Chapter 22 Microbial Diseases of the Nervous System

The Nervous System Figure 22.1

Structure and Function of the Nervous System Central nervous system (CNS): brain and spinal cord –Controls the entire body Picks up sensory information from the environment Interprets the information Sends impulses that coordinate the body’s activities –Covered and protected by 3 continuous membranes (cranial meninges & spinal meninges) Cerebrospinal fluid (CSF) between arachnoid & pia matter membranes (subarachnoid space)

The Meninges and Cerebrospinal Fluid Figure 22.2

Structure and Function of the Nervous System Peripheral nervous system (PNS): all the nerves that branch off from the brain and spinal cord –Lines of communication between the central nervous system to various parts of the body, and the external environment

Microbes enter the nervous system via: Trauma –Skull or backbone fractures –Medical procedures –Along peripheral nerves –Blood or lymph Pathogens capable of causing diseases of the nervous system have virulence characteristics –Enable them to penetrate host defenses

Microbial Diseases of the Nervous System Bacteria can grow in the cerebrospinal fluid (CSF) in the subarachnoid space of the CNS –CSF have low level of complement, circulating Ab, few phagocytic cells The blood brain barrier (capillaries) prevents passage of some materials (such as antimicrobial drugs) into the CNS –Capillaries less permeable than others in the body

Bacterial Diseases of the Nervous System –Only drugs that are lipid-soluble can cross blood-brain barrier Meningitis –Inflammation of meninges Encephalitis –Inflammation of the brain

Majority (more than 70%) caused by Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae –All three have capsules –Nearly 50 other species of bacteria (opportunistic pathogens) occasionally cause meningitis Listeria monocytogenes, group B streptococcus, staphylococci, and certain gram-negative bacteria Fever, headache, stiff neck Followed by nausea and vomiting Bacterial Meningitis

May progress to convulsions and coma Death occurs very quickly from shock and inflammation –Release of endotoxins, or release of cell wall fragments (peptidoglycans and teichoic acids) of gram-positive bacteria Mortality rate depends on pathogen (but generally high) Diagnosis by Gram stain of CSF Treated with cephalosporins

Occurs mostly in children (6 months to 4 years) Gram-negative aerobic bacteria, normal throat microbiota Capsule antigen type b Prevented by Hib vaccine –See decrease in incidence; before Hib vaccine, 45% of bacterial meningitis caused by H. influenzae Also frequent cause of pneumonia, otitis media, and epiglottitis Haemophilus influenzae Meningitis

Figure 22.3

Neisseria Meningitis (Meningococcal Meningitis) Figure 22.4 N. meningitidis –Gram-negative aerobic cocci, capsule Occurs usually in children under 2 years Throat infection Bacteremia Meningitis

10% of people are healthy nasopharyngeal (nose and throat) carriers Begins as throat infection, rash (does not fade when pressed) –Symptoms mainly caused by endotoxin Serotype B is most common in the U.S. Vaccine against some serotypes is available (not effective against serotype B) Treated with penicillins and cephalosporins Neisseria Meningitis (Meningococcal Meningitis)

Streptococcus pneumoniae Meningitis (Pneumococcal Meningitis) Gram-positive diplococci, capsule; common inhabitant of nasopharyngeal region –Best known for causing pneumonia 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 conjugated vaccination Problem with antibiotic-resistant strain (about 35%)

Bacterial Meningitis Table 22.1

Listeria monocytogenes –Occasionally cause meningitis as opportunistic pathogen Gram-positive aerobic rod; can grow at refrigerator temperature Excreted in animal feces; widely distributed in soil and water Usually foodborne (esp. dairy products), can be transmitted to fetus –Cause abortion or stillbirth in a pregnant woman Listeriosis

–Neurological disease in animals Two basic forms: 1) infect adults, 2) infect fetus and newborn –Adult symptoms usually milder; 60% mortality rate for infants Reproduce in phagocytes (primarily in liver); can move directly from one phagocyte to an adjacent one Treated with penicillin G

