Chapter 22: Microbial Diseases of the Nervous System

==The central nervous system (CNS) consists of the brain and the spinal cord==
The peripheral nervous system (PNS) consists of all the nerves that branch off from the brain (cranial nerves) and spinal cord (spinal nerves).
Between the pia mater and arachnoid membranes is a space called the subarachnoid space, in which an adult has 100 to 160 ml of cerebrospinal fluid (CSF) circulating.
These remarkable results were the first evidence of an important feature of anatomy: the blood–brain barrier.
An inflammation of the meninges is called meningitis.
An inflammation of the brain itself is called encephalitis.
- If both the brain and the meninges are affected, the inflammation is called meningoencephalitis.

Viral meningitis is probably much more common than bacterial meningitis but tends to be a mild disease
Haemophilus influenzae type B, once responsible for a majority of cases, has been nearly eliminated in the United States since introduction of an effective vaccine.
Meningococcal meningitis is caused by Neisseria meningitidis
- The symptoms of meningococcal meningitis are mostly caused by an endotoxin that is produced very rapidly and is capable of causing death within just a few hours.
A diagnosis of bacterial meningitis requires a sample of cerebrospinal fluid obtained by a spinal tap, or lumbar puncture
- ==Bacterial meningitis is life-threatening and develops rapidly.==
In recent years, the disease listeriosis has changed from a disease of very limited importance to a major concern for the food industry and health authorities.
The causative agent of tetanus, Clostridium tetani, is an obligately anaerobic, endospore-forming, gram-positive rod
To minimize the production of more toxin, damaged tissue that provides growth conditions for the pathogen should be removed, a procedure called debridement and antibiotics should be administered
Botulism, a form of food poisoning, is caused by Clostridiumbotulinum, an obligately anaerobic, endospore-forming grampositive rod found in soil and many aquatic sediments.
==Hansen’s disease is the more formal name for leprosy; it is sometimes used to avoid the dreaded name==

Poliomyelitis (polio) is best known as a cause of paralysis.
Animals with furious (classic) rabies are at first restless, then become highly excitable and snap at anything within reach.
- Some animals suffer from paralytic (dumb or numb) rabies, in which there is only minimal excitability.
Rabies is usually diagnosed in the laboratory by detection of the viral antigen using the direct fluorescent-antibody (DFA) test, which is nearly 100% sensitive and highly specific.
- If the animal is positive for rabies, the person must undergo postexposure prophylaxis (PEP)—meaning a series of anti rabies vaccine and immune globulin injections.
The original Pasteur treatment, in which the virus was attenuated by drying in the dissected spinal cords of rabies infected rabbits, has long been replaced by __human diploid cell vaccin__e (HDCV), or chick embryo–grown vaccines.

The central nervous system is seldom invaded by fungi.
The disease cryptococcosis is caused by fungi of the genus Cryptococcus
- The best serological diagnostic test is a latex agglutination test to detect cryptococcal antigens in serum or cerebrospinal fluid.

African trypanosomiasis, or sleeping sickness, is a protozoan disease that affects the nervous system.
- The disease is caused by two subspecies of Trypanosoma brucei that infect humans: Trypanosoma brucei gambiense and T.b. rhodesiense
- Typanosomiasis is treated with suramin and pentamidine, but these do not alter the course of the disease once the CNS is affected
Naegleria fowleri is a protozoan (ameba) that causes a neurological disease, primary amebic meningoencephalitis (PAM)
A similar neurological disease is granulomatous amebic encephalitis (GAE).

In recent years, the study of these diseases, called transmissible spongiform encephalopathies (TSE), has been one of the most interesting areas of medical microbiology.
A typical prion disease in animals is sheep scrapie, which has been long known in Great Britain and made its first appearance in the United States in 1947.
Humans suffer from TSE diseases similar to scrapie; Creutzfeldt-Jakob disease (CJD) is an example.
- A TSE that is much in the news is bovine spongiform encephalopathy (BSE).

In August 2014 and November 2016, the CDC received increased reports of people with acute flaccid myelitis (AFM).
Bell’s palsy occurs when a nerve that controls facial muscles is inflamed and can’t communicate with muscles.
There is no diagnostic test for chronic fatigue syndrome (CFS).