As of December 30, 2024, 66 human cases of highly pathogenic avian influenza (HPAI) H5N1 have been identified in the United States, including the first-ever severe case detected on December 18. For the moment, almost all cases are of moderate intensity and only two severe cases have been reported in North America, the second being reported in Canada in a young 13-year-old patient. No deaths occurred.
Having noted no human-to-human transmission, the US Centers for Disease Control and Prevention (CDC) is keeping the public health risk low but monitoring the situation closely.
For the American patient, the hypothesis retained is that of contamination by dead or sick wild birds in his garden, a first in the United States, which is experiencing a surge in human cases of H5N1. By sequencing the virus present in this patient, the CDC identified a mutation that is not found in poultry and livestock. This suggests that this viral genomic change takes place in the patient, at an advanced stage of infection.
Its D1.1 genotype is different from the B3.13 virus that is spreading today, but it is particularly close to other viruses detected in 2024 in wild or farmed birds in the United States. A sequence is identical to the virus found in the Canadian teenager.
Encouraging news, the mutation seems to have vaccine potential: the HA genes of the virus are similar to those targeted by vaccine candidates A/Ezo red fox/Hokkaido/1/2022 and A/Astrakhan/3212/2020 to a few amino acids. This would allow a rapid response in the event of a human epidemic.
Conjunctivitis, fever and respiratory symptoms
A study published on December 31 in the New England Journal of Medicine (NEJM) draws up an inventory of the 46 cases recorded from 1is March to October 31, 2024 in the United States: sources of contamination, protective equipment and symptoms. Twenty patients were in contact with contaminated poultry and all were involved in avian depopulation activities. For the 25 working in the dairy industry, 16% were exposed to cows, 84% to cows and raw milk.
The main symptoms were conjunctivitis (93% of patients, a third without other symptoms), fever (49%) and respiratory problems (36%), with a median duration of illness of 4 days (based on available data). , or 16 patients). Fever is more often found among workers in contact with poultry (60 versus 40%), the same for headaches (55 versus 35%), myalgia (55 versus 32%) and respiratory symptoms (45 versus 28%). .
The last patient in the series has no identified source. The presentation of the illness was somewhat different: acute chest pain, nausea and vomiting, diarrhea and weakness, without respiratory symptoms.
“Suboptimal” use of protective equipment
Some of the workers wore personal protective equipment (PPE): gloves for 71% of them, eye protection for 60% and masks for almost half. Only a third of patients used masks and eye protection together. Figures that the authors of the study describe as “suboptimal”. They raise the need to deploy additional strategies to reduce the risk of exposure.
Thirty-nine patients were treated with oseltamivir for a median duration of five days. The CDC recently changed its instructions for oseltamivir, recommending a longer duration of treatment for hospitalized individuals and twice-daily administration for prophylaxis. In an editorial published in the NEJMDrs Michael G. Ison and Jeanne M. Marrazzo, both from the US National Institute of Allergy and Infectious Diseases (NIAID), comment: “We must continue to develop and test medical countermeasures. Circulating virus isolates are susceptible to all neuraminidase inhibitors, adamantanes and baloxavir marboxil. » Indeed, they note that the Canadian patient had a higher viral load in the lower respiratory tract and prolonged viral excretion despite the treatment.
Finding the balance between increased vigilance and the status quo
In their editorial, Drs Ison and Marrazzo are clear: “Collaboration between investigators in human and veterinary medicine, public health decision-makers, the healthcare system and agricultural authorities is essential. » They highlight detection of H5N1 cases made possible thanks to a standard surveillance approach that “relies on trust between many entities but also with patients presenting for symptoms of interest, including conjunctivitis”.
The two infectious disease specialists recall the importance of One Health when, to date, scientists seriously lack critical genomic data in understanding the spread of the virus. “Such data would also offer us the opportunity to early detect mutations with strong tropism for the respiratory epithelium”they add.
With the increase in the number of cases in the United States in recent weeks, editorialists call for a balance to be found between increased vigilance and business as usual. “Without a better understanding of the extent of exposure, infection, evolution of the virus and its transmission, we will be unable to protect our communities from a pathogen that has proven to be formidable. for human and animal health ».
Two new outbreaks of H5N1 on French farms
On December 27 and 28, two outbreaks of highly pathogenic avian influenza (HPAI) H5N1 were detected on French farms, in Eure and Calvados. Thus, France loses its HPAI-free status which it had regained on December 15. For the moment, no human cases have been observed in the territory. The Ministry of Agriculture and Food Sovereignty indicated in a press release that it had initiated the biosecurity measures planned in the event of new outbreaks: slaughter, cleaning and disinfection of the two sites, 3 km protection zone for neighboring farms and surveillance of 3 to 10 km around the outbreaks.
The second compulsory vaccination campaign for ducks continues, “a pillar of prevention against HPAI, complementary to surveillance and biosecurity”we read in a press release from the ministry. France remains at the “high” epizootic HPAI risk level, particularly with regard to the possibilities of infections linked to migration while the circulation of the virus among wild birds is active in Europe.
