BSE - Faculty and Staff
Archived from the original on 28 September The cow was included in the United States Department of Agriculture's surveillance program, specifically targeting cattle with BSE . Views Read Edit View history. The traditional method of diagnosis relies on histopathological examination of the medulla oblongata of the brain, and other tissues, post mortem.
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BSE has a long incubation period , of 2. The cause of BSE, like other Transmissible spongiform encephalopathies is unknown, however, it is thought to be caused by a misfolded protein — a prion. The disease may be most frequently transmitted to humans by eating food contaminated with the brain, spinal cord, or digestive tract of infected carcasses. A British and Irish inquiry into BSE concluded the epizootic was caused by cattle, which are normally herbivores , being fed the remains of other cattle in the form of meat and bone meal MBM , a protein supplement in concentrated feeds.
The cause of BSE may be from the contamination of MBM from sheep with scrapie that were processed in the same slaughterhouse. The epidemic was probably accelerated by the recycling of infected bovine tissues prior to the recognition of BSE. BSE is a transmissible disease that primarily affects the central nervous system ; it is a form of transmissible spongiform encephalopathy , like Creutzfeldt—Jakob disease and kuru in humans and scrapie in sheep, and chronic wasting disease in cervids.
Symptoms are not seen immediately in cattle due to the disease's extremely long incubation period. This results in poor balance and coordination.
Some rare but previously observed symptoms also include persistent pacing, rubbing or licking. Additionally, nonspecific symptoms have also been observed which include weight loss, decreased milk production, lameness, ear infections and teeth grinding due to pain.
Some animals may show a combination of these symptoms, while others may only be observed demonstrating one of the many reported. Once clinical symptoms arise, they typically get worse over the upcoming weeks and months, eventually leading to recumbency, coma and death. The identity of the infectious agent responsible for BSE and other transmissible spongiform encephalopathies is unknown, and there are many theories as to its causation. The prevailing theory is that it is caused by a specific type of misfolded protein called a prion.
Eventually, the prions aggregate into an alpha helical , beta pleated sheet , which is thought to be toxic to brain cells. The agent can be transmitted to humans by eating food contaminated with it.
The agent is not destroyed even if the beef or material containing it is cooked or heat-treated. In the brain, the agent causes native cellular prion protein to deform into the misfolded state, which then goes on to deform further prion protein in an exponential cascade.
This results in protein aggregates, which then form dense plaque fibers. Brain cells begin to die off in massive numbers, eventually leading to the microscopic appearance of "holes" in the brain, degeneration of physical and mental abilities, and ultimately death.
Different hypotheses exist for the origin of BSE in cattle. Two leading hypotheses suggest it may have jumped species from the disease scrapie in sheep, or that it evolved from a rare spontaneous form of "mad cow disease" that has been seen occasionally in cattle for many centuries. Other theories state that the agent is a virus ,  virino ,  Spiroplasma species, or Acinetobacter species. The pathogenesis of BSE is not well understood or documented like other diseases of this nature.
Even though BSE is a disease that results in neurological defects, its pathogenesis occurs in areas that reside outside of the nervous system. It has not, however, been determined to be an essential part of the pathogenesis of BSE.
Accumulation of PrP Sc was also found in follicular dendritic cells; however, it was of a lesser degree. This led researchers to believe that the disease agent replicates here. Generally, in clinical experiments, high doses of the disease are administered. In natural cases, it was hypothesized that low doses of the agent were present, and therefore, infectivity could not be observed.
Diagnosis of BSE continues to be a practical problem. It has an incubation period of months to years, during which no symptoms are noticed, though the pathway of converting the normal brain prion protein PrP into the toxic, disease-related PrP Sc form has started. At present, virtually no way is known to detect PrP Sc reliably except by examining post mortem brain tissue using neuropathological and immunohistochemical methods.
Accumulation of the abnormally folded PrP Sc form of PrP is a characteristic of the disease, but it is present at very low levels in easily accessible body fluids such as blood or urine.
Researchers have tried to develop methods to measure PrP Sc , but no methods for use in materials such as blood have been accepted fully. The traditional method of diagnosis relies on histopathological examination of the medulla oblongata of the brain, and other tissues, post mortem. Immunohistochemistry can be used to demonstrate prion protein accumulation. The method combines amplification with a novel technology called surround optical fiber immunoassay and some specific antibodies against PrP Sc.
After amplifying and then concentrating any PrP Sc , the samples are labelled with a fluorescent dye using an antibody for specificity and then finally loaded into a microcapillary tube. This tube is placed in a specially constructed apparatus so it is totally surrounded by optical fibres to capture all light emitted once the dye is excited using a laser.
The technique allowed detection of PrP Sc after many fewer cycles of conversion than others have achieved, substantially reducing the possibility of artifacts, as well as speeding up the assay.
The researchers also tested their method on blood samples from apparently healthy sheep that went on to develop scrapie. The results showed very clearly that PrP Sc could be detected in the blood of animals long before the symptoms appeared.
