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This is the story of a disease that caused the brain of a cow to turn into a sponge and how it affected not only cattle, but every human on a global scale.
The story can be traced back to Great Britain in 1986, where a cow fed on meat that had been invaded by prions (CDC, 2019). Prions refer to proteins, tiny molecules that are essential to our overall health, that have become misfolded. The shape of a protein aids in its ability to carry out its normal functions. In the case of a deformed protein, well… the effects can be quite devastating. Consuming the spoiled meat led to the prions wreaking havoc on the cow’s central nervous system (consisting of the brain and spinal cord) as well as the eyes (UCSF Health, 2019). So, what exactly does this mean? The destruction caused by the abnormal protein resulted in the cow experiencing changes in its behavior, such as an increase in aggression. The United States Department of Agriculture notes in addition to erratic behavior, these cows also experienced a lack of coordination and less milk production. These symptoms are characteristics of the disease caused by this dangerous protein, Mad Cow Disease. While Mad Cow Disease (medically referred to as Bovine Spongiform Encephalopathy) has an impact on cattle, it can also have detrimental effects on humans.
You may be wondering, “Well, why did these cows begin to act out in strange ways in the first place and how did this lead to consequences suffered by humans?” The answer to this lies in the ecological perspective of the pathogenic prion. Like many of you have probably assumed, cows are typically known to be animals that eat grass and other plants. The consumption of meat lends to the idea that the diet of cows was changed by farmers in Great Britain, possibly to increase the amount of milk and meat that humans already had. Since cows ate the spoiled meat, the deformed protein was able to be passed into humans if they consumed meat from an infected cow. Like all pathogens (disease-causing bacteria or other microscopic organisms), the deformed protein that causes Mad Cow Disease interacts with and can be influenced by its environment (such as the inside of the human body). Whether or not a human begins to experience and show signs consistent with the symptoms of Mad Cow Disease depends on the incubation period, the time that has passed between an individual’s first exposure to the harmful protein and when symptoms first appear. As a matter of fact, one study found that individuals with a higher level of the deformed protein were more likely to transmit the disease at a faster pace because the incubation period was short-lived (Bartz, 2021). Not only can the protein be influenced inside the human body, it can also be influenced by other environmental factors such as temperature. It is important to note that prions, unlike many bacteria, are resistant to heat. Even when heat is applied to the deformed protein in an effort to kill it, the protein is able to resist the extreme temperature and survive. The study previously mentioned also found that because this protein can enter the environment through the release of cow waste, climate conditions (such as wind, rain, and snow) can influence the level of infectiousness in a human.
The resistance to heat that is observed in the deformed protein that causes Mad Cow Disease brings us to its evolution. Like every other species known to man, prions evolve or develop and gain new abilities over time. Over time, simple human activities can change the environment to the point where the arrival of a new disease could be a result of a deadly bacteria that was once harmless. In the case of Mad Cow Disease, this is certainly a possibility. One study found that “BSE prions, consistent with the hypothesis that the rendering process used in meat and bone meal production may have contributed to the emergence of BSE” (Bartz, 2021). The deformed proteins with the ability to resist heat most likely developed into a family of proteins that can cause the disease. While the diet of the cows could have been changed followed by humans consuming the infected meat, there are factories where machines are used to produce various forms of meat for public consumption. The use of these machines involves heat which could have increased the likelihood of the protein’s function changing and as a result, increased the chance that the deformed protein would cause disease. Other human activities that could have an impact on the evolution of these deformed proteins is pharmaceutical treatment, such as vaccines. In addition to introducing vaccines, the resistance to such treatments depends on the arrangement of the protein and how it replicates. One study found that “human prion particles replicate independently and undergo competitive selection of those with lower initial conformational stability” (Kabir, 2014). The evolution of organisms can occur through a process referred to as natural selection. This is the method by which individuals are likely to survive and have children, resulting from gaining abilities that allow them to be more successful in their environment. This process applies to the Mad Cow Disease-causing proteins where the proteins in the less stable arrangement are more likely to replicate much more quickly compared to a protein that is more stable. The same study discussed the “recently observed drug-induced evolution of mammalian prions” (Kabir, 2014). One consequence to note here is that when a drug was introduced, the protein that is unstable and depends on the drug evolved much more quickly. Instead of decreasing the possibility that the protein would survive, the drug indeed made matters worse by increasing its chance of survival and reproduction. While the drug proved to be ineffective in terms of slowing down the evolution of the deformed protein to decrease the likelihood of causing disease, it provides a closer look into the necessary steps that need to be taken to discover different options for treatment of diseases like Mad Cow Disease.
Mad Cow Disease is one of many prion diseases that can lead to devastating effects in not only animals, but humans as well. Despite regulations set in place by North American countries after the first case of Mad Cow Disease of the early 2000s was reported in Canada, the disease was found in individuals across the globe in countries such as Italy, Saudi Arabia, and Japan (University of Rochester, 2017). To this day, there is an absence of a treatment (vaccine or other forms of a medication) that can successfully treat cases of Mad Cow Disease in both cattle and humans. Despite the lack of treatments, the brains of both cattle and humans are tested by using scans (like MRIs) to determine what the brain looks like when the individual has been infected with the deformed protein. The studies discussed in this blog post sheds light on the research that has been completed relating to how this disease can be treated. Even though the treatment was not successful, it does provide insight into which topics further studies can explore (such as development of an effective treatment for not only Mad Cow Disease, but other diseases caused by deformed proteins that affect the brain and spinal cord). In the event a world-wide outbreak of Mad Cow Disease does occur, previous regulations like closing the border between neighboring countries has the potential of decreasing the risk of the disease passing between animals and humans. It is by discussing Mad Cow Disease that will spark encouragement in others to pursue research into this topic so that we can be better equipped in successfully treating this disease and many others like this one.