Rabies is a viral infection that affects the central nervous system and is almost always fatal once symptoms appear. It is primarily spread through the bite or scratch of an infected animal, most often a dog. Rabies causes about 59,000 deaths worldwide per year, with over 95% of cases occurring in Africa and Asia. While rabies remains endemic in many parts of the world, it is preventable through prompt treatment. Here is an overview of rabies, how it is transmitted, the symptoms, and how a doctor can determine if someone is infected.
What is rabies and how is it transmitted?
Rabies is caused by a virus in the genus Lyssavirus. There are multiple strains of rabies, with the most common being the rabies virus (RABV). It is most often spread through the bite or scratch of an infected animal. In up to 99% of rabies cases transmitted to humans, the virus is passed on through a bite. Less commonly, scratching, open wounds, and mucous membranes contaminated with saliva or other infectious material can transmit rabies.
In the Americas, wild animals are the most common source of infection for humans, especially raccoons, skunks, foxes, and bats. In other parts of the world, domestic dogs are the main transmitter, accounting for up to 99% of cases. Cats and livestock like cattle can also spread rabies to humans.
Once in the body, the virus travels through the nerves towards the brain. It has an incubation period that ranges from several days to months, often being between 2-8 weeks. During this time, an infected individual will not show any symptoms. Once in the brain, the virus causes swelling and interferes with normal neurological functioning. This is when symptoms of rabies start to appear.
What are the symptoms of rabies?
The symptoms of rabies can be divided into three stages:
Prodromal stage
This initial phase can last 2-10 days before more serious symptoms emerge. Some signs of early rabies include:
– Fever
– Headache
– Nausea
– Vomiting
– Fatigue
– Discomfort or tingling around the bite area
Excitative stage
In the excitative or furious stage, hyperactivity and agitation occur:
– Anxiety
– Confusion
– Agitation
– Hallucinations
– Insomnia
– Partial paralysis
– Abnormal behavior
– Hydrophobia (fear of water)
– Hypersalivation
Paralytic stage
Finally, paralysis sets in 3-4 days after the excited stage:
– Paralysis, starting with the bitten limb and spreading
– Coma
– Death, usually from respiratory failure
Once clinical signs of rabies appear, the disease is nearly always fatal. However, the progression can vary from person to person. Sometimes these phases are less defined. Rare cases of survival from rabies once symptoms start have occurred but this is very uncommon.
How does a doctor test for rabies?
When someone may have been exposed to rabies, the doctor will first thoroughly assess the risk of rabies transmission based on:
– Animal involved: Was it a known rabid animal or likely carrier?
– Type of exposure: Bite, scratch, or other means?
– Where exposure occurred: High vs low risk country?
Physical exam
A full physical exam will be done, looking for any bite marks or scratches. The doctor will also check for signs of rabies like spasms of the throat muscles when offered water.
Lab tests
If rabies is suspected, samples can be collected and tested:
Saliva, tears, urine, and skin: Can be tested for the presence of rabies virus genetic material using techniques like polymerase chain reaction (PCR).
Spinal fluid: A sample of cerebrospinal fluid obtained by lumbar puncture (spinal tap) may show the rabies antibody.
Blood: Testing blood can reveal rabies antibodies, which the body starts making shortly after infection.
Nuchal skin biopsy: Taking a skin sample from the neck can help detect rabies antibodies.
Postmortem, doctors can also check the brain directly for signs of the rabies virus.
Medical imaging
Brain imaging like MRI scans may show subtle changes associated with rabies encephalitis. But these are not definitive for diagnosing rabies.
How is rabies treated?
If a doctor believes rabies was transmitted, he or she will start postexposure prophylaxis (PEP) right away. This involves:
Wound cleansing: Thoroughly washing any bite marks or scratches with soap and water, detergent, or other virucides like povidone-iodine. This immediately reduces viral load.
Vaccination: A fast-acting rabies vaccine is given as soon as possible following potential exposure. This prompts the immune system to start making antibodies against the virus. Multiple vaccine doses are given over 14 days along with another medication called rabies immune globulin that provides immediate antibodies.
Immunoglobulin: Injecting rabies immune globulin (antibodies obtained from vaccinated humans) at the exposure site provides some immediate protection until the vaccine kicks in.
As long as PEP is started promptly, it is nearly 100% effective at preventing someone from developing rabies after being bitten by an animal. If treatment is delayed, the risk that the virus progresses in the body goes up. Once symptoms like fever and agitation appear, rabies is almost always fatal.
Conclusion
While rabies remains endemic in many regions, it can be prevented through prompt postexposure treatment. Doctors can test for rabies by looking for the virus in body fluids and the antibody response. Characteristic symptoms also provide clues, but at that advanced stage, mortality is exceptionally high. However, modern vaccines and immunoglobulin make rabies highly preventable after a potential exposure occurs and before symptoms develop. This requires quickly seeking medical care if bitten or scratched by a potentially rabid animal.