Plate 86
Viral Diseases of the Nervous System
Nervous System
• Central nervous system:– The meninges– The brain– The spinal cord
• Peripheral nervous system:– Nerves radiating out from
the spinal cord
Viral Diseases in the Nervous System
• Viruses enter the nervous system after passing through the bloodstream and lymph system
• Nerve cells (neurons) are killed during viral replication
• Neurons, especially in the CNS, regenerate very slowly, if at all
Poliomyelitis (Polio)
• Unenveloped RNA virus• Icosahedral shape• 3 strains of poliovirus exist• Also known as “infantile paralysis”• Poliovirus infects motor cells in
the spinal cord, resulting in paralysis
• 1938, FDR founds the National Foundation for Infantile Paralysis
Polio Symptoms
• About 95% of people infected with polio do not have any symptoms
• 4-8% of people get minor symptoms– Fever– Fatigue– Headache– Stiffness in the neck and back– Pain in limbs
Polio Symptoms• Less than 1% of
infected people suffer from permanent paralysis of their limbs
• Of those who are paralyzed, 5-10% die from the paralysis of their respiratory muscles
• Death rate increases with age
Polio Transmission
• Spread through person-to-person contact and contaminated food/drink
• 1952, the U.S. had 57,628 polio cases
Polio Vaccine• 1955, Dr. Jonas Salk creates the first
vaccine containing inactivated polioviruses
• 1955-1957, U.S. polio cases drop by 85-90%
• 1961, Dr. Albert Sabin creates an oral vaccine using attenuated polioviruses
• 1979, last U.S. case caused by wild poliovirus
• 2004, only 1,263 polio cases worldwide
Progress to Eradicate Polio
Rabies
• Unenveloped RNA virus
• Helical shaped• Distinct “bullet” shape• Incubation period may
last for weeks or months
Rabies Symptoms
• Symptoms appear at first to be similar to the flu:– Fever– Headache
• Within a few days, symptoms worsen:– Insomnia– Anxiety– Confusion– Hallucinations– Hypersalivation– Hydrophobia
Rabies Symptoms
• Once signs of rabies appear, the disease is almost always fatal
• Less than 10 documented cases in which people survived rabies
Rabies Transmission• All mammals are susceptible to rabies infection• Primarily found in dogs, raccoons, skunks, foxes, coyotes, and
bats• Typically spread from the bite of a rabid animal (virus is found
in the saliva)• Only case caused by human-to-human transmission occurred
among recipients of transplanted corneas and organs
Rabies Treatment
• Rabies is 100% preventable through prompt medical care
• More than 55,000 people (mostly in Africa and Asia) die every year
• Human rabies immune globulin and vaccine are recommended for people who have been exposed to the virus
• September 28 – World Rabies Day