#18,422
Two weeks ago Mexico's MOH Reported Their 1st Human H5N1 Case involving a 3 y.o. child from the state of Durango, who fell ill in early March, and was reportedly hospitalized in the city of Torreón and listed in serious condition.
The patient was reported to have died of respiratory failure several days later.
Last year Mexico announced the death of a 58-year-old man (who also suffered from serious comorbidities) who tested positive for H5N2, becoming the first laboratory-confirmed human case of influenza A(H5N2) infection reported globally.
While the subtypes differ, in both cases the source or route of exposure to these viruses remains a mystery.
Late yesterday the WHO published a DON (Disease Outbreak News) report on this latest case (excerpts below). The big reveal is that this H5N1 virus was clade D1.1, which has previously been linked to a more serious infections in both the United States and Canada.
Due to its length, I've only posted some excerpts, so follow the link to read the update in its entirety. I'll have more after the break.
Disease Outbreak News
Avian Influenza A(H5N1) - Mexico
17 April 2025
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 Peña 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.
(SNIP)
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.
One of the challenges in dealing effectively with H5N1 are delays in diagnosing this subtype. In this case, the girl had been ill for > 25 days - and hospitalized for 19 days - before a positive H5N1 diagnosis was confirmed.
While PCR is a highly sensitive and reliable influenza test, the window for detecting an influenza A infection is relatively narrow, with best results obtained during the first week of infection. After 7 days, the ability to reliably detect Influenza A infection drops off sharply.We've seen similar delays with other H5 cases, including here in the United States. Three months ago the we looked at a CDC HAN which urged Accelerated Subtyping of Influenza A in Hospitalized Patients for this very reason.
Making the negative results from close contacts - who are often tested weeks after exposure - less probative than they might appear.
While most known human H5 infections have been epidemiologically linked to a specific agricultural exposure (cows, chickens, wild birds, etc.), over the past year we've seen a handful (U.S. x 4, Mexico x 2, Canada x 1) where the source of exposure remains unknown.
Given the limits of surveillance and testing (see above), it is highly likely there are other H5 cases going undetected.
While there is still no evidence of efficient human-to-human transmission, that is something that can only be detected after it's begun in earnest (see UK Novel Flu Surveillance: Quantifying TTD).
Stay tuned.
