Date: 21 January 2019 By: Anton van Zyl
In the Vhembe District residents have become used to a disease such as foot-and-mouth disease (FMD). For as long as we all can probably remember, the “red line zone” at the northern parts or towards the Kruger National Park has been there. We may, however, forget why such a zone is necessary and what the dangers of a highly infective disease entail.
To understand why FMD is such a danger, one must understand epidemics and how they spread. We have many examples in history, the most severe probably being the Black Death, which peaked in Europe between 1347 and 1351. This outbreak of bubonic plague wiped out almost 60% of Europe’s population. It may have reduced the world population from an estimated 450 million down to 350-375 million.
FMD is, of course, not a deadly infection that affects humans directly, but the disease is one with an extremely high spreading rate. To understand what a spreading rate is, we can use gossip as an example.
Let’s presume you hear a very saucy piece of information, some really scandalous stuff. Imagine that you’re living in the age before social media (yes – no Facebook) and you can only tell it, in the strictest of confidence, to two of your friends. These two blabbermouth friends, of course, cannot keep it to themselves and within half an hour they have each told two friends. Naturally their friends cannot keep the secret and within another half an hour they have each shared the gossip with two friends. And so the process continues…
If you shared the news for the first time at 08:00 that morning and you try and estimate how many people know the news by 20:00 that night, you may be in for a surprise. During this 12-hour period, 24 intervals of 30 minutes each have occurred during which the news was shared, and it has literally gone viral. By 20:00 that night, 33 554 431 people would know the secret.
The spreading rate of the news would, of course, be determined by many factors such as the “availability” of two friends not knowing the news. If some of the friends hearing the gossip tell only one other friend, the spreading rate is drastically affected. If the spread factor drops below one (i.e. fewer than an average of one person gets told the news), the gossip starts dying out.
This spread factor is what is so important for epidemiologists when looking at diseases. It also depends on a number of other factors, such as the nature of the virus or bug itself and the infectious period. Some germs are very powerful and can infiltrate the body in many ways. Others, such as HIV, are not particularly easy to transmit but have a high spread factor because the virus can survive for a long time.
All of these factors are taken into consideration and an estimated spread factor is calculated. Diseases such as smallpox have a typical infectious period of four years with a spread factor of 4. Measles have an infectious period of 14 days, but a spread factor of 17. (The spread factor consists of rough averages and will differ in countries and areas.)
This brings us to the dreaded foot-and-mouth disease. Some epidemiologists estimate its spread factor as over 100. The reason for this is because FMD replicates extremely rapidly and can affect a wide range of domestic and wild, cloven-footed animals. (It is not limited to cattle and is spread by pigs, sheep and in South Africa by buffalo and other wild animals). The virus has a short incubation period and can spread quickly over relatively large distances. The virus can be spread by infected animals through contact with contaminated farming equipment, vehicles, clothing, feed and by domestic and wild predators. The virus can also be distributed by air, under certain conditions.
In 2010, an FMD outbreak occurred in Japan. The first strategy of the authorities was to try and stamp it out where it was reported, disinfect the areas and restrict movement. This did not prove sufficient, and emergency vaccination was adopted. The epidemic occurred in an area with a high density of cattle and pigs, making disease control difficult. A total of 292 outbreaks were subsequently confirmed and 290 000 animals had to be culled.
In South Africa, and more specifically in the Vhembe area, the outbreak should, in theory, be easier to contain. Animals in the area where it was reported can be isolated and the movement of livestock can be limited. A proper vaccination programme will make it difficult for the virus to spread further. Although scientists’ opinions differ, the FMD virus will probably not survive more than three months without a host.
If, however, residents ignore the warnings and move infected animals to other areas, a crisis will be a distinct possibility.
(Main source for statistical analysis: How Long is a Piece of String by Rob Eastaway & Jeremy Wyndham.)
Anton van Zyl has been with the Zoutpansberger and Limpopo Mirror for over 27 years. He graduated at the the Rand Afrikaans University (now University of Johannesburg) and obtained a BA Communications degree. He is a founder member of the Association of Independent Publishers.