What is rabies?
Rabies is a viral disease that causes inflammation of the brain in humans and other mammals. It is transmitted through the bite or scratch of an infected animal, most commonly dogs. The rabies virus infects the central nervous system, causing brain inflammation that is nearly always fatal once symptoms appear.
How do you get rabies?
Rabies is spread through the saliva of infected animals. In most cases, it is transmitted through a bite that breaks the skin and introduces the virus into muscle or nerve tissue. Less commonly, rabies can be contracted if infected saliva comes into contact with open wounds or mucous membranes such as the eyes, nose, or mouth.
Rabies cannot be spread through contact with blood, urine, or feces of an infected animal. It also cannot be transmitted through touching or petting fur. Only close contact with saliva from an infected animal can lead to rabies infection.
What animals carry rabies?
In the United States, several animal species are known reservoirs of the rabies virus:
- Bats – Most human rabies deaths in the U.S. are caused by bat rabies variants.
- Raccoons
- Skunks
- Foxes
- Coyotes
Dogs and cats can also transmit rabies, but this has become less common in areas where animal vaccination programs are in place. Wild animals like rodents and lagomorphs (rabbits, hares) very rarely carry rabies.
What are the symptoms of rabies?
The symptoms of rabies occur in two phases:
Prodromal Phase
This is the initial stage after the rabies virus enters the body. The prodromal phase usually lasts 2-10 days. Symptoms include:
- Fever
- Headache
- Nausea and vomiting
- General weakness and discomfort
Acute Neurologic Phase
After the initial flu-like symptoms, more severe neurologic symptoms set in. This indicates that the virus has spread to the brain and central nervous system. Symptoms include:
- Insomnia
- Confusion
- Agitation
- Hallucinations
- Irritability
- Paralysis
- Hydrophobia (fear of water)
- Hyperventilation
- Seizures
Once the acute phase starts, rabies is almost always fatal within a few days due to dysfunction of the brain and other vital organs.
How is rabies diagnosed?
Rabies has a wide range of non-specific symptoms, so it can be difficult to diagnose clinically – especially in the early stages. Laboratory testing is needed to confirm the disease. Samples used include:
- Saliva – Can detect rabies virus genetic material in the saliva
- Skin biopsy – Testing nerve endings in the skin for rabies antigens
- Spinal fluid analysis
- Blood tests for rabies antibodies
Imaging tests like MRI scans may also show characteristic patterns of brain inflammation. However, lab tests remain the gold standard for confirming rabies infection.
Is rabies curable?
Unfortunately, there are no treatments currently available that can cure rabies once symptoms set in. Rabies has one of the highest fatality rates of any infectious disease – close to 100% once the infection reaches the brain and central nervous system.
Why is rabies incurable once symptoms start?
There are several key reasons why rabies is almost always fatal:
Extremely rapid disease progression
Once the virus reaches the brain and symptoms start, rabies progresses extremely quickly. Patients typically die within 3-10 days. This small window leaves very little time to diagnose and initiate treatment.
Viral properties
The rabies virus has evolved to evade and inhibit immune responses in the body and brain. It can limit the effectiveness of vaccines and drugs once an infection sets in.
Blood-brain barrier
The unique blood vessels and membranes around the brain block most drugs and antibodies from entering the central nervous system. This means treatments often can’t reach rabies virus hidden in nerve cells.
Neuronal damage
As the virus replicates, it causes severe inflammation and damage in nerve cells. Even if the virus was cleared, the effects of this brain damage are generally irreversible and catastrophic.
Could gene editing play a role in curing rabies?
Gene editing technologies like CRISPR show potential for treating viral infections like rabies in the future. By precisely editing human DNA, it may be possible to make immune cells or neurons resistant to the rabies virus. However, gene editing for rabies is still in the basic research stage and is not a feasible treatment today. The rapid speed of rabies progression makes it very challenging to apply any genetic therapy in time.
What about the Milwaukee Protocol and other treatments?
The Milwaukee Protocol is an experimental treatment approach, first developed in 2004, that has been used in a small number of cases to try to save rabies patients. It includes:
- Inducing a coma to protect the brain
- Antiviral drugs like ketamine and ribavirin
- Immune therapies with rabies antibodies
However, most patients treated with this protocol have still died. To date, less than 10 potential survivors have been documented worldwide. Experts believe this approach is not effective enough to be considered a cure or standard treatment. Other experimental therapies like neural stem cell transplants have also failed to demonstrate efficacy.
Can rabies be prevented?
The good news is that rabies can be prevented with proper public health measures:
Animal control and leash laws
Having strict regulations for animal control, leashes, and behavior reduces bites and potential rabies transmission. Stray dogs are especially high-risk in spreading rabies to people.
Animal vaccination programs
Vaccinating domestic dogs, cats, and livestock protects both animals and humans by eliminating animal reservoirs. More than 300 million dogs alone are vaccinated globally each year.
Prophylaxis after a bite
If a bite occurs from a potentially rabid animal, prompt washing and vaccination with rabies immune globulin and vaccine is extremely effective in preventing the disease. This urgent treatment should start within 24 hours.
Pre-exposure prophylaxis
People with a high risk of exposure, such as veterinarians, can receive a pre-exposure rabies vaccine course for protection before any bite or exposure occurs. This primes the immune system to better respond to the vaccine after a bite.
The keys to rabies prevention
Here is a summary of the most important public health steps for controlling rabies:
| Method | How it works |
|---|---|
| Animal vaccination | Stops rabies virus transmission at the source |
| Leash laws and stray control | Prevents animal bites and contact with rabies |
| Bite prophylaxis | Rabies immune globulin and vaccine prevent the virus from infecting nerves and the brain |
| Pre-exposure immunization | Primes immune system to better respond to vaccine after a bite |
Conclusion
Rabies is almost 100% fatal once symptoms start, due to rapid virus spread to the brain, immune evasion, and irreparable neuronal damage. However, it can be readily prevented through bite avoidance, animal control, and vaccination programs. By understanding how rabies transmission occurs and implementing public health measures, the threat of this terrifying disease can be overcome.