Makindo Medical Notes

Related Subjects: |Herpes Varicella-Zoster (Shingles) Infection |Chickenpox Varicella Infection |Varicella Cerebral Vasculopathy |Herpes Viruses |Herpes Zoster Ophthalmicus (HZO) Shingles |MonkeyPox |Mumps |Measles |Rubella (German Measles) |Epstein-Barr Virus infection |Cytomegalovirus (CMV) infections |CMV retinitis infections |Toxoplasmosis

📖 About

• 🦠 Rabies is a zoonotic viral disease that primarily affects the CNS.
• 🌍 Rare in the UK and absent in Australia, but common in Asia & Africa.
• 🐕 Reservoirs: dogs (most common worldwide), bats, raccoons, and wild animals.
• Transmission via bites, scratches, or saliva contacting broken skin/mucosa.

🧬 Aetiology & Pathogenesis

• Caused by single-stranded RNA Lyssavirus (Rhabdoviridae family).
• 🎯 Infects local muscle cells → binds to nicotinic acetylcholine receptors at NMJs.
• 📡 Travels via retrograde axonal transport into CNS.
• Spreads to brain → salivary glands → allows host-to-host transmission.

🩺 Clinical Presentation

• ⏱️ Incubation: 1 week–1 year (typically 20–90 days).
• Prodrome: fever, headache, malaise, tingling/itching at bite site.
• Encephalitic (furious) rabies (80%):
  • Agitation, delirium, ataxia, bizarre/aggressive behaviour.
  • 💧 Hydrophobia: pharyngeal spasms on swallowing liquids.
  • Hypersalivation, dilated pupils, myoclonus, priapism.
• Paralytic rabies (20%):
  • Flaccid paralysis starting locally, mimics Guillain–Barré.
• ➡️ Progresses to coma, seizures, arrhythmias, DIC, death.

🔎 Investigations

• 🩸 Serology: neutralising antibodies (often negative early).
• 💉 CSF: mild ↑WCC, ↑protein.
• 🧠 Histology: Negri bodies in hippocampus & Purkinje cells.
• 🔬 Skin biopsy: rabies antigen in hair follicle base.
• 🧪 PCR: detects viral RNA in saliva, CSF, or tissue.

💊 Management

• Once symptomatic: Almost universally fatal → palliative care only.
• PEP (Post-Exposure Prophylaxis):
  • Immediate wound washing with soap & water (≥15 minutes).
  • Rabies vaccine series (active immunity, effective in 7–10 days).
  • Rabies Immunoglobulin (RIG) infiltrated into wound → passive immediate protection (t½ ≈ 21 days).
• 🤰 Pregnancy: Vaccine & RIG are safe.
• 🐕 If possible: euthanize & test offending animal brain tissue (Negri bodies/PCR).
• Hydrophobia, agitation, or coma → comfort measures & palliation.

⚠️ Complications

• Neurological failure → seizures, coma, brainstem dysfunction.
• Autonomic storm → hypersalivation, arrhythmias, temperature instability.
• Death usually from cardiorespiratory failure within 2–10 days of symptoms.

💡 Exam Tip: - Think rabies in a traveller returning from Asia/Africa with neurological symptoms + hydrophobia. - PEP = vaccine + RIG → start before symptoms develop. - Once symptoms start → universally fatal → palliation only.

📚 References

• CDC – Rabies
• WHO – Rabies Fact Sheet