Listeriosis Figure 22.5

Clostridium tetani Gram-positive, endospore-forming, obligate anaerobe Grows in deep wounds Tetanospasmin released from dead cells blocks relaxation pathway in muscles Prevention by vaccination with tetanus toxoid (DTP) and booster (dT) Treatment with tetanus immune globulin Tetanus

Figure 22.6

Clostridium botulinum Gram-positive, endospore-forming, obligate anaerobe Intoxication due to ingesting botulinal toxin Botulinal toxin blocks release of neurotransmitter causing flaccid paralysis Prevention: –Proper canning –Nitrites prevent endospore germination in sausages Botulism

Treatment: supportive care and antitoxin Infant botulism results from C. botulinum growing in intestines Wound botulism results from growth of C. botulinum in wounds. Botulism

Type A –60-70% fatality –Found in CA, WA, CO, OR, NM Type B –25% fatality –Europe and eastern U.S. Type E –Found in marine and lake sediments –Pacific Northwest, Alaska, Great Lakes area Botulism

Diagnosis Figure 22.7

Mycobacterium leprae Acid-fast rod that grows best at 30°C Grows in peripheral nerves and skin cells Transmission requires prolonged contact with an infected person Tuberculoid (neural) form: Loss of sensation in skin areas; positive lepromin test Lepromatous (progressive) form: Disfiguring nodules over body; negative lepromin test Leprosy

Figure 22.8

Poliovirus Transmitted by ingestion Initial symptoms: sore throat and nausea Viremia may occur; if persistent, virus can enter the CNS; destruction of motor cells and paralysis occurs in <1% of cases Prevention is by vaccination (enhanced- inactivated polio vaccine) Poliomyelitis

Figure 22.10

Transmitted by animal bite Virus multiplies in skeletal muscles, then brain cells causing encephalitis Initial symptoms may include muscle spasms of the mouth and pharynx and hydrophobia Furious rabies: animals are restless then highly excitable Paralytic rabies: animals seem unaware of surroundings Rabies virus (Rhabdovirus)

Preexposure prophylaxis: Infection of human diploid cells vaccine Postexposure treatment: Vaccine + immune globulin

Rabies virus (Rhabdovirus) Figure 22.11

Rabies virus (Rhabdovirus) Figure 22.12

Arboviruses are arthropod-borne viruses that belong to several families. Prevention is by controlling mosquitoes Arboviral Encephalitis

Cryptococcus neoformans Meningitis (Cryptococcosis) Soil fungus associated with pigeon and chicken dropping Transmitted by the respiratory route; spreads through blood to the CNS Mortality up to 30% Treatment: amphotericin B and flucytosine

Cryptococcus neoformans Meningitis (Cryptococcosis) Figure 22.14

Trypanosoma brucei gambiense infection is chronic (2 to 4 years) T. b. rhodesiense infection is more acute (few months) Transmitted from animals to humans by tsetse fly Prevention: elimination of the vector Treatment: Eflornithine blocks an enzyme necessary for the parasite Parasite evades the antibodies through antigenic variation African Trypanosomiasis

Figure 22.15

Protozoan infects nasal mucosa from swimming water Naegleria fowleri Figure 22.16

Caused by prions –Sheep scrapie –Creutzfeldt-Jakob disease –Kuru –Bovine spongiform encephalopathy Transmitted by ingestion or transplant or inherited Chronic, fatal Transmissible Spongiform Encephalopathies

Figure 22.17a

Chapter Review 1. Know how microbes enter the nervous system Microbes enter the nervous system via trauma –Skull or backbone fractures –Medical procedures (invasive medical procedures) –Along peripheral nerves –Blood or lymph 2. Know the structure of central nervous system (CNS); where bacteria can grow and why they can grow there

