Nervous System Defenses

Transcription

1 Chapter 19 Infectious Diseases: Nervous System Topics - Nervous System Defenses - Nervous System Diseases Nervous System Defenses Nervous system Normal flora 1 2 Nervous system Central nervous system (CNS) Peripheral nerves CNS Brain Spinal cord Neurons cells that make-up the brain and spinal cord Defenses 3 4 1

2 Defenses A diagram of the central nervous system and the peripheral nerves. Meninges surround the brain and spinal cord Cerebrospinal fluid (CSF) Bone casing Blood-brain barrier Immunologically privileged 5 6 Normal flora Structures of the brain and spinal cord that provide defenses. Absent Viruses can exist in a dormant state in the nervous system 7 8 2

3 Nervous System Diseases Meningitis Meningitis Neonatal meningitis Meningoencephalitis Acute encephalitis Subacute encephalitis Rabies Poliomyelitis Tetanus Botulism Many different species of bacteria Neisseria meningitis Streptococcus pneumoniae Haemophilus influenzae Listeria cytogenes Coccidiodes immitis Yeast Cryptococcus neoformans Co- or previous viral infections can facilitate meningitis 9 10 African sleeping sickness Transmission electron micrograph (TEM) of Neisseria, a causative agent of meningitis. Dissemination from a meningococcal nasopharyngeal infection causes serious complications if the bacteria enter the blood and CSF (meningococcemia)

4 Oxidase test confirms the presence of Neisseria or Branhamella (causatives for meningitis) Stains can show palisades for Listeria monogenes, another cause of meningitis. Black = + * Not Black = (-) 13 (* palisade = cells closely aligned side by side) 14 Cyptococcus neoformans, from infected spinal fluid, another meningitis cause. Example Cryptococcosis Capsules and budding, characteristics of a yeast. Binding of the yeast to the meninges or brain can produce a characteristic gelatinous exudate. Capsule Bud Negative Stain (India ink)

5 Stages in coccidiodes infection, leading to coccidiodomycosis. Endemic areas of the US for Coccidoides immitis, a causative agent of meningitis Features of meningitis, various causes Neonatal meningitis Bacterial infection Contracted from mother (utero or birth canal) Premature babies (immature immune system) are at risk

6 Features of neonatal meningitis. Meningoencephalitis Protozoa infection Naegleria fowleri Acanthamoeba Inflammation of the brain (encephalitis) Accidental infection Scanning electron micrograph (SEM), Naegleria fowleri, a causative agent of amoebic meningoencephalitis. Features of meningoencephalitis

7 Arboviral encephalitides is prevalent worldwide. Acute encephalitis Viral infection Arboviruses Herpes simplex 1 or 2 JC virus Features of acute viral encephalitis. Subacute encephalitis Mostly a protozoan infection Viral infection Prion infection Symptoms develop slowly

8 Spongiform Encephalopathy Normal and prion infected brain tissue comparison. The life cycle and morphological forms of the protozoan Toxoplasma gondii, the causative agent of subacute encephalitis Features of subacute encephalitis Rabies Viral infection Slow, progressive zoonotic disease Fatal Distinct pathogenesis and symptoms

9 Rabies virus unique bullet-like structure. Diagnosis of Rabies- Neuronal brain cells with intracytoplasmic inclusions (Negri bodies) Features of rabies. Poliomyelitis Viral infection Spinal cord infection Common vaccine Small children are at risk Neurotrophic Paralytic

10 The anterior horn of the spinal cord is a target for the poliovirus. The poliovirus (picornavirus) has an icosahedral capsid shell Poliomyelitis - Unique stages of infection and pathogenesis Various levels of severity for a poliovirus infection

11 Features of poliomyelitis. Tetanus Bacterial infection Neuromuscular disease Tetanospasmin (neurotoxin) Endosporulation and germination Clostridium tetani (tetanus) has unique tennis racket morphology. Neonatal tetanus can occur due to application of mud, dung, or ashes to the umbilical stump

12 Bacterial invasion, release of bacterial toxin, and symptoms associated with tetanus. Features of tetanus Botulism Botulin (botulism toxin) can prevent the release of acetylcholine so muscle contractions can not occur. Bacterial infection Exotoxin Forms Food-borne Infant Wound Infectious botulin toxemia Can cause fatalities in livestock

13 Features of botulism. African Sleeping Sickness Protozoan infection trypanosomiasis Infects humans, domestic animals and wild mammals Prevalent in African The life cycle and spread of Trypanosoma brucei (African sleeping sickness) Features of African sleeping sickness

14 Summary: Diseases in the nervous system. Infectious Diseases Affecting the Nervous System