Bovine Spongiform Encephalopathy

Bovine spongiform encephalopathy (BSE), widely referred to as "mad cow disease," is a chronic degenerative disease affecting the inner nervous system of cattle. The disease be first diagnosed in 1986 contained by Great Britain.

BSE has have a substantial impact on the livestock industry in the United Kingdom. The disease also has be confirmed in native-born cattle surrounded by Belgium, Denmark, France, Germany, Italy, Ireland, Liechtenstein, Luxembourg, the Netherlands, Northern Ireland, Portugal, Spain, and Switzerland. The U.S. Department of Agriculture's (USDA) Animal and Plant Health Inspection Service (APHIS) is enforcing introduction restrictions and is conducting surveillance for BSE to ensure that this serious disease does not become established in the United States.

Clinical Signs

Cattle affected by BSE experience progressive degeneration of the fearful system. Affected animals may display changes contained by temperament, such as nervousness or aggression, uncharacteristic posture, incoordination and difficulty in rising, decreased milk production, or loss of body freight despite continued appetite. Affected cattle die. The causative agent of the disease is not completely characterized, and there is neither any treatment nor a vaccine to prevent the disease.

The incubation time of year (the time from when an animal becomes infected until it first shows disease signs) is from 2 to 8 years. Following the birth of clinical signs, the animal's condition deteriorates until it either dies or is destroyed. This process usually take from 2 weeks to 6 months. Most cases in Great Britain enjoy occurred surrounded by dairy cows between 3 and 6 years of age.

Currently, there is no trial to detect the disease in a live animal; veterinary pathologists confirm BSE by postmortem microscopic nouns of brain tissue or by the detection of the abnormal form of the prion protein. BSE is so name because of the spongy appearance of the brain tissue of infected cattle when sections are examined lower than a microscope.

History

Since November 1986 (when BSE was first identified as a separate disease entity), 177,531 manager of cattle in 35,118 herd have be diagnosed with BSE within Great Britain as of Dec. 1, 2000. The epidemic peaked in January 1993 at approximately 1,000 new cases reported per week. Agricultural official in Great Britain enjoy taken a series of actions to eradicate BSE, including making BSE a notifiable disease, prohibiting the inclusion of mammalian meat-and-bone teatime in nurture 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 adjectives animals showing signs of BSE and other animals at high risk of developing the disease.

As a result of these whereabouts, most notably the imposition of nurture bans, the rate of not long reported cases of BSE is decreasing.

Epidemiology

Epidemiologic data suggest BSE within Great Britain is an extended common source epidemic involving animal nurture containing contaminated meat and bone meal as a protein meat source.

There are different proven hypotheses concerning the origins of BSE. BSE in Great Britain may have be caused by feed cattle rendered protein produced from the carcasses of scrapie-infected sheep or cattle next to a previously unidentified TSE. The practice of using products such as meat-and-bone collation as a source of protein in cattle rations has be common for several decades. Changes surrounded by rendering operations surrounded by the early 1980's may own played a part contained by the appearance of the disease.

There is no evidence that BSE spreads horizontally, i.e., by contact between unrelated adult cattle or from cattle to other species. Limited research suggests that caring or vertical transmission may ensue at a very low horizontal. This low level most expected would not perpetuate the epidemic underneath British farming conditions. Research continues here area.

BSE is classified as a transmissible spongiform encephalopathy (TSE). The agent responsible for BSE and other TSE's is smaller than the smallest set virus and has not be completely characterized. There are three main theories on the disposition of the agent: (1) the agent is a virus with unusual characteristics, (2) the agent is a prion--an exclusively host-coded protein specifically modified to a partially protease-resistant form after infection, and (3) the agent is a virino--a small, noncoding regulatory nucleic acerbic coated with a host-derived protective protein. The BSE agent is extremely resistant to roast and to normal sterilization processes. It also does not evoke any detectable immune response or inflammatory hostile response in host animals.

In cattle instinctively infected with BSE, the BSE agent have been found simply in brain tissue, in the spinal cord, and in the retina. The distal ileum, bone marrow, dorsal root ganglion, and trigeminal ganglion from experimentally infected cattle be found to be infective.

The presence of the BSE agent in tissues is determined by inoculating animals, usually mice, with stuff believed to be infected with BSE. Mouse inoculation studies appropriate a long time (up to 700 days) to detect the agent, and failure to identify it surrounded by tissues may indicate either true bunking off of the agent or simply the limited sensitivity of current diagnostic methods.

Related Diseases

The TSE family circle of diseases includes scrapie, which affects sheep and goats; transmissible mink encephalopathy; feline spongiform encephalopathy; chronic wasting disease of deer and elk; and in humans, kuru, both classic and adaptation Creutzfeldt-Jakob disease, Gerstmann-Straussler-Scheinker syndrome, and fatal familial insomnia. TSE's hold also been reported surrounded by captive exotic ruminants, and exotic and domestic cats. The agent isolated from several of these cases is indistinguishable from BSE in cattle suggesting the phenomenon of TSE's in these species resulted from BSE-contaminated nurture.

On March 20, 1996, the United Kingdom's Spongiform Encephalopathy Advisory Committee (SEAC) announced the identification of 10 cases of departure Creutzfeldt-Jakob disease. These 10 cases have a all your own clinical and pathological phenotype which differed from other routinely diagnosed cases of classic (sporadic) CJD in that they are characterized by a younger age at onset of symptoms, hold behavioral change symptoms, longer duration of syndrome, a non-diagnostic or normal EEG tracing, and, underneath microscopic examination, different lesion in brain tissues.

