SNAPDATE: H7N9 by map...

With the latest numbers out from Hong Kong's Centre for Health Protection, Week 10 marks the second week of around a dozen human spillover cases - likley to be poultry to human infections.

Click on image to enlarge.

While the number of cases at each geographic location within China is small given the millions living in each region, this week's cases are spread across 10 provinces or municipalities. A huge area. 

Guangxi province is adjacent to Vietnam. It's always worth remembering that an outbreak anywhere can turn into a threat everywhere. 

From these numbers, there is no obvious escalation of human cases to suggest anything has changed in the way H7N9 infections are acquired; they remain relatively rare and from animal-to-human close contact.

While the cases are still coming, the totals (see weekly and daily bars below) shows a levelling off - at last suggesting a slowing of this season's epidemic. But stay tuned.

Numbers of human H7N9 cases.

Image taken from the VDU static H7N9 graphs and numbers page.

Click on image to enlarge.

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.