Monday, 13 August 2007

Foot and Mouth Disease

I've received numerous questions on Foot and Mouth Disease (FMD), of which there's an outbreak in Britain at the moment. I thought I'd give an overview in the form of short questions and answers.

What is the cause of FMD?
FMD is caused by a virus, brilliantly named Foot-and-mouth disease virus. For those interested, it's a member of the Aphthovirus genus, and the Picornaviridae family.

Which organisms are affected?
Amongst farm animals, FMD predominantly affects cattle, sheep, pigs and goats. But it isn't limited to such an artificial category as 'farm animals' obviously. According to Britain's Department of Environment, Food and Rural affairs, the virus can also affect "elephants, hedgehogs, rats and any wild cloven-footed animals".
Here's surprising fact number one: FMD is exceptionally rare in humans.

What symptoms does it cause?
There is an intial incubation period of about 3-8 days. That is, after infection, the virus produces no noticeable effects for this period (although it is still actively replicating behind the scenes).
The first signs of the disease are non-specific: the animal develops a fever, loss of appetite, and a fall in milk production. An alert person would notice that the animal is sick, but many different diseases can cause these initial symptoms.
Two to three days later, the animals develop blisters in the mouth and/or on the feet, around the 'toes' (claws, hoof, etc., depending on the animal). As a result of this, animals tend to salivate excessively or smack their lips and/or become lame. Around 24 hours later, the blisters rupture, leaving erosions.
If all goes, well, the animals recover in 1-2 weeks.

The folowing two pictures are from Wikipedia (which had the best free pictures!):

FMD in animals has been compared to influenza (the 'flu, not the common cold, more on this later) since in both cases, the disease is usually symptomatically quite severe, although the animal usually makes a complete recovery. However, like influenza, the disease can be fatal, especially to the young (it is even a cause of abortion to cow fetuses). Other common complications include bacterial infection of the erosions in the mouth, loss of weight which takes months to recover from, and infection of the heart muscle (myocarditis).

In humans, in the rare cases where we are affected, the affects are very minor, and we always make a full recovery.

How is it spread?
Interesting fact number two: FMD is probably the most highly infectious disease affecting animals, including humans. It is shed in huge quantities from the blisters when they rupture. It is also transmissable from other body fluids - milk, saliva, urine, faeces, and even semen. So great is the viral replication in an affected animal that "their expired air is virtually a cloud of virus" (in the words of one Australian government agency).

Outside the body, the virus can survive for great lengths of time if the enivironment is favourable. Thus, major sources of infection include contaminated animals' pens, trucks used to transport them, farmer's gloves and boots, etc. Apparently, even roads can become 'infected', so that passing cars pick up the virus on their wheels and spread it to distant areas!

The virus is killed by temperatures of > 50ºC and by pHs of <>humans can't get the disease by eating infected meat - our stomach acid (which can get to pH 0.8!) rapidly destroys any virus. Uncooked meat (which is never exposed to 50ºC) is a potential source of infection to susceptible animals though. It is thought that the outbreak of FMD in Britain in 2001 was at least partially caused by feeding pigs food-refuse products that carried the disease.

Is there any treatment?
No. Once FMD is diagnosed, the emphasis is on control, not treatment. Thus, affected areas are partially 'locked down' to prevent the spread of the disease. Thereafter, the mainstay of control is the slaughtering of affected animals and possibly infected animals. There is also the potential for emergency vaccination (see below) to help prevent the spread of disease.

What about vaccination?
There are vaccines available. However, there are two big 'but's:

Firstly there are actually seven 'serotypes' (layman's term: subspecies) of the virus. Furthermore, each serotype has several subtypes of its own, which vary significantly from each other. What this means is that a vaccine for one type of FMD infection tends not to be effective as a vaccine for any other types of FMD infections. So you'd need tends of different vaccines to cover FMD. Furthermore, vaccination is only effective for several months or years, so it needs to be repeated at regular intervals. Bottom line: it's tough to vaccinate routinely (as a preventative measure). But any particular infection is caused by only one serotype of virus, though, so vaccination is to be more successful when it is used to halt the progression of an already present outbreak. This is known as emergency vaccination.

Secondly, and far more importantly, countries importing meat prefer it if the country is both (a) disease free AND (b) vaccine-free. Why the latter? Well, there are concerns about vaccination in some quarters (does it mask the actual disease? does it cause the actual disease? etc.). In other words, it literally pays countries NOT to vaccinate, as odd as that sounds. In fact, the European Union actually bans prophylactic vaccination, although it is less strict on emergency vaccination (i.e. once an outbreak is confirmed, it is permissible to vaccinate others to stop the disease, but you can't vaccinate to prevent disease in the first place). However, the EU bans the export of the 'emergency-vaccinated' animals' meat for months thereafter, so governments are reluctant to do this.
There's much more on vaccination here.

Does FMD have anything to do with Hand, Foot and Mouth disease?
Nope. HFMD is a common disease in human children. It isn't caused by the same virus, although the two viruses are distantly related.


  1. Hi all,

    I got a question from Lorna about this topic. She asks:

    I have been reading about and trying to understand the drastic reactions to outbreaks of this virus for some years. I cannot come to terms with the wholesale slaughter every time an outbreak occurs of all and any cloven hoofed animals in the vicinity.

    Your blog info is comprehensive about the ability for the virus to spread over a wide area on the 'airwaves', but is there perhaps a way of creating an immunity by trying to isolate the affected animals and let the virus run its course and learn what they achieved internally/externally to get healed?

    Is it a case that the loss and devastation to the farmers involved could also be just as much a financial burden in the long run to the economy?

    Also, what is it with England that it keeps having these outbreaks? In New Zealand we never hear of any others. Are they happening elsewhere too and never reported?

  2. Thanks for the email. The issue bothers me greatly as well. I think the problem is that the disease is so infectious that trying to contain it without animal slaughter is too risky, as depressing as that sounds. The trick would be to identify and isolate the infected animals as quickly as possible so that the number required to slaughter is small.

    As for why it is England that keeps getting outbreaks, I'm really not sure. A few things come to mind though, and the first is that England has only had two outbreaks in the last forty years, so it might be a little too early to establish a trend. Secondly, the latter of the two outbreaks was in all probability caused by contamination from a nearby lab that was working on the virus. Whether this was accidental or an act of sabotage remains to be seen.

    You also ask whether outbreaks of foot-and-mouth disease are appearing elsewhere in the world and just not being reported. Well, in countries like England, the country is thought to be disease-free. They also do not vaccinate, mainly for economic reasons (better access to the markets). Thus, when an outbreak happens, it seems to come from nowhere and spreads rapidly. FMD is endemic in areas of South America and Africa, however. Many of these countries vaccinate against the disease and so keep the infection down to a kind of grumbling low grade infection in the area.

    Anyone else care to offer an answer? (I'm a bit out of my depth here: it isn't really a human disease.)