SEAC concluded that, although at hand was no direct quantifiable evidence of a link between BSE and vCJD, base on current data and surrounded by the absence of any credible alternative, the most potential explanation at that time was that the cases be linked to exposure to BSE since the introduction of a specified bovine offal (SBO) ban at slaughter surrounded by 1989. The SBO ban excluded from human consumption brain, spinal cord, and other organs next to potential BSE infectivity. As of Dec. 28, 2000, 88 cases of vCJD had be identified in the United Kingdom, one in Ireland, and two in France.

It is prominent to further clarify the difference between classic CJD and vCJD. Classic CJD occurs respectively year at a rate of 1 to 2 cases per 1 million people throughout the world, including in the United States and other countries where on earth BSE has never occur and among vegetarians and meat eaters alike. Classic CJD occur sporadically (about 90 percent of cases), through iatrogenic transmissions (less than 1 percent) or genetically (about 10 percent). According to the U.S. Centers for Disease Control and Prevention (CDC), no cases of vCJD have be identified in the United States.

Current evidence suggest that vCJD is a innovative condition, clinically and pathologically. The epidemiological evidence is consistent with BSE and the contributory agent and recent laboratory evidence provides strong support to the hypothesis of a causal knit between BSE and vCJD.

USDA Actions in Response to BSE

BSE have not been diagnosed surrounded by the United States, and USDA has worked proactively to hang on to it that way. In cooperation beside USDA's Food Safety and Inspection Service (FSIS), APHIS has taken stringent measures in prevention, instruction, surveillance, and response.

To prevent BSE from entering the country, since 1989 APHIS has prohibited the importation of live ruminants from countries where on earth BSE is known to exist within native cattle. Other products derived from ruminants, such as fetal bovine serum, bonemeal, meat-and-bone meal, bloodmeal, offal, fat, and glands, are also prohibited from entry, except under special conditions or below USDA permit for experimental or research purposes.

On December 12, 1997, APHIS extended these restrictions to include all of the countries within Europe due to concerns about general risk factors and lacking surveillance for BSE.

As of December 7, 2000, USDA prohibited all import of rendered animal protein products, regardless of species, from Europe. This decision followed the recent determination by the European Union that nurture of nonruminant origin be potentially cross-contaminated with the BSE agent. The restriction applies to products originate, rendered, processed or otherwise associated with European products. USDA is taking this emergency bustle to prevent potentially cross-contaminated products from entering the United States. The same type of rendered product from ruminant origin have been prohibited from BSE-infected countries since 1989.

APHIS educate veterinary practitioners, veterinary laboratory diagnosticians, industry, and producers on the clinical signs and pathology of BSE.

APHIS leads an ongoing, comprehensive, interagency surveillance program for BSE in the United States. BSE is a reportable disease by endorsed veterinarians. APHIS veterinary pathologists and field investigators own received training, including training from their British counterparts in diagnosing BSE. The surveillance samples include corral cases of cattle exhibiting signs of neurological disease, cattle condemned at slaughter for neurologic reasons, rabies-negative cattle submitted to public robustness laboratories, neurologic cases submitted to veterinary diagnostic laboratories and teaching hospitals, and sampling of cattle that are nonambulatory (downer cattle/fallen stock) at slaughter. APHIS' surveillance program is base on laboratories' histopathologically examining brains and using a technique called immunohistochemistry to interview brain tissues for the presence of the abnormal prion protein. As of Dec. 31, 2000, more than 11,953 brains from the United States and Puerto Rico hold been examined near no evidence of BSE or other TSE detected.

APHIS also monitors the remaining cattle imported from Great Britain, Belgium, and other European countries (before the ban on imports from those countries go into effect). As of Dec. 31, 2000, of the 496 cattle imported from Great Britain and Ireland between 1981 and 1989, four animals are still alive. The animals are quarantined and observed regularly. To date, no evidence of BSE or a TSE have been detected. APHIS continues to attempt to purchase the four live animals for diagnostic research purposes. The 25 European cattle import in 1996-97 that are still alive are currently below quarantine, and APHIS is attempting to buy these animals as well.

APHIS, contained by cooperation with the Food Safety and Inspection Service, have also drafted an emergency response plan to be used in the event that BSE is identified within United States. In addition, APHIS' TSE Working Group monitors and assesses adjectives ongoing events and research findings regarding TSE's. APHIS continually revises and adjust prevention and diagnostic measures as it receives spanking new information and knowledge.

As an further preventative measure, APHIS supports the Food and Drug Administration's (FDA) regulation (effective August 4, 1997) prohibiting the use of most mammalian protein (with confident exceptions) in the create of animal feeds given to ruminants. In tallying, the final regulation also requires process and control systems to ensure that ruminant feed does not contain the prohibited mammalian tissues.

Getting the Word Out

As portion of its increased surveillance activities, APHIS is continuing an childhood effort to inform U.S. cattle producers and veterinarians in the region of this disease. Numerous briefings have be held for industry groups. In addition to press releases and factsheets, a videotape on BSE and an information packet be distributed to all APHIS paddock offices, State veterinarians, extension veterinarians, colleges of veterinary tablets, and industry groups.