H7N9 Continues Slow Spread, Animal Reservoir Still Uncertain

A steady, but slow and at least for now, not accelerating, spread of the new H7N9 bird flu virus continues. Although infection of poultry in markets in Shanghai has been confirmed and thousands of birds culled, ongoing work on the virus has yet to provide what appears to be a full description of how the virus spreads in animal hosts and gets transmitted to humans.

The latest figures from China put the death toll at 9 and the number of confirmed cases at 28 people infected. The question of whether the virus can be passed from one person to another is still under intense investigation, and two possible family clusters are being investigated. WHO spokesman Gregory Hartl was quoted by Xinhua:

“At this point, there is no evidence of sustained human to human transmission,” he said, adding that there are some “suspected but not yet confirmed cases of perhaps very limited transmission between close family members.”

“They are still being investigated,” he said.

Hartl told Xinhua one of the suspected family clusters was in Shanghai, with three family members having similar symptoms and one of them being confirmed of H7N9.

The confirmed case died, so has another suspected family member, according to Hartl.

The other suspected family cluster, which included two family members with one of them being confirmed, was in Jiangsu Province, he said.

Hartl said that even if the infection of H7N9 is confirmed in other family member, further investigations are still needed to make sure whether that’s a human to human transmission between constant and close contacts or an infection with virus from the same environmental source.

That final point from Hartl illustrates the difficulties that scientists face in developing a full description of how the disease is transmitted. At the same time that we do not yet know fully which animals are the reservoir from which humans are infected, we are simultaneously trying to determine whether family members are passing the virus to one another. That question is complicated by the fact that because the family members live in close proximity to one another but by definition also are exposed to the same local environment, multiple family members could have been infected from the same animal source or one family member could have passed the disease to another.

Moving to the question of the animal host, the same Xinhua article that quotes Hartl also informs us that no pigs have been found to be infected with the virus. Recall that large numbers of pig carcasses had been disposed of in rivers in the same areas of China around the same time H7N9 emerged, so some scientists wondered whether the virus arose in pigs and caused those deaths. There were also observations of dead birds. Xinhua has new information on analysis of bird infections:

A preliminary analysis shows that H7N9 bird flu has not triggered an epidemic among poultry, according to a Tuesday report in the People’s Daily that cited a veterinary expert.

Of the 738 samples collected from three live poultry markets in Shanghai, where the first known human deaths of the disease were reported, only 20 samples contained H7N9 virus, including 10 from chickens, three from pigeons and seven from environmental samples, the report said.

It would be helpful to know more about how these tests were carried out, especially whether the virus-positive birds were in clusters coming from single suppliers at the markets or if more than one poultry producer had virus-positive birds among the ones they brought there. It also is not clear from this article what is meant by “environmental samples”. Were these samples from bird droppings that could have been either from market poultry or from wild birds in the area? Or does that mean that the samples were known to come from wild birds in the market area? Whatever the source of the environmental samples was, though, since they were a significant portion of the positive samples, that is an area that needs lots of attention as work continues.

Unlike the SARS outbreak in 2002, China is being praised by scientists and the World Health Organization for its open and rapid response to the outbreak. As with any new outbreak, access to accurate information is key. In that regard, it stands out as significant that the number of people China has now punished under charges of spreading inaccurate information about the outbreak, 10, is larger than the number of people known to have died from the virus, 9. The Reuters article notes, however, that Chinese online activists claim that they have pressured China into being more open about the outbreak.

In its update and advisory on the outbreak yesterday, WHO said:

WHO does not advise special screening at points of entry with regard to this event, nor does it recommend that any travel or trade restrictions be applied.

Vietnam is screening at airports in Ho Chi Minh City and Hanoi anyway:

As reported, HCMC’s Tan Son Nhat Airport has used tele-thermometers to measure the body temperatures of all visitors to HCMC for detection of abnormality since last Saturday, April 6.

A similar precaution has also been carried out at Noi Bai International Airport in Hanoi, where two temperature scanners are currently in operation.

This newly emerging virus certainly is worthy of close monitoring, but at the present time does not look to me as though it is going to turn into a major outbreak without further evolution to become more rapidly transmitted to and among people. Since WHO is not recommending limits on travel or screening of travelers, it would appear that they do not expect the virus to turn into a significant global event.

Postscript: I owe a huge tip of the hat to commenter klynn, who has provided us with a steady stream of very useful links in the two previous H7N9 posts. The first link in this post comes from one of those comments and has a number of very informative graphics. The Vietnam link at the end of the post was from klynn as well.

