Microbial Diseases of the Nervous System: Structure, Pathogenesis, and Clinical Features

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Microbial Diseases of the Nervous System

Structure and Protection of the Nervous System

The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord, while the PNS includes all nerves branching from the CNS. The brain and spinal cord are protected by three layers of connective tissue called meninges (dura mater, arachnoid mater, and pia mater), and the subarachnoid space contains cerebrospinal fluid (CSF) for cushioning. The blood-brain barrier (BBB) is a highly selective, semipermeable barrier formed by endothelial cells, restricting the passage of substances from the bloodstream into the CNS.

Diagram of the nervous system showing CNS and PNS Diagram of the meninges and blood-brain barrier

Common Signs and Symptoms of Nervous System Infections

Microbial infections of the nervous system often present with characteristic symptoms. Meningitis is the inflammation of the meninges, encephalitis is inflammation of the brain, and meningoencephalitis involves both. Common symptoms include fever, headache, stiff neck, nausea, vomiting, sensitivity to light (photophobia), and altered mental status. Severe cases may progress to convulsions, coma, and death due to shock and inflammation.

Symptoms of meningitis

Bacterial Infections of the Nervous System

Bacterial infections are among the most severe causes of nervous system diseases. The most common forms include bacterial meningitis, listeriosis, tetanus, and botulism.

Bacterial Meningitis

Haemophilus influenzae: Gram-negative aerobic bacteria, normal throat microbiota, pathogenic due to capsule antigen type B. Most common in children (6 months to 4 years). Prevented by the Hib vaccine.
Neisseria meningitidis: Gram-negative aerobic cocci with capsule, causes meningococcal meningitis. Outbreaks common in crowded settings. Mortality rate is high without antibiotics.
Streptococcus pneumoniae: Gram-positive encapsulated diplococcus, causes pneumococcal meningitis. Most common in children and elderly. Prevented by a conjugated vaccine.

Table of nervous system diseases: pathogens, transmission, treatment, prevention Photograph of inflamed meninges in bacterial meningitis SEM of Neisseria meningitidis on ciliated cells

Diagnosis of Meningitis

Diagnosis often involves a lumbar puncture (spinal tap) to collect cerebrospinal fluid for laboratory analysis.

Lumbar puncture procedure for CSF collection

Listeriosis

Listeria monocytogenes is a Gram-negative aerobic rod, usually foodborne. It can cause sepsis and meningitis, especially in immunocompromised individuals and pregnant women (can cross the placenta and cause stillbirths). Prevention includes proper food handling and cooking.

Listeriosis infographic: symptoms, risk groups, prevention

Tetanus

Clostridium tetani is a Gram-positive, endospore-forming, obligate anaerobe. It produces tetanospasmin, a neurotoxin that blocks inhibitory neurotransmitter release, causing rigid paralysis and potentially death from respiratory muscle spasms. Prevention is by vaccination with tetanus toxoid (DTaP), with boosters every 10 years.

Classic rigid paralysis (opisthotonos) in tetanus Tetanus infographic: symptoms, prevention, treatment Tetanus facts and prevention

Botulism

Clostridium botulinum is a Gram-positive, endospore-forming, obligate anaerobe. It produces a potent exotoxin that blocks acetylcholine release at neuromuscular junctions, causing flaccid paralysis. Transmission is usually via ingestion of preformed toxin in improperly canned foods, but can also occur in infants (from honey or soil) and wounds. Treatment includes respiratory support and antitoxins.

Mechanism of botulinum neurotoxin action Coffins from a botulism outbreak (historical) Mouse bioassay for botulism diagnosis Symptoms of botulism Infant botulism and honey Improperly canned foods as a source of botulism

Leprosy (Hansen’s Disease)

Mycobacterium leprae is an acid-fast rod that grows best at 30°C, with a slow generation time. It infects peripheral nerves and skin, surviving in macrophages and invading the myelin sheath. Transmission requires prolonged contact or inhalation of secretions; armadillos are a zoonotic reservoir. Two forms exist: tuberculoid (neural, with loss of sensation) and lepromatous (progressive, with disfiguring nodules). Treated with antibiotics such as dapsone or rifampin for 6–24 months.

Leprosy infographic: transmission, symptoms, treatment Tuberculoid and lepromatous leprosy clinical images Leprosy facial disfigurement (historical)

Summary Table: Nervous System Infections

Disease	Pathogen	Portal of Entry	Method of Transmission	Treatment	Prevention
Haemophilus influenzae meningitis	H. influenzae	Respiratory tract	Endogenous infection, aerosols	Cephalosporin	Capsular Hib vaccine
Meningococcal Meningitis	Neisseria meningitidis	Respiratory tract	Aerosols	Cephalosporin	Capsular vaccines against serotypes A, B, C, Y, W
Pneumococcal Meningitis	Streptococcus pneumoniae	Respiratory tract	Aerosols	Cephalosporin	Polysaccharide vaccine
Listeriosis	Listeria monocytogenes	Mouth	Foodborne infection	Penicillin G	Pasteurizing and cooking food
Cryptococcosis	Cryptococcus neoformans, C. grubii, C. gattii	Respiratory tract	Inhaling soil contaminated with spores	Amphotericin B, flucytosine	None
Primary Amebic Meningoencephalitis	Naegleria fowleri	Nasal mucosa	Swimming	Amphotericin B	None
Granulomatous Amebic Encephalitis	Acanthamoeba spp., Balamuthia mandrillaris	Mucous membranes	Swimming	Amphotericin B, miltefosine	None