Rabies, Polio & Oncogenic Viruses: Virology Essentials

Rabies is caused by a bullet-shaped rhabdovirus that travels along nerves from a bite wound to the brain. Once symptoms like hydrophobia appear, it is almost always fatal, making immediate wound care and vaccination after any animal bite a life-or-death matter. Polio, an enterovirus spread through contaminated food and water, can invade the spinal cord and permanently paralyze children.

These viruses plus the oncogenic (cancer-causing) viruses show the range of viral harm: rabies teaches post-exposure prevention, polio shows vaccination nearly wiping out a disease (India certified polio-free in 2014), and oncogenic viruses prove some cancers are preventable infections.

Key Concepts

• Neurotropic spread: rabies climbs inside peripheral nerves toward the brain, giving an incubation period usually of 20 to 60 days.
• Negri bodies: characteristic inclusions in brain cells, a classic rabies finding on microscopy.
• Post-exposure prophylaxis (PEP): 15-minute soap-and-water wound wash plus rabies vaccine, plus immunoglobulin for deep (category III) bites; works only before symptoms appear.
• OPV vs IPV: oral (Sabin) live vaccine immunizes the gut and spreads protection to contacts; inactivated (Salk) injection protects the individual. India used OPV in pulse campaigns.
• AFP surveillance: every sudden limb weakness in a child under 15 is investigated as suspected polio with stool testing.
• Oncogenic viruses: HPV causes cervical cancer; hepatitis B/C cause liver cancer; EBV causes Burkitt lymphoma and nasopharyngeal carcinoma; HTLV-1 and HHV-8 cause adult T-cell leukemia and Kaposi sarcoma.

How It Works

Rabid saliva enters the wound; virus infects nerve endings and moves toward the central nervous system. In the brain it causes encephalitis with agitation and hydrophobia, then spreads to salivary glands for the next bite. Nerves and the blood-brain barrier shield it from immunity, so PEP must act during the silent journey. Poliovirus multiplies in throat and gut, and in a few children reaches spinal motor neurons, destroying them and causing flaccid paralysis. Oncogenic viruses act slowly: HPV proteins block tumor-suppressor controls, hepatitis viruses drive decades of liver inflammation, and EBV pushes B lymphocytes into uncontrolled growth.

Worked Example

A district with 800,000 children under 15 detects 20 non-polio AFP cases in a year. The non-polio AFP rate is:

1. Cases = 20; population = 800,000
2. Rate = (20 ÷ 800,000) × 100,000 = 0.000025 × 100,000 = 2.5 per 100,000

The target is at least 2 per 100,000, so 2.5 means surveillance is sensitive enough that a real polio case would not be missed.

Common Misconceptions

• "Rabies can be cured after symptoms start." Essentially never; it is ~100% fatal once symptomatic. Prevention through wound washing and PEP is the only treatment.
• "Polio vaccine gives children polio." Injected IPV cannot; the risk from wild poliovirus is enormously greater than any vaccine risk.
• "Viruses cannot cause cancer." HPV, hepatitis B/C and EBV cause a large share of world cancers, making their vaccines anti-cancer vaccines too.

Real-World Applications

• PEP clinics: wound washing, vaccine schedules and immunoglobulin in deep wounds save lives daily across India.
• Pulse polio campaigns: national immunization days with OPV drops stopped wild poliovirus transmission in India.
• HPV and hepatitis B vaccines: prevent infections that lead to cervical and liver cancer decades later.
• AFP lab surveillance: stool testing of every flaccid paralysis case keeps India polio-free by catching imported virus early.

Rabies kills by travelling up nerves and can only be stopped before symptoms; polio was defeated in India by mass oral vaccination plus AFP surveillance; several common viruses cause cancer through chronic infection, preventable by vaccines. For these viruses, timely prevention matters far more than treatment after damage.