23 replies
  1. Jim White says:

    From a tweet by Laurie Garrett, we have this news from Xinhua:

    A top Chinese biology lab has ascribed the H7N9 avian influenza to genetic reassortment of wild birds from east Asia and chickens from east China.

    The researchers found that no genes in H7N9 were traceable to pigs, thus excluding pigs as intermediate hosts for the deadly new strain of bird flu, the Chinese Academy of Sciences’ Key Laboratory of Pathogenic Microbiology and Immunology said on Wednesday.


    So the absence of pig infections is confirmed by the absence of any pig virus gene sequences in H7N9.

  2. P J Evans says:

    Since WHO is not recommending limits on travel or screening of travelers, it would appear that they do expect the virus to turn into a significant global event.

    Shouldn’t that be ‘they do not expect the virus’?

  3. Rayne says:

    So if it’s not spread by pigs, we may be relying once again on the death spiral that is ducks’ genitalia.

    No, seriously.

    See First evidence that bird flu is spread sexually 19OCT2009 (among ducks, people—not among humans that we know of)

    Also Ballistic penises and corkscrew vaginas – the sexual battles of ducks 22DEC2009

    As I understand it — can’t find the article which stitches this together, natch — the virus is spread sexually, but the ducks genitalia acts to reduce spread. (Duck A to Duck C: “Your corkscrew is unapproved! Only Duck B accepted!” Duck C to Duck A: “Oh yeah? Take that! Uh, OUCH!” *fail*)

    With sexual transmission among ducks, the disease therefore has a predictable peak time of exposure. That’s mating season among ducks, which is right now or has just wrapped up depending on how close the breeding takes place in relation to the equator. Areas south of the equator are heading into winter, so no real risk for 5-6 months from dispersion among breeding ducks.

    The other factor is the flyways used by these birds; unless a human or exported animal is shipped, the natural path of dispersion will be along migratory paths. The previous bird flu strain didn’t make it to North/South America because this is not the same migratory path taken by birds in Asia, where the last strain originated.

    Ostensibly, scientists have a narrow window of time in which to track this down before the next mating season begins, south of the equator. Gov’ts have a limited time to develop a screening and shipping policy wrt ducks and other animals exposed to them.


  4. P J Evans says:

    Asian ducks can make it to Alaska during the summer – it’s a known possibility. (Check Audubon Society and Cornell for better probability estimates.)

  5. Jim White says:

    @Rayne: Thanks for that. That explains why my Twitter timeline exploded a couple of days ago about duck genitalia. I hadn’t gotten around to checking on what all the commotion was about.

    Keep in mind also that the “high technology” used to produce flu vaccines is to inject the virus directly into chicken eggs and then harvest lots more virus after it reproduces to high numbers. That is relying on a version of the sexual transmission of the virus and why you always have to sign a release before getting the injection stating that you aren’t allergic to the proteins in chicken eggs.

  6. Rayne says:

    @P J Evans: Can, along Pacific flyway, but in what numbers and then in what degree of contact with humans? (There’s also some highly limited contact along Atlantic flyway, too.)

    The article I can’t find included some commentary on the viability of the virus for long flights, too; something about the demands of migration also discouraging dispersion. I wish I had bookmarked that article, must be 3-4 years old. *sigh*

    @Jim White: I can’t even begin to imagine what the search records looked like.

    If you saw “long duck dong” though, they were looking for Sixteen Candles by director John Hughes (1984).

  7. P J Evans says:

    I’d worry about their contact with related native ducks – the Anatidae (which includes mallard and domestic ducks) are fairly common, and male mallards will mate with any female anatid they can get to (hence the duck genitalia). Once the virus gets into the native population, it’s going to spread, because birds migrate. Whether it will get into the pigeon population, or domestic chickens and turkeys, is more of a question.

    You can get some idea of the potential by looking at, for example, the National Geographic bird guide, which includes all of North America and casual and vagrant birds from Eurasia.

  8. Dennis says:

    @klynn: And, with this (if true), one can now surmise that the immediate source of this particular strain now circulating in humans, birds, pigs(?) is …… humans, with reassortment of segments occurring sometime during this (very long) winter in China. I doubt too many Chinese domestic poultry farmers are spending money to dose their fowl with Tamiflu, right?

  9. Jim White says:

    @Dennis: @klynn: While that is a disturbing mutation to be found, note that the article says that the actual virus still showed sensitivity. For the mutation to show that it was the result of selection for resistance during a human infection, it would need to show pretty strong resistance, so it would seem to me that this more likely was just a naturally occurring, but disturbing, mutation.

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