detections in US Wild Birds. https://www.cdc.gov/bird-flu/situation-summary/data-map-wild-birds.html .
Accessed October, 8th, 2024.
[4] HPAI Confirmed Cases in Livestock.
Accessed October, 8th, 2024.
[6] [7] [8] CDC Situation Report, H5 Bird Flu: Current Situation.
https://www.cdc.gov/bird-flu/situation-summary/index.html .
Accessed November, 6th, 2024.
[7] CDC Statement, CDC Confirms Human H5 Bird Flu Case in Missouri, September, 6th, 2024.
https://www.cdc.gov/media/releases/2024/s0906-birdflu-case-missouri.html .
Accessed October, 8th, 2024.
[8] [9] Mandavilli, Apoorva, Missouri Reports Bird Flu in a Patient Without a Known Risk, September, 6th 2024.
https://www.nytimes.com/2024/09/06/health/bird-flu-missouri-cdc.html .
Accessed October, 8th, 2024.
[10] [14] [25] Mandavilli, Apoorva, Anthes, Emily, Possible Cluster of Human Bird-Flu Infections Expands in Missouri, September, 27th, 2024.
https://www.nytimes.com/2024/09/27/health/bird-flu-cluster-missouri.html .
Accessed October, 8th, 2024.
[11] [12] Mandavilli, Apoorva, Anthes, Emily, As Bird Flu Spreads, Additional Human Infection is Reported in Missouri, October, 24, 2024.
https://www.nytimes.com/2024/10/24/health/bird-flu-missouri.html .
Accessed November, 6th, 2024.
[13] Marcos Pérez-Losada,a,b Miguel Arenas,c Juan Carlos Galán,d,e Ferran Palero,e,f and Fernando González-Candelas, Recombination in viruses: Mechanisms, methods of study, and evolutionary consequences, Infect Genet Evol. 2015 Mar; 30: 296–307. Published online 2014 Dec 23.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7106159/ .
Accessed October, 8th, 2024.
[15] [16] Mandavilli, Apoorva, Anthes, Emily, New Mutations Identified in Bird Flu Virus, May, 3, 2024.
https://www.nytimes.com/2024/05/03/health/bird-flu-cows-mutations.html?searchResultPosition=11 .
Accessed November, 6th, 2024.
[17] Prof KY Yuen, MRCPatha, PKS Chan, MRCPathb, Dr M Peiris, FRCPatha, DNC Tsang, MRCPathc, TL Que, MRCPathc, KF Shortridge PhD and members of the H5N1 study group, Clinical features and rapid viral diagnosis of human disease associated with avian influenza A H5N1 virus, February, 14th, 1998, Volum 351, Issue 9101, P. 467-471, The Lancet.
https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(98)01182-9/fulltext .
Accessed October, 8th, 2024.
[18] Centre Canadien d’Hygiène et de Sécurité au Travail, Risques biologiques, Influenza.
https://www.cchst.ca/oshanswers/biol_hazards/influenza.html# .
Accessed October, 8th, 2024.
[19] [20] [21] [22] [23] [24] Institut Pasteur, Grippe aviaire.
https://www.pasteur.fr/fr/centre-medical/fiches-maladies/grippe-aviaire .
Accessed October, 8th, 2024.
[Cover Image] Photo by SHVETS production: licensed under Pexels.
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