Human Rabies - Transmission and Vaccine

Rabies is a zoonosis (disease transmitted from animals to humans) caused by a virus. It is one of the most serious diseases known, with a mortality rate of almost 100%. No other infectious disease has so high mortality rate.

Despite the availability of vaccine and immunoglobulin, which help to prevent human rabies, still approximately 70,000 people worldwide die of rabies each year.

Human rabies
Human rabies

What is human rabies?

Rabies is a serious infectious disease caused by viruses of the genus Lyssavirus, family Rhabdoviridae, which leads to death virtually 100% of infected patients. Since the nineteenth century, however, there is a vaccine against rabies, which is very effective in preventing the progression of the disease, if administered in time.

Rabies is a disease transmitted only by mammals, usually through biting and inoculation of virus in the saliva into the skin.

Rabies virus is attracted by the cells of the nervous system, the peripheral nerves are invaded immediately after being inoculated through the skin. When in the nerves, the virus begins to move slowly, about 12 mm per day, toward the central nervous system. Upon arriving in the brain, the virus causes encephalitis, rabies, the dreaded complication that leads patients to death.

Transmission of rabies

Rabies is a zoonosis. The virus is transmitted through bites and scratches from infected mammals. In most cases the disease is transmitted by dogs or bats. However, several other mammals can transmit the disease, including:
Transmission of rabies
Transmission of rabies
  • Ferrets
  • Foxes
  • Coyotes
  • Raccoons
  • Skunks
  • Cats
  • Monkeys

Mammals, which are not carnivores, such as pig, cow, goat, horse, etc are also associated with rabies cases, but these are rarer.

Small rodents, such as squirrels, rats, rabbits, guinea pigs and hamsters are not usually transmitters of rabies, with no reports in the medical literature of cases of human rabies. Not mammal pets like lizards, fish and birds NEVER transmit rabies.

Since the implementation of programs of vaccination against rabies in dogs and cats, the number of human rabies cases dropped. In Europe and the US, for example, rabies virus circulates more in foxes and bats than in dogs, which reduces the risk of human exposure.

Virtually all cases of human rabies are transmitted through bites or scratches from infected animals. Because the virus is present in the saliva of infected animals, another possible transmission route, but much less common, is through licks on mucous membranes such as mouth, or open wounds. That old habit of dogs to provide wound licking, besides facilitating bacterial infection of the lesion can also be a source of contamination.

There is no transmission between humans, with no risk to relatives or to the medical team that cares for patients. The transmission does not also occur by objects or food, since the virus cannot survive in the environment, dying quickly when exposed to sunlight or when contaminated saliva dries. There are no cases of rabies transmission through fruits touched by infected bats.

Contact with intact skin is not liable even if the animal licks you. Similarly, touching infected animals such as dogs to pet or just lay a hand on a bat has also no risk of contamination. The transmission is possible only when the virus is present in saliva, with no risk of contamination when there is contact with blood, feces or urine of infected animals.

Symptoms of rabies

The rabies virus is attracted to the central nervous system and lodge in the brain often after long trip through peripheral nerves.

Encephalitis, inflammation of the brain, is the end result of the appearance and multiplication of the virus in the central nervous system. Symptoms of rabies are all due to this involvement of the brain. They are:
  • Confusion
  • Disorientation
  • Aggressiveness
  • Hallucinations
  • Difficulty in swallowing
  • Motor paralysis
  • Muscle spasms
  • Excessive salivation

Once neurological symptoms started, the patient progresses to death in 99.99% of cases.

The evolution of rabies can be divided into 4 parts:

1) Incubation - The virus spreads through the peripheral nerves slowly. Since the bite to the appearance of neurological symptoms usually 1 to 3 months pass. Biting on the face or hands is more dangerous and have a shorter incubation time.

2) Prodromes - These are nonspecific symptoms that occur before the encephalitis. In general, it consists of headache, malaise, fever, sore throat and vomiting. There may also be numbness, pain, and itching at the site of the bite or scratch.

3) Encephalitis - It is the inflammation of the central nervous system previously described.

4) Coma and death - occur on average 2 weeks after the onset of symptoms.

Treatment of rabies

Rabies treatment
Rabies treatment
If on one hand almost 100% of patients die after the onset of symptoms, on the other hand, there is vaccine and prophylactic treatment with immunoglobulins (antibodies).

In case of a bite by any mammal, we should wash the wound with soap and water to prevent contamination by bacteria in saliva of animals. After this initial cleaning, the patient should seek a medical center for the health care team to assess whether there is a need to initiate prophylactic (preventive) vaccination against rabies. It is also important to vaccinate the patient against tetanus, if the last vaccination was more than 10 years ago.

If the animal is domestic it is important to get the vaccination of the animal, certifying their immunization against rabies. Pets not properly vaccinated for rabies are transmission sources. In these cases, there is no need to start any treatment unless the animal shows symptoms a few days after the bite.

In dogs, cats and ferrets, the maximum time of disease progression, since the appearance of the virus in saliva to death, is only 10 days. When someone is bitten or scratched by one of these animals, they are indicated the same observation for up to 10 days. If the animal is not sick in this range because it was not a contaminant on the bite, and there is therefore no risk of rabies for the patient.

If the animal is a dog, stray or wild, like a bat or fox, it is important to capture it so it can be examined by a veterinarian to look for signs of rabies. If the capture of the animal is not feasible, prophylactic treatment should be given, assuming that it is contaminated with rabies virus. Therefore, treatment should be started as soon as possible, as prophylaxis against rabies is considered a medical emergency.

Biting the head or neck is more serious because they are close to the brain. Hands and feet are also dangerous because they are innervation areas and facilitate the arrival of the virus to the peripheral nerves. In these cases the travel time of the virus to the brain is much shorter than usual, the incubation period may be a few days. These patients should receive prophylactic urgent situation regardless of the animal.

The most important thing is to understand the seriousness of rabies. You should never neglect a bite or scratch by animals. Do not rely solely on the appearance of the animal to determine if this is not rabies. Once bitten, seek a health center to get instructions.

Treatment of rabies is divided into pre-exposure prophylaxis and post-exposure prophylaxis. Let's talk a little bit about them.

Pre-exposure prophylaxis

The pre-exposure prophylaxis is preventative treatment for individuals who have not been exposed to the virus. It is made with the rabies vaccine and is only indicated for individuals with a high risk of contamination as:
  • Veterinary surgeons
  • Biologists
  • Agrotechnical workers
  • People working in virology laboratories
  • People working with wild animals
  • People involved in the capture and study of animals suspected of rabies
  • People traveling to areas where there is no control of rabies in animals

The rabies vaccine is administered in three doses on days 0, 7 and 28. Two weeks after the end of vaccination blood should be collected to evaluate whether there was an immune response with production of suitable antibodies.

Post-exposure prophylaxis

The post-exposure prophylaxis is made only after an individual has suffered a bite from a mammal.

There are several prophylactic regimens, involving vaccines and immunoglobulins. Depending on the severity of the injury, the scheme can include up to 10 days followed by more vaccinations with daily administration of immunoglobulin. Every patient attacked by animals should seek a health clinic as soon as possible to receive guidance on the treatment.

Bats and rabies

Bats are animals commonly infected by rabies. In the U.S. more than 90% of rabies cases were caused by bat bites over the past 15 years.

The big problem is that the bite may go unnoticed, especially while the victim sleeps. Post-exposure prophylaxis is therefore recommended for all those who find a bat in their room, even with no signs of bite or scratch. When in doubt, you should always assume that the bite happened.

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