March 3, 2014
China reports additional cases of H7N9
China reported three more cases of H7N9 virus, as new research findings implicated chickens as the main source of the virus and emphasised the importance oropharyngeal swabs for testing birds.
Human cases in the outbreak''s second wave continue to taper, with sporadic cases mainly reported from recent hot spots, as well as other provinces that reported earlier cases.
Two of the new case-patients are from Hunan province, a 77-year-old man and a 41-year-old man who are hospitalised, according to a provincial health department statement.
The third case-patient is from Jiangsu province, a 42-year-old man who apparently bought chickens at a local market and is hospitalised in serious condition, according to a provincial notice.
These new cases boost the overall outbreak total to 376 infections, with the number of deaths holding steady at 114. So far 240 bird flu illnesses have been confirmed in the second wave that''s currently under way, compared with 136 recorded last spring during the first wave.
On the other hand, the World Health Organization (WHO) provided details on five more case notifications it received from China on February 23 and February 24, all from Guangdong province. Three are men, and patient ages range from 31 to 76.
Before they got sick, four of the five patients had been exposed to live poultry. Illness-onset dates range from February 16 to February 19. Four of them are hospitalised in critical condition, while one is listed in stable condition.
Meanwhile, experiments that involved infecting different poultry species with H7N9 conducted at the USDA Southeast Poultry Research Laboratory (SEPRL) in Athens yielded new clues about likely reservoirs and promising testing methods. The group published its findings in the latest online issue of the Journal of Virology.
Many human cases had involved live poultry or their environments, and health officials have suspected that poultry infected with low-pathogenic viruses, which typically infect birds without causing symptoms, are the main drivers of the outbreak.
Agriculture officials in China have tested thousands of birds, and have found H7N9 in only a small number of them. These have included chickens, plus a small number of pigeons and ducks. Also, a recent report from Chinese researchers described the isolation of H7N9 from an apparently health tree sparrow collected last spring in Shanghai.
In order to know which species are most likely to be infected and shed enough viruses to infect humans, the SEPRL intranasally inoculated chickens, Japanese quail, pigeons, Peking ducks, mallard ducks, Muscovy ducks, and Emden geese with H7N9 virus. The birds became infected but showed no clinical signs.
Quail and chickens shed the virus at much higher levels and for longer times than other birds. The team found that quail transmitted the virus to their direct contacts, but pigeons and Peking ducks didn''t.
For all of the species, researchers recovered the virus at much higher levels from oropharyngeal swabs than from cloacal swabs. Researchers said that the findings show that quail and chickens probably play an important role in spreading the virus to humans.
In other developments, researchers from China looked back at 27 human H7N9 cases detected in Jiangsu province to get a better idea of the incubation period for the disease. Their report appeared online February 24 in Epidemiology and Infection.
The incubation period for H7N9 is generally thought to be three to seven days, but it has been reported to be as long as 10 days. The US Centres for Disease Control and Prevention, recommends that close contacts of H7N9 case-patients be monitored for 10 days after their last known exposure.
A detailed look at patients'' poultry exposures and infection onsets found that the median incubation period was six days with a single known exposure (range two to 10 days) and 7.5 days when patients were exposed on multiple days (range, 6.5 to 12.5 days). Taken together, the overall median incubation period was 7.5 days.
The group noted that the findings suggest that health officials should extend the medical surveillance period from seven days to 10 days.
Source: CIDRAP - Centre for Infectious Disease Research and Policy