The Scariest Disease Ever- Rabies

Jan 03, 2024

The Scariest Disease Ever- Rabies

Rabies is a disease that instills great fear, often perceived as one of the most horrifying illnesses known to humans. This dread emanates from the exceptionally aggressive nature of its symptoms and its nearly certain fatal outcome if untreated. In some popular discussions, the disease has been likened to a form of zombification. This stems from how the virus manipulates the host's behavior, causing bouts of agitation and aggression and sometimes inducing the host to bite other individuals, facilitating the virus's spread.

Comparison of Rabies with Zombies

However, the comparison to zombies is a dramatic over-simplification. Though shocking, the aggression displayed by infected individuals is not the relentless, mindless assault seen in fictional zombies. Moreover, biting as a means of transmission, while common in infected animals, is much rarer in human cases of rabies. This difference is likely due to behavioral distinctions; unlike many mammals, humans do not typically use biting as a defensive strategy.

While there may be some superficial similarities between the portrayals of zombies and the symptoms of rabies, it is important to recognize that these comparisons are mainly sensationalized. Despite this, there is no denying the severity of the rabies disease and its horrifying impact on those infected. Its capacity to cause a rapid deterioration in behavior and physical health, and its high fatality rate, make it a significant concern in areas where the disease is prevalent.

Definition and causes of Rabies

Icon Domestic Animals, Exotic Pet Species, Bats, and other wild animals are reservoirs for rabies. Rabies is a disease typically caused by the Rabies virus, which belongs to a group of viruses known as Lyssaviruses. The term 'Lyssa' translates to 'violent,' a fitting descriptor considering the severe symptoms and outcomes often associated with this disease. Although other viruses can cause Rabies, the Rabies virus is the most common culprit. Its defining characteristic is its neurotropic nature, which targets explicitly and replicates within the host's nervous system.

The global impact and death rates due to Rabies

Regarding its global impact, rabies remains a significant public health concern. It is responsible for between 50,000 and 70,000 yearly deaths, underscoring its devastating effect. The disease is known as a zoonotic disease, as it is primarily transmitted from animals to humans. While human-to-human transmission has been reported in some cases, such as through organ transplants, these instances are exceptionally rare. Instead, most human cases result from transmission from infected mammals such as dogs, bats, and raccoons.

The Rabies virus is neurotropic, targeting the nervous system.

Although it can infect and cause disease in various tissues, the Rabies virus is neurotropic, making the nervous system its primary target. This property plays a significant role in why the disease is so challenging to treat and progresses rapidly once symptoms manifest. Understanding this attribute of the Rabies virus is crucial in appreciating the disease's severity and underscores the importance of timely medical intervention in preventing its deadly outcomes.

Transmission of Rabies

Rabies is primarily a zoonotic disease, meaning its transmission occurs predominantly from animals to humans. This transmission mode sets the stage for an epidemiological pattern implicating many mammals, from domestic to wild species. Notably, mammals such as cows, bats, dogs, and cats play pivotal roles in the transmission cycle of the virus.

Bats are of particular concern due to their mobility and widespread distribution. Equally, due to their proximity to humans, dogs are considered the leading source of human rabies deaths, according to WHO, up to 99% contributing of all rabies transmissions to humans. Likewise, cats and cows, given their interactions with humans in rural and urban settings, can also serve as transmission vectors.

Although it's far less common, human-to-human rabies transmission is not entirely unheard of. One documented transmission route is via organ transplantation from an infected donor. These cases, while extremely rare, underscore the importance of robust pre-transplant screening for infectious diseases, including rabies.

Despite these instances of human-to-human transmission, the primary transmission pathway remains animal bites, particularly from infected mammals. The best way to prevent rabies in humans is by controlling the disease in animals and practicing responsible pet ownership, including regular vaccinations for pets. Prompt and appropriate medical care, including post-exposure prophylaxis, is also vital when a potentially rabid animal bites a person.

