Situation at a glance
On 2 April 2025, the International Health Regulations (IHR) National Focal Point (NFP) for Mexico notified the World Health Organization (WHO) of the country’s first laboratory-confirmed human infection with an avian influenza A(H5N1) virus in the state of Durango. In response, local and national health authorities have implemented a range of measures to monitor, prevent, and control the situation. There have been reports of A(H5N1) outbreaks in birds in Durango, although the exact source of infection in this case remains under investigation. To date, no further cases of human infection with influenza A(H5N1) linked to this case have been identified. In accordance with the IHR (2005), any human infection caused by a new influenza A virus subtype is considered a potentially significant public health event and is subject to mandatory notification to WHO. Based on the information currently available on this and previous cases, WHO assesses the risk to the general population posed by A(H5N1) viruses as low. For individuals with occupational exposure to these viruses, the risk of infection is considered low to moderate. The situation may change as more information is gathered and so WHO continues to closely monitor these viruses and the global epidemiological situation.
Description of the situation
On 2 April 2025, the Mexico IHR National Focal Point (NFP) notified the World Health Organization of a laboratory-confirmed human infection with an avian influenza A(H5N1) virus in the state of Durango.

This case represents the second reported human infection with avian influenza A(H5) in Mexico, and the first confirmed case of infection with an influenza A(H5N1) virus in the country.

The case is a child under the age of 10 years from the state of Durango who tested positive for influenza A(H5N1) at the Instituto de Diagnóstico y Referencia Epidemiológicos (InDRE, by its Spanish acronym). The case did not have any underlying medical conditions, had not received seasonal influenza vaccination, and had no history of travel.

Symptoms began on 7 March 2025 with fever, malaise, and vomiting. On 13 March, the case was admitted to hospital due to respiratory failure and antiviral treatment was initiated the next day. The case was transferred to a tertiary care hospital on 16 March and died on 8 April due to respiratory complications.

On 18 March, a nasopharyngeal swab was collected, and the sample was processed by real-time polymerase chain reaction (RT-PCR). The result was influenza A, non-subtypable. The sample was sent to the Centro de Investigación Biomédica del Noroeste (CIBIN, by its Spanish acronym), IMSS Monterrey, where the result was confirmed as influenza A, non-subtypeable, along with simultaneous detection of parainfluenza 3 virus. On 31 March, the sample was forwarded to the Laboratorio Central de Epidemiología (LCE, by its Spanish acronym) “La Raza,” where it was molecularly identified as influenza A(H5). On 1 April, the sample was received by InDRE, where the positive result for influenza A(H5N1) was confirmed by RT-PCR. The sample was further characterized as avian influenza A(H5N1) clade 2.3.4.4b genotype D1.1.

The source of infection remains under investigation. During contact tracing, 91 individuals were identified, including 21 household contacts, 60 healthcare workers, and 10 individuals from a childcare center. Pharyngeal and nasopharyngeal swab samples collected from 49 contacts tested negative for influenza A(H5N1). To date, no further cases of human infection with influenza A(H5N1) linked to this case have been identified.

According to information from the National Service for Agrifood Health, Safety and Quality (SENASICA per its acronym in Spanish), between January 2022 and August 2024, 75 outbreaks of A(H5N1) in poultry were reported across various regions of Mexico including: Aguascalientes (5), Baja California (4), Chiapas (1), Chihuahua (3), Guanajuato (2), Jalisco (17), México City (7), Michoacán (1), Nuevo León (1), Oaxaca (2), Puebla (2), Sonora (8), Tamaulipas (1), Veracruz (1), Yucatán (20). At the end of January 2025, SENASICA confirmed a new case of high pathogenicity avian influenza (HPAI) A(H5N1) in a sick vulture at the Sahuatoba Zoo in Durango, the state where the case lived. Following this, the death of a Canada goose with neurological and hemorrhagic symptoms was reported at the Pe?a del Aguila dam in Durango. A total of 25 sick birds were reported, and the presence of HPAI A(H5) was confirmed at a laboratory in Gómez Palacio, in Durango. A positive case of avian influenza A(H5) was also recorded in a bird at Las Auras Park.

