Rabies Virus and Post-Exposure Prophylaxis
On this page
Direct answer
Rabies virus, a lyssavirus of family Rhabdoviridae, causes an encephalitis that is almost invariably fatal once clinical symptoms begin. Post-exposure prophylaxis (PEP) is therefore the key intervention, starting with immediate thorough wound washing, followed by vaccine and, for severe exposures, rabies immunoglobulin. The WHO exposure category decides whether treatment is needed at all, and only a non-bite licking of intact skin needs no treatment.
What you must remember
- Structure: Bullet-shaped, enveloped, negative-sense single-stranded RNA virus; the glycoprotein G is the main antigen and a determinant of virulence.
- Negri bodies: Eosinophilic cytoplasmic inclusions in Purkinje cells of the cerebellum and pyramidal cells of the hippocampus (Ammon's horn), diagnostic on histology.
- Antemortem diagnosis: Direct fluorescent antibody testing or RT-PCR on a nape-of-neck skin biopsy, saliva and corneal impression; brain examination confirms after death.
- Category I: Touching or feeding animals and licks on intact skin; no treatment is needed.
- Category II: Nibbling of uncovered skin and minor scratches without bleeding; vaccine alone.
- Category III: Transdermal bites or scratches, licks on broken skin and mucosal contamination; vaccine plus rabies immunoglobulin.
- Wound care: Washing with soap and water for at least 15 minutes, followed by a virucidal agent such as povidone iodine.
- Regimens: The Zagreb 2-1-1 schedule gives two doses on day 0, one on day 7 and one on day 21; intradermal regimens use smaller volumes and are used only with licensed vaccines.
A pathway from bite to treatment decision
A bitten patient in a clinic needs a decision made in minutes. The order of actions matters more than any single drug.
- Wash first: Wash the wound with soap and running water for 15 minutes, then apply a virucidal agent; this step is simple and lowers risk.
- Classify the exposure: Assign WHO Category I, II or III based on the type of contact and whether the skin is broken.
- Decide on vaccine: Category I needs no vaccine, while Category II and III start the vaccine schedule on day 0.
- Add immunoglobulin for Category III: Human rabies immunoglobulin is infiltrated into the wound as early as possible, ideally at the first visit.
- Observe the animal: If a dog or cat remains healthy for 10 days after the bite, rabies is unlikely in that animal and treatment may be stopped.
- Complete the course: Finish the full vaccine schedule, even when the wound looks healed.
Where the exam tries to catch you
Rabies items usually test the exposure category, the sequence of actions and the injection rules.
- Trap: Starting the vaccine while skipping wound washing. Correct: Washing is free and is the first essential step, and it can prevent infection on its own.
- Trap: Giving immunoglobulin for a minor scratch from a healthy pet. Correct: Immunoglobulin is reserved for Category III, while Category II exposures need vaccine alone.
- Trap: Injecting immunoglobulin and vaccine at the same site. Correct: Any remaining immunoglobulin is given at a site separate from the vaccine, because it can blunt the vaccine response.
Frequently asked questions
What are Negri bodies and where are they found?
Negri bodies are eosinophilic intracytoplasmic inclusions found in neurons, classically the Purkinje cells of the cerebellum and pyramidal cells of the hippocampus. Their presence on histology is diagnostic of rabies virus infection.
Which WHO exposure category needs rabies immunoglobulin?
Category III exposures need rabies immunoglobulin along with vaccine, including transdermal bites, scratches with bleeding and licks on broken skin or mucous membranes. Category II exposures need vaccine alone.
How long should a biting dog be observed?
A dog or cat that remains healthy for 10 days after biting is considered unlikely to have been rabid at the time of the bite. Treatment can then usually be stopped, although the decision also depends on the animal's status and local advice.
Which test confirms rabies in a living patient?
Direct fluorescent antibody testing or RT-PCR on a nape-of-neck skin biopsy, along with saliva and corneal impression, can confirm rabies in a living patient. Brain tissue examination is confirmatory after death.
Why is rabies almost always fatal once symptoms appear?
Once clinical symptoms develop, rabies is almost always fatal because the virus has reached the central nervous system and no treatment reliably reverses the encephalitis. Post-exposure prophylaxis before symptom onset is therefore the only effective strategy.