Rabies: Etiology and Epidemiology

• Rabies is a preventable viral disease of mammals most often transmitted through the bite of a rabid animal

Etiology

• Caused by a neurotropic virus in the genus Lyssavirus, family Rhabdoviridae.
• The virus travels to the brain by following peripheral nerves.
• Once the virus reaches the brain, it multiplies rapidly, leading to severe neurological symptoms
• Several variants of rabies virus exist, associated with different reservoir species, including bats, raccoons, skunks, and foxes.
• Transmission primarily occurs through the saliva of infected animals, usually via a bite.
• Less common routes include contamination of mucous membranes or open wounds with infected saliva, or through aerosol transmission (rare, e.g., in bat caves).

Epidemiology

• Rabies is present worldwide, but is more common in some regions than others.
• In the United States, rabies is most often found in wild animals, such as bats, raccoons, skunks, and foxes.
• Globally, dogs are the primary source of rabies transmission to humans.
• Human rabies cases are rare in developed countries because of effective animal vaccination programs and post-exposure prophylaxis.
• Most human cases occur in developing countries, particularly in areas with large populations of unvaccinated dogs.

Pathogenesis

• After the virus enters the body, it replicates locally at the site of the bite.
• It then enters peripheral nerves and travels to the central nervous system (CNS).
• The incubation period can vary from weeks to months, depending on the location of the bite, the severity of the wound, and the amount of virus introduced.
• Once in the CNS, the virus causes inflammation of the brain (encephalitis).
• The virus spreads throughout the brain, leading to neurological dysfunction and the development of clinical signs.
• From the CNS, the virus travels via peripheral nerves to other tissues, including the salivary glands, where it can be shed in saliva.

Clinical Signs

• Rabies can manifest in two main forms: furious rabies and paralytic rabies.
• Furious rabies is characterized by hyperactivity, agitation, hydrophobia (fear of water), aerophobia (fear of drafts or fresh air), and aggression.
• Paralytic rabies is characterized by muscle weakness, paralysis, and eventually coma.
• Initial symptoms may include fever, headache, malaise, and itching or tingling at the site of the bite.
• As the disease progresses, neurological symptoms develop, such as anxiety, confusion, hallucinations, and seizures.
• Difficulty swallowing and excessive salivation are common, contributing to the classic sign of "foaming at the mouth."
• Respiratory failure is the ultimate cause of death.

Diagnosis

• Diagnosing rabies can be challenging, especially early in the course of the illness.
• Direct fluorescent antibody (DFA) test detects rabies virus antigens in brain tissue and is considered the gold standard for postmortem diagnosis in animals.
• Real-time polymerase chain reaction (RT-PCR) assay detects rabies virus RNA in saliva, cerebrospinal fluid (CSF), or skin biopsies.
• Virus isolation can be attempted from saliva or brain tissue, but it is time-consuming.
• Antibody detection in serum or CSF can be useful, but the absence of antibodies does not rule out rabies, especially early in the disease.
• Postmortem diagnosis in humans typically involves testing brain tissue samples.

Treatment

• Once clinical signs of rabies appear, the disease is almost always fatal.
• There is experimental treatment called the Milwaukee protocol.
• Supportive care is essential to manage symptoms and minimize suffering.

Prevention

• Vaccination of domestic animals, especially dogs and cats, is a crucial component of rabies prevention.
• Avoid contact with wild animals, and report any animal bites or exposures to local health authorities.
• Post-exposure prophylaxis (PEP) should be administered to individuals who have been potentially exposed to rabies.
• PEP consists of a series of rabies vaccine injections and, in some cases, rabies immunoglobulin (RIG).
• RIG provides immediate, passive immunity by neutralizing the virus at the site of the exposure.
• The rabies vaccine stimulates the body's immune system to produce antibodies against the virus, providing long-term protection.
• Pre-exposure vaccination is recommended for people at high risk of exposure, such as veterinarians, animal handlers, and travelers to rabies-endemic regions.

Public Health Significance

• Rabies is a significant public health concern, particularly in developing countries.
• It is a neglected tropical disease that disproportionately affects poor and rural populations.
• Controlling rabies in animal reservoirs is essential for preventing human cases.
• Mass dog vaccination campaigns have been shown to be effective in reducing the incidence of rabies in both animals and humans.
• Education and awareness programs are important for promoting responsible pet ownership and preventing rabies exposures.
• Prompt administration of post-exposure prophylaxis is critical for preventing the development of rabies in exposed individuals.

Rabies is a preventable viral disease transmitted through the bite of a rabid animal. It is caused by a neurotropic virus that travels to the brain, leading to neurological symptoms. The disease is present worldwide and is commonly found in wild animals.