Influenza and chips: tracking bird movements using transmitters

Understanding bird migration is one important aspect to better understanding of influenza viruses. This is because water birds, including ducks, geese, swans, gulls, terns and waders are natural hosts for low pathogenicity avian influenza viruses (LPAI). High pathogenicity avian influenza (HPAI) viruses are mostly assembled in/found in poultry.

Little detail exists on the extent of wild bird movements from wintering areas to breeding grounds and back again, in both hemispheres. An interactive map that presents some of those data addresses some of this.  The map is located on a Food and Agriculture Organization of the United Nations (UNFAO) and United States Geological Survey (USGS; (1)) website here.

While this map does not include analysis of bird movements further southwards, it is clear that the tracked birds have distinct origins and endpoints. There is also visible overlap between different bird's flyways and endpoints. Such overlap represents chances for different viral passengers to be shed and acquired by the migrating birds, resulting in the production of new influenza virus subtypes and variants. At these endpoints there is also the possibility of local birds, poultry, pigs and perhaps other animals being infected by the visiting birds, also creating the possibility for new viral subtypes and variants to result.

Bird migration clearly involves countries all over the world. It is also seasonal. So just how big is the role for water bird movements in the "seasonality" of influenza outbreaks among poultry? I don't know but the answer is influenced by additional variables including the species and age of the birds, their interactions, their previous exposures to influenza viruses, health and immune status, differences between how and where wild birds exist, how and where poultry are farmed and caged and the health and environmental factors affecting virus survivability including humidity and temperature. 

From our human point of view, we sit at various points along this migratory transmission/acquisition chain, and that shows up when viruses spillover to us and cause overt disease. 

Amazing it doesn't happen more often really.

Links of interest...

1. FAO-USGS Avian Influenza Projects at the USGS WERC
   http://www.werc.usgs.gov/ResearchTopicPage.aspx?id=17
2. H7N9 in wild birds...a review of the literature (VDU post)
http://virologydownunder.blogspot.com.au/2013/09/h7n9-in-wild-birdsa-review-of-literature.html
3. UN FAO Avian influenza telemetry studies
   http://www.fao.org/avianflu/en/wildlife/sat_telemetry.htm
4. Persistence of highly pathogenic avian influenza viruses in natural ecosystems.
   http://wwwnc.cdc.gov/eid/article/16/7/pdfs/09-0389.pdf

Humans unlikely to infect poultry with H7N9? Data please!

The United Nations Food and Agriculture Organization (FAO) has said that poultry is not at risk of being infected by humans carrying H7N9 virus.

In fact, we have no evidence that affected people could transmit the virus to other species, including birds. The highest risk of virus introduction is uncontrolled live poultry trade between affected and unaffected areas.

But absence of evidence is not evidence of absence.

We have seen studies, like this one, that use a human H7N9 virus and use it to successfully infect chickens. So the virus is capable of replicating even if it is inefficient at spreading to other chickens or even ferrets ( a human surrogate of influenza infection). But then we do know that humans get infected from exposure to something in poultry markets.

I agree (for what that's worth), that the risk of spreading virus is more in the area of moving infected birds around, as well as their own migration movements. But I think it is too early be early to issue strong denials that humans may infect poultry until we find some data to support them.

Sources...

• CIDRAP article.
  http://www.cidrap.umn.edu/news-perspective/2014/02/china-reports-one-h7n9-case-fao-says-human-illnesses-arent-threat-poultry
• H7N9 transmissibility article
  http://www.sciencedirect.com/science/article/pii/S0042682213006855
• FAO statement
  http://www.fao.org/news/story/en/item/214244/icode/

Taihu lake & influenza viruses Part II: people, pigs, poultry and migratory birds

Source of H5N1/H7N9 spatial overlap figure: Many thanks to Dr Ricardo J. Soares Magalhaes, The Univeristy of Queensland.

The figure below, from the Letter I talked about yesterday, published by Wang and colleagues in Emerging Infectious Diseases, Vol 19(11) shows the Lake Tai region.

To clarify, the paper talked about an area of high risk of infection. It did not specify whether the risk was due to exposure to poultry or wild birds. The issue of visiting LBMs and exposure to poultry and their excrement was secondary to the finding of overlapping regions of human cases and proposed region of greater risk.

Having said that, it appears (and these are all web sources so take them with a grain of chicken salt) that a domestic breed of pig and poultry may be farmed around this lake, one of China's largest fresh water bodies containing dozens of islands. Water quality and its levels algae and contaminating animal and human waster have also been issue for the lake, which supplies drinking water to approximately 30-million people in cities within Jiangsu and Zhejiang provinces. 

Expansion of poultry farm seems to have been stopped, if not contracted, and better management of aquaculture and livestock and poultry wastes has been recommended.

However, wild waterfowl as well as duck and goose farms seem to remain around the lake according to at China Travel and the maps at the bottom of this post. There seem to be monkeys and caves (bats?) too and as you would expect, this is also a thoroughfare and winter stopover for wild birds. It's also about 380km north-east of Poyang lake, another important wintering ground for wild waterbirds and one that is known to harbour influenza viruses.

• A study by Duan and colleagues  of >11,500 cloacal swabs from migratory ducks and >36,400 swabs from sentinel ducks identified 90 and 1,681 influenza isolates, respectively during 2002-2007. he sentinel duck seasonal influenza peak overlapped with the migratory duck over-wintering period. Major haemagglutinin (HA) types included H3, H4, H6 and H10. H5N1 was detected during 2005. H7 was also found. The major neuraminidase (NA) type was N6. N9 was not identified. These combined to form 27 HA/NA antigenic combinations.

You can see the overlap between areas of human infections with influenza A(H7N9) virus (green circles; area bounded in blue and green) and H5N1 (red triangles; area bounded in pink).

Below, I have excerpted 2 maps from William Wint and Timothy Robinson's document, Gridded Livestock of the World 2007 written for the Food and Agriculture Organization (FAO) of the United Nations¹. They show using livestock data modelling (which is described in the full document) that there were certainly lots of pigs and poultry in that region in 2007. 

So, the 3-Ps are in place: People, Pigs, Poultry probably kept freshly supplied with out-of-town influenza by migratory birds. 

1. FAO. 2007. Gridded livestock of the world 2007, by G.R.W. Wint and T.P. Robinson. Rome, pp 131.