Mad Cow Disease: Advice for Expatriates and Travelers.
-- Frank Gillingham, MD
Many expatriates, travelers, and study abroad participants wonder about the safety of beef and other products derived from cattle. Will they get Mad Cow disease from eating a hamburger or steak?
What is Mad Cow Disease?
Mad Cow Disease is a somewhat mysterious disease of cattle that was first recognized in Britain about 15 years ago. Afflicted cattle behave strangely, displaying nervousness or aggressive behavior. They also may exhibit abnormal posture, clumsiness, decreased milk production and weight loss. They die a few weeks or months after symptoms begin.
Mad Cow began to get a lot of attention in the mid to late 1990's when its human form, now known as vCJD, was first recognized. The disease is as dreadful in humans as it is in cattle. Victims gradually lose their ability to think, reason and remember, and often suffer hallucinations and uncontrolled body movements. Diagnosis is made by a physician based on the patient's symptoms, with the help of an EEG (brain wave test), MRI and/or Tonsil Biopsy. Patients die within a year or two after symptoms begin (which is usually many years after the infection occured--see below). Both Mad Cow and its human variant are thought to be caused by poorly understood, misshapen proteins called Prions, which are also discussed below.
The Terminology is Confusing
As noted above, Mad Cow is a disease of cattle. It is sometimes referred to as Bovine Spongiform Encephalopathy, or BSE, because at autopsy the brains of cattle that die of it look somewhat like a sponge. This general class of disease is sometimes referred to as Transmissable Spongiform Encephalopathies, or TSEs. The human form of Mad Cow/BSE is generally referred to as a "variant of Creudtzfeldt-Jakob Disease" or "vCJD." It is also sometimes known as "new-variant of Creudtzfeldt-Jakob Disease" (nvCJD). These latter terms all mean the same thing. Creudtzfeldt-Jakob (CJD) is a disease that has been known for many years which has similar symptoms and appears to have a similar cause as vCJD, though it is spread in different ways.
The Outbreak of Mad Cow and vCJD
Mad Cow was first discovered in 1986 though it probably began in the 1970's. Because sheep suffer from a similar disease called scrapie, scientists immediately suspected that cattle feeds containing meat and bone meal from other animals, including sheep, may have led to a new disease, similar to scrapie, in cattle. In the UK use of these feeds was partially banned in 1988, with further restriction coming in 1994 and 1996. Because it was not known that the disease could or would jump from cattle to humans, however, infected cattle continued to enter the food supply even after the outbreak was first discovered (scrapie, the sheep disease, has never jumped to humans).
In 1996 human cases of vCJD were first proven to be related to Mad Cow. As a result the British government in particular began to fund an enormous research effort into the disease, an effort that continues to this day. Hundreds of thousands of cattle were destroyed and dozens of public health measures taken to improve the safety of the food supply and to prevent further the spread of the disease in both cattle and humans. However, it has been estimated that as many as one million infected cattle entered the food chain in the UK.
In the UK the public response to the outbreak, to the destruction of cattle (a disaster for British farmers), and to the worldwide ban on British beef, was vociferous. Some observers believe that former British Prime Minister John Major and his conservative government suffered their eventual electoral downfall due to their handling of the crisis. In October of 2000, the first cases of Mad Cow were discovered on the European continent. Many of these have been traced to cattle that originated in the UK.
Fortunately, as tragic as the disease is, it appears to be quite rare. Since the beginning of the outbreak in 1996, about 100 cases of vCJD have been diagnosed in the UK, a handful in France and one in Ireland. New cases continue to be diagnosed. Most of those diagnosed have died from the disease.
The possibility remains that large numbers of humans are harboring the disease. Many scientists believe the number of humans cases will continue to grow even after the food supply becomes safe, as individuals who acquired the disease many years before eventually become sick. In addition, the epidemic might appear to grow, even when new infections are actually shrinking, because surveillance and testing have increased so dramatically. Cases that were previously attributed to other diseases that cause memory loss and personality change may now be diagnosed as vCJD, making it appear as if the disease is spreading.
Prions and other general facts.
As noted above, scientists believe that misshapen proteins called Prions cause Mad Cow and its human form vCJD. Prions are unusual because they do not contain genetic material (DNA or RNA), as do other infectious agents like viruses and bacteria, not to mention all other living things. Prion-like proteins appear normally in human and animal brains, but when they become misshapen they can cause disease, apparently by inducing other proteins to assume an abnormal shape. Eventually groups of these misshapen proteins form toxic tangles or plaques that damage the brain and spinal cord. Dr. Stanley Prusiner won a Nobel Prize for decades of pioneering work on Prions.
Prions are mysterious. They're difficult to test for and even harder to destroy--in fact, they can withstand radiation, chemicals, even commercial autoclaves that are used to sterilize surgical instruments. There are no treatments available for the diseases Prions cause, which generally occur anywhere from a few years to a decade or more after the initial infection (doctors call this a long 'incubation' period). Thus infected cattle and humans generally carry the disease for many years before becoming ill.
Is European beef safe?
Like most things in medicine and public health, there is no guarantee, just as there is no guarantee that some cattle in the US aren't infected. Many observers believe that the food supply is safer than ever in the UK and in Europe. An enormous number of precautions have been put into place to prevent infected cattle from entering the food supply--in fact all cattle over the age of 30 months are tested. Cattle younger than 30 months have never been infected, supporting the belief that the removal of meat and bone meal from cattle feed has eliminated new infections in cattle.
Europeans are eating more beef now than they were at the end of 2000, though consumption remains below its historical peak. Some observers expect it to return to pre-panic levels by the end of the year (year 2000 consumption in Britain exceeded consumption in 1995, the year before the diagnosis).
Last updated: July 12, 2001.
The author thanks Dr. Nancy Salzman, Paris, France, for assistance in preparing this article.