In April 2024, laboratory results from a hospitalized patient in Mexico City showed the first direct evidence of human infection caused by influenza A virus subtype H5N2 (A/H5N2). The patient died, and the case fatality was reported to the World Health Organization (WHO) on 23 May 2024.
In a new paper (pre-print), researchers provide additional context on the clinical case and phylogenetic analysis.
The patient initially developed developed fever, shortness of breath, diarrhoea, nausea and general malaise. About a week after symptom onset, on 24 April, the patient sought medical attention, was hospitalized at the National Institute of Respiratory Diseases “Ismael Cosio Villegas” (INER per its acronym in Spanish). At admission the patient was severely ill, with uremia, renal failure and metabolic acidosis, and a bacteremic infection originating likely from peritonitis. The patient deteriorated rapidly and died the same day. It is uncertain what was the contribution of the influenza virus H5N2 to the final clinical status of the patient.
The primary avian influenza subtypes implicated in causing respiratory diseases in
humans are H5N1, H7N9, and H5N6. Additionally, avian influenza viruses like H5N1 or H7N3 have also been implicated in human infections causing conjunctivitis but not respiratory disease. H5N2 has been associated primarily with migratory birds and commercial and backyard poultry infections.
This was the first laboratory-confirmed human case of infection with an influenza A(H5N2) virus reported globally and the first avian H5 virus infection in a person reported in Mexico. Although the source of exposure to the virus in this case is currently unknown, A(H5N2) viruses have been reported in poultry in Mexico.
The patient had multiple underlying medical conditions, and relatives reported that the patient had already been bedridden for three weeks, for other reasons, prior to the onset of acute symptoms.
Results from RT-PCR of a respiratory sample collected and tested at INER on 24 April indicated a non-subtypeable influenza A virus. On 8 May, the sample was sent for sequencing to the Laboratory of Molecular Biology of Emerging Diseases Center for Research in Infectious Diseases (CIENI per its acronym in Spanish) of INER, which indicated that the sample was positive for influenza A(H5N2). On 20 May, the sample was received at the Institute of Epidemiological Diagnosis and Reference (InDRE per its acronym in Spanish) of the Mexico National Influenza Centre, for analysis by RT-PCR, obtaining a positive result for influenza A. On 22 May, sequencing of the sample confirmed the influenza subtype was A(H5N2).
No further cases were reported during the epidemiological investigation. Of the 17 contacts identified and monitored at the hospital where the case died, one reported a runny nose between 28 and 29 April. Samples taken from these hospital contacts between 27 and 29 May tested negative for influenza and SARS-CoV 2. Twelve additional contacts (seven symptomatic and five asymptomatic) were identified near the case’s residence. Samples of pharyngeal exudate, nasopharyngeal swabs and serum were obtained from these individuals. On 28 May, the InDRE reported that all twelve samples from contacts near the patient’s residence tested negative for SARS-CoV-2, influenza A and influenza B, as determined by RT-PCR.
Molecular evidence suggests that the strain possibly derived from a common avian H5N2 ancestor from 2019 of Central Mexico. Although a direct contact of the patient in this study with poultry or other domestic animals could not be confirmed, it is plausible that this avian virus, causing high disease burden in chickens in this geographical area in 2024 could be the source of the human case described here, as human to human transmission seems implausible.
Several comorbidities in the case described here led to a fatal outcome, but the pathogenicity of the isolate needs to be further studied. Further studies are required to determine the predicted pathogenicity of the virus and to predict its capability for human-to-human transmission and potential threat to human health.
READ MORE:
First laboratory-confirmed human case of infection with influenza A(H5N2) virus reported in Mexico, medRxiv (pre-print).
Disease Outbreak News: Avian Influenza A(H5N2) – Mexico. WHO