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A History of Bovine Tuberculosis and the Creation of the First TB Resistant Cattle
Tuberculosis, also known simply as TB and formerly known as consumption, is a highly infectious bacterial disease that can be spread through the air. The strains of mycobacteria responsible for causing TB in humans, cattle, and other types of mammal, usually affect the lungs primarily, but can spread to other parts of the body, particularly as the disease progresses. Most TB infections produce no symptoms, this is known as latent TB. However, approximately one in ten cases does progress to the full disease, with roughly a 50% survival rate. The remaining population carrying the inactive form of the disease, are thankfully not contagious.
Evidence of TB in humans has been found in records and remains dating back many thousands of years. Egyptian mummies, and even older skeletal remains have been discovered with signs of highly advanced, lethal TB. However, bovine remains dating back much farther have also been found to display signs of the disease. It is not clear whether TB originated in humans or bovines, and that is a conundrum that will probably never be solved.
The mycobacteria responsible for bovine TB is called Mycobacterium bovis (M.Bovis) and is closely related to the human form, Mycobacterium tuberculosis. This means that, although human infection is rare, the bovine form can transfer to humans and other mammals. Badgers are particularly prone to carrying bovine TB, and due to their wandering nature, often are responsible for transferring infections between herds. Thus, badgers are often culled, a controversial piece of legislation amongst some parties.
Symptoms of bovine TB are similar to that seen in humans, but are often less pronounced until the disease has entered its later stages. Symptoms include; weight loss, recurrent fever, weakness, loss of appetite, swollen lymph nodes, a cough and udder infections.
A History of Bovine Tuberculosis in the UK and USA
- In the early 1900’s many countries worldwide took measures to deal with the bovine TB problem. In the USA, eradication procedures were immediately set in place, with cattle being tested and the disease immediately being not only quantified, but slowly reversed. However, in the UK, although the Royal Commission on Tuberculosis was formed in 1907, no real eradication measures were taken until the 1930’s, by which time bovine TB was affecting approximately 40% of dairy herds. At this same time in the USA, only 1.8% of cattle was testing positive, an indication of the true value of the rapid reaction to the spread of the disease.
- In 1934, in the UK, the Milk Act was passed, freeing up many herds, but under a scheme of strict testing.
- 1935 saw the introduction of Attested Herds Scheme in the UK. Under this scheme, herds that had passed three consecutive tests for the disease, earned attested herd status. The owner of the herds were then had to follow strict rules in order to prevent re-infection.
- By 1938, the UK bovine TB figures had dropped to 13%.
- The second world war seriously hindered control programmes on either side of the Atlantic, particularly in the UK. However, the Attested Herd Scheme was continued in 1944, and by 1947, 14% of UK herds were registered. Progress continued in the USA, with more states becoming TB free.
- In 1950, in the UK, an Area Eradication Plan was announced. This meant that large areas were placed under strict government eradication programs, where all infected cattle were immediately slaughtered, with a small compensation going to the owners. By 1960, the whole of the UK was an attested area. But the disease was not gone... residual infections latent in herds, as well as the infection of other species, meant that bovine TB still occurred in cattle, and also in humans.
- TB control persevered with much success on both sides of the Atlantic, while other countries continued to face a great battle with the disease. However, in 1971 in the UK, bovine TB was first detected in badgers. Since this discovery, the focus of management of TB in the UK has been firmly on the badger population. Throughout the late 1970’s and 80’s, badgers were culled in huge numbers.
- The UK outbreak of BSE in 1993, as well as a relaxation in TB testing, led to the infection rates rising. By 1998, figures had quadrupled from pre-BSE statistics.
- The following year in the USA, bovine TB was discovered in wild deer. This led to extensive wildlife testing, revealing the disease in other species, such as elk, bobcats, coyotes and raccoons.
- The UK’s 2001 foot and mouth epidemic, once again caused disruption in TB control. Figures rose again, to over 8000 infected cattle.
- In 2006, movement controls were imposed on cattle in the UK.
- 2008 saw improved testing procedures, allowing for much faster detection, improving bovine TB control worldwide.
The New Breakthrough
Up until now, the only real means of controlling bovine TB has been through the testing of herds, and slaughtering of infected cattle. However, with the huge leaps in genetic testing and engineering seen in recent years, a much greater understanding of the mechanisms of both infection and resistance has been gained.
Much research has been carried out for the last decade on the possible impact of variations of a specific gene on the development and resistance to TB of all forms. The SP110 gene encodes a leukocyte specific nuclear body component. This immune system component plays a role in gene activation, cell differentiation and the production of cellular components.
In the early 2000’s this gene and its variants were shown to be a major factor in TB resistance in mouse models. Since then, the research has produced huge developments. Now, scientists in China may finally have made the breakthrough that leads to the eradication of bovine TB worldwide. Using a highly advanced gene editing tool, called TALEN, the team have genetically altered a number of calves, using a modified version of the SP110 gene. These calves have displayed a massively slower disease multiplication rate than standard cattle. In one test, nine of the altered calves, along with nine standard animals, were exposed to TB. All of the unaltered cattle contracted an aggressive form of the disease, while only three of the genetically altered animals showed any signs, and this was minimal.
Although this is not a cure for the disease, or a particularly rapid solution to any degree, the breakthrough is music to the ears of scientists, farmers and authorities worldwide, who for over a century have had to resort to the mass culling of animals, at a great cost to all concerned.
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