Chinese health authorities have identified a brand-new type of bird flu that killed an elderly woman in November and infected at least one other person in January.
That trend prompted the experts to call for stepped-up surveillance to track the new H10N8 influenza virus in poultry markets and in human patients.
"The pandemic potential of this novel virus should not be underestimated," the medical team wrote in a report published Wednesday by the journal Lancet.
Genetic analysis of the H10N8 influenza virus revealed that it has two mutations that make flu viruses more virulent in mammals, according to the Lancet report.
But the researchers also shared some encouraging news. Investigators have not found any evidence of person-to-person transmission so far, and tests showed that the virus is sensitive to the drugs Tamiflu (oseltamivir) and Relenza (zanamivir).
The new strain is the first flu virus found in humans that combines a gene to make an H10 hemagglutinin protein and a gene to make an N8 neuraminidase protein. Hemagglutinin allows flu particles to latch onto a host cell, which it enters to make copies of itself. Then neuraminidase allows the new flu particles to leave the host and attack other cells. (For more on how flu viruses work, read this explainer from the early days of the H1N1 swine flu outbreak.)
"Human infection with avian influenza A H10N8 virus has not been reported previously," the authors wrote.
Here's what health officials were able to determine about the initial H10N8 victim, a 73-year-old woman from Nanchang City:
She was already suffering from high blood pressure, coronary heart disease and a neuromuscular disorder called myasthenia gravis when her flu symptoms appeared on Nov. 27, 2013. At first, she had a cough and chest tightness. Two days later, she started to run a fever.
The woman was admitted to a hospital on Nov. 30 with a temperature of nearly 101.5 degrees Fahrenheit. Her fever later rose to nearly 103 degrees F. CT scans revealed that portions of her lungs had filled with liquid. Then both sides of her lungs developed pleural effusions, a dangerous condition of fluid buildup in the space that surrounds the lungs.
After one week, blood tests showed signs of liver and kidney failure. She was treated with antibiotics, antiviral drugs, steroids and a blood protein called albumin. Doctors put her on a mechanical ventilator to help her breathe.
Despite these efforts, "the patient's condition became progressively serious: she developed severe pneumonia, septic shock, and multiple organ failure," according to the Lancet study. The woman died nine days after she fell ill.
Specimens from her trachea showed that H10N8 was the dominant flu in her system. The research team concluded that the H10 gene was most closely related to a virus found in Chinese ducks and that the N8 gene originated in birds from North America. The other genes from the flu strain were probably from an H9N2 virus circulating in Chinese poultry. The researchers hypothesized that an as-yet undetected strain of H10N8 in wild birds infected a poultry bird with H9N2, and that the two strains then re-combined to form the virus that killed the elderly woman.
But for now, this scenario remains speculative. The woman did visit a live poultry market four days before she became sick, but she stayed for only five minutes and never handled any live chickens herself. Tests of birds in that market have so far failed to turn up any samples of the fatal H10N8 virus.
The epidemiological portion of the investigation also found that the woman did not encounter anybody with flu symptoms in the two weeks before she became sick. None of her 17 close contacts – including family members, caregivers and healthcare providers – had the flu before or after her illness.
The patient's family did not allow doctors to conduct an autopsy, which prevented the investigators from conducting some of the tests they normally do.
Still, the experts said they know enough to be wary of the H10N8 virus, which could become extremely dangerous if it were to develop the ability to jump from person to person. The research team noted that there was a six-month gap between the first human case of H5N1 flu (in Hong Kong in 1997) and the next 17 cases, so now is the time to be vigilant with H10N8.
"The first human infection with novel avian influenza A H10N8 virus further increases the importance of surveillance for pandemic preparedness and response," they wrote.