 Impact and Propagation of the Virus

Once it has infiltrated the body, the disease follows a path primarily concentrated within the nervous system. The rabies virus is neurotropic, meaning it has a particular affinity for the nervous tissue, which it targets and invades with devastating efficiency.

How does the Rabies virus propagate through the body?

Replication of the virus

Despite being characterized as a fast-acting virus, rabies follows a deceptive trajectory after the initial infection. It begins its journey within the host's body by slowly replicating within the muscle tissue at the site of the bite. This slow replication phase can create a misleading period of quiet, during which the infected individual may show no observable symptoms. This phase can last from days to years, contributing to the unpredictable nature of rabies incubation.

Signs of Virus replication  

However, once the virus transitions into the nervous system, its impact becomes more pronounced. The initial symptoms may manifest as numbness and tingling at the bite site, indicative of the virus's entry into the nervous system. These are systemic signs, such as fever and headache, suggestive of the body's mounting defense against the viral invasion.

A critical juncture in the disease progression is when the virus reaches the spinal cord, a part of the central nervous system. From here, it has a straight shot to the brain, the body's control center. The speed at which the virus reaches the brain significantly depends on the location of the bite. Bites closer to the head hasten the virus's journey to the brain due to the reduced distance it travels. According to the National Institute for Health (NIH), the average incubation period is 1 to 3 months. Still, it can vary from one week to one year, mainly depending on the location of the bite.

This propagation of the rabies virus and its affinity for the nervous system makes its impact particularly severe. It leads to devastating neurological symptoms and, if left untreated, invariably results in death. This highlights the importance of prompt post-exposure prophylaxis upon any suspected rabies exposure.

Effects on the Brain and Spinal Cord

Once the rabies virus reaches the brain, its detrimental effects become pronounced. The virus rapidly divides, infecting neurons and causing a condition known as encephalitis, which is the swelling or inflammation of the brain. This swelling disrupts normal brain function, leading to various symptoms, including significant neurological and behavioral changes.

Effects and symptoms of the Rabies virus on the brain

The first symptoms, such as fever, headache, and general weakness, can often resemble the flu. As the disease progresses, more specific signs that are characteristic of the virus's devastating impact on the brain develop. Individuals infected with rabies may experience anxiety, confusion, agitation, and insomnia. An abnormally high level of aggression can also be manifested; a symptom that starkly reflects the brain's deteriorating condition.

One of the more terrifying symptoms of rabies is paralysis. The virus's destructive pathway through the nervous system can eventually lead to muscle weakness and paralysis. Paralysis generally starts from the bite or scratch site and gradually extends to other parts of the body.

Different forms of Rabies

Rabies can present in two forms: furious and paralytic. According to News Medical, furious rabies, which accounts for approximately 80% of human cases, is characterized by hyperactivity, excitable behavior, and hydrophobia (fear of water). Paralytic rabies, on the other hand, is less dramatic but equally fatal. It leads to muscle weakness and eventually paralysis, often misdiagnosed as Guillain-Barré syndrome or other forms of neuropathy.

In both forms, once clinical signs of rabies appear, the disease is nearly always fatal, and treatment is typically supportive. This underscores the paramount importance of preventing the virus from ever reaching the brain—a goal achievable by promptly administering post-exposure prophylaxis following any potential exposure to rabies.


Spread of the Virus


How does the virus start pushing out from the brain to organs?

After the rabies virus has wreaked havoc on the brain, it begins a devastating march throughout the rest of the body. It moves from the central nervous system through the peripheral nerves, reaching various organs and tissues. The salivary glands are particularly affected, which is a critical factor in the virus's transmission, as it enables the virus to pass from host to host through bites.

As the virus spreads, the affected individual's condition worsens. Symptoms, including nausea, vomiting, and abdominal pain, may occur. These symptoms can be misleading, often mistaken for other conditions such as gastroenteritis. An infected individual may also develop an abnormal heartbeat or breathing difficulties. Victims may sometimes suffer from hyperactivity, hallucinations, or hydrophobia (fear of water) due to the virus's effect on the brain.

