A 3-year-old child infected with the highly pathogenic (H5N1) avian influenza virus in Mexico has died from respiratory complications. This marks the fourth fatality from avian influenza since the first case appeared in the United States earlier this year, following two fatalities in Cambodia.
According to the Mexican Ministry of Health on the 9th (local time), the deceased child was hospitalized after showing symptoms of respiratory disease following H5N1 virus infection, eventually succumbing to multiple organ failure as respiratory failure, renal failure, and liver failure occurred simultaneously.
Epidemiological investigation revealed that all 38 individuals who had close contact with the child tested negative. Health authorities have initiated infection route tracing targeting wild birds in the area where the child lived.
Recently, with the H5N1 virus spreading among poultry and wild birds primarily in the United States and Mexico, global fears are increasing as it is transmitted to humans. Avian influenza H5N1 is a variant of the A-type influenza virus, named because the proteins hemagglutinin (HA) and neuraminidase (NA) on its surface are classified as type 5 and type 1, respectively. HA acts as a key for the virus to attach to human respiratory cells, while NA allows the virus to break out of the cells after replication.
H5N1 is known to have a high fatality rate when it infects humans. According to the World Health Organization (WHO), the fatality rate is nearly 50% upon H5N1 infection. Generally, it is transmitted from birds to humans, and human-to-human transmission is considered rare.
To date, a total of four confirmed fatalities have been reported. In January, a 65-year-old patient in the United States died following H5N1 infection, having been exposed to backyard chickens and wild birds. Additional fatalities were reported in February in Cambodia, where two individuals, including a child sleeping near a chicken coop with 15 dead chickens, lost their lives.
The Centers for Disease Control and Prevention (CDC) in the United States confirmed over 70 cases of human infection with avian influenza last year, but experts noted that "the actual number of infected individuals is likely much higher," expressing concern over underreporting. Experts are particularly focused on the potential for infection spread given the active migratory patterns of wild birds and poultry farming near the Mexico-U.S. border.
Particularly, concerns have increased as Mexico was the epicenter of the H1N1 "swine flu" pandemic in 2009. At that time, more than 1.4 billion people globally contracted the swine flu. The H1N1 influenza virus that circulated then was a hybrid strain with genes from swine, avian, and human sources, colloquially referred to as "swine flu."
The WHO has stated that no human-to-human transmission of the H5N1 virus has been reported. Cases of transmission from animals to humans continue to emerge, but it has not yet spread among humans. Nonetheless, the WHO has urged governments to strengthen surveillance of animal and human infections and to share virus samples and genetic sequencing information with the international community.