According to the World Organization for Animal Health (WHO), bovine spongiform encephalopathy (BSE) is a progressive and fatal disease of the nervous system of cattle, caused by the accumulation of an abnormal protein called “prion” in nervous tissue.
Two forms or strains can be distinguished: the classical form of BSE occurs in cattle following ingestion of the prion in contaminated feed; and an uncommon form of BSE that is believed to appear spontaneously in all bovine populations.
BSE is considered a zoonotic disease because of its presumed link to the emergence of a new variant of Creutzfeldt-Jakob disease (v-CJD) in humans, a form of brain damage that leads to a rapid decrease in movement and loss of mental function. goes. OMSA has established official recognition of health risk status for the classic form of BSE.
Public health risk
BSE is a disease of the nervous system of cattle, with an incubation period that can last for years. In cattle, it is characterized by symptoms such as loss of coordination, nervous or aggressive behavior, hypersensitivity, tremors, posture, weight loss, decreased milk production, dementia, and death, which is why it is known as “cow disease”. , There is currently no cure or vaccine.
Because of its transmissibility and subtle changes, it is included in a group of diseases called transmissible spongiform encephalopathies (TSEs), diseases affecting both animals and humans that cause central nervous system (CNS) degeneration. are formed, causing spongiform changes. This tissue.
The OMSA states that the transmission of the BSE prion to humans, which evolves into V-CJD, together with the inability to predict V-CJD epidemics, resulted in a public health crisis during the 1990s. To date, the number of identified clinical cases of V-CJD is extremely small.
There is good evidence that v-CJD can be acquired through consumption of contaminated meat products, or by contact with medical equipment contaminated with BSE prions. The prion is heat-resistant, which means it cannot be destroyed during offal processing. However, red meat (i.e., boneless skeletal muscle), milk and milk products are considered safe to eat.
When did the disease first appear?
It was first detected in the UK in 1986, but it is estimated that it may have been present in UK cattle populations since the 1970s or even earlier. Later, the disease was reported in 25 countries, mainly in Europe, Asia, the Middle East and North America.
According to the article «Bovine spongiform encephalopathy. The ‘epizootic of the 21st century’, the disease was spread through feed made from meat and bone meal of sheep infected with scrapie, a disease of sheep. In addition to the high prevalence of scrapie in the United Kingdom in those years, the manufacturing process of these flours was altered by the oil crisis, with a change in temperature that was insufficient to destroy the transmitting agent or prion.
In the 1980s and 1990s the UK was hit by an outbreak of BSE and its human counterpart, Creutzfeldt–Jakob disease (vCJD). More than four million cattle were culled in an attempt to contain the outbreak, and 178 people died after contracting it. By eating vCJD infected beef.
Classic BSE Case Timeline
The first confirmed case of an animal being ill occurred in the United Kingdom in 1986, and the following year laboratory tests indicated the presence of BSE; In November 1987, the British Ministry of Agriculture acknowledged it had a new disease on its hands. The Center for Food Safety describes the timeline as follows:
In 1988, 421 cattle were diagnosed with BSE in Great Britain. The following year, the government of this country prohibited human consumption of certain viscera, including the brain and spinal cord. For its part, the US restricted the importation of live cattle, sheep, buffalo and goats from countries where BSE is present in indigenous livestock.
In the early 1990s, the British government insisted that the disease was not a threat to humans. Domestic cats started dying from beef by-products in pet food and 5 types of antelope died in British zoos because they were fed commercial livestock feed. Despite all this, the British government continues to strongly insist that British beef is completely safe and that BSE does not pose a danger to humans.
In 1993, already 120,000 bovine diagnoses have been made. In the middle of the decade, the UK decreed that meat and bone meal could not be fed to animals or used as agricultural fertiliser, and required tracing of individual animals and any over 30 months old. Has started testing cow that are destined for human consumption.
In May 1995, 19-year-old Stephen Churchill became the first victim of a new variant of Creutzfeldt–Jakob disease (vCJD), the first of 3 vCJD deaths that year. In March 1996, the British Health Secretary announced in the House of Commons that mad cow disease was “at present the most likely explanation” for “one in 10 cases of CJD in people under the age of 42”. It is the first time that the British government has acknowledged that BSE can be transmitted to humans in a variant form of CJD. After this point, 4.5 million cattle perish.
In the same year, Japan refused to import UK meat and bone feed, while the European Union did the same for UK meat and offal. In August, the UK Department of Agriculture confirmed that mad cow disease can be transmitted from cow to calf.
It added that a British coroner ruled that Peter Hall, a 20-year-old vegetarian who died of vCJD, contracted it from eating meat burgers as a child. This is the first judgment to legally link a human death to BSE. It is believed that 3 British farmers committed suicide every week around this time due to the outbreak.
As of July 1997, 21 vCJD cases have been confirmed in the UK, and in August the US Food and Drug Administration (FDA) banned proteins made from cow, sheep, deer and other ruminants for other ruminants. Gave. Two years later, in August 1999, the UK beef trade ban was lifted after 3 1/2 years.
However, in June of the following year, the UK announced that a cow born after measures to eliminate BSE had contracted the disease. In September 2001, the first BSE outbreak occurred in Japan. The affected animal was imported from the United States, and several cases have since been reported in the country.
The first confirmed case of vCJD in the US occurred in April 2002 in a 22-year-old British woman living in Florida. In August a Canadian man died of the disease after apparently contracting it in the UK.
In May 2003 a bull in Canada tested positive for BSE, the first confirmed case of North American born bovine. On 23 December of the same year, a cow in the state of Washington (USA) tested positive for BSE. As a result, on December 30, the US Department of Agriculture (USDA) ruled that food for humans may not be prepared from the remains of fallen cattle (sick or injured), as well as materials and tissues with specific risks, such as the brain and spinal cord. May go. Meat from cattle over 30 months old and mechanically separated.
On January 26, 2004, the FDA banned the feeding of cow blood, poultry waste, and restaurant scraps to cattle. Across the Atlantic, 143 people in Great Britain are infected with vCJD and 180,000 cattle have been diagnosed with BSE.
Since then, cases of BSE in cattle have been reported in Texas in 2005, Alabama in 2006, and California in 2012. That year, the Japanese government banned the import of raw beef from Brazil, based on reports that a cow had died in 2010. In southern Brazil it will contain proteins indicative of disease.
It has been detected in other countries such as France, Spain, Portugal, Belgium, Germany, South Korea, Australia and Brazil. According to OMSA, currently, as a result of the successful implementation of effective control measures, the prevalence of classical BSE is extremely low, as is its global health impact and risk to public health.