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BSci106:
MICROBIOLOGY and
PARASITOLOGY
UNIT 8
Common Infectious Diseases of Humans

BSci106:
MICROBIOLOGY and
PARASITOLOGY
Chapter 18
Viral Infections of Humans

Chapter 18 Outline
• Introduction
• How do Viruses Cause
Disease?
• Infectious Diseases of the
Skin
• Viral Infections of the Ears
• Viral Infections of the Eyes
• Viral Infections of the
Respiratory System
• Viral Infections of the Oral
Region
Gastrointestinal Tract
Genitourinary System
Circulatory System
• Viral Infections of the Central
Nervous System
• Recap of Major Viral
Infections of Humans
• Appropriate Therapy for Viral
Infections

How Do Viruses Cause Disease?
• Viruses multiply within host cells.
• It is during their escape from those cells—either by
cell lysis or budding—that the host cells are
destroyed.
• This cell destruction leads to most of the symptoms
of a viral infection, which vary depending on the
location of the infection.

Viral Infections of the Skin
• Chickenpox and shingles
– Varicella-zoster virus (a
DNA virus which is also
known as human
herpesvirus 3)
• German measles (rubella)
– Rubella virus, an RNA virus
• Measles (hard measles, rubeola)
– Measles (rubeola) virus, an
RNA virus
– Koplik spots
• Monkeypox
– Monkeypox virus, a
DNA virus
• Smallpox
– Two strains of variola
virus (variola minor
and variola major), a
DNA virus
• Warts
– At least 70 different
types of human
papillomaviruses
(HPV), DNA viruses

Chickenpox and Shingles. (a) Chickenpox (also known as varicella)
is an acute, generalized viral infection, with fever and a skin
rash. It is usually a mild, self-limiting disease, but can be
severely damaging to a fetus. Chickenpox is the leading cause of
vaccine-preventable death in the United States.
(b) Shingles (also known as herpes zoster) is a reactivation of the
varicella virus, often the result of immunosuppression. Shingles
involves inflammation of sensory ganglia of cutaneous sensory
nerves, producing fluid-filled blisters, pain, and paresthesia
(numbness and tingling). Shingles may occur at any age, but is
most common after age 50.
Patient Care. Use Airborne and Contact Precautions for hospitalized
patients until their lesions become dry and crusted.

Reservoirs and Mode of Transmission. Infected humans serve as
reservoirs. Transmission is from person to person by direct
contact or droplet or airborne spread of vesicle fluid or secretions
of the respiratory system of persons with chickenpox.
Laboratory Diagnosis. Diagnosis is usually made on clinical and
epidemiologic grounds. Immunodiagnostic and molecular
diagnostic procedures are available, as are cell culture and
electron microscopy.

German Measles (Rubella). German measles is a mild, febrile viral
disease. A fine, pinkish, flat rash begins 1 or 2 days after the onset
of symptoms; rash starts on the face and neck and spreads to the
trunk, arms, and legs; first trimester of pregnancy, rubella may
cause congenital rubella syndrome in the fetus leading to
intrauterine death, spontaneous abortion, or congenital
malformations of major organ systems.
Patient Care. Use Droplet Precautions for hospitalized patients until 7
days after the onset of rash.
reservoirs; transmission occurs by droplet spread or direct contact
with nasopharyngeal secretions of infected people.
Laboratory Diagnosis. Immunodiagnostic and molecular diagnostic
procedures; virus can be propagated in cell culture.

Measles (Hard Measles, Rubeola). Measles is an acute, highly
communicable viral disease with fever, conjunctivitis, cough,
photosensitivity (light sensitivity), Koplik spots in the mouth, and
red blotchy skin rash; Koplik spots are small red spots, in the
center of which can be seen a minute bluish white speck when
observed under a strong light.
Patient Care. Use Airborne Precautions for hospitalized patients
until 4 days after the onset of rash.
reservoirs. Airborne transmission occurs by droplet spread, direct
contact with nasal or throat secretions or with articles freshly
soiled with nose and throat secretions.
Laboratory Diagnosis. Diagnosis is usually made on clinical and
epidemiologic grounds. Immunodiagnostic and molecular
diagnostic procedures are available, and the virus can be isolated
in cell culture.

Monkeypox. Is a rare viral disease that causes fever, headache,
muscle aches, backache, lymphadenitis, malaise (fatigue), and a
rash; milder disease than smallpox and occurs primarily in
central and western Africa.
patients.
Reservoirs and Mode of Transmission. Infected animals serve as
reservoirs. Transmission occurs via animal bite or contact with
an infected animal’s blood, body fluids, or rash. Person-to-person
transmission does occur.
Laboratory Diagnosis. Monkeypox can be diagnosed by molecular
diagnostic procedures, cell culture, electron microscopy, or
immunodiagnostic procedures.

