Rabies is a zoonotic virus, which means that it can transfer from infected mammals to humans. Even though it has existed for over 4,000 years, modern medicine has not yet found a cure for the disease; once an infected patient begins exhibiting symptoms, the chances of them surviving the infection are under 1%. According to the MDPI Journal on Viruses, the rabies virus causes "more than 55,000 annual human deaths" that primarily occur in impoverished countries (Shimao). This large number of deaths is especially tragic when considering that developing a rabies infection is completely preventable, which really underlines the need for better education and more reliable access to medical care in vulnerable demographics.

The rabies virus primarily attacks the central nervous system, which is made up of the spinal cord and the brain. The central nervous system has many important roles, as explained in the article "Nervous System" by Anette O'Connor out of the Salem Press Encyclopedia of Science, which are abridged below:

•  it receives data from the five human senses and transports them to the brain to be processed;

• it handles the functions of conscious thinking, emotion expression and regulation, and memory storage/recall;

• it affects muscle tone and "controls posture and locomotion by stimulating the skeletal muscles";

• it handles the digestion and movement of food by controlling the muscles of and blood flow to the bowels;

• it is responsible for the release of adrenaline in response to stressful or frightening stimuli; and

• it controls salivary gland secretions.

These roles are extremely important to human survival; imagine how a person's quality of life might be affected if just one of these functions was impaired or completely disabled. The rabies virus affects all of these functions, though it especially has an impact on muscle tone, cognitive functioning, and saliva secretions (Hoagstrom).

By far, the most common means of rabies acquisition is through direct saliva-to-blood contact, which happens when an infected animal bites and breaks the skin of its next victim. In humans, rabies is most frequently acquired through bat bites (in the United States) and dog bites (in the Pacific Asia and Middle East regions) (Hoagstrom). Dogs being responsible for a large majority of non-US rabies transmissions can be surprising to many people, as it is a common belief that the animal most likely to transmit rabies to a human on a global scale would be "wildlife", such as a bat or raccoon, but it is important to consider that most people would not willingly approach and attempt to pet an animal they classify as "wild" the way that they might approach an attempt to pet a dog, even if both are equally feral. Many cultures harbor a general trust and affection for canines due to their common role as a domesticated pet; for example, in the United States, dogs are generally never allowed to "free roam" or live "wild lives," and thus it is widely accepted that most dogs seen wandering the streets in the United States are pet dogs who have escaped their living area. People in the United States widely expect that dogs are vaccinated, relatively friendly, and generally safe to handle. In most other countries, such as in Pacific Asia or the Middle East, dogs are allowed to live "feral" lives with minimal human intervention, to include a lack of rabies vaccinations and rabies prevention measures, and foreigners who come to these countries not understanding the cultural difference and who attempt to pet or handle the dogs end up bitten and exposed to rabies (Ghasemzadeh).

In humans, rabies has a predictable series of symptoms that occur in three stages: the incubation stage, the aggression stage, and the paralytic stage (Pattanaik). The symptoms that are presented by rabies patients will vary depending on what stage of the virus infection they are undergoing. All three stages below are presented as they would occur in humans, as rabies that occurs in other mammals can have different symptoms and different timelines.

THE INCUBATION STAGE

The incubation stage is the period of time between when the rabies virus is first introduced to the new host-- when the bite by the infected animal occurred-- and when the very first symptoms of infection appear. This stage can last anywhere from one day to one year based on many factors such as the bite location, patient immune system status, how soon medical care was received after a bite, and more. In the article "Rabies viral encephalitis with probable 25 year incubation period!" published in Annals of Indian Academy of Neurology, a medical journal by the Indian Academy of Neurology, author Anita Mahadevan breaks down the incubation rates as they appear in clinical studies: "the overall reported incubation period varies from 30 days in 30% of the cases, 31–90 days in 54%, greater than 90 days in 15% and in 1% of the cases beyond 1 year is recorded." As you can see, in over half of infected human patients, rabies completed its incubation stage between thirty one and ninety days. This delay in symptom onset can make it difficult for providers and patients alike to identify when, exactly, the infection occurred. Sometimes the delay can make it difficult for healthcare providers to recognize the illness as rabies in the first place, such as in traveling patients who were infected elsewhere in the world and then arrive to hospitals in countries that do not usually see rabies cases.

There are no symptoms that occur in the incubation stage.

THE AGGRESSION STAGE

The aggression stage immediately follows the incubation stage; it occurs once the rabies virus has multiplied enough to reach the meninges, the spinal cord, and the brain. The meninges are the layers of tissue that surround and protect both the spinal cord and the brain (O'Connor). Once the rabies virus has arrived at the central nervous system, symptoms begin. These initial symptoms include fever, general anxiety and irritability, insomnia, and sore throat (Hoagstrom). Within days these symptoms escalate into delirium and altered mental status; violence and aggression, often resulting in the patient wearing soft restraints or being medically sedated; a fear of water that causes painful spasms in the throat when the patient attempts to drink; heavy salivation; and insomnia that progresses into a complete inability to sleep (Willoughby).

This stage can last from one week to two weeks.

THE PARALYTIC STAGE

The final stage of the rabies infection in humans, the paralytic stage, is where the patient's vital signs and overall health begins to completely deteriorate. The patient will become completely disoriented to their surroundings; the patient becomes unable to recognize other people, themselves, or what time it is; the patient will experience muscle weakness in the arms and legs that progresses to complete paralysis of the limbs; the patient will experience seizures; and the paralysis experienced by the patient will spread to the heart and lungs, eventually resulting in the heart and/or the lungs to stop functioning, ultimately resulting in the death of the patient (Hoagstrom).

The paralytic stage generally lasts under one week. The aggression stage and paralytic stage combined will usually begin and end within a two week period. Once symptoms begin, there is very little that can be done to save the life of an infected patient-- this is why bite prevention education and access to medical facilities that are equipped to treat rabies bites is so important.