Bird Flu On the Move?
By Stan Deresinski, MD, FACP, FIDSA
Clinical Professor of Medicine, Stanford University, Editor of Infectious Disease Alert
In the last 11 months of 2013, there was a total of 144 confirmed cases of H7N9 infection in China, with 46 deaths. This case total was almost duplicated during one month — January of this year — during which 127 cases were reported. No evidence of sustained person-to-person spread of H7N9 has been found, though some evidence points to limited person-to-person spread in rare circumstances. No cases of H7N9 outside of China have been reported. The new H7N9 virus has not been detected in people or birds in the United States
Human cases of influenza due to the avian virus, H7N9, were first detected in February 2013 in China. During spring of that year, the World Health Organization (WHO) reported 132 human H7N9 infections, with 44 deaths, with most cases having illness onset during the month of April. The following month, however, the number of cases plummeted, likely as a result of both a change in seasons (like seasonal influenza, avian viruses circulate at higher levels in cold compared to warm weather) and control measures, including the closure of live bird markets. This respite was short-lived, with cases once again appearing in October and in January alone there was a total of 127 cases, with 44 deaths. These 127 cases were just 17 fewer than reported in all of 2013.
Contact with infected poultry accounts for almost all cases of infection, which can be asymptomatic. Serosurvey data from outbreak areas found no instances of seropositivity among 1129 general population subjects, while >6% of 396 poultry workers had a hemagglutination inhibition titer of ≥ 80.1
Human-to-human transmission has occurred and an example is illustrated by a report of 15 cases from China received on February 7 and 9 of 2013. Thirteen had been exposed to live poultry. Of the 14 people who have survived their infections at the time of the report, 8 were hospitalized in critical condition, 5 were in severe condition, and one, a 5-year-old boy, had a mild illness. The boy who was a close contact with a 41-year old woman with infection. Of note is that this family is from Guangxi province, which borders Vietnam. Fortunately, sustained human-to-human transmission has not been observed.
H7N9 is resistant to adamantanes but, with some exceptions, is susceptible to neuraminidase inhibitors. An amino acid change in the viral neuraminidase associated with drug resistance, NA-R292K (N2 numbering), has been found in some H7N9 clinical isolates.2 These isolates are highly resistant to both oseltamivir and peramivir and have reduced susceptibility to zanamivir. Unfortunately, this mutation does not impair viral fitness since H7N9 reassortants with and without the resistance mutation demonstrate comparable replication within human respiratory epithelial cells, as well as similar virulence in mice and transmissibility in guinea pigs.
Travelers to countries with known outbreaks of avian influenza should avoid poultry farms, contact with animals in live bird markets, entering areas where poultry may be slaughtered, or contact with any surfaces that appear to be contaminated with faeces from poultry or other animals. Frequent hand washing should be performed, as well as maintenance of food safety and hygiene. WHO does not advise special screening at points of entry with regard to this event, nor does it currently recommend any travel or trade restrictions.
- Yang S, et al. Avian-Origin Influenza A(H7N9) Infection in Influenza A(H7N9)Affected Areas of China: A Serological Study. J Infect Dis 2014;209: 265-9.
- Hai R, et al. Influenza A(H7N9) virus gains neuraminidase inhibitor resistance without loss of in vivo virulence or transmissibility. Nature Comm 2013; Dec 10;4:2854. doi: 10.1038/ncomms3854.