Encephalopathy – BSE –
Mad-Cow Disease
We've heard so much about it over recent years that “Mad-Cow Disease” has become part of our day-to-day vernacular. But how much do we really know about the disease. Once the facts are examined we find that not THAT many facts truly exist and that much of the hysteria is generated from theory bent, folded or mutilated by the media. Let's take a look at what we do know:
Bovine spongiform encephalopathy (BSE) is a fatal brain disease of cattle. The disease is believed to be caused by a "self-replicating" protein (a prion) rather than a bacteria or virus. Meat and milk have not been shown to carry the infective agent and measures have been taken to exclude those parts shown to carry the infective agent (primarily brain and nervous tissue) from the food supply. BSE, a transmissible spongiform encephalopathy (TSE) of cattle, was first observed in Great Britain in April 1985, and was specifically diagnosed in 1986. By June 1990, there were some 14,000 confirmed cases out of an estimated population of 10 million cattle in Great Britain. Since 1986, more than 173,000 cases of BSE in cattle have been identified in Britain. The epidemic peaked in 1992-93 at almost 1,000 cases per week. Control measures have reduced incidence and currently, less than 100 cases are being reported per week.
Cause
The Europeans have determined from epidemiological analysis that the primary cause of BSE is consumption of contaminated feed. What is not so clear is what was the initial source of the BSE agent in feed. There are four main possibilities and in each case, it appears that the many transmission route was the utilization of rendered by-products, predominantly meat and bone meal in the feed or supplement. Let me emphasize that these are conditions identified by the British and European cattle industries.
1) Origin from scrapie in sheep; Scrapie (a parasitic organism) has been prevalent in the sheep population of Great Britain for at least two centuries. There was a significant increase in the sheep population in GB from 1980 onwards, and possibly an increase in the prevalence of scrapie. This explanation probably best fits the data we have.
2) Exposure to rare sporadic BSE. It is possible that BSE is a naturally occurring and long established disease of cattle, but which occurs extremely rarely. Passing infectious material from such an animal through a rendering process no longer capable of destroying the agent could have led to contamination of the cattle feed chain. However, there is no reason why, if BSE is a natural, sporadic but very rare disease of cattle, that it should be confined to the United Kingdom, with no traces of the disease have been diagnosed before 1985. Similarly, the occurrence of BSE in other countries is consistent with exposure from imported cattle or meat and bone meal from Great Britain. This explanation, though consistent with the epidemiological data, seems less likely than a scrapie origin.
3) A new strain of scrapie which was particularly infectious to cattle might have arisen and then entered the cattle feed chain through meat and bone meal. One would expect any such new strain of scrapie to emerge first in a single flock of sheep and so any epidemic resulting from exposure to it to begin in a geographically localized area. However, the BSE epidemiology shows a geographically widespread occurrence with simultaneous onset and not one which starts from a single point of infection, and this explanation is not consistent with the development of a new strain.
4) Imported African bone meal - Early epidemiological investigations ruled out the use of imported feed ingredients as a factor in the epidemic. Several cases of BSE have been diagnosed in captive ruminants in British Zoo's. While the most likely explanation is that the exotic ruminants became infected by the same route as British cattle, via concentrate feed containing meat and bone meal, it has also been suggested that the BSE epidemic may have arisen from an African source.
Regardless of the initial origin of BSE in cattle, it is clear that the epidemic was sustained and boosted by the recycling of BSE infected cattle material to other cattle from the mid 1980s onwards. The vast majority of cases have therefore been caused by cattle material being fed to other cattle.
Control
Uncertainty of the precise origin of BSE does not affect the control measures taken - the ruminant feed ban removes both sheep and cattle material from ruminant rations, and is designed to prevent transmission in feed between, as well as within, species. Affected cattle are destroyed and burned or buried and exports of cattle from affected countries has been highly restricted. In the United States ruminant feed materials have been banned from use in cattle and swine rations as a proactive measure although no BSE has been reported.
Hoof and Mouth Disease
Also known as Foot-and-Mouth Disease, HMD is a highly contagious viral disease of cattle, sheep, hogs, and other animals with cloven (divided) hoofs. Hoof and Mouth Disease is considered the most costly of all animal diseases. First, it is often necessary to conduct wholesale slaughter of animals wherever there is an outbreak. Second, no animals from an area not declared free of the disease may be moved to other locations or used in trade (including trade in semen) except as processed food subjected to high temperatures. It is also one of the most contagious. FMD is a viral disease that can infect all cloven-hoofed animals – cattle, goats, sheep, pigs, water buffalo, deer, bison, antelope, reindeer, llamas, chamois, alpacas, vicunas, giraffes, elephants, elk, and camels. Infection does not actually affect the hard structures of the hoof, but rather the soft tissues around it. Foot-and-mouth disease occurs among livestock in many regions of the world, particularly in Africa, Asia, and South America. The disease is rare in Australia, much of Europe, and North America.
Cause and Symptoms
A small, ball-shaped virus causes foot-and-mouth disease. Healthy livestock may acquire the disease through contact with infected animals or with objects that have been contaminated by saliva, other body fluids, or wastes from infected animals. Winds and animals that are not themselves affected by foot-and-mouth-disease, such as birds, cats, and rats, may spread the virus. People may also spread it if they have been in direct contact with the virus. It is possible for people to develop a mild, temporary infection.
The virus produces painful, fluid-filled blisters on the lips, tongue, gums, nostrils, and upper part of the foot. In animals, blisters also develop in the tissue between the two parts of the hoof. The blisters break open after a few days and become raw sores. Infected animals also develop a high fever, salivate (drool) excessively, have difficulty walking, and lose weight. In female animals, the virus also affects the milk-producing glands, decreasing their yield. Foot-and-mouth disease rarely kills adult animals, but it causes a higher death rate among the young. The disease hurts farmers economically by reducing their livestock's meat and milk production.
Control
There are no specific cures or treatments for foot-and-mouth disease, but farmers use a variety of methods to control or prevent it. In the African, Asian, and South American countries where the disease is endemic (found regularly), livestock owners control it chiefly through the use of vaccines. Veterinarians must administer vaccines at regular intervals because most protect the animals for only a short period. The vaccines are also expensive, and in some cases, they accidentally contain live viruses that may infect the animals.
In the United States and most other countries where the disease is not endemic, it is controlled chiefly through import restrictions and quarantine procedures. Such measures normally prevent the introduction of the virus. These countries also have policies for eliminating the virus if an outbreak occurs. As stated previously, most such policies call for slaughtering the infected animals, burying or burning their carcasses, and decontaminating the area where the animals lived
Conclusions
The United States has been fortunate not to be affected directly by either of these conditions. It is vital that the industry remain vigilant to prevent an introduction of either of these conditions. It is also vital that we take a proactive stance in controlling the media hysteria that could serve to have serious negative effects on our market. In the next issue we'll discuss what type of effects these situations have had on the market here in the United States and what implications may lie ahead.
Dr. Steve Blezinger is a management and nutritional consultant with an office in Sulphur Springs, TX. He may be contacted at P. O. Box 653 Sulphur Springs, TX 75482, by phone at (903) 885-7992 or by e-mail at sblez@peoplescom.net
