The Flu Network
Informationisbeautiful.net took a look at animals that can catch variants of the influenza virus and created a Venn diagram which visually displays the overlap of flu viruses that can infect multiple species including humans, horses, pigs, birds, seals, and bats. We are most familiar with types B and C of the influenza virus. They cause the stereotypical flu symptoms we are all familiar with. The B and C type viruses, however, are only found in humans, and while the spread of these types of the flu can create a disease network amongst humans, it is the type A influenza virus that can create bridges to other species. Type A influenza viruses include the H2N2 “Asian Flu” that caused a pandemic in 1957, the H5N1 “Bird Flu” which kills sixty percent of humans it infects, and the H1N1 “Swine Flu” which killed 15,000 people in the 2009-2010 pandemic and killed between 50-100 million people in 1981 under the “Spanish Flu” alias. As these names suggest, there are numerous and deadly strains of the flu that humans can contract from birds and pigs, and we can even contract a strain from seals. In addition to humans and pigs, birds can have virus overlap with horses and seals. Seals also share a few common strains with horses. The H17 virus that bats can contract is not known to appear in the other species.
When we think about the spread of disease, which has been a hot topic of late in regards to ebola, we often only consider transmission from human to human. However, the nastiest types of the flu usually come from other animals. Considering global connectivity and concepts like six degrees of separation, some believe it is fair to assume that the human network is a single component, or very close to it. Compared to how connected humans are to each other, there are relatively few who are connected enough to pigs, birds, and seals strongly enough that disease contraction is possible. These connections might be viewed as local bridges. The relatively small amount of connections between humans and these animals keeps the type A flu viruses out of our daily lives for the most part, but if a virus is able to cross the local bridge into the human component, it could spread very quickly, which has happened and lead to pandemics. It was also interesting to note that if one uses the number of common strains of influenza between two species to decide if they are strongly or weakly connected (more than two common strains = strong connection), it can be observed that the network satisfies the Strong Triadic Closure Property.
Source: http://www.informationisbeautiful.net/visualizations/which-flu-virus/
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