Rabies is a neurological disease spread by the saliva of infected animals. While it can be prevented by vaccination, it is deadly once symptoms appear. Learn more about this disease and the virus that causes it.
When you think of the word ‘rabid,’ you may picture a crazed animal — maybe like the dog in Stephen King’s Cujo — foaming at the mouth and acting aggressive.
But you might not know much more about the actual rabies disease that causes this behavior.Rabies is caused by a virus that is found in the saliva of infected animals. The saliva must come in contact with an open wound, so it is usually spread through bites. The virus can infect any mammal but is mostly found in wild animals like bats, raccoons, foxes, and skunks.
Domestic animals like cats and dogs can also be infected, which is why there are laws requiring them to be vaccinated against the virus.
Disease Function and Progression
If someone were to be infected with rabies, the first goal of the virus is to make it to the brain. The rabies virus first infects a nerve cell near the site of the bite and then spreads from nerve to nerve until it reaches the spinal cord and then the brain. The time it takes for the virus to reach the brain is known as the incubation period.
During this period, an infected person or animal doesn’t show any symptoms and can’t spread the virus. There are a lot of factors influencing the length of the incubation period, including the type of animal the virus came from, but it can last anywhere from weeks to months.Once the virus reaches the brain, the symptoms of rabies start to show. After symptoms begin, there is no way to cure or treat the virus.
It is almost always fatal. The virus replicates in the brain, causing a lot of inflammation or swelling. The earliest signs may be similar to having the flu with fever, headache, and weakness. As the disease progresses, the infected person would start to have more severe symptoms such as confusion, difficulty thinking, and hallucinations leading to abnormal behavior. This abnormal behavior is also observed in rabid wild animals, which is why they are sometimes aggressive or more likely to approach people.
After reaching the brain, the virus also infects the salivary glands in the mouth that produce saliva. This can cause an excess production of saliva, leading to the foaming mouth typically associated with rabies. This is also why rabies is transmitted through the saliva rather than blood — the virus only replicates in the brain and salivary glands.
Treatment and Prevention
In domestic animals like cats and dogs, rabies can be prevented by a vaccine. Vaccines work by training your immune system to recognize the virus. After a rabies vaccination, the body produces proteins called antibodies that recognize and specifically bind to only the rabies virus. If you are infected after you get the vaccine, the antibodies bind to the virus and keep it from causing disease.
People are generally not vaccinated against rabies, so they must receive treatment as soon as possible after being exposed. The treatment if you were to be exposed to the rabies virus is called postexposure vaccination, and it helps your body fight off the virus before it is able to reach the brain. If it does reach your brain, and you begin showing symptoms of a rabies infection, there is a low chance you will survive.
Viral Structure and Replication
The rabies virus belongs to a family known as Rhabdoviridae.
These viruses are bullet-shaped as can be seen in the electron micrograph image below.
The outside of the virus is an envelope coated in the viral glycoprotein ( G). Inside the virus, the matrix protein (M ) provides structure to the viral envelope. The viral genome is single-stranded RNA.
This is coated in many copies of the nucleoprotein (N). The RNA and N protein form the ribonucleoprotein core (RNP). The RNP is like a long strand of beads that wraps around the inside of the virus, binding to M and forming a spiral. The other two proteins, a polymerase (L) and a phosphoprotein (P), are also inside the virus.The G protein binds to cells and starts the infection.
The virus uncoats inside the cell, which means that the RNP is released into the cytoplasm where viral replication can takes place. The first step is for the virus to make its proteins. The viral RNA is used as a template for the L protein to transcribe messenger RNAs (mRNAs). These mRNAs tell the cell’s ribosomes to make viral proteins instead of the cell’s proteins.Once enough viral proteins are made, the L protein starts to make new copies of the viral genome. This RNA is bound by new copies of the L, P, and N proteins forming new RNPs. These are covered with M protein and then gain an envelope with the G protein as they leave the cell to form new infectious viruses.
The rabies virus causes a deadly neurological disease spread by the saliva of infected animals. The virus has a long incubation period during which there are no symptoms, but the disease can still be cured using postexposure vaccination. Symptoms begin when the virus reaches the brain and begins replicating.
Once symptoms appear, the disease is almost always fatal. The virus has only five proteins and an RNA genome. After uncoating in the cell’s cytoplasm, it directs the cell to make viral proteins and starts producing new viruses.