SITNFlash

Greetings SITN members!

Well, it's that time…. time to announce the topics of the Science in the News 2006 seminar series! Please see below for details about the 2006 schedule which starts this September. We have quite a diverse line-up of scientific topics this year covering everything from global warming to heart disease. In response to your feedback, we have retained some popular topics, such as obesity and diabetes, but even if a topic has been covered in previous years, rest assured that new information will be presented for those of you who have been with us before. We also will have some brand new topics, such as the latest research in the field of growing organs for therapeutic purposes, which promises to be a particularly fun and informative evening. Remember our seminars are totally free of charge and you can attend as many as you want. We hope you are as excited about this line-up as we are, and we look forward to seeing you at the seminars. In the meantime, we hope you enjoy all the pleasures of summer, and of course, the latest NewsFlash article.

Enjoy!

On February 27, 2006, a cattle farm owner in Alabama reported a sick cow on his land. The cow could not stand and exhibited head tremors. The local veterinarian could not provide a conclusive diagnosis. The cow was euthanized and brain samples were sent for analysis to several laboratories across the country. On March 15, the National Veterinary Services Laboratory concluded that the cow was sick with Mad Cow Disease. Although the U.S. Department of Agriculture (USDA) concluded that there was no potential contamination of the food supply with tissues from this cow, the incident has led to renewed fears about the safety of the U.S. beef supply and warrants a closer look at the threat of Mad Cow Disease. With the summer barbeque season upon us, one has to wonder: how safe is the U.S. beef supply?

What causes Mad Cow Disease?

In order to differentiate between the real risks and consequences of Mad Cow Disease and the panic incited by the frequent and sometimes incendiary media reports, it is important to understand what causes the disease and how it is transmitted. The cause of the disease, otherwise known as Bovine Spongiform Encephalopathy (BSE), puzzled researchers for many years, until Stanley Prusiner, M.D., a professor of neurology at the University of California in San Francisco, characterized a novel infectious agent, referred to as the prion. For this groundbreaking work, he was awarded the Nobel Prize in Physiology and Medicine in 1997.

Although prions themselves were identified relatively recently, the neurodegenerative diseases caused by them have been documented for over 200 years. One of the first of these diseases to be described was scrapie, in sheep. In cows, the disorder is known as Mad Cow Disease or BSE, while the human form of BSE is called variant Creutzfeldt-Jakob Disease (vCJD), a distinct form of CJD that is contracted from consuming mutant prion-contaminated beef. The symptoms of vCJD in humans include dementia, memory loss, personality changes, speech impairment, and motor dysfunction. The incubation period, or the length of time following infection before clinical symptoms appear, is approximately 4 to 5 years in cattle, and about 10 years in humans. Currently, no treatment is available for this disease.

The first BSE cases were reported in the United Kingdom in 1986. It is thought that use of meat and bone meal (MBM)derived from scrapie-infected sheep and included in cattle feed as a protein source was responsible for the spread of the infectious agent. The number of cows infected with BSE in the U.K. at that time was estimated to be in the hundreds of thousands. To date, 190 people worldwide have died from vCJD, with two of those deaths occurring in the U.S. It is important to note, however, that none of those people became infected from beef that was raised on U.S. soil.

Prions are drastically different from all microbes or pathogens identified to date. Prions are neither viruses nor bacteria. They contain no genetic material, such as RNA or DNA, to direct their activities and replication. A prion is a single protein, called prion protein. In its normal form, it is found throughout all the cells in the body, and at especially high concentrations in nervous system tissue. It is only when normal prion protein is converted to its mutant form, that it becomes a threat to the cell. The precise mechanism of this conversion is not entirely clear, but it is known that the mutant protein can act as a catalyst in the conversion of normal prion proteins to the mutant protein form, thus initiating a chain reaction.

