The Foot-and-mouth Disease in the UK
This article talks about one of the largest disease outbreak in the recorded history of UK. In 2001, there were over 2000 cases of foot-and-mouth disease. While this virus outbreak not only caused detrimental effects to the economy of UK, it also dealt a huge blow to the natural ecosystem of the rural area of UK as the government authority had to cull large number of animals in order to prevent the disease from spreading further. According to the article, it took an estimated total of £8bn and nine months to bring the foot-and-mouth disease under control.
While I am not particularly concerned with the adverse economic impacts caused by the outbreak in this commentary, upon closer inspection, we can actually analyze the incident using the concepts we learned in networks, in particular, the theory about basic reproductive number. The basic reproductive number, denoted R0, is the expected number of new cases of the disease caused by a single individual. Suppose in a given model relating to the foot-and-mouth disease above, every animal meets k new animals and infects each with probability p. In this case, the basic reproductive number is given by R0 = pk. Furthermore, if Ro < 1, then with probability 1, the disease dies out after a finite number of waves. If Ro > 1, then with probability greater than 0, the disease persists by infecting at least one animal in each wave. In order to bring the disease under control, we should lower the basic reproductive number Ro such that it eventually becomes smaller than 1. To lower the basic reproductive number, we can either (1) lower the probability p of which each animal infects each with, or (2) lower the number of new animals k that every animal meets. By killing the animals in the affected farms and rural areas, this effectively reduces both the probability p and the number of new animals that animals k meet. As a result, when a certain number of animals are killed such that the basic reproductive number becomes lower than 1, then the disease will certainly die out after some time and the situation becomes under control.
http://www.bbc.com/news/magazine-35581830