Apr 5, 2013 (CIDRAP News) – Chinese agriculture officials today confirmed the H7N9 virus in chickens and pigeons from Shanghai markets, providing new clues about how humans may have been exposed to the virus, which has since yesterday been detected in two more people.
Details of the lab confirmations came in two reports from China's agriculture ministry to the World Organization for Animal Health (OIE). They describe findings on birds from three different markets in the Shanghai area.
Global total climbs to 16 cases
Confirmations of the two additional human cases came through the news media and in updates from health groups, including the World Health Organization (WHO). The two newest H7N9 cases are both older adults from Jiangsu province, which is about 190 miles west of Shanghai. They raise the global total to 16 infections, which includes 6 deaths.
The WHO's report today said the two patients from Jiangsu province are a 61-year-old woman who got sick on Mar 20 and a 79-year-old man who started having symptoms on Mar 21. Both are hospitalized in critical condition. A statement today from Hong Kong's Centre for Health Protection (CHP) said no epidemiologic links have been found between the two patients.
So far no evidence of human-to-human spread has been detected in the follow-up of 520 close contacts of the confirmed cases, the WHO said. However, health officials in Jiangsu are investigating a report of flulike symptoms in one of the contacts of a confirmed case in Jiangsu province.
At a media telebriefing today, Tom Frieden, MD, director of the US Centers for Disease Control and Prevention (CDC) said Chinese health officials are investigating possible illnesses in two families of confirmed cases. However, he said authorities are confident that the virus isn't spreading widely.
Meanwhile, the European Centre for Disease Prevention and Control (ECDC) today released an epidemiologic update that contained the same case and fatality counts as the WHO's. The ECDC said five of the patients had contact with animals, four with poultry and one with pigs.
The ECDC provided an epidemiologic chart reflecting symptom-onset dates ranging from Feb 19 to Mar 29.
Lab positives in market pigeons and chickens
Yesterday the Chinese media, citing official agriculture ministry sources, reported that the H7N9 virus had been detected in pigeons from an agricultural market and that the H7 virus had been detected in other unidentified samples.
Two OIE reports, released late yesterday and early today, contained several more details about the positive H7N9 test findings. The first said the virus was detected in one pigeon for sale for consumption at a wholesale agricultural market in Shanghai's Songjiang district. Tests on seven chicken samples and one environmental sample from the same market were also positive for the virus. The report said the birds had subclinical illness and the virus that infected them is a low-pathogenic strain.
Officials emphasized that so far there is no evidence that the source of the human cases was an infected pigeon, but further investigations were under way.
In the second OIE report, a chicken and an environmental sample at a market in the city's Minhang district yielded the H7N9 virus. It also described positive findings in two chicken samples, two pigeon samples, and four environmental samples from a different market in the same district. As in the first report, the birds didn't show symptoms and the virus was a low-pathogenic strain.
Juan Lubroth, DVM, PhD, chief veterinary officer for the United Nations Food and Agriculture Organization (FAO), told CIDRAP News that it's difficult to identify the route of exposure or how extensive the virus circulation is from so few positive samples. However, he said information is coming in at a brisk pace, and the FAO is in close and frequent communication with China's agriculture industry and has a team at its office in Beijing.
In light of the initial positive findings, the FAO today issued a statement warning farmers, merchants, and others that the H7N9 virus is hard to detect because it causes few signs of disease in birds. Lubroth said in the statement that against the backdrop of silent infections in poultry, biosecurity and hygiene measures become even more important for protecting people and animals from the virus circulating in seemingly healthy birds or other animals.
In an accompanying frequently-asked-question document on the H7N9 detections, the FAO said that although commercial H7 vaccines are on the market for poultry, the organization isn't currently recommending them for poultry in areas where the virus has been found, because their effectiveness against the strain is not known. The FAO said it is reviewing genetic information to determine if the vaccine is likely to be effective against the virus.
In the FAO statement Lubroth also praised China for its quick notification of human cases, release of detailed information to the public on the nature of the virus, and institution of precautionary measures.
Findings so far appear to confirm some expert predictions that chickens are involved but that other animals may harbor the virus as well. Some virologists who have examined H7N9 genetic sequences from databases have said the virus shows signs of adaptation to mammals.
The lab findings triggered the culling of 20,536 birds, including chickens, ducks, geese, and pigeons, from a live poultry trading zone in Shanghai, according to a report today from Shanghai Daily, an English-language newspaper.
Experts look for clues in bird detections
Les Sims, BVSc, an animal health consultant based in Australia who has extensive experience with avian influenza in Asia, has been closely following H7N9 developments in China through media and scientific reports. He said that news photos of culling exercises show poultry wholesale markets that typically don't house mammal species but that it's difficult to rule out the possibility of other animals having been housed in the area. He also noted that it is uncertain whether the photos are current or that they actually depict the markets that were the source of the positive findings.
News that officials are temporarily shuttering some live poultry markets isn't surprising, Sims said. "There was probably no other choice but to close the markets given the number of cases and apparently detection of virus in more than one market," he added. "This assumes that poultry are an important source of infection for humans and if so this will reduce the risk at least in the short term for the urban population of Shanghai."
Pigeons are generally considered less suitable hosts for avian influenza viruses compared with other avian species, he said. The lower susceptibility in pigeons has been shown in published studies comparing tracheal organ cultures of various avian influenza subtypes from different birds.
"Until there are more experimental data on the current virus in pigeons and other birds, all we can do is rely on earlier studies and assume that the H7N9 virus is probably not well adapted to pigeons, suggesting there may well be other sources of virus," Sims said.
Richard Slemons, DVM, PhD, professor in the department of veterinary preventive medicine at Ohio State University (OSU), said until scientists get more data, questions about the virus are going to keep coming up, and most observations about the H7N9 virus in China are going to be speculative.
He said one point of confusion is the public's understanding of low-pathogenic and highly pathogenic avian influenza viruses. The low-pathogenic designation, which includes the H7N9 detected in the Chinese market pigeons and chickens, relates how likely the virus is to kill chickens—not humans, he noted.
The strain's low pathogenicity means that infections in poultry are hard to detect without outward signs of illnesses or deaths. Without ongoing active surveillance, Slemons said it's hard to tell if H7N9 has been circulating in poultry for a long time or if it is a recent spillover.
A public health issue that's often overlooked is the devastation that a highly pathogenic strain can cause, he said. Besides posing a pandemic threat, it can wipe out a country's protein supply and devastate its economy, he added.
Veterinary officials will learn more about the source of the virus as they expand and intensify their surveillance, but for now it's all speculation, stated Slemons. Detecting the virus in an animal doesn't mean it is the source, and while it's doubtful that pigeons can harbor the virus, chickens can maintain them, he said.
If the virus has been circulating in China and the Shanghai area, the Chinese New Year observances might have played a role in the spread of the virus and the timing of its emergence, according to Slemons. He noted that the Chinese New Year celebration took place in early and mid February, and the first illness emerged just days later.
"People travel a lot and frequently carry presents, and some of those can be poultry," Slemons said, adding that the practices have the potential to spread the virus from an urban center like Shanghai to more rural locations such as Jiangsu or Zhejiang provinces, two areas that have reported human H7N9 infections.
Experts are speculating about many different routes of the infection, and with time research will provide the answers to many questions about the source and spread of the virus, he said. "Should we panic? No, but we should be concerned."
Apr 4 OIE report
Apr 5 OIE update
Apr 5 FAO statement
Apr 5 FAO FAQ
Apr 5 WHO statement
Apr 5 ECDC epidemiological update
Apr 5 CHP statement
Apr 5 Shanghai Daily story