Rabies is a severe viral disease that affects the central nervous system, leading to acute encephalomyelitis in humans and animals. Once clinical symptoms emerge, the disease is almost universally fatal, with a near 100% fatality rate. It is present globally, impacting over 150 countries and all continents except Antarctica.
The Deadly Path of Rabies
The rabies virus, a neurotropic pathogen, enters the body through a bite or scratch from an infected animal. After inoculation, the virus may initially replicate in muscle tissue near the entry site, remaining localized for a period, usually 1 to 3 months. It then enters the peripheral nervous system, traveling along nerve pathways.
The virus utilizes retrograde axonal transport to move from the peripheral nerves to the spinal cord and then rapidly disseminates throughout the central nervous system. Once in the brain, the virus causes acute encephalomyelitis, which is inflammation of the brain and spinal cord.
This widespread neurological dysfunction impairs the brain’s ability to control bodily functions. The functional alteration of the central nervous system leads to severe disruptions in bodily systems, ultimately resulting in organ failure and death. The virus can also spread from the central nervous system to other organs, including the salivary glands, where it replicates and is released into saliva, facilitating transmission.
Recognizing the Signs
The progression of rabies in humans unfolds in distinct phases, beginning with non-specific symptoms. The initial prodromal phase, lasting 2 to 10 days, can include malaise, fever, headache, muscle pain, and gastrointestinal issues like nausea, vomiting, or diarrhea. Individuals may also experience unusual sensations such as burning, itching, tingling, pain, or numbness at the site of the bite wound.
As the virus reaches the central nervous system, the acute neurological phase begins, marked by more severe and specific symptoms. This stage involves significant nervous system dysfunction, manifesting as anxiety, agitation, and episodes of delirium. Individuals often develop hydrophobia, a fear of water, which can involve painful spasms when attempting to drink or even when exposed to water visually or auditorily. Aerophobia, an aversion to drafts or fresh air, can also occur.
Rabies presents in two main forms: furious rabies and paralytic rabies. Furious rabies, affecting about two-thirds of cases, is characterized by hyperactivity, aggression, restlessness, and sometimes hallucinations or seizures. These episodes can be intermittent, with periods of calm in between.
Paralytic rabies, accounting for approximately 20% of human cases, follows a less dramatic course. Symptoms often begin with weakness and paralysis at the bite site, gradually spreading throughout the body. This form may present with headache, neck stiffness, and tingling sensations, eventually leading to generalized paralysis and a slow progression to coma. Both furious and paralytic forms ultimately lead to coma and death, often due to cardio-respiratory arrest.
Preventing a Fatal Outcome
Preventing death from rabies relies entirely on prompt measures taken before symptoms appear. The first step after any suspected exposure, such as a bite or scratch from a potentially rabid animal, is thorough wound washing. The wound should be flushed with plenty of running water and soap or detergent for at least 15 minutes to reduce the virus. Applying an antiseptic like povidone-iodine after washing is also recommended.
Following wound care, Post-Exposure Prophylaxis (PEP) is the emergency response that can prevent the virus from reaching the central nervous system. PEP consists of two main components: rabies vaccine and, when indicated, rabies immunoglobulin (RIG). The rabies vaccine stimulates the body to produce its own antibodies against the virus. A PEP regimen for individuals without previous vaccination involves a series of four vaccine doses given intramuscularly on days 0, 3, 7, and 14 after the first dose.
Rabies immunoglobulin (RIG) provides immediate, passive immunity by delivering pre-formed antibodies directly to the body. RIG is infiltrated around the wound site, with any remaining amount administered intramuscularly at a distant site. This is important for unvaccinated individuals because the vaccine takes time to stimulate the body’s own immune response. RIG should be administered as soon as possible after exposure, ideally on Day 0, and can be given up to Day 7; beyond Day 7, it is not indicated as the vaccine’s antibody response has begun.
Pre-exposure vaccination is recommended for individuals at higher ongoing risk of rabies exposure, such as veterinarians, animal handlers, wildlife workers, and certain travelers to rabies-endemic regions. This prophylactic vaccination involves a two-dose series given on days 0 and 7. While pre-exposure vaccination does not eliminate the need for PEP after an exposure, it simplifies the post-exposure regimen by eliminating the need for RIG and reducing the number of vaccine doses required to two doses on days 0 and 3. Once clinical symptoms of rabies appear, prevention is the only effective strategy.