Bovine Spongiform Encephalopathy
Bovine Spongiform Encephalopathy (BSE) is a deadly neurologic disease of cattle. It’s a progressive disease with a long incubation period of three to six years and is identified by the presence of abnormal infectious proteins known as prions. BSE belongs to the family of transmissible spongiform encephalopathies, which include scrapie, chronic wasting disease, and other brain affecting diseases. It was first diagnosed in cattle in the United Kingdom in 1986. There have been zero reported cases in Minnesota and seven cases in the United States (Washington, Texas, Alabama, California, and South Carolina).
 This photomicrograph of a brain tissue specimen, reveals the histopathologic changes that were found in a case of bovine spongiform encephalopathy (BSE), also referred to as mad cow disease. Note the presence of numerous vacuoles, or microscopic holes in the gray matter, imparting the spongy appearance to the brain of BSE-affected cows. Photo courtesy of the CDC Public Health Image Library
Transmission
There are two types of BSE, classic and atypical. The classic form is spread through cattle feed that includes meat and bone meal from prion infected animals. Atypical BSE is rare and spontaneous; it’s unknown how this form is spread in cattle. BSE and other prion diseases are more difficult to control because, unlike bacteria and viruses, prions are resistant to inactivation by heat, freezing, ultraviolet light, or chemical disinfectants.
Diagnosis
Decreased milk production and weight loss are the primary signs of BSE in cattle. Other signs indicate nervous system damage and include behavior changes, lack of coordination, unusual stance or posture, and difficulty standing from a lying position. These signs are not unique to BSE and may be caused by other diseases. However, the surveillance program for BSE in U.S. cattle includes testing animals with these signs to make sure the disease is not in the U.S. cattle population.
Testing can only be conducted on a dead animal because it requires examination of the brain in a laboratory to confirm. If a veterinarian suspects clinical signs of BSE, the animal should be euthanized so the brain tissue can be analyzed for the disease.
Treatment
There is no effective treatment or vaccine for BSE. Euthanasia is recommended after a clinical diagnosis because animals become dangerous to themselves, other animals, and humans.
Prevention
The U.S. has safeguards in place to prevent this disease in U.S. cattle. They include prohibiting mammalian protein from rendered animals going into feed for cattle and other ruminants. The U.S. also places restrictions on the importation of live ruminants like cattle, sheep, goats, and certain other ruminant products from countries where BSE was known to exist.
Human risk
According to the Centers for Disease Control, “There exists strong epidemiologic and laboratory evidence for a causal association between [classic BSE and] a human prion disease variant called Creutzfeldt-Jakob disease (vCJD),” a neurological disease in people.
People are at risk if they consume meat from an infected animal. There are several preventative measures in place to reduce exposure to this risk. They include the measures to eliminate the spread of BSE infection in cattle and remove any cattle suspected of BSE infection from the human food chain. An additional measure is prohibiting the visible neurologic and lymphatic tissue of all adult cattle from going into the human food chain. These tissues are where prions concentrate in infected animals. Milk and milk products are considered safe.
The outbreak of BSE peaked in the early 1990s in the United Kingdom where it was first identified and where most of the cases occurred. The U.S. has only found seven infected cattle and one of those cases was the classic form of the disease. Measures put into place since the 1990s to control cattle feed ingredients and eliminate the pathway for transmission of the classical form of the disease.
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