A May 6 study in Science with the banal title of “Relationship Between Clinical Signs and Transmission of an Infectious Disease and the Implications for Control,” written by a number of scientists at the Institute for Animal Health in Surrey and the Centre for Immunity, Infection and Evolution at the University of Edinburgh, has garnered a lot of publicity. The study involved foot-and-mouth disease, a worldwide scourge for cattle which had had its most virulent outbreak in a developed country in the United Kingdom in 2001.
What is revolutionary about the study may be surprising to non-scientists. What the scientists did with cattle was to study the interaction between infected animals and healthy ones in order to learn exactly when the infected animals were actually transmitting the disease. You may well think, "don’t we know this already? Was I coughing into my elbow for no reason at all?" The answer is, we didn’t know it at this level of detail, and when fashioning quarantines of people or animals, or mandatory culls of animals, knowing it at this level of detail can save lives and money. As Mark Woolhouse, one of the scientists who co-authored the study, said as quoted in Science Daily,
If you do things like measure virus in the blood, you’re taking no account of the clinical state of the animal. People might imagine that the clinical signs of a virus — the symptoms, such as sneezing — have something to do with its transmission. But, while there has been a lot of thoughtful speculation on the topic, there haven’t been many actual studies.
As a result of the study, for these animals and with this one disease, they estimated that the actual period of transmission was much shorter than had been previously thought, and not necessarily related to the animal showing the outward signs of the disease.
In reading this, I was reminded of a statement in Simon Winchester’s Atlantic, where he points out how much more we know about the surface of the moon than the undersea part of the surface of the earth. The same can be said for the way microorganisms operate in the environment as close as your nose or a cut on your skin. Although it is obviously a different thing to study foot-and-mouth disease for cows, who are unwitting subjects, than, say, influenza on humans, these techniques may be applicable in some ways to study a whole range of diseases, which can refine the public health reaction to a host of outbreaks. The study suggests that if diagnostic tools can be found to pinpoint the moment of contagion, quarantine can be more effective and possibly both shorter and involving fewer subjects, and more destructive means of prevention like culling may be avoided. To quote further from Woolhouse’s interview with Science Daily:
We now know that there is a window where, if affected cattle are detected and removed from the herd promptly, there may be no need for pre-emptive culling in the immediate area of an infected farm. We have an opportunity now to develop new test systems which can detect infected animals earlier and reduce the spread of the disease.
This is a two-edged sword, and potentially both edges can be used for good. If we can develop tools to find contagious subjects more exactly, we can take effective steps to quarantine them for just the right period of time. And we would be able to rule out non-contagious subjects that are currently impacted out of an abundance of caution.
Which brings us back to the past. Now that we know what we know, what of the thousands of British cows slaughtered in 2001, including those at farms where the cows showed no symptoms but were located next to the outbreaks? The study certainly suggests that this was unnecessary. But before any British cattle farmers consider calling in a solicitor, however, they need to understand a couple of things. First, public health officials have historically always been given a lot of leeway in terms of making decisions to promote the general welfare. When the cows are showing signs of disease, no one has the time to do a ten-month study; you do what you can right then. Second, and most germane, liability, if any, would be based on the state of knowledge at the time of the incident. It could hardly be treated any other way. This both acknowledges the state of (or lack of) knowledge and encourages the advance of scientific learning. If you try one solution and it seems like it could be improved, you’re less likely to improve it if you might end up being liable for how your first attempt worked out.