Epidemiology
Animal influenza viruses typically circulate within animal populations but some have the potential to infect humans. Human infections are predominantly acquired through direct contact with infected animals or exposure to contaminated environments. Based on the original host species, influenza A viruses can be categorized into subtypes such as avian influenza, swine influenza, and other animal-origin influenza subtypes.

Human infection with avian influenza viruses may result in a spectrum of illness, ranging from mild upper respiratory tract symptoms to severe, life-threatening conditions. Clinical manifestations include conjunctivitis, respiratory, gastrointestinal symptoms, encephalitis, and encephalopathy. In some cases, asymptomatic infections with the A(H5N1) virus have been detected in individuals with known exposure to infected animals and environments.

A definitive diagnosis of human avian influenza infection requires laboratory confirmation. WHO regularly updates its technical guidance on the detection of zoonotic influenza, utilizing molecular diagnostic methods such as RT-PCR. Clinical evidence indicates that certain antiviral agents, particularly neuraminidase inhibitors (e.g., oseltamivir, zanamivir), have been shown to shorten the duration of viral replication and improve patient outcomes in some cases.

From 2003 to 10 April 2025, 972 cases of human infections with avian influenza A(H5N1), including 470 deaths (CFR 48.4%), have been reported to WHO from 24 countries. Almost all of these cases have been linked to close contact with infected live or dead birds, or contaminated environments.

Public health response
In response to this detection, additional investigation and surveillance activities are underway, coordinated by local and national health authorities, with involvement from both the animal and environmental sectors. These activities include:

Conducting a comprehensive epidemiological investigation of the case and contacts, including the collection of respiratory samples from symptomatic household contacts and healthcare workers, alongside ongoing follow-up and monitoring of close contacts.
Strengthening surveillance of respiratory viruses (including influenza-like illness [ILI] and severe acute respiratory infection [SARI]), with a particular focus on influenza viruses, in order to identify and analyze any atypical respiratory patterns or trends in the region.
Activating the One Health approach, involving SENASICA and national environmental agencies (SEMARNAT and CONANP), to ensure inter-institutional coordination, assess potential animal health risks, evaluate possible exposures within the community and animal populations, and notify the National Epidemiological Surveillance Committee (CONAVE).
Undertaking regular reporting of HPAI incidence in poultry and wild birds to the World Organisation for Animal Health (WOAH). The latest update on 5 March 2025 reported active surveillance and timely outbreak notifications, with a recent detection in the State of Durango. Consequently, local poultry farmers have been urged to reinforce biosecurity measures on their farms and backyard operations, and to immediately report any observed anomalies in animal health to the relevant authorities. Ongoing epidemiological surveillance is being maintained in poultry production units, backyards, federally inspected slaughterhouses, municipal slaughterhouses, and through national-level monitoring of wild bird populations.
WHO risk assessment
This case represents the second documented case of human infection with avian influenza A(H5) in Mexico and the first confirmed case of infection with an A(H5N1) influenza virus. Ongoing investigations are focused on identifying the source of infection and monitoring contacts. To date, no additional human cases of A(H5N1) virus infection have been identified in relation to this case, nor have any been detected through routine influenza surveillance.

Outbreaks of HPAI A(H5) viruses, including A(H5N1), in poultry have been reported across multiple states in Mexico since January 2022, including in the state of Durango.

When avian influenza viruses circulate in poultry populations, there is an inherent risk of human infection through exposure to infected birds or contaminated environments. As such, sporadic human cases are expected.

Although limited human-to-human transmission of A(H5) viruses was observed in isolated events between 1997 and 2007, sustained human-to-human transmission of A(H5) viruses has not been documented. Available epidemiological and virological data suggest that A(H5) viruses from previous outbreaks have not acquired the capacity for sustained human-to-human transmission.

Based on current information, the WHO assesses the overall public health risk associated with A(H5) viruses as low. However, for individuals with occupational exposure, the risk of infection is considered low to moderate.

The risk assessment will be updated as new epidemiological or virological information emerges in relation to this event.