Table of Contents
What is rabies?
Rabies is a zoonotic disease caused a virus named after the disease called Rabies Virus (also called Lyssavirus). It is a deadly disease that causes progressive and inevitably fatal encephalitis.
Cause of Rabies (Etiology of Rabies)
Rabies virus (also known as Lyssavirus) is the cause of rabies. It is spread by bites from animals or licking of mucosal membranes (such as the mouth) by infected animals.
Rabies occurs worldwide and it is a significant public health problem in many countries in the Tropics. The reservoir for type 1 lyssavirus includes wild animals such as foxes and it is also transmitted by dogs in Asia whereas lyssavirus type 2, 3, 4, 5, 6 and 7 are transmitted by bats in Europe, Africa, Australia and Asia.
When the Rabies virus gains entry into the body through bite from a rabid animal via the skin or mucous membrane, the virus initial replicates in the muscles around point of entry after which it ascends to the central nervous system (CNS) through the neuromuscular junction. Once in the CNS, the rabies virus replicates in the gray matter and may be spread to other organs of the body such as the kidneys, heart, skin and salivary glands and the accompanying symptoms related to these affected organs will manifest.
Types of rabies based on Epidemiological setting
- Urban rabies: transmitted to humans through the bite of dogs (in most cases) and cats (less frequently)
- Sylvan rabies (wild rabies): this type of rabies is maintained by wild animals which serve as the reservoirs of the infection. These animals include foxes, bats, jackals and skunks.
Types of Rabies based on clinical features
- Furious rabies: this is the commonest type of rabies and transmitted by domestic animals such as dogs and cats; it causes aggressiveness and furiousness. There is no generalized paralysis in this type but rather respiratory paralysis occurs with cardiac arrhythmias, which are the cause of death.
- Dumb rabies (also known as Paralytic rabies because it causes generalized paralysis): this type of rabies is transmitted by rabid bats and symptoms include symmetrical ascending paralysis that resembles Guillain-Barre syndrome. The affected person or animal looks dumb or not aggressive because of paralysis.
Rabies Transmission (How do people get Rabies?)
Rabies is spread by the bite of a rabid animal, mostly dogs; other animals that can transmit rabies when they bite include cats, bats, wolves, cattle, badgers, raccoon, cattle, skunk and squirrels.
What does Rabid Animal mean?
A Rabid animal is an animal manifesting the symptoms of Rabies; this means the animal has been infected and can transmit the infection to a Human when it bites. For you to identify a rabid animal, you should have not the behavior of the animal prior to the suspicion of the disease in the said animal. The normal behavior becomes altered and a dog that was once friendly becomes aggressive and fears water (hydrophobia).
A rabid dog is a dog showing the symptoms of rabies and which has been infected by rabies virus. For you to know whether a dog has rabies or not, you have to observe it; Diagnosis of rabies in dogs is confirmed by identifying Negri bodies in the brain of the dog under a microscope.
How do dogs get rabies?
You may wonder how do other animals get rabies to transfer to humans; well animals such as dogs get rabies from other reservoir animals whenever another infected animals excretes the rabies virus in its feces and the an uninfected animal eats anything contaminated with the feces or saliva of the infected animal. So dogs may get it from infected saliva or contaminated food with saliva or feces of another dog, cat, skunks, foxes (dogs that are used for hunting), bats etc. Transmission may occur from a lactating mother to young animals (this occurred in animals only but has not occurred in humans).
Rabid Dog Symptoms
- Aggressiveness of the dog
- A rabid dog can be identified when an initially lovely dog that was once friendly now becomes anti-social and withdrawn
- The dog may wander aimlessly and would be seen moving from one place to another because of sudden restlessness
- Profuse salivation will manifest as rabies progresses in the dog because the jaws become paralyzed and the rabid dog will be unable to close its mouth
- Death of the dog may occur about 2 or more days from onset of paralysis of jaws
The symptoms of a dog with rabies manifest within 10 days (it has shorter incubation period compared with humans). It is mandatory to observe the dog for 10 to 14 days.