After further development and testing, this method could be of great value in surveillance as a blood- or urine-based screening test for BSE. A ban on feeding meat and bone meal to cattle has resulted in a strong reduction in cases in countries where the disease has been present.
In disease-free countries, control relies on import control, feeding regulations, and surveillance measures. In UK and US slaughterhouses , the brain, spinal cord, trigeminal ganglia , intestines, eyes, and tonsils from cattle are classified as specified risk materials , and must be disposed of appropriately. As of , there is no cure for BSE. Some of the symptoms like twitching can be managed but otherwise treatment is palliative care. The tests used for detecting BSE vary considerably, as do the regulations in various jurisdictions for when, and which cattle, must be tested.
For instance in the EU, the cattle tested are older 30 months or older , while many cattle are slaughtered younger than that. At the opposite end of the scale, Japan tests all cattle at the time of slaughter.
Tests are also difficult, as the altered prion protein has very low levels in blood or urine, and no other signal has been found. Newer tests [ specify ] are faster, more sensitive, and cheaper, so future figures possibly may be more comprehensive.
Even so, currently the only reliable test is examination of tissues during a necropsy. As for vCJD in humans, autopsy tests are not always done, so those figures, too, are likely to be too low, but probably by a lesser fraction.
In the United States, the CDC has refused to impose a national requirement that physicians and hospitals report cases of the disease. To control potential transmission of vCJD within the United States, the American Red Cross has established strict restrictions on individuals' eligibility to donate blood.
Individuals who have spent a cumulative time of 3 months or more in the United Kingdom between and , or a cumulative time of 5 years or more from to present in any combination of countries in Europe, are prohibited from donating blood. The first known U. The cow was included in the United States Department of Agriculture's surveillance program, specifically targeting cattle with BSE .
Canada announced two additional cases of BSE from Alberta in early Clifford , chief veterinary officer for the United States Department of Agriculture animal health inspection service, confirmed a fully domestic case of BSE in Texas. Soybean meal is cheap and plentiful in the United States , and cottonseed meal 1. Historically, meat and bone meal, blood meal, and meat scraps have almost always commanded a higher price as a feed additive than oilseed meals in the U.
As a result, the use of animal byproduct feeds was never common, as it was in Europe. In , regulations prohibited the feeding of mammalian byproducts to ruminants such as cattle and goats.
However, the byproducts of ruminants can still be legally fed to pets or other livestock, including pigs and poultry. In addition, it is legal for ruminants to be fed byproducts from some of these animals. Compliance with the regulations was shown to be extremely poor before the discovery of a cow in Washington infected with BSE in , but industry representatives report that compliance is now total.
Even so, critics call the partial prohibitions insufficient. Indeed, US meat producer Creekstone Farms was forcibly prevented from conducting BSE testing by the USDA , which under an obscure law had the authority to restrict sales of BSE testing kits, allegedly to protect other producers from being forced to conduct the same tests to stay competitive. The USDA has issued recalls of beef supplies that involved introduction of downer cows into the food supply.
In December , Japan once again allowed imports of US beef, but reinstated its ban in January after a violation of the US-Japan beef import agreement: Tokyo yielded to US pressure to resume imports, ignoring consumer worries about the safety of US beef, said Japanese consumer groups. Sixty-five nations implemented full or partial restrictions on importing US beef products because of concerns that US testing lacked sufficient rigor. As a result, exports of US beef declined from 1,, metric tons in , before the first mad cow was detected in the US to , metric tons in This has increased since then to , metric tons in and to 1,, metric tons by On 31 December , Hematech, Inc, a biotechnology company based in Sioux Falls , South Dakota, announced it had used genetic engineering and cloning technology to produce cattle that lacked a necessary gene for prion production — thus theoretically making them immune to BSE.
Cattle are naturally herbivores , eating grasses. In modern industrial cattle-farming, though, various commercial feeds are used, which may contain ingredients including antibiotics , hormones , pesticides , fertilizers , and protein supplements.
The use of meat and bone meal , produced from the ground and cooked leftovers of the slaughtering process, as well as from the carcasses of sick and injured animals such as cattle or sheep, as a protein supplement in cattle feed was widespread in Europe prior to about However, soybeans do not grow well in Europe, so cattle raisers throughout Europe turned to the cheaper animal byproduct feeds as an alternative.
The British Inquiry dismissed suggestions that changes to processing might have increased the infectious agents in cattle feed, saying, "changes in process could not have been solely responsible for the emergence of BSE, and changes in regulation were not a factor at all. The first confirmed instance in which an animal fell ill with the disease occurred in in the United Kingdom , and lab tests the following year indicated the presence of BSE; by November , the British Ministry of Agriculture accepted it had a new disease on its hands.
Also, some concern existed about those who work with and therefore inhale cattle meat and bone meal , such as horticulturists , who use it as fertilizer. For many of the vCJD patients, direct evidence exists that they had consumed tainted beef , and this is assumed to be the mechanism by which all affected individuals contracted it.