An 11-year old Thai girl who died last September after contracting the avian flu from sick chickens is believed to have passed the disease on to her mother and aunt, raising concerns the bird flu may lead to the world's next pandemic.
The case, described yesterday in an early report from the New England Journal of Medicine, stands as the first probable person-to-person transmission of the H5N1 influenza virus that originated in Asian poultry in 1997. As of November of 2004, avian flu has resulted in 44 human infections and 32 deaths in Vietnam and Thailand. While some suspect the disease has spread in mild forms to health-care workers, there has been no evidence that serious, or lethal infection can pass between humans.
But in this case, the girl's 26-year-old mother died within two weeks of developing symptoms, and the aunt, 32, survived only after battling severe infection in hospital.
(World health experts had previously suspected the girl passed the H5N1 virus to family members. But it took several months to do lab tests and interview people who had contact with the family. The study in the New England Journal of Medicine represents the end result of that detailed investigation.)
"The current family cluster is unique in that the secondary infections resulted in severe disease and death, and the epidemiological circumstances and laboratory findings made it possible to rule out transmission from poultry," writes Dr. Kumnuan Ungchusak, lead author and researcher with the Bureau of Epidemiology and Thailand's public-health ministry.
The girl is believed to have contracted the H5N1 avian flu by sleeping and playing under her aunt's elevated house, where sick chickens were also present. However, the girl's mother, who lived in another province and worked in a garment factory, had no contact with the chickens.
For this reason, health officials believe the mother picked up the infection when she tended her sick daughter for 16 hours in hospital just before she died on Sept. 8. The mother developed a fever Sept. 11 and died Sept. 21.
While the aunt did have contact with the infected poultry, she had killed and buried all the sick chickens by Aug. 30 and did not develop symptoms until Sept. 16. Officials believe this puts her case outside the normal incubation period of bird-to-human transmission. The aunt's bedside contact with the sick child suggests she, too, contracted the infection from her niece.
Still, the authors note "no additional chains of transmission" were identified among other family, neighbours or friends of the little girl, her mother or her aunt. As well, samples of the virus from autopsy specimens also suggest the H5N1 strain has not undergone the types of changes, such as the sharing of genetic material with a human virus, that would allow it to spread widely through human populations, as health officials fear.
"These findings confirmed that the virus was not a new variant that has gained the ability to transmit itself from person to person more efficiently," wrote Dr. Ungchusak, who also worked with scientists at the U.S. Centers for Disease Control and Prevention in Atlanta. But the authors added that the avian flu virus has undergone numerous other changes in its genetic structure since it was first identified.
"If influenza A (H5N1) remains endemic for months to years to come in the eight countries that contain more than 30 per cent of the world's population, it is likely that such clusters will appear again," they write, and public-health officials will have to determine quickly if a "critical change in the virus" has occurred.
Arnold Monto, a professor of epidemiology at the University of Michigan School of Public Health, noted in an accompanying editorial that the new report raises the question as to whether small local outbreaks in Asia might be contained, or prevented, if people in contact with those who develop avian flu take an antiviral medication as a precaution.
Meanwhile yesterday, Vietnamese newspapers reported that three brothers in the north of the country who contracted avian flu drank raw duck blood at a family feast before falling ill. The news calmed fears that the virus had spread within the family from person to person, rather than through poultry. One of the men died of bird flu on Jan. 9 and his two brothers fell ill later.