The mutant form of prion protein is “sticky” and leads to the formation of large aggregates of prion protein within the cells of the infected organism. These aggregates appear to contribute to the death of brain cells, called neurons. The loss of neurons, in turn, leads to the sponge-like, or spongiform, appearance of brain tissue and diverse neurological symptoms.

How is BSE transmitted?

In BSE-infected cows, mutant prion protein is primarily found in neuronal tissue, such as cells of the brain, but also at lower levels in the small intestine. Both cows and humans contract the disease by consuming tissues contaminated with mutant prion protein; there is no existing evidence to suggest that direct cow-to-cow or person-to-person contact can spread the disease. During the preparation of ground beef, neuronal tissues can come in contact with muscle tissue, thus contaminating the beef with infectious prion particles. Ground beef, as well as other forms of processed meat such as hot dogs and sausages, pose a specific threat in the transmission of BSE to the human consumer. Less processed meat, such as steak, is less likely to have come in contact with infected neuronal tissue and is, therefore, less likely to transmit BSE. Importantly, prions are unlike other food-borne pathogens in that thorough cooking of the meat does not decrease their infectivity.

What safeguards are in place to prevent spread of the disease?

The clinical assays used to test for the presence of prions include examination of brain tissue under a microscope for the tell-tale signs of mutant prion-induced destruction of the brain’s architecture, as well as molecular biology techniques to test for the presence of mutant prion protein. Unfortunately, these diagnostic tests require invasive procedures to collect samples, meaning that they must be performed post-mortem. Currently, there are no Food and Drug Administration (FDA)-approved tests available to easily test living subjects for the presence of prions.

A number of laws and regulations have been put in place by the FDA and the USDA in order to protect the U.S. beef supply from contamination with BSE-infected material. All beef imports from European countries with documented incidents of BSE were banned as of July of 1989. This ban was subsequently extended to all European countries in 1997. Also in 1997, the FDA banned the use of animal by-products, such as MBM, in cattle feed in order to prevent spread of BSE in U.S. cattle herds. Additionally, no material from “downer” cows (those that cannot walk) is permitted to enter the human food supply. New regulations have also been applied to the slaughtering process in order to minimize the risk of spread of BSE within meat processing plants. All products from animals that are being tested for BSE are withheld from the market until the tests return negative. Routine surveillance and testing of cattle deemed to be at high risk for BSE helps to prevent potentially infected beef from reaching the grocery aisle.

BSE and its causative agent are under intense investigation in laboratories around the world. Current studies are focused on learning more about the cause of the disease and how it spreads, as well as on developing better diagnostic tests and potential treatments. In the meantime, the precautions taken by government agencies to safeguard the beef supply greatly decrease the possibility of a BSE outbreak in the U.S. The exceedingly low incidence of cows with BSE in the U.S., the ban on beef imports from at-risk countries, combined with the fact that no one has yet contracted the disease from U.S. beef, should calm fears of an imminent BSE epidemic. So fire up the barbeque: in all likelihood, the biggest danger lurking in your burger is saturated fat.

-- Anna S. Kushnir, Harvard Medical School

For More Information:

FDA information about BSE: <http://www.fda.gov/oc/opacom/hottopics/bse.html>
General resource for BSE facts and news: <http://www.BSEInfo.org>
Alabama BSE Investigation, Final Epidemiology Report, May 2, 2006: <http://www.BSEInfo.org>
Mayo Clinic information on CJD: <http://www.mayoclinic.com/health/creutzfeldt-jakob-disease/DS00531>

Here's the schedule for the 2006 lecture series! The series kicks off on September 21st with an introductory lecture entitiled "Making Sense of Science in the News," with a new lecture every week thereafter on a wide range of topics in the headlines, from mental health to global warming. Lastly, this year we will be continuing to offer or lectures on two night at two locations, so feel free to attend the seminar that is more convenient for you! Here is the full schedule:

Of course, this information may change as we get closer to the start of the series, so check http://sitn.hms.harvard.edu/ for the latest updates!