Bovine Spongiform Encephalopathy, widely referred to as mad cow disease has had a dramatic effect on the livestock industry in the United Kingdom and Europe and is causing significant concern in the United States.
Information available from the World Health Organization indicates that BSE is not only of concern to the livestock industry, but also because many people in the United Kingdom and Europe believe there is a link between BSE and Creutzfeldt-Jacob disease.
BSE is classified as a transmissible spongiform encephalopathy. The agent responsible for BSE and other TSEs is smaller than the smallest known virus and is not completely characterized.
Three theories.
There are three main theories on the nature of this disease agent:
* The agent is a virus with unusual characteristics.
* The agent is a prion-a type of protein that carries some genetic code and is highly resistant to breakdown by enzymes, heat and disinfectants.
* The agent is a virino-a small noncoding nucleic acid coated with a protective protein.
The BSE agent is extremely resistant to heat and to normal sterilization processes. It does not evoke any normal detectable immune response or inflammatory reaction in host animals.
Back in the news.
BSE has been in headlines once again in recent weeks. Europeans and citizens of the United Kingdom have experienced a series of discoveries resulting in government restrictions on mammalian meat and bone meal in feeds for all food producing animals. Agricultural officials in Great Britain have taken a series of steps to eradicate BSE, including: making BSE a notifiable disease, prohibiting the inclusion of mammalian meat-and-bone meal in feed for all food-producing animals, prohibiting the inclusion of animals more than 30 months of age in the animal and human food chains, and destroying all animals showing signs of BSE.
During the period from 1986 (when BSE was first identified as a separate disease), until July, 1999 more than 175,000 head of cattle from more than 34,000 herds were diagnosed with BSE in Great Britain. The epidemic peaked in January 1993 at almost 1,000 new cases per week.
Currently, according to the USDA’s Animal and Plant Health Inspection Service, the rate of newly reported cases is decreasing and is below 60 per week. BSE has also been confirmed in domestic cattle in Belgium, France, Liechtenstein, Luxembourg, the Netherlands, Portugal and Switzerland. APHIS is enforcing import restrictions and is conducting surveillance for BSE to ensure that this serious disease does not become established in the United States.
Risk Factors relative to BSE:
* BSE may be transmissible to humans.
* The causative agent of BSE is not known for sure.
* There is no test to detect BSE in a live animal.
* There is no treatment for BSE.
* There is no vaccine.
Clinical signs.
Cattle affected by BSE show no symptoms for two to eight years after infection. Affected animals experience progressive degeneration of the nervous system. These animals display changes in temperament such as nervousness or aggression, abnormal posture, incoordination, difficulty in rising, decreased milk production or loss of body weight despite continued appetite. Affected cattle die.
From onset of symptoms, the animals die or must be destroyed within two weeks to six months. Most cases in Great Britain have occurred in dairy cows between 3 and 6 years of age. In cattle infected with BSE, the BSE agent has been found only in brain tissue, the spinal cord and the eye.
How does BSE spread?
There is no evidence that BSE spreads directly from animal to animal, although some research suggests that there may be transmission from mother to offspring. Data from Great Britain suggest that BSE may have resulted in cattle from feeding rendered protein produced from the carcasses of scrapie-infected sheep.
Another theory is that BSE has existed at undetectable levels in the British cattle population prior to 1986. The practice of using products such as meat-and-bone meal as a source of protein in cattle rations has been common for several decades. Changes in rendering operations in the early 1980s may have played a part in the appearance of the disease and the large number of cases that developed.
Related diseases.
The TSE family of diseases includes scrapie of sheep and goats, transmissible mink encephalopathy, feline spongiform encephalopathy, and chronic wasting disease of deer and elk. Kuru, classical and variant Creutzfeldt-Jakob disease, Gerstmann-Straussler-Scheinker syndrome and fatal familial insomnia are five rare diseases in humans that are also TSE’s.
In 1996 the United Kingdom’s Spongiform Encephalopathy Advisory Committee announced that although there was no direct scientific evidence of a link between BSE and classical or variant Creutzfeldt-Jakob disease, the most likely cause of ten new cases of variant Creutzfeldt-Jakob disease in Great Britain was exposure to BSE before the specific bovine offal ban at slaughter in 1989. The ban excluded from human consumption brain, spinal cord, and other organs with potential BSE infectivity.
What is the difference?
Classical Creutzfeldt-Jakob disease occurs each year at a rate of one to two cases per one million people throughout the world, including in the United States and in other countries where BSE has never occurred and among vegetarians and meat-eaters alike.
Classical Creutzfeldt-Jakob disease occurs sporadically and is not linked to BSE. According to the U.S. Department of Health and Human Services’ Centers for Disease Control, no cases of variant Creutzfeldt-Jakob disease have been found in the United States.
Research published in October, 1997 found evidence to further link variant Creutzfeldt-Jakob disease to BSE. Investigators in the United Kingdom found that BSE and variant Creutzfeldt-Jakob disease are of the same “strain.” In addition, classical Creutzfeldt-Jakob disease and known scrapie strains are not similar to variant Creutzfeldt-Jakob disease or BSE.
USDA actions.
The United States has one of the most aggressive BSE surveillance programs in the world. BSE has not been diagnosed in the United States and USDA has worked proactively to keep it that way. In cooperation with USDA’s Food Safety and Inspection Service, APHIS has taken stringent measures in prevention, education, surveillance, and response.
To prevent BSE from entering country, since 1989 APHIS has prohibited the importation of live ruminants from countries where BSE is known to exist in native cattle. Other products derived from ruminants such as fetal bovine serum, bonemeal, meat-and-bone meal, bloodmeal, offal fats, and glands are also prohibited from entry except under special conditions or under USDA permit for scientific or research purposes.
On Dec. 12, 1997, APHIS, stopped the importation of all live ruminants and most ruminant products, meat-and-bone meal, offals, glands, etc. from Europe until APHIS scientists can assess the disease risk and evaluate surveillance activities in individual countries.
APHIS leads an ongoing, comprehensive interagency surveillance program for signs of BSE in the United States. FSIS pre-slaughter inspection procedures include identifying animals with certain nervous system conditions. Such animals are prohibited from slaughter and are referred to APHIS for review. APHIS labs examine brains from high-risk cattle exhibiting signs of neurological disorders. Scientists also test for the presence of the disease agent. To date, no evidence of BSE has been detected in the United States.
Response plan.
APHIS has drafted an emergency response plan to be used in the event that BSE is detected in the United States. As an additional measure, APHIS supports the Food and Drug Administration’s regulation (effective Aug. 4, 1997) prohibiting the use of most mammalian protein in the manufacture of animal feeds for ruminants. The regulation also requires process and control systems to ensure that ruminant feed does not contain the prohibited mammalian tissues.
For information about BSE contact:
USDA, APHIS, Veterinary Services Emergency Programs 4700 Riverdale Road, Unit 41 Riverdale MD 20737-1232 or by telephone at 609-259-5825 or 301-734-8073.
(The author is an agricultural extension agent in Columbiana County. Questions or comments can be sent in care of Farm and Dairy, P.O. Box 38, Salem, OH 44460.)