Rabies incubation period in Humans
The incubation period of Rabies in humans ranges from 50 days to 60 days averagely (the incubation period varies widely in humans; some people may even take years to show symptoms). This means that it may not be the same in all persons affected with rabies because the rabies virus prefers to attack neurons and the closer the site of the bite from the brain, the shorter the incubation period of rabies; bites on the face or trunk (abdomen and chest) have shorter incubation periods compared to bites from a rabid animal that occurred on the legs or the hands which have longer incubation period.
Signs and Symptoms of Rabies in Humans
The symptoms of rabies in Humans are similar to that of dogs; there are early symptoms (prodromal period) and late symptoms.
Early Symptoms of Rabies in Humans (Prodromal stage)
- Intense restlessness
- Paraesthesia (tingling or pricking sensation because the rabies virus affects nerves)
- Hyperaesthesia (hypersensitivity or over-sensitivity of the skin) even normal stimuli that are not supposed to cause pain may actually cause pain.
- The most important early symptom of rabies is Pain occurring at the site of bite from a rabid dog or animal
- Unspecific symptoms such as Fever, malaise, headache, and anxiety
Late symptoms of Rabies in Humans
- Hallucinations sets in as the disease progresses the person sees what others do not see or the person may hear or feel what others do not feel.
- Wild dreams
- Lacrimation excessive tears production
- Salivation excess production of saliva
- Increased perspiration (excessive sweating)
- Muscle spasm this can be triggered by the slightest touch that ordinarily would not have cause spasm in a normal person. Muscle spasms may occur around the throat when the muscles of swallowing are affected causing pain on swallowing (dysphagia)
- Aerophobia (fear of air) is considered pathognomonic of rabies; the presence of aerophobia is indicative of rabies.
- Fear of water (Hydrophobia) the fear of water is not because the person does not want water to touch the body but because the attempt to drink water or even the sight of water triggers laryngeal spasm that are so painful that the person may become asphyxiated (suffocation may occur)
- Convulsions result from the slightest stimuli; these are particularly
- Paralysis of the muscles of the body is the last symptom and death occurs within a day or two
Rabies Diagnosis (Rabies Test)
- Diagnosis is by clinical symptoms and signs
- Skin punch biopsies are used to detect rabies virus antigen with immunofluorescent antibody test on frozen section
- Viral RNA can be isolated using the reverse transcription polymerase chain reaction (RT-PCR)
- Isolation of the rabies viruses from culture of specimens such as saliva also helps to confirm diagnosis
- Serological test help to show the presence of antibodies in blood or CSF
- In death animals or autopsy specimen, the presence of Negri bodies also confirms diagnosis of rabies in 90% of all patients with rabies. Negri bodies are eosinophilic and ovoid bodies that are seen in greatest numbers in the neurones of the hippocampus and the cerebellum.
Rabies Vaccine and Anti rabies Immunoglobulin
The rabies vaccine was developed by Louis Pasteur in 1885. There are two forms of prophylaxis given: the pre-exposure prophylaxis and post-exposure prophylaxis. Immunity against rabies can be gotten either as active immunity (using the rabies vaccine) or passive immunity (using the anti-rabies immunoglobulin).
This offers active immunity to the individual and it is best. It triggers the body of the person to develop antibodies against the rabies virus that fights the virus and prevents fatal disease. There are two types of the rabies vaccine: the Human Diploid Cell Vaccine (which is the best and has fewer side effects) and the Purified chicken embryo cell vaccine which is also called the attenuated Rabies Vaccine (made of nerve cell tissue from chick fibroblast and it has serious adverse reactions)
Rabies Immunoglobulin (Anti rabies Serum)
This offers passive protection because your body does not produce antibodies against the rabies virus. It is gotten from serum of humans who have produced antibodies against the rabies virus and such antibodies are then taken and purified and given to someone who is suspected to be bitten by a rabid animal. This offers temporary protection before the Rabies vaccine is given.
