Meninges

• layers that protect the brain and spinal cord

Blood-brain barrier

• infections compromise this

Meningitis

• inflammation of meninges

Encephalitis

• inflammation of the brain

Meningoencephalitis

• inflammation of both meninges and brain

Bacterial Meningitis

• Initial symptoms of fever, headache, and stiff neck
• Followed by nausea and vomiting
• May progress to convulsions and coma
• Diagnosis by Gram stain and latex agglutination of CSF
• Treatment: Cephalosporins, vancomycin
• Most common causes in US:
• Haemophilus influenzae
• Neisseria meningitidis
• Streptococcus pneumoniae

Haemophilus influenzae Meningitis

•  Occurs mostly in children (6 months to 4 years)
• Gram-negative aerobic bacteria, normal throat microbiota
• 80% of people are healthy nasopharyngeal carriers
• Prevented by Hib vaccine

Neisseria Meningitis

• Also called meningococcal meningitis
• Caused by N. meningitidis
• Gram-negative, aerobic cocci with a capsule
• 10% of people are healthy nasopharyngeal carriers
• Begins as throat infection, rash
• Vaccination recommended for college students

Streptococcus pneumoniae Meningitis

•  Also called pneumococcal meningitis
• Caused by S. pneumoniae (a gram-positive diplococcus)
• 70% of people are healthy nasopharyngeal carriers
• Most common in children (1 month to 4 years)
• Mortality: 30% in children, 80% in elderly
• Prevented by vaccination

Tetanus

• Caused by Clostridium tetani
• Gram-positive, endospore-forming, obligate anaerobe
• Grows in deep wounds
• Tetanospasmin (neurotoxin) released from dead cells blocks relaxation pathway in muscles
• Lockjaw presents first
• Prevention by vaccination with tetanus toxoid (DTP) and booster (dT) required every 10 years
• Treatment with tetanus immune globulin

Botulism

• Caused by Clostridium botulinum
• Gram-positive, endospore-forming, obligate anaerobe
• Intoxication comes from ingesting botulinal toxin
• Botulinal toxin blocks release of neurotransmitter, causing flaccid paralysis; die from respiratory and cardiac failure
• Prevention
• Proper canning
• Nitrites prevent endospore germination in sausages
• Botox
• Chronic headaches, muscle contractions, Parkinson’s, MS
• Treatment: Supportive care and antitoxin

   

   

Infant Botulism

• results from C. botulinum growing in intestines

Wound Botulism

• results from growth of C. botulinum in wounds

Leprosy

• Also called Hansen’s disease
• Historical and biblical disease
• Isolation could have led to its near disappearance
• Caused by Mycobacterium leprae
• Acid-fast rod that grows best at 30°C.
• Grows in peripheral nerves and skin cells
• Transmission (via secretions) requires prolonged contact with an infected person
• Disfiguring nodules over body
• Immunocompromised individuals

Poliomyelitis (Polio)

• Poliovirus
• Fecal-oral transmission
• Outbreak in Vermont in summer of 1894
• Initial symptoms: Sore throat and nausea
• Viremia may occur; if persistent, virus can enter the CNS and cause respiratory failure
• Destruction of motor cells and paralysis occurs in <1% of cases
• Prevention: vaccination
• Sabin vaccine: oral; live virus that is shed in feces
• Vaccine derived cases
• Salk vaccine: inactivated virus; series of 3 shots
• Eradication of polio targeted by CDC

Rabies

• Caused by the rabies virus
• Untreated- fatal
• Transmitted by animal bite

Furious rabies

• animals are restless then highly excitable

Paralytic rabies

• animals seem unaware of surroundings

Preexposure prophylaxis

• injection of human diploid cells vaccine (HDCV)

Postexposure treatment

• vaccine plus rabies immune globulin (RIG)

Arboviral Encephalitis

• Arboviruses
• Arthropod-borne viruses that belong to several families
• Symptoms range from chills, headache, fever to death
• Prevention: controlling mosquitoes
• Diseases associated: Western equine encephalitis, Eastern equine encephalitis, St. Louis encephalitis, California encephalitis, and West Nile encephalitis

Cryptococcus neoformans Meningitis

• Also called cryptococcosis
• Soil fungus associated with pigeon and chicken droppings
• Transmitted by the respiratory route; spreads through blood to the CNS
• Mortality up to 30% in immunocompromised patients

African Trypanosomiasis

• African sleeping sickness
• Trypanosoma brucei
• Chronic (2 to 4 years); fever, deterioration of CNS
• Fatal without treatment
• Transmitted from animals to humans by tsetse fly
• Prevention: Elimination of the vector

Naegleria fowleri

• Protozoan infects nasal mucosa from swimming water
• Lakes in summertime
• Proliferates in brain, feeds on brain tissue
• 100% fatal

Transmissible Spongiform Encephalopathies

• Caused by prions
• Normal protein in brain encounters the abnormally folded form of the same protein (prion)
• Causes sponginess in brain
• Typical diseases
• Sheep scrapie
• Creutzfeldt-Jakob disease
• Bovine spongiform encephalopathy (Mad Cow Disease)
• Chronic and fatal

Creutzfeldt-Jakob disease

• Unknown source
• Transmissible via transplants
• Human growth hormone
• prion disease of nervous system

Bovine spongiform encephalopathy

•  Outbreak in cattle 1986 in Great Britain
• Cattle feed from sheep infected with scrapie
• FDA banned parts of cattle carcass likely to contain prions or meat from “fallen” cattle
• Percentage of cattle tested in US; all are tested in Europe and Japan
• prion disease of nervous system

Preventing prion diseases

• Difficult to destroy
• Surgical instruments sterilized by
• NaOH
• + extended autoclaving at 134°C