Smallpox. Is a systemic viral infection with fever, malaise,
headache, prostration, severe backache, a characteristic skin
rash, and occasional abdominal pain and vomitting. The rash is
similar to, and must be distinguished from, the rash of
chickenpox; can become severe, with bleeding into the skin and
mucous membranes, followed by death.
patients; use N95 or higher respiratory protection.
Reservoirs and Mode of Transmission. Infected humans were the
only source of the virus; no known animal or environmental
reservoirs; person-to-person transmission is via the respiratory
tract (droplet spread) or skin inoculation.
Laboratory Diagnosis. Physicians must become familiar with the
clinical and epidemiologic features of smallpox and how to
distinguish smallpox from chickenpox. Laboratory diagnosis is by
cell culture, virus neutralization tests, molecular diagnostic
procedures, or electron microscopy (BSL4 facilities).

Warts. Warts consist of many varieties of skin and mucous
membrane lesions, including common warts (verrucae vulgaris),
venereal warts, and plantar warts. Most are harmless, but some
can become cancerous.
reservoirs. Transmission usually occurs by direct contact. Genital
warts are sexually transmitted. They are easily spread from one
area of the body to another, but most are not very contagious
from person to person (genital warts are an exception).
Laboratory Diagnosis. Diagnosis is made on clinical grounds.

Chickenpox

Child with Rubella

Child with Measles (Rubeola)

Koplik Spots (an Early Sign of Measles)

Child with Monkeypox

Viral Infections of the Eyes
• Adenoviral conjunctivitis and keratoconjunctivitis—caused
by various types of adenoviruses
• Herpes simplex and varicella-zoster viruses can also
cause keratoconjunctivitis.
• Hemorrhagic conjunctivitis—caused by adenoviruses and
enteroviruses (causative agent of sore eyes)
• People with viral infections (e.g., cold sores) should wash
their hands thoroughly before inserting or removing
contact lenses or otherwise touching their eyes.

Viral Infections of the
Upper Respiratory Tract
• The common cold (acute viral rhinitis, acute coryza)
– Many different viruses cause colds.
– Rhinoviruses (more than 100 serotypes) are the
major cause in adults.
– Other cold-causing viruses include coronaviruses,
parainfluenza viruses, respiratory syncytial virus
(RSV), influenza viruses, adenoviruses, and
enteroviruses.
– Transmission occurs via respiratory secretions by
way of hands and fomites or direct contact with or
inhalation of airborne droplets.

Lower Respiratory Tract
• Acute, febrile, viral respiratory disease
– Caused by parainfluenza viruses, respiratory syncytial
virus (RSV), adenovirus, rhinoviruses, certain
coronaviruses, coxsackieviruses, and echoviruses;
transmission occurs via direct oral contact or by droplets.
• Avian influenza (bird flu)
– Avian influenza virus type A; three prominent subtypes –
H5, H7, and H9; bird-to-human transmission occurs via
contact with infected poultry or contaminated surfaces.
• Hantavirus pulmonary syndrome (HPS)
– Caused by at least five different hantaviruses (Sin
Nombre, Bayou, Black Creek Canal, New York-1,
Monongahela); transmission occurs via inhalation of
aerosolized rodent feces, urine, and saliva.

Lower Respiratory Tract (cont.)
• Influenza, flu
– Influenza viruses, types A,
B, and C; RNA viruses;
transmission is via infected
humans; pigs and birds
also serve as reservoirs
• Severe acute respiratory
syndrome (SARS)
– SARS-associated
coronavirus (SARS-CoV)
(shown here)
– Transmission occurs via
infected individuals by
respiratory droplets, or by
touching the mouth, nose,
or eye after touching a
contaminated surface or
object.
– SARS-Cov-2 (Covid 19
Disease)

Viral Infections of the Oral Region
• Cold sores (fever blisters, herpes labialis)
– Usually caused by herpes simplex virus type 1 (HSV-1), but can
be caused by herpes simplex type 2 (HSV-2)
– DNA viruses in the family Herpesviridae
– Either HSV-1 or HSV-2 can also infect the genital tract, although
genital herpes infections are most often caused by HSV-2.

Cold Sore Caused by Herpes Simplex

Viral Infections of the GI Tract
• Viral gastroenteritis (viral enteritis, viral diarrhea)
– The most common viruses infecting children in their
first years of life are enteric adenoviruses,
astroviruses, caliciviruses, and rotaviruses.
– Viruses infecting children and adults include
norovirus-like viruses and rotaviruses.
– Transmission occurs via infected humans, most often
by way of the fecal–oral route; possibly from
contaminated water and shellfish.

Most Common Types of Viral Hepatitis
• Type A hepatitis (HAV infection,
infectious hepatitis, epidemic
Hepatitis)
– Hepatitis A virus (HAV)—a
linear ssRNA virus
– Fecal–oral transmission
• Type B hepatitis (HBV infection,
serum hepatitis)
– Parenteral
– Hepatitis B virus (HBV)—an
enveloped, circular dsDNA
virus
– Sexual transmission or
household contact with an
infected person; injected
drug use; tattooing;
needlesticks
• Type C hepatitis (HCV infection,
non-A non-B hepatitis)
– Hepatitis C virus (HCV)—an
enveloped, linear ssRNA
virus
– Primarily parenterally
transmitted; rarely
sexually
• Type D hepatitis (HDV infection,
delta hepatitis)
– Parenteral
– Hepatitis D virus (HDV,
delta virus)—an enveloped,
circular ssRNA viral
satellite; coinfection with
HBV is necessary
– Exposure to infected blood
and body fluids, etc.