Pre-exposure prophylaxis Rabies Vaccine
This is given to people at high risk of getting rabies such as laboratory workers, veterinary workers and animal handlers. 2 doses of human diploid cell vaccine (HDCV) are given 4 weeks apart and are administered through the intramuscular route or subcutaneously. A booster dose is then given after every 12 month period continuously as long as the person keeps handling animals or working in veterinary lab. In some countries, the vaccines of nervous-tissue origin are used but this type of vaccine has serious side effects and should be avoided if the human diploid cell vaccine is available.
First action to be taken is the local wound care of irrigating the wound thoroughly and then 20 IU/kg of Human rabies immunoglobulin should be given immediately; half is usually injected around the bite area and the remaining half is given intramuscularly. 5 injections of HDCV (1.0 ml each) are usually given with the first dose being on day 0, followed by others on days 3, 7, 14 and 28. Side effects of human diploid cell vaccine are not common.
When the risk of getting rabies is high, a combination of human rabies immune globulin or rabies antiserum and a course of vaccination give the best protection.
Rabies Treatment in Humans
- Rabies Prophylaxis is the most effective form of treatment of rabies in humans; the prophylaxis given is the Human Diploid Cell Vaccine (HDCV). This rabies vaccine is usually given when there is a bite from a suspected rabid animal. There should be no delay in giving the rabies vaccine because every minute counts in saving the life of the affected person.
- Veterinary workers and people that handle animals should be given Pre-exposure prophylaxis
- When the human diploid cell vaccine is not available, then attenuated rabies virus vaccine can be given see the attenuated rabies vaccine schedule below.
- Immediate local wound care following bite from a rabid dog: immediately irrigating the bite wound with soap solution reduces the mortality rate of rabies from 90% to 5%. See local wound care below.
- Tetanus toxoid should be given to prevent tetanus
- Antibiotics should also be given to guard against infections of wound that may lead to osteomyelitis, sepsis etc
Local Wound care following a bite from a rabid animal
The local wound care is first aid that should be done immediately to reduce the mortality rate and increase the survival rate of anyone bitten by a rabid animal. This is done by irrigating the bite wound with soap solution. This simple first aid can reduce the mortality rate from 90 percent to 5 percent and also prevents the disease in most cases from manifesting the symptoms (it prevents clinical rabies). The wound should not be sutured.
Rabies vaccine schedule
The attenuated rabies vaccine schedule consists of daily anti rabies injections of 2ml of 5% tissue emulsion for a period of 14 to 21 days; it is given through subcutaneous route. Booster doses are then administered (one is given 10 days after the first dose and the second booster rabies vaccine is given 21 days after the first dose).
Rabies vaccine side effects
- The most serious adverse effect of rabies vaccine is from the vaccine made with duck eggs which can cause neuroparalysis; this side effect occurs in about 1 in 30,000 persons receiving this vaccine
- Less serious side effect include Headache
- Itching of the injection site
- Redness at the site of injection
- Pain and Swelling at the site of injection
These side effects do not occur in all patients and not all the side effects will occur in one person. The side effects do occur frequently when intradermal injections are given and less side effect in intramuscular injections.
- Prevention of rabies includes registering of all dogs and vaccinating the dogs against rabies infection
- Prompt treatment of any dog bite victim with the rabies vaccine before symptoms develop
- Pre-exposure vaccination of people handling animals and veterinary workers
Is there a cure for rabies?
Rabies cannot be cured and it is not treatable but can be prevented with the Rabies Vaccine. Once the CNS symptoms have developed, any medication given is to help reduce the suffering but does not change course of the disease because death may be inevitable. The patients are normally nursed in a quiet dark room.
Rabies Survival Rate
There are only 6 survivors of Rabies; once symptoms have developed, death is almost always inevitable.