Download Chapter 22: Infectious Diseases Affecting the Nervous System

Chapter 22
Infectious Diseases Affecting the Nervous System
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
o The meninges are three membranous coverings of the brain and
spinal cord
o Bacterial meningitis can be caused by several bacterial species
o Neisseria meningitides causes
meningococcal meningitis
 It is spread through person-to-person transfer of largedroplet respiratory secretions
o In young children, meningococcal meningitis can cause
Waterhouse-Friderichsen syndrome
 This results in hormone imbalances
o Streptococcus pneumoniae causes pneumococcal meningitis, as
well as pneumonia
o Haemophilus influenzae type b was once thought to cause
influenza, but it actually causes Haemophilus meningitis
o All 3 species can cross the blood-brain barrier, inflaming the
meninges
 This causes pressure on the brain and spinal cord
o The disease can cause
 deafness
 blindness
 paralysis
 if untreated it can lead to coma and death
o Antibiotics are used to treat bacterial meningitis, and vaccines are
available
 Listeriosis Usually Manifests Itself as Meningoencephalitis or Septicemia
o Listeriosis is caused by Listeria monocytogenes
o It is usually transmitted by
 food contaminated with feces
 contaminated animal products like cold cuts and soft
cheeses
o Listeriosis usually affects pregnant women, the elderly, or
immunocompromised
o Meningoencephalitis is characterized by
 headaches
 stiff neck









delirium
Coma
o Septicemia is a blood disease involving high numbers of infected
monocytes
o Infection of the uterus can occur in women
Bacterial intoxications can affect the CNS
Tetanus Causes Hyperactive Muscle Contractions
o Tetanus is caused by Clostridium tetani
o Spores can enter the body through a wound and produce toxins
o Tetanospasmin inhibits compounds needed to inhibit muscle
contraction
 This leads to continuous, uncontrolled muscle contraction
o 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
o Sedatives, muscle relaxants, and penicillin are used in treatment
Tetanus toxoid is used in vaccination
Bacterial Food Poisoning Can Result from an Intoxication
o 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
o If treated early, large doses of antitoxins can neutralize the toxin
o Most outbreaks are related to home-canned foods or from foods
eaten cold (heat destroys the toxin)
o 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
o It is caused by Mycobacterium leprae, an obligate intracellular
parasite
o About 95% of the world’s population is immune to leprosy
o It is spread through nasal secretions
o It has a long incubation period of 3–6 years
o Leprosy causes
 disfigurement of skin and bones
 twisting of limbs and curling of fingers
 loss of facial features
o In multibacillary or lepromatous leprosy, tumor-like lepromas form
on the skin and respiratory tract
 The immune system does not react
o WHO is making efforts to eliminate leprosy
22.3 Viral and Viral-like Diseases of the Central Nervous System
 Some viruses cause aseptic meningitis
o Viral meningitis is milder than bacterial meningitis
o 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
o 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
o There is no vaccine or specific treatment for West Nile fever
o 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
o It has the highest mortality rate of any human disease
o Animal rabies occurs in warm-blooded animals
o It enters the body through a skin wound contaminated with a
bodily fluid from an infected animal
o 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
o Fever, headache, and increased muscle tension develop
o Patients become alert and aggressive, followed by paralysis and
brain degeneration
o Death from respiratory paralysis occurs within days
o Post-exposure immunization can be done immediately after
exposure


o 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
o Polioviruses multiply in
– tonsils
– lymph tissue
– gastrointestinal tract
o Sometimes the viruses pass through the bloodstream to the
meninges
– This can result in paralysis of limbs and trunk
o In bulbar polio, the viruses infect the medulla, affecting nerves in
the
– neck
– face
– upper torso
o Trivalent vaccines contain all 3 types of poliovirus
o Postpolio syndrome occurs in individuals who had the disease
decades ago
Prions Are Infectious Proteins
o Transmissible spongiform ecephalopathies (TSEs) can occur in
humans and other animals
 For example, mad cow disease
o TSEs are neurologic degenerative diseases that can be transmitted
within or between species
o Originally, scientists believed TSEs were caused by a virus
o Stanley Prusiner discovered the proteinaceous infectious particle
(prion)
o The protein-only hypothesis predicts that prions are composed only
of protein and contain no nucleic acids
o Normal cellular prions have a different shape than abnormal
prions, the latter of which cause TSEs
o TSEs may spread when infectious prions bind to normal prions
 This causes normal prions to change shape and become
abnormal
o Abnormal prions do not trigger an immune response
o Death of the host occurs from nerve cell death leading to spongelike holes in brain tissue
 Symptoms include
– dementia
– weakened muscles
–

loss of balance
This results from insoluble aggregates of abnormal prions
in the brain
o 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
o Cryptococcus neoformans
 Protozoal parasites also cause infections of the CNS
 Primary amoebic meningoencephalitis is a rare disease
o Naegleria fowleri
 The Trypanosoma Parasites Can Cause Life-Threatening Systemic Diseases
o Trypanosomiasis is the name for 2 diseases caused by species of
Trypanosoma
o Human African sleeping sickness is caused by T. 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
o 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
o T. brucei var. rhodesiense causes a more acute form, with high
fever and rapid coma preceding death