Todayโs path rounds are on ๐ฆ๐๐ ๐๐จ๐ฐ ๐๐ข๐ฌ๐๐๐ฌ๐, more appropriately known as ๐๐จ๐ฏ๐ข๐ง๐ ๐ฌ๐ฉ๐จ๐ง๐ ๐ข๐๐จ๐ซ๐ฆ ๐๐ง๐๐๐ฉ๐ก๐๐ฅ๐จ๐ฉ๐๐ญ๐ก๐ฒ (BSE)!
๐๐ก๐๐ญ ๐ข๐ฌ ๐ข๐ญ?
BSE is a disease of ๐ฉ๐ซ๐ข๐จ๐ง๐ฌ, which are small proteins found primarily in nervous tissue. The exact function of these little proteins is unknown, however they can have big effects when they are ๐ฆ๐ข๐ฌ๐๐จ๐ฅ๐๐๐ (change in shape).
๐๐ก๐จ ๐ ๐๐ญ๐ฌ ๐ข๐ญ?
Cattle get BSE specifically, however there are other prion diseases that affect wild deer and elk, sheep, cats, and even humans.
๐๐ก๐๐ญ ๐๐๐ฎ๐ฌ๐๐ฌ ๐ข๐ญ?
There are a few different theories about how prion diseases work, but the most commonly accepted theory is called the ๐ฉ๐ซ๐จ๐ญ๐๐ข๐ง-๐จ๐ง๐ฅ๐ฒ ๐ก๐ฒ๐ฉ๐จ๐ญ๐ก๐๐ฌ๐ข๐ฌ, because it does not involve any other infectious agents like viruses or bacteria. In this hypothesis, the introduction of one misfolded prion into the body triggers misfolding of other prions, causing a cascade of protein misfolding and thus leading to the disease.
Based on this idea, there have been two forms of BSE that have been identified: classical BSE and atypical BSE. In classical BSE, cattle are infected by ingesting a misfolded prion in their diet, often from eating feed containing meat or bone meal from a BSE-infected cow. In atypical BSE, a prion protein spotaneously misfolds in an animal with no exposure to misfolded proteins, thus causing the disease.
๐๐ก๐ฒ ๐ข๐ฌ ๐ญ๐ก๐ข๐ฌ ๐ ๐ฉ๐ซ๐จ๐๐ฅ๐๐ฆ?
Itโs not really known why, but these misfolded prions cause neuron degeneration, which subsequently leads to neurologic signs like aggression, abnormal posture and incoordination. Eventually, the animal will die from this condition.
While thatโs a pretty sad time for the animal, thatโs not the biggest issue with BSE. BSE is considered to be a serious public health concern, because ingestion of meat from BSE-infected animals has been linked to ๐๐ซ๐๐ฎ๐ญ๐ณ๐๐๐ฅ๐๐ญ-๐๐๐ค๐จ๐ ๐๐ข๐ฌ๐๐๐ฌ๐, which is a prion disease in people. Remember how cattle can get BSE from ingesting a misfolded protein? A similar thing happens in these affected humans. Scary!
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐๐ข๐๐ ๐ง๐จ๐ฌ๐๐?
Animals are often suspected to have BSE based on their clinical signs, and from there the animal is euthanized. The brain is then removed and sent to a diagnostic laboratory to identify the disease. Under the microscope, a pathologist can see ๐ฏ๐๐๐ฎ๐จ๐ฅ๐๐ซ ๐๐๐ ๐๐ง๐๐ซ๐๐ญ๐ข๐จ๐ง of neurons, where the neurons look like they have large holes in them. These holes also give the brain tissue the appearance of a sponge, hence the word ๐ฌ๐ฉ๐จ๐ง๐ ๐ข๐๐จ๐ซ๐ฆ in the disease name. To help confirm the diagnosis, ๐ข๐ฆ๐ฆ๐ฎ๐ง๐จ๐ก๐ข๐ฌ๐ญ๐จ๐๐ก๐๐ฆ๐ข๐ฌ๐ญ๐ซ๐ฒ can be used to attach a dye molecule to the misfolded prions and allow them to be visualized.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ญ๐ซ๐๐๐ญ๐๐? ๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ฉ๐ซ๐๐ฏ๐๐ง๐ญ๐๐?
Unfortunately, there is no treatment for BSE. But, because of the massive human health impacts, there have been global efforts to prevent BSE, and control its spread if it does occur. The main prevention steps that have been taken are banning all mammalian meat and bone products in cattle feed, and removing and destroying the high-prion tissues of cattle during meat processing for human consumption. Because of these actions, the rate of BSE cases worldwide has decreased to less than 10 cases per year!
๐๐ก๐จ๐ญ๐จ๐ฌ
1) A โlow powerโ view of brain tissue, showing how it looks like a sponge!
2-4) Examples of vacuolar degeneration in neurons of cattle with BSE.
5) An example of using immunohistochemistry to identify misfolded proteins.
๐๐จ๐ฎ๐ซ๐๐๐ฌ
Maxie, G. Jubb, Kennedy and Palmerโs Pathology of Domestic Animals, Volume 1. Sixth Edition.
USDA Animal and Plant Health Inspection Service. Bovine Spongiform Encephalopathy. 2020.
Photos 1-4 courtesy of Noahโs Arkive.
Photo 5 courtesy of Dr. Peter Hooper at the Australian Animal Health Laboratory.
