Let's talk infectious diseases, the reason for vaccines: ᴿᵃᵇⁱᵉˢ

Rabies is a deadly virus spread to people from the saliva of infected animals. The rabies virus is usually transmitted through a bite. In rare cases, rabies can be spread when infected saliva gets into an open wound or the mucous membranes, such as the mouth or eyes. This could occur if an infected animal were to lick an open cut on your skin.

Any mammal can transmit the rabies virus. The animals most likely to transmit the rabies virus to people include: Cats, Cows, Dogs, Ferrets, Goats, Horses, Bats, Beavers, Coyotes, Foxes, Monkeys, Raccoons, Skunks, Woodchucks.

To reduce your risk of coming in contact with rabid animals:

▪️Vaccinate your pets.

▪️Keep your pets confined.

▪️Protect small pets from predators.

▪️Report stray animals to local authorities.

▪️Don't approach wild animals.

▪️Keep bats out of your home.

▪️Consider the rabies vaccine if you're traveling. If you're traveling to a country where rabies is common and you'll be there for an extended period of time, ask your doctor whether you should receive the rabies vaccine. This includes traveling to remote areas where medical care is difficult to find.

Despite being rare in the United States, rabies remains a frightening prospect due to the speed neurological symptoms can develop and progress.

This type of virus, known the lyssavirus, moves through the network of nerve cells, causing progressive symptoms as it gradually infiltrates the brain and central nervous system. That's why, unlike some infectious diseases, you cannot wait for signs of the illness to appear. You must seek treatment the moment you come you are bitten or scratched by an animal that has or is suspected to have rabies.

The symptoms of rabies can be characterized by the stages of infection, broadly described as the incubation period, the prodromal period, the acute neurologic period, and coma preceding death.

The incubation period is the time between exposure to the virus and the first appearance of symptoms. Symptoms of rabies during the incubation period may include:

▪️Fever

▪️Headache

▪️Tingling or burning sensation at the site of the exposure (known as paresthesia)

The prodromal period is described by the first appearance of symptoms. This is when the virus first enters the central nervous system and begins to cause damage.

The prodromal phase tends to run from two to 10 days on average and may cause such symptoms as:

▪️Fatigue

▪️A general feeling of unwellness

▪️Loss of appetite

▪️A sore, swollen throat

▪️Nausea

▪️Vomiting

▪️Diarrhea

▪️Agitation

▪️Insomnia

▪️Anxiety and depression

The acute neurologic period lasts anywhere from two to ten days and will almost invariably end in death. The types and characteristics of symptoms can vary, depending largely on how severe or mild the initial exposure was.

Symptoms of rabies occurring during the acute neurologic period may include:

▪️Hyperactivity

▪️Excessive salivation

▪️Hydrophobia

▪️Priapism

▪️Extreme sensitivity to light

▪️Paranoia

▪️Confusion and incoherence

▪️Aggression

▪️Hallucinations

▪️Seizures

▪️Partial paralysis

▪️Delirium

These symptoms will soon lead to a coma as the rabies infection causes massive brain inflammation. Without intensive supportive care, death will usually occur within hours or days.

There are three types of rabies that can be contracted.

(1) 𝙁𝙪𝙧𝙞𝙤𝙪𝙨 𝙧𝙖𝙗𝙞𝙚𝙨 is the type most people with experience. As its name suggests, this form of rabies is characterized by violent physical and neurologic symptoms. Symptoms may come and go, and will often be interspersed with moments of calm and lucidity. Death will most often be caused by cardio-respiratory arrest.

(2) 𝙋𝙖𝙧𝙖𝙡𝙮𝙩𝙞𝙘 𝙧𝙖𝙗𝙞𝙚𝙨 affects up to 20% of people and will cause muscles to gradually weaken, starting from the site of the exposure and expanding outward. Paralysis and death will eventually ensue (usually by respiratory failure). Most paralytic cases are believed to be caused by a minor injury, such as a nip, that has gone unnoticed.

(3) 𝘼𝙩𝙮𝙥𝙞𝙘𝙖𝙡 𝙧𝙖𝙗𝙞𝙚𝙨 is a type most often associated with bat bites. It may involve symptoms from both furious and paralytic forms of the disease. The variations in symptoms and severity can often make it hard to recognize a case as rabies.

In 1831 a schoolboy in Arbois, France, observed first hand a rabies outbreak spread by the bites of rabid animals. He never forgot that. His name? Louis Pasteur.

Fast forward to 1880. Pasteur had successfully created the first laboratory-created vaccine and he started studying rabies in earnest. One of the difficulties with studying rabies is that the time between introduction of the infectious agent and signs of the disease varies greatly. Pasteur was able to advance his studies by shortening this period: first, he selected for the most lethal, fast-acting strains of the virus, and, second, he injected infectious material directly into rabbit brains (in the wild, the virus is introduced via a bite and travels slowly up a nerve to the brain).

In 1884 Pasteur was able to successfully use a series of less-attenuated vaccines over several days to prevent rabies in dogs that had been infected. The work was dangerous: he and his assistants often had to handle the rabid animals and take samples from them.

In July 1885, he successfully prevented rabies in 9 year old Joseph Meister by post-exposure vaccination. And in October of that same year Pasteur successfully repeated his rabies vaccinations on a shepherd who had been severely bitten by a rabid dog. After Pasteur published word of the success, people fearing rabies from animal bites began to seek him out for the series of vaccinations.

It wasn't until 1946 that Pasteur's rabies vaccine was looked at again. Physician Hilary Koprowski adapted a rabies virus strain in chick embryos. He hoped to avoid using nervous system tissue as a medium for cultivating rabies virus because vaccine containing such tissue could cause serious side effects, such as encephalitis.

Additionally, Koprowski wanted to improve upon the immunogenicity of the older vaccines and to create a vaccine that would not result in as many vaccine failures as the older vaccines.

His new strain was successful and he called it HEP (for high-egg passage), as he continued to work on a new rabies vaccine.

In 1961, scientists tested different live virus preparations of Koprowski’s HEP rabies vaccine virus in animal and human trials. Most studies showed adequate antibody response and minimal side effects.

Jump forward to 1971. Koprowski’s team of scientists wanted to improve on the antibody response created by the experimental HEP live-virus vaccines. They looked to a cell line created from human embryonic cells as a medium for cultivating the rabies virus. Their initial tests successfully used live vaccine virus, as had the previous HEP tests. But medical resistance was strong to using a live virus rabies vaccine. The risk for inadvertent infection with a fatal illness was seen to be too high. Accordingly, Koprowski’s team used a chemical disinfectant to inactivate their rabies vaccine virus.

The rabies vaccine produced by Koprowski’s team at the Wistar Institute, called HDCV (human diploid cell vaccine), was licensed in Europe in 1976 and in the United States in 1980. One of its principal advantages was that the vaccine was given in five injections rather than the course of 14-21 injections used in the older vaccines.

HDCV is still widely used, but it is expensive to produce. Other rabies vaccines containing viruses grown in other types of cell culture have been licensed in different parts of the world. A few vaccines created with nervous system tissue continue to be used in Asia, Africa, and South America.

{You can find all the sources I used by clicking here.}