Eventually, the individual may fall into a coma due to the severe neurological damage caused by the virus. Death usually follows within a few days, typically due to respiratory failure.

The speed of the virus' impact and the difficulty in treating 

One of the most disturbing aspects of rabies is the speed at which the virus's effects can manifest once symptoms start appearing. From the first signs of illness to death, the timeline can be as short as a few days. This rapid progression underscores the difficulties in treating rabies once the virus has reached the central nervous system, making prevention and early intervention crucial. This is why seeking immediate medical attention after a potential exposure before the virus can reach the brain and cause irreparable harm is essential.

Transmission to the Next Host

The cycle of rabies virus transmission doesn't stop at the initial host. One of the chillingly effective strategies of the rabies virus is its ability to position itself for transmission to the next host. As it replicates within the body, the virus travels along the nerves to the salivary glands, which triggers hypersecretion of saliva, turning the infected host into a prime vehicle for transmission.

 How does the virus promote biting as a transmission strategy in four-legged creatures?

In the case of four-legged creatures, the rabies virus induces behavioral changes to promote its propagation. Infected animals exhibit increased aggression and a heightened propensity to bite, precisely the method through which the virus is most often transmitted. This viral behavior modification is a powerful transmission strategy: by manipulating the host's behavior, the rabies virus maximizes its chances of spreading to new hosts.

The uniqueness of biting in human Rabies cases

Such aggressive behavior and biting tendencies are relatively uncommon in humans, making human-to-human transmission rare. Instead, most human rabies cases result from being bitten by an infected animal, often a dog. The World Health Organization estimates that dogs are responsible for up to 99% of all human rabies transmissions. While biting is less common in human cases, the virus still travels to the salivary glands in humans, meaning that it could theoretically be transmitted through a bite or even a kiss. However, such transmissions are extremely rare.

Other Symptoms and Prevention Mechanisms

Rabies causes myriad symptoms that are horrifying for the infected individual and serve the virus's own propagation strategy. One such symptom pertains to the pharynx and the esophagus. The virus induces spasms in these parts of the body, thereby preventing the swallowing of saliva. This symptom ensures that the virus-laden saliva remains in the mouth and does not get diluted or neutralized by the digestive system, thus maximizing the chances of successful transmission to the next host through biting or saliva exchange.

Hydrophobia is a symptom induced by painful spasms.

One of the most characteristic symptoms of rabies infection, and perhaps one of the most misunderstood, is hydrophobia or fear of water. This is not a psychological fear as it might sound; instead, it is a physical response caused by the rabies virus. In individuals infected with rabies, attempts to drink water or even the sight or sound of water can trigger severe, painful throat spasms due to the effect, as mentioned earlier, on the pharynx and esophagus. This incapacitating reaction, leading to an aversion to water, is why the symptom is hydrophobia. Hydrophobia is typically seen in the later stages of rabies, and it is a rough indication of the rapid progress of the disease.

Prevention of rabies

Rabies prevention primarily relies on rabies vaccines and controlling animal populations, especially dogs, in high-risk areas. Vaccination after exposure, known as post-exposure prophylaxis (PEP), can prevent the virus from entering the nervous system and thus stop the disease from developing. However, once symptoms appear, rabies is almost universally fatal. Consequently, rapid response and prevention mechanisms are paramount in managing this terrifying disease.

Bottom Line

While rabies is a terrifying disease with symptoms that seem eerily similar to those of fictional zombies, the comparison doesn't hold under scrutiny. Rabies-infected individuals are not relentless, emotionless creatures but unfortunate victims of horrific illnesses. The notion of a "zombie virus" remains firmly within science fiction, while rabies remains a real-world public health concern that requires our attention and efforts toward prevention.