Nuzzo says it’s very likely that the Louisiana patient’s pre-existing conditions contributed to the severity of the disease, but he also points to the case of a Canadian teenager who was hospitalized with bird flu in November.
A 13-year-old girl was initially admitted to an emergency department in British Columbia with fever and conjunctivitis in both eyes. She was discharged home without treatment and developed cough, vomiting, and diarrhea. A few days later, she returned to the emergency room for respiratory failure. She was admitted to the pediatric intensive care unit where she developed respiratory failure, but eventually recovered after treatment. According to A case report published in the New England Journal of Medicinethe girl had a history of subtle asthma and an elevated body mass index. It is not known how she contracted the virus.
“What this tells us is that we have no idea who will develop mild disease and who will develop severe disease, so we have to take these infections very seriously,” Nuzzo says. “We should not assume that all future infections will be mild.”
There is another clue that may explain the severity of the cases in Louisiana and British Columbia. Virus samples from both patients showed some similarities. First, they were both infected with the same subtype of H5N1 called D1.1, which is the same type of virus found in wild birds and poultry. It differs from the B3.13 subtype, which is dominant in dairy cows.
“The question right now is, is this a more serious strain than the dairy cattle strain?” says Benjamin Anderson, assistant professor of environment and global health at the University of Florida. So far, scientists don’t have enough data to know for sure. A handful of Washington poultry farm workers tested positive for the D1.1 subtype, but these people had subtle symptoms and did not require hospitalization.
“In the case of the infection in Louisiana, we know the person had underlying health conditions. We know it was an elderly person. These are factors that contribute to more earnest consequences even in the case of respiratory infections,” says Anderson.
In the cases of Louisiana and British Columbia, there is evidence that the virus may have evolved to cause more severe disease in both patients.
AND CDC report from late December discovered genetic mutations in the virus from a patient in Louisiana that may have allowed it to increase its ability to infect the upper respiratory tract in humans. The report indicated that the observed changes likely arose from viral replication during the patient’s illness rather than being transmitted at the time of infection, meaning the mutations were not present in the birds to which the person was exposed.
Writing in New England Journal of Medicinethe team caring for the Canadian teenager also described “concerning” mutations detected in her virus samples. These changes may have allowed the virus to more easily bind to and enter cells in the human respiratory tract.
In the past, bird flu was rarely transmitted from person to person, but scientists fear a scenario in which the virus acquires mutations that make it more likely to transmit the virus to humans.
For now, people who work with or have recreational contact with birds, poultry or cows are at greater risk of contracting bird flu. To prevent disease, health officials recommend avoiding direct contact with wild birds and other animals infected or suspected of being infected with bird flu viruses.