Rabies (Genus Lyssavirus)

Summary

Rabies, an ancient and deadly disease, has been known for over 4,000 years, with early records suggesting transmission through animal saliva. Caused by the Lyssavirus, rabies spreads primarily through bites from infected animals. The virus attacks the central nervous system, leading to symptoms like fever, confusion, and hydrophobia, ultimately progressing to coma and death. While rabies is preventable with vaccines, post-exposure prophylaxis is essential if exposed. Though rare in vaccinated pets in the U.S., rabies remains a significant threat in parts of Asia and Latin America, where unvaccinated stray dogs are common. Worldwide, about 59,000 people die from rabies each year.

Takeaways

• 😀 Rabies is an ancient disease, at least 4,000 years old, and has been documented by various historical figures like doctors, poets, and philosophers.
• 😀 The first recorded evidence of rabies dates back to 1900-1600 BCE, hinting at its transmission through the saliva of infected animals.
• 😀 Louis Pasteur developed the first successful rabies vaccine in the 1880s, which was a breakthrough in preventing death from rabid animal bites.
• 😀 The rabies virus is a member of the Lyssavirus genus in the Rhabdoviridae family, characterized by its simple structure with only five proteins.
• 😀 Rabies virions are bullet-shaped, enveloped, and contain a helical nucleocapsid made of negative sense RNA, which helps the virus replicate.
• 😀 The virus infects host cells through glycoprotein spikes, triggering endocytosis, followed by fusion with the endosome to release its nucleocapsid for replication.
• 😀 The replication process produces viral RNA and proteins, which assemble into new virions that bud out of the host cell to infect others.
• 😀 Rabies can be transmitted through animal bites, inhalation of aerosolized virus, organ transplants, or mucosal membrane inoculations, with bites being the most common method.
• 😀 After entering the body, the virus replicates at the bite site (incubation phase) before traveling to the central nervous system, causing neurological symptoms and eventually death.
• 😀 The prodrome phase of rabies lasts 2-10 days and includes symptoms like fever, headache, malaise, and gastrointestinal issues, before progressing to the neurologic phase with hydrophobia, seizures, and paralysis.
• 😀 Rabies is a zoonotic disease primarily transmitted by dogs in urban areas, but in places like Latin America and Asia, unvaccinated stray dogs are the main carriers, leading to thousands of cases annually.

Q & A

What is the history of rabies and when was it first mentioned?

Rabies is an ancient disease, at least 4,000 years old. It was mentioned in the writings of various professionals, including doctors, veterinarians, and philosophers. The earliest records hint at the transmission of rabies through the saliva of infected animals, dating back to around 1900-1600 BCE.

How did the understanding of rabies transmission evolve over time?

Over the centuries, scientists and medical practitioners speculated about the causes and treatments for rabies. Some remedies involved herbs or religious practices, while others included extreme measures like amputation or burning the bite wound with religious relics. It wasn't until the 1880s that Louis Pasteur developed the first successful killed-rabies vaccine.

What is the structure of the rabies virus?

The rabies virus belongs to the genus Lyssavirus in the Rhabdoviridae family. It is a simple, bullet-shaped virus with glycoprotein spikes on its surface. Inside, it has a helical nucleocapsid containing a single-stranded RNA genome, which is about 12,000 bases long.

How does the rabies virus replicate inside a host cell?

The rabies virus attaches to a host cell through its glycoprotein spikes, triggering endocytosis. The virus is enclosed in a vesicle and its envelope fuses with the vesicle membrane, releasing the nucleocapsid into the cytoplasm. There, the virus uses its enzymes and host cell machinery to transcribe viral RNA and produce proteins. New virions are assembled and released through a process called budding.

What are the primary ways rabies is transmitted?

Rabies is typically transmitted through the bite of an infected animal, as the virus is present in the saliva. Other transmission methods include inhaling aerosolized virus (e.g., in bat caves), receiving an organ transplant with infected tissue, or being inoculated through mucosal membranes, such as a scratch.

What happens during the incubation period of rabies?

During the incubation period, which can last from days to months, the virus replicates in the muscle tissue near the bite site. This phase typically has no symptoms, making it difficult to detect early on.

What are the early symptoms of rabies once clinical disease begins?

Once symptoms begin, they are often nonspecific and may include fever, headache, itching at the site of the bite, malaise, gastrointestinal issues, fatigue, and anorexia. This phase is known as the prodrome phase and lasts between two and ten days.

What happens during the neurologic phase of rabies?

In the neurologic phase, the virus infects the brain, particularly the brainstem and hippocampus, leading to symptoms such as fear of water (hydrophobia), seizures, disorientation, hallucinations, and paralysis. This phase lasts between two and ten days and typically ends with coma and death.

How does rabies spread globally and which animals are primarily responsible for transmission?

Rabies is endemic worldwide except in Australia. In urban areas, dogs are the main transmitters, but wild animals like raccoons, skunks, bats, foxes, and farm animals can also spread the virus, particularly to unvaccinated pets. In parts of Latin America and Asia, stray dogs are a major source of rabies transmission.

How is rabies diagnosed and what can be done after exposure?

Rabies is diagnosed based on symptoms and antibody tests, but by the time symptoms appear, it's usually too late for intervention. Post-exposure prophylaxis (PEP), which involves administering the rabies vaccine after exposure, is the only way to prevent the disease from progressing.