Unprecedented Avian Influenza Fatality in Mexico
In an alarming disclosure, the World Health Organization (WHO) revealed that a man in Mexico succumbed to a hitherto undocumented strain of avian influenza, H5N2. This variant has never before been detected in humans, despite its known presence in Mexican poultry.
Official Report
On May 23, 2024, the Mexico International Health Regulations (IHR) National Focal Point (NFP) communicated to PAHO/WHO a verified mortal case of human infection with avian influenza A(H5N2) virus in a resident of the State of Mexico, hospitalized in Mexico City. This instance marks the inaugural laboratory-confirmed human infection of the influenza A(H5N2) virus globally, and the first recorded avian H5 virus infection in a human in Mexico.
The WHO’s statement underscores the ambiguity surrounding the man’s exposure to the virus, though A(H5N2) presence in Mexican poultry is documented. The IHR mandates notification of novel influenza A virus subtypes in humans due to their potential significant public health impact. Currently, WHO assesses the risk posed to the general populace by this virus as minimal based on available data.
Case Overview
The confirmed case involves a 59-year-old inhabitant of the State of Mexico, who had been hospitalized in Mexico City. Despite no recorded contact with poultry or other animals, the patient had multiple pre-existing medical conditions. Family members reported the patient had been bedridden for three weeks prior to the emergence of acute symptoms.
On April 17, the patient exhibited fever, dyspnea, diarrhea, nausea, and general malaise. Seeking medical intervention on April 24, the patient was admitted to the National Institute of Respiratory Diseases “Ismael Cosio Villegas” (INER) but succumbed the same day due to complications.
Initial Real-Time Polymerase Chain Reaction (RT-PCR) testing of a respiratory specimen at INER indicated a non-subtypeable influenza A virus. Sequencing on May 8 by the Laboratory of Molecular Biology of Emerging Diseases at CIENI confirmed the sample was positive for influenza A(H5N2). Further analysis on May 20 at the Institute of Epidemiological Diagnosis and Reference (InDRE) corroborated these findings.
During the ensuing epidemiological investigation, no additional cases surfaced. Among the 17 monitored hospital contacts, only one reported a transient nasal discharge. Testing between May 27-29 returned negative results for influenza and SARS-CoV-2. Twelve additional contacts, comprising symptomatic and asymptomatic individuals, were identified near the patient’s residence. All samples from these contacts tested negative for influenza A, B, and SARS-CoV-2, though serological results remain pending.
Recent Poultry Outbreaks
March 2024 witnessed a high pathogenicity avian influenza A(H5N2) outbreak in a backyard poultry farm in Michoacán, adjacent to the State of Mexico. Additionally, low pathogenicity avian influenza (LPAI) A(H5N2) outbreaks were reported in March in Texcoco and in April in Temascalapa, both within the State of Mexico. The connection between these poultry outbreaks and the human case remains undetermined.
A 2022 study documented the continuous circulation of low pathogenicity avian influenza H5N2 viruses in Mexico and their dissemination to various countries.
Epidemiological Context
Typically, animal influenza viruses circulate among animals but can also infect humans, often through direct contact with infected animals or contaminated environments. Human infections with avian influenza viruses can range from mild upper respiratory tract infections to severe or fatal cases, and can include symptoms such as conjunctivitis, gastrointestinal disturbances, encephalitis, and encephalopathy.
Diagnosis of human influenza infections requires laboratory tests. WHO routinely updates protocols for zoonotic influenza detection using molecular techniques like RT-PCR. Antiviral medications, particularly neuraminidase inhibitors (oseltamivir and zanamivir), have shown efficacy in reducing viral replication duration and improving survival outcomes for some cases.