Mad Cow Disease in Humans

Mad cow disease is a neurologically degenerative disease in individuals that appeared in the late 20th century. What causes this disease? Well, it is suggested that the disease is contracted by consuming contaminated beef.

Mad cow disease is a neurological disease in which certain abnormal proteins known as prions, induce the formation of lesions/plaques in the brain tissue of the infected animal. This disease is as old as 300 years, when it was reported in sheep as 'scrapie'.

Other than cows and sheep, this disease can infect cats, deer, and elk as well. However, the bad news is that the infection is not restricted only to animal species.

Mad cow disease, in humans, is known as the variant Creutzfeldt-Jakob disease (vCJD), or the new variant Creutzfeldt-Jakob disease (nvCJD), and there is strong evidence that it is contracted by eating beef that came from infected cows.

Causes

The classic Creutzfeldt-Jakob disease (CJD) (which not the same as the vCJD/nvCJD) was described in the 1920s by German neurologist Hans Gerhard Creutzfeldt and Alfons Maria Jakob, giving the disease its name.

Although it is often called the mad cow disease in human beings, this is a wrong association. The mad cow disease which is also known as the bovine spongiform encephalopathy (BSE), CJD, vCJD, and nvCJD are all types of transmissible spongiform encephalopathy (TSE), which is characterized by spongy appearance of the brain tissue of the infected organisms.

The most widely accepted theory about the causative agent of the TSE is the prion theory. Prions are abnormal proteins that are a result of a fault in the way they fold during their synthesis. All proteins are strings of amino acids that need to fold as per the sequence of amino acids.

Prions are the result of faults in their folding pattern that make them harmful. In addition to this, they disrupt the folding of other normal proteins as well. Those that oppose the prion theory believe that the causative agent of TSE is a virus-like agent that carries nucleic acid.

Although some researchers dispute the role of the prion, till date, the prion theory is the most widely accepted cause of the TSE. However, greater characterization of this protein is required.

Before we move on to the vCJD, let us understand a little about the classic CJD. The classic Creutzfeldt-Jakob disease can occur in three different ways. In over 80% of the cases, it occurs sporadically for no apparent reason. Almost 5% to 10% of the cases of CJD are hereditary, that are passed on as a result of gene mutation.

A small percentage of classic CJD is contracted through contamination. The diseased prions may be present in the brain, spinal cord, retina, and other tissues of the nervous system of the affected animals or humans.

The abnormal prions may be passed on through these tissues to healthy individuals through medical procedures like grafts of dura mater (a tissue covering the brain), transplanted corneas, or injections of contaminated pituitary growth hormone. The classic CJD typically occurs in the older population.

However, in the 1990s, certain individuals showed signs of neurological disorder and they all were reported to have consumed beef. These individuals who were younger than those afflicted with classic CJD were diagnosed with a new form of CJD, that was named the variant Creutzfeldt-Jakob disease (vCJD).

Although more conclusive research is required, the disease in humans is believed to have been caused by consumption of infected cattle beef, carrying the agent of BSE.

Besides the co-relation between the consumption of infected beef products, the fact that healthy cows when fed with tissue infected with BSE agent (prion) also contracted the disease has lent further ground to the theory of the disease being transmitted to human beings through infected bovine tissue.

Also, a recent clinical study in mice has shown stunning similarity between the transmission characteristics of BSE and vCJD. All these findings point to both conditions sharing a similar causative agent, which causes the disease in humans, and as per current understanding, this infection is through the consumption of infected beef and beef products.

Symptoms
Although both are forms of TSE, the effects of mad cow disease are different from those of classic CJD. In case of classic CJD, dementia and neurological degradation make an early appearance; whereas, the effects of mad cow disease start with psychiatric or behavioral problems like depression and anxiety.

As the disease progresses, neurological signs like unsteadiness, difficulty in walking, involuntary, jerky movements appear. Towards the end, an individual loses control over his mental and physical functions completely and dies.

BSE has a longer illness duration of 13 - 14 months as opposed to 4 - 5 months in the case of classic CJD. The average age of death in case of classic CJD is 68 years, whereas in case of BSE, it is only 28 years.

Diagnosis
Only a brain biopsy, which can be done after the death of an infected individual, can confirm BSE. Unless the clinical symptoms have surfaced, there are no definitive diagnostic tests that can confirm mad cow disease in human beings.

However, magnetic resonance scans, tonsillar biopsy, and cerebrospinal fluid tests are some diagnostic tests that healthcare professionals rely on, in case the disease has been suspected in individuals.

Treatment and Prevention
There is no cure for this disease. Doctors concentrate on reducing pain and alleviating the symptoms. For preventive measures, WHO recommends strict regulation of meat and meat products from animals that show signs of TSE.

The international body also suggests that pharmaceutical industries should avoid making vaccines using materials from animals that can be infected with prions.

Be it the CJD or the mad cow disease, the problem is its unusually long incubation period that makes it difficult to trace the source from which the disease was contracted. Mad cow disease in humans is a relatively new disease and researchers are trying to gain more insight into the cause and ways to prevent the disease.