Chapter Review CNS covered and protected by 3 continuous membranes (cranial meninges & spinal meninges) –Cerebrospinal fluid (CSF) between arachnoid & pia matter membranes (subarachnoid space) Bacteria can grow in the cerebrospinal fluid (CSF) in the subarachnoid space of the CNS –CSF have low level of complement, circulating Ab, and few phagocytic cells

Chapter Review 3. Know the microorganisms that can cause meningitis (inflammation of meninges). They (bacteria and protozoa pathogens) all have capsule that allow them to evade the host’s immune system (phagocytosis) Majority of bacterial meningitis (more than 70%) caused by Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae

Chapter Review Start out with Fever, headache, stiff neck Followed by nausea and vomiting May progress to convulsions and coma Death occurs very quickly from shock and inflammation –Release of endotoxins, or release of cell wall fragments (peptidoglycans and teichoic acids) of gram-positive bacteria 1) Haemophilus influenzae meningitis –Gram-negative aerobic bacteria, normal throat microbiota

Chapter Review –Occurs mostly in children (6 months to 4 years) –Capsule antigen type b –Prevented by Hib vaccine –Before Hib vaccine, 45% of bacterial meningitis caused by H. influenzae; See decrease in incidence with introduction of Hib vaccine –Also frequent cause of pneumonia, otitis media, and epiglottitis 2) Neisseria Meningitis (Meningococcal Meningitis)

Chapter Review –N. meningitidis: gram-negative aerobic cocci, capsule –Occurs usually in children under 2 years –Throat infection bacteremia meningitis –Begins as throat infection, rash (does not fade when pressed) Symptoms mainly caused by endotoxin –10% of people are healthy nasopharyngeal (nose and throat) carriers –Serotype B is most common in the U.S. –Vaccine against some serotypes is available (not effective against serotype B)

Chapter Review 3) Streptococcus pneumoniae Meningitis (Pneumococcal Meningitis) –Gram-positive diplococci, capsule; common inhabitant of nasopharyngeal region –Best known for causing pneumonia –70% of people are healthy nasopharyngeal carriers –Most common in children (1 month to 4 years) –Highest mortality rates among 3 bacterial meningitis: 30% in children, 80% in elderly –Prevented by conjugated vaccination

Chapter Review –Problem with antibiotic-resistant strain (about 35%) 4) Cryptococcus neoformans Meningitis (Cryptococcosis) –Soil fungus associated with pigeon and chicken dropping –Transmitted by the respiratory route; spreads through blood to the CNS –Mortality up to 30% –Have huge capsule around fungal cell

Chapter Review 4. Know the pathogens that cause tetanus and botulism Both are caused by Clostridium species: gram-positive, endospore-forming, obligate anaerobe Tetanus (caused by Clostridium tetani) –Grows in deep wounds –Tetanospasmin released from dead cells blocks relaxation pathway in muscles muscles contract & result in the characteristic muscle spasms

Chapter Review –Prevention by vaccination with tetanus toxoid (DTP) and booster (dT) Botulism (caused by Clostridium botulinum) –Intoxication due to ingesting botulinal toxin –Botulinal toxin blocks release of neurotransmitter causing flaccid paralysis –Prevention: Proper canning Nitrites prevent endospore germination in sausages –Infant botulism results from C. botulinum growing in intestines (caused by eating honey usually)

Chapter Review Figure Know how rabies are contracted Rabies virus (Rhabdovirus) Transmitted by animal bite Initial symptoms may include muscle spasms of the mouth and pharynx and hydrophobia Encephalitis: inflammation of the brain

Chapter Review 6. Know prion-caused diseases (transmissible spongioform encephalopathies) Examples: –Sheep scrapie –Creutzfeldt-Jakob disease (human) –Bovine spongiform encephalopathy (mad-cow disease) Transmitted by ingestion or transplant or inherited Chronic, fatal Incineration is the only way to disinfect prion- contaminated tissues or materials