̽��ֱ�� of Cambridge - H1N1 influenza

Threat of novel swine flu viruses in pigs and humans

Anonymous — Wed, 27 Apr 2016 11:21:37 +0000

While swine flu viruses have long been considered a risk for human pandemics, and were the source of the 2009 pandemic H1N1 virus, attention has recently turned to the transmission of flu viruses from humans to pigs.

"Once in pigs, flu viruses from humans continue to evolve their surface proteins, generically referred to as antigens, resulting in a tremendous diversity of novel flu viruses that can be transmitted to other pigs and also to humans," explains first author Nicola Lewis from the ̽��ֱ�� of Cambridge.

"These flu viruses pose a serious threat to public health because they are no longer similar enough to the current human flu strains for our immune systems to recognise them and mount an effective defence. Understanding the dynamics and consequences of this two-way transmission is important for designing effective strategies to detect and respond to new strains of flu."

Humans and pigs both experience regular outbreaks of influenza A viruses, most commonly from H1 and H3 subtypes. Their genetic diversity is well characterised. However, the diversity of their antigens, which shapes their pandemic potential, is poorly understood, mainly due to lack of data.

To help improve this understanding, Lewis and her team created the largest and most geographically comprehensive dataset of antigenic variation. They amassed and characterised antigens from nearly 600 flu viruses dating back from 1930 through to 2013 and collected from multiple continents, including Europe, the US, and Asia. They included nearly 200 viruses that had never been studied before.

Analysis of their data reveals that the amount of antigenic diversity in swine flu viruses resembles the diversity of H1 and H3 viruses seen in humans over the last 40 years, driven by the frequent introduction of human viruses to pigs. In contrast, flu from birds has rarely contributed substantially to the diversity in pigs. However, little is currently known about the antigenic relationship between flu in birds and pigs.

"Since most of the current swine flu viruses are the result of human seasonal flu virus introductions into pigs, we anticipate at least some cross-protective immunity in the human population, which could potentially interfere with a re-introduction of these viruses. For example, the H1N1pdm09 viruses circulating in both humans and pigs are antigenically similar and therefore likely induce some immunity in both hosts," says Lewis.

"However, for the H1 1C, H3 3A, and H3 3B human seasonal lineages in pigs, the risk of re-introduction into the human population increases with the number of people born after the circulation of the human precursor virus, and is increased by the antigenic evolution of these viruses in pigs. Earlier introduced lineages of human H1 and H3 viruses therefore pose the greatest current risk to humans, due to the low or negligible predicted levels of cross-immunity in individuals born since the 1970s."

Swine flu causes symptoms such as coughing, fever, body aches, chills, and fatigue in humans. Pigs can also experience fever and coughing (barking), along with discharge from the nose or eyes, breathing difficulties, eye redness or inflammation, and going off feed - although some display no clinical signs at all.

Vaccination to control flu in pigs is used extensively in the US and occasionally in other regions. Control strategies vary by region, with some countries not using any vaccinations, while others produce herd-specific vaccines for individual producers. There is no formal system for matching vaccine strains with circulating strains, however, and no validated protocols for standardisation and effective vaccine use.

" ̽��ֱ��significant antigenic diversity that we see in our data means it is highly unlikely that one vaccine strain per subtype would be effective on a global scale, or even in a given region," says co-author Colin Russell, also from the ̽��ֱ�� of Cambridge.

"Our findings therefore have important implications for developing flu vaccines for pigs. They also emphasise the need for more focused surveillance in areas with a high pig population density, such as China, and situations where humans and pigs have close contact, in order to better assess the incidence of transmission between the animals and risk of spreading to humans."

Reference:

̽��ֱ��paper ' ̽��ֱ��global antigenic diversity of swine influenza A viruses' can be freely accessed online at http://dx.doi.org/10.7554/eLife.12217.

Originally published as a press release by eLife.

̽��ֱ��wide diversity of flu in pigs across multiple continents, mostly introduced from humans, highlights the significant potential of new swine flu strains emerging, according to a new study.

