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