Infectious Diseases Affecting the Nervous System

Chapter 22

22.1 The Structure and Infection Defenses of the Nervous System

The nervous system is composed of the central and peripheral nervous systems

The nervous system lacks an indigenous microbiota

The brain has a blood-brain barrier that controls what substances can enter the CNS

The brain and spine are “immune-privileged”

22.2 Bacterial Diseases of the
Central Nervous System

Bacterial Meningitis Can Be Life Threatening
The meninges are three membranous coverings of the brain and spinal cord
Bacterial meningitis can becaused by several bacterialspecies
Neisseria meningitides causesmeningococcal meningitis
It is spread throughperson-to-person transfer of large-droplet respiratory secretions
In young children, meningococcal meningitis can cause Waterhouse-Friderichsen syndrome
This results in hormone imbalances
Streptococcus pneumoniae causes pneumococcal meningitis, as well as pneumonia
Haemophilus influenzae type b was once thought to cause influenza, but it actually causes Haemophilus meningitis
All 3 species can cross the blood-brain barrier, inflaming the meninges
This causes pressure on the brain and spinal cord
The disease can cause
deafness
blindness
paralysis
if untreated it can lead to coma and death
Antibiotics are used to treat bacterial meningitis, and vaccines are available

Listeriosis Usually Manifests Itself as Meningoencephalitis or Septicemia
Listeriosis is caused by Listeria monocytogenes
It is usually transmitted by
food contaminated with feces
contaminated animal products like cold cuts and soft cheeses
Listeriosis usually affects pregnant women, the elderly, or immunocompromised
Meningoencephalitis is characterized by
headaches
stiff neck
delirium
Coma

Septicemia is a blood disease involving high numbers of infected monocytes

Infection of the uterus can occur in women

Bacterial intoxications can affect the CNS

Tetanus Causes Hyperactive Muscle Contractions
Tetanus is caused by Clostridium tetani
Spores can enter the body through a wound and produce toxins
Tetanospasmin inhibits compounds needed to inhibit muscle contraction
This leads to continuous, uncontrolled muscle contraction
Symptoms of tetanus include
Trismus (lockjaw) involves spasms of the jaw muscle and clenching of the teeth
Opisthotonus involves muscle spasms that cause an arching of the back
Spasmodic inhalation and seizures in the diaphragm and rib cage

–This reduces ventilation

Sedatives, muscle relaxants, and penicillin are used in treatment

Tetanus toxoid is used in vaccination

Bacterial Food Poisoning Can Result from an Intoxication
Clostridium botulinum is the source of botulism
C. botulinum produces a deadly exotoxin that attacks the nervous system, causing flaccid paralysis
Death is caused within 1–2 days of symptom onset by respiratory paralysis
If treated early, large doses of antitoxins can neutralize the toxin
Most outbreaks are related to home-canned foods or from foods eaten cold (heat destroys the toxin)
Wound botulism occurs when a wound is infected with C. botulinum

Infant botulism, a.k.a. floppy baby syndrome, frequently occurs when an infant is fed honey

Minute doses of botulinum toxin can be used to treat movement disorders and to remove facial wrinkles

Leprosy (Hansen Disease) Is a Chronic, Systemic Infection
It is caused by Mycobacterium leprae, an obligate intracellular parasite
About 95% of the world’s population is immune to leprosy
It is spread through nasal secretions
It has a long incubation period of 3–6 years
Leprosy causes
disfigurement of skin and bones
twisting of limbs and curling of fingers
loss of facial features
In multibacillary or lepromatous leprosy, tumor-like lepromas form on the skin and respiratory tract
The immune system does not react
WHO is making efforts to eliminate leprosy

22.3 Viral and Viral-like Diseases of the Central Nervous System

Some viruses cause aseptic meningitis
Viral meningitis is milder than bacterial meningitis
Viral encephalitis can be a consequence of a primary or secondary infection
Some forms of encephalitis are due to herpesviruses
Arboviral encephalitis is a result of a primary viral infection

–Encephalitis is an acute inflammation of the brain

Arboviral encephalitis patients may suffer

–pain in the head and neck

–convulsions

–coma

Those who recover may have paralysis and mental disorders

There are many forms, many transmitted by mosquitoes and ticks

Many infected people remain asymptomatic or are ill for a few days
Rarely, the patient will develop encephalitis or meningitis

–This can result in permanent neurologic effects or death

There is no vaccine or specific treatment for West Nile fever

West Nile fever is an emerging disease in the Western hemisphere
It can infect birds, mosquitoes, humans, and some other mammals
Humans generally contract it through mosquito bites

The Rabies Virus Is of Great Medical Importance Worldwide
It has the highest mortality rate of any human disease
Animal rabies occurs in warm-blooded animals
It enters the body through a skin wound contaminated with a bodily fluid from an infected animal
The incubation period varies from 6 days to 1 year
It depends on the location of entry and the amount of virus entering the body
Fever, headache, and increased muscle tension develop
Patients become alert and aggressive, followed by paralysis and brain degeneration
Death from respiratoryparalysis occurs withindays
Post-exposureimmunization can bedone immediately afterexposure
In animals
Furious rabies involves violent symptoms like

–wide eyes

–drooling

–unprovoked attacks

Animals with dumb rabies are docile and lethargic

Wild animals are vaccinated with inoculated dog food and fish meal

The polio virus may be the next infectious disease eradicated
Polioviruses multiply in

–tonsils

–lymph tissue

–gastrointestinal tract

Sometimes the viruses pass through the bloodstream to the meninges

–This can result in paralysis of limbs and trunk

In bulbar polio, the viruses infect the medulla, affecting nerves in the

–neck

–face

–upper torso

Trivalent vaccines contain all 3 types of poliovirus

Postpolio syndrome occurs in individuals who had the disease decades ago

Prions Are Infectious Proteins
Transmissible spongiform ecephalopathies (TSEs) can occur in humans and other animals
For example, mad cow disease
TSEs are neurologic degenerative diseases that can be transmitted within or between species
Originally, scientists believed TSEs were caused by a virus
Stanley Prusiner discovered the proteinaceous infectious particle (prion)
The protein-only hypothesis predicts that prions are composed only of protein and contain no nucleic acids
Normal cellular prions have a different shape than abnormal prions, the latter of which cause TSEs
TSEs may spread when infectious prions bind to normal prions
This causes normal prions tochange shape and becomeabnormal
Abnormal prions do not trigger animmune response
Death of the host occurs from nerve cell death leading to sponge-like holes in brain tissue
Symptoms include

–dementia

–weakened muscles

–loss of balance

This results from insoluble aggregates of abnormal prions in the brain

The human form of TSE is called variant CJD (Creutzfeldt-Jakob disease)

22.4 Diseases of the Nervous System Caused by Eukaryotic Organisms

A few fungi are associated with diseases of the CNS
Cryptococcus neoformans

Protozoal parasites also cause infections of the CNS

Primary amoebic meningoencephalitis is a rare disease
Naegleria fowleri

The Trypanosoma Parasites Can Cause Life-Threatening Systemic Diseases
Trypanosomiasis is the name for 2 diseases caused by species of Trypanosoma
Human African sleeping sickness is caused byT. brucei
It is transmitted by the tsetse fly
A chancre forms at the bite site
Parasites invade the bloodstream and then the central nervous system
T. brucei var. gambiense causes a chronic form characterized by
bouts of fever
headaches
changes in sleep patterns and behavior
wasting
when parasites enter the brain, coma ensues
T. brucei var. rhodesiense causes a more acute form, with high fever and rapid coma preceding death