These flu viruses pose a serious threat to public health because they are no longer similar enough to the current human flu strains for our immune systems to recognise them

Nicola Lewis

Robert Shell

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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New analysis of 'swine flu' pandemic conflicts with accepted views on how diseases spread

sc604 — Tue, 01 Jul 2014 08:12:49 +0000

̽��ֱ��most detailed analysis to date of the spread of the H1N1 2009 pandemic influenza virus, known informally as ‘swine flu’, has found that short-range travel was likely the primary driver for the 2009 pandemic in the United States, in contrast with popularly accepted views on the way diseases spread.

̽��ֱ��study, based on data gathered from health insurance claims made throughout 2009, found that international air travel, which was previously thought to be important in the pandemic, played only a minor role in its spread within the US.

A team of researchers from ̽��ֱ�� of Cambridge and the US, including Princeton ̽��ֱ�� and National Institutes of Health, analysed data from 271 American cities and their surrounding suburban areas, covering 90% of the population of the 48 contiguous states.

̽��ֱ��data were used to test mathematical models to pinpoint the role and importance of factors associated with H1N1’s arrival and spread, including demographics, school opening dates, humidity levels and immunity from previous outbreaks.

According to this new analysis, school-age children accelerated the spread of the pandemic, which was transmitted over short distances, in contrast with widespread reports at the time linking the pandemic to international air travel and population density. ̽��ֱ��results are published in the journal PLOS Computational Biology.

̽��ֱ��H1N1 influenza virus spread rapidly around the globe in 2009 after it was first identified in Mexico. ̽��ֱ��US Centers for Disease Control (CDC) estimates that the global death toll from the 2009 pandemic was more than 284,000.

̽��ֱ��virus hit the United States in two distinct waves during 2009: one in the spring, which was limited mainly to the North Eastern part of the country; and a second wave in the autumn, which started in the South Eastern US and gradually spread across the whole country over a period of three months.

Previous research on the pandemic found that environmental factors, timing of the end school holidays, population sizes and air travel contributed to its spread, but this new research has found that transmission occurred primarily over short distances and that school age children may have catalysed the spread.

“There is so little detailed analysis of the way in which pandemics spread – so much of the current thinking is based on opinion and presumption,” said Dr Julia Gog of Cambridge’s Department of Applied Mathematics and Theoretical Physics, who led the research. “We have a view of how diseases spread in the medieval times, and it is often said that the modern world is completely different as we have long distance high volume air travel. However what we find here is that although air travel must have caused the initial ‘sparks,’ the bulk of the pandemic wave was very slow, travelling at about 22 kilometres per day. This really challenges our views of modern pandemics.”

In collaboration with researchers from a number of American universities, Dr Gog analysed weekly numbers of patients who reported influenza-like illnesses to their physician, organised by zip code. ̽��ֱ��data enable the researchers to explore the pandemic’s spread in more detail than had previously been possible, as well as identify any gaps in the data and validate existing models.

“It’s remarkable that in an era of widespread air travel and regional ground transport that this pandemic spread so slowly,” said Dr Gog. While international air travel did play a role in the initial seeding of the outbreaks in spring 2009, it played a relatively minor role in the later spread. ̽��ֱ��researchers hypothesise that H1N1’s relatively low rate of transmission meant that in many cases, the virus failed to ‘take’ after being introduced to a community through air travel. In contrast, repeated transmission over short distances started chains of infection which then contributed to the overall spatial spread of the pandemic.

̽��ֱ��travel patterns of children also appear to have played an important role. While one might assume that the movements of children would primarily be between home and school, there is little available information to confirm this. “This is just not studied,” said Dr Gog. “Especially in densely populated areas, any parent will tell you that their child travels over relatively short distances each day, but we simply don’t have the data to back that up.”

In addition to broadening understanding the dynamics of a pandemic, the researchers hope that the potential role of children in influenza spread might lead to more information on this age group’s role in infection transmission.

New analysis of the 2009 H1N1 influenza pandemic in the US shows that the pandemic wave was surprisingly slow, and that its spread was likely accelerated by school-age children.

There is so little detailed analysis of the way in which pandemics spread – so much of the current thinking is based on opinion and presumption

Julia Gog

Mapping the spread of H1N1 influenza

Julia Gog

Map of the H1N1 influenza pandemic in 2009. ̽��ֱ��size of the dots is relative to city size, and the colours relate to the number of influenza cases, with green the lowest and purple the highest.

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