Mutated Bird Flu Strikes First Human Case in Canada, Raising Concerns Over Severe Illness

A 13-year-old girl from British Columbia, who was unexpectedly hospitalized for several weeks in late last year due to bird flu, has been found to possess a mutated strain of the virus. This alarming discovery was documented in a recent report published in the New England Journal of Medicine.

First Human Infection in Canada

This incident marked the first recorded instance of human infection with avian influenza in Canada, coinciding with at least 66 reported cases in the United States since the previous March, as noted by the Centers for Disease Control and Prevention. Among these cases was Louisiana's inaugural severe case of the virus in December.

Mild Symptoms Predominant

Despite the concerning occurrences, most bird flu cases in North America have exhibited mild symptoms, including conjunctivitis (pink eye), runny nose, chills, cough, and sore throat. Dr. Chanu Rhee, an infectious disease expert at Brigham and Women's Hospital and an associate professor at Harvard Medical School, expressed concern over the sporadic severe cases, emphasizing the potential for even seasonal influenza to occasionally induce serious illness. The situations involving the Canadian teenager and the Louisiana patient stand as isolated instances but underscore the virus's capacity to inflict severe harm.

Mutations in the Virus

The report reveals that the virus samples from both cases displayed mutations that enabled it to attach more effectively to cells in the mucous membrane of the upper respiratory tract. These mutations are particularly concerning as they signify the virus's enhanced ability to infect humans. Dr. William Schaffner, a professor of infectious diseases at Vanderbilt University School of Medicine, explained that the average bird flu virus is not well-suited for binding to human cells, making these mutations noteworthy.

Transmission Uncertainties

While the presence of these mutations raises caution, it's essential to note that it doesn't confirm the virus's capability to spread between individuals. Angie Rasmussen, a virologist at the University of Saskatchewan's Vaccine and Infectious Disease Organization, emphasized that despite the mutations, no secondary infections occurred, indicating that the virus did not demonstrate the ability to transmit between humans in these cases.

Viral Adaptations

The mutations observed in the bird flu viruses causing severe infections in British Columbia and Louisiana primarily occurred in a protein responsible for cell attachment, analogous to the spike protein of the coronavirus. Typically, these proteins on the H5N1 virus are adapted to attach to receptors in birds, which explains the virus's effectiveness in infecting avian species. However, the mutations seen in the severe cases allowed these viral variants to bind to receptors in the human mucous membrane, signifying a potential adaptation for human infection.

Impact of Prolonged Infection

In individuals who are immunocompromised or possess underlying health conditions that compromise their immune response, viruses enjoy enhanced replication opportunities. The prolonged presence of the virus facilitates numerous replication cycles, increasing the likelihood of mutations that can enhance its transmissibility. The study further revealed that the British Columbia teen's virus sample exhibited a mutation that accelerated replication within infected cells, a trait not present in the Louisiana patient's virus sample. This differentiation underscores the diverse adaptations the virus can undergo in different hosts.

Concurrent Infections and Their Risks

The simultaneous infection of humans by the avian flu virus, especially in conjunction with the seasonal flu, poses an additional concern. The mingling of H5N1 and seasonal flu viruses during replication events, a phenomenon known as reassortment, can lead to the emergence of new, potentially more virulent strains. Dr. Rasmussen highlighted the analogy of this process to shuffling two decks of cards, emphasizing its potential to facilitate significant evolutionary advancements for the virus.

Pathways of Infection

Although the precise pathways of infection for the Canadian girl and the Louisiana patient remain unclear, it is believed that both individuals encountered the virus through contact with birds, albeit through different means. The report indicates that the Canadian girl was exposed to a variant of the virus associated with wild birds in British Columbia, while the Louisiana patient’s exposure was traced to a backyard flock. Other reported cases in the U.S. have also been linked to contact with poultry or dairy cows.

Prolonged Hospitalization

The Canadian girl initially presented with mild symptoms, including conjunctivitis and fever, and visited the emergency room on November 4. However, her condition deteriorated, leading to a subsequent emergency room visit where she exhibited respiratory distress and organ dysfunction. The severity of her illness necessitated transfer to the pediatric intensive care unit on November 8, followed by the application of advanced life support measures on November 9. After weeks of intensive treatment involving antivirals and mechanical ventilation, the patient's breathing tube was successfully removed on November 28, signaling significant improvement.

Potential for Antiviral Resistance

Notably, despite the observed mutations, the avian flu virus remained susceptible to available antivirals, providing a ray of hope in managing such infections. Dr. Schaffner acknowledged the continued susceptibility of this virus, akin to other bird flu strains, to existing antiviral treatments, underscoring the importance of timely intervention in severe cases.

The complexities of human immunity to avian flu are influenced by various factors, including prior exposure to different influenza strains. While some viral immunologists speculate the potential for crossover protection based on historical interactions with influenza viruses, the extent of this protection is expected to be limited.