Most Common Types of
Viral Hepatitis (cont.)
• Type E hepatitis
– Hepatitis E virus (HEV)—a nonenveloped, ssRNA
virus
– Fecal–oral transmission; primarily fecally
contaminated drinking water; also person-to-person

Viral STDs
• Anogenital herpes viral infections (genital herpes)
– Usually caused by HSV-2; occasionally by HSV-1
– Transmission occurs via infected humans by direct
sexual contact; oral-genital, oral-anal, or anal-genital
contact when lesions are present.
• Genital warts (genital papillomatosis, condyloma
acuminatum)
– Human papillomaviruses (HPV); DNA viruses
– Transmission occurs via infected humans by direct
contact, usually sexual.
– Genital warts can become malignant.

Viral Infections of the Circulatory System
• Human immunodeficiency virus (HIV) infection, acquired
immunodeficiency syndrome (AIDS)
– HIV—two types: HIV-1 (most common) and HIV-2;
ssRNA viruses
– Transmission occurs via infected humans, by direct
sexual contact; contaminated needles/syringes;
transfusion of contaminated blood; transplacental
transfer from mother to child; transplantation of HIV-
infected tissues or organs; needlestick, scalpel, and
broken glass injuries.

Common Modes of Transmission of HIV

Circulatory System (cont.)
• Infectious mononucleosis ( “mono,” “kissing disease”)
– Caused by Epstein–Barr virus (EBV), which is also
known as human herpesvirus 4; a DNA virus in the
family Herpesviridae
– Transmission occurs via infected humans, person-to-
person, direct contact with saliva.
• Mumps (infectious parotitis)
– Caused by mumps virus—an RNA virus
– Transmission occurs via infected humans by droplet
spread and direct contact with saliva.

Child with Mumps

Viral Hemorrhagic Diseases (Viral
Hemorrhagic Fevers)
• Caused by many different viruses, including dengue
virus, yellow fever virus, Crimean-Congo hemorrhagic
fever virus, Lassa virus, Ebola virus, and Marburg virus
• Ebola and Marburg viruses are extremely large
filamentous viruses.
• Infected humans serve as reservoirs; infected African
green monkeys also serve as reservoirs in Marburg
infection.
• Transmission is person-to-person via direct contact with
infected blood, secretions, internal organs, or semen;
also needlestick.

Viral Infections of the CNS
• Lymphocytic choriomeningitis
– Caused by lymphocytic choriomeningitis virus (LCMV)
– Transmission occurs via exposure to mouse urine,
droppings, saliva, or nesting materials.
• Poliomyelitis (polio, infantile paralysis)
– Caused by polioviruses—RNA viruses
– Transmission is person-to-person, primarily via the
fecal–oral route; also throat secretions.

Viral Infections of the CNS (cont.)
• Rabies
– Caused by rabies virus; a bullet-shaped, enveloped
RNA virus
– Many reservoirs, including dogs, foxes, coyotes,
wolves, jackals, skunks, raccoons, mongooses, bats
– Transmission occurs via the bite of a rabid animal
which introduces virus-laden saliva; airborne
transmission from bats in caves also occurs.
• Viral meningitis (aseptic meningitis, abacterial
meningitis)
– Caused by many different viruses

Selected Arthropodborne Viral
Encephalitides of the United States
Disease Reservoirs Vectors
Eastern equine
encephalitis (EEE)
Birds, horses
Aedes, Coquilletidia,
Culex, and Culiseta
mosquitoes
California encephalitis Rodents, rabbits
Aedes and Culex
mosquitoes
LaCrosse encephalitis Chipmunks, squirrels Aedes mosquitoes
St. Louis encephalitis Birds Culex mosquitoes
West Nile virus
encephalitis
Birds, perhaps horses Culex mosquitoes
Western equine
encephalitis (WEE)
Birds, horses
Aedes and Culex
mosquitoes

END OF CHAPTER 18

BSci106:
MICROBIOLOGY and
PARASITOLOGY
Chapter 19
Bacterial Infections of
Humans

Chapter 19 Outline
• Introduction
• How do Bacteria Cause
Disease?
• Bacterial Infections of the
Skin
Ears
Eyes
Respiratory System
Oral Region
Gastrointestinal Tract
Circulatory System
Central Nervous System

Chapter 19 Outline (cont.)
• Diseases Caused by
Anaerobic Bacteria
• Diseases Associated With
Biofilms
• Recap of Major Bacterial
• Recap of Major Bacterial
Pathogens of Humans
• Appropriate Therapy for
Bacterial Infections

How Do Bacteria Cause Disease?
• Adherence and colonization factors
• Factors that prevent activation of complement
• Factors that enable escape from phagocytosis by
white blood cells
• Factors that prevent destruction within phagocytes
• Factors that suppress the host immune system (i.e.,
factors that cause immunosuppression)
• Endotoxin (a component of the cell walls of Gram-
negative bacteria)

How Do Bacteria Cause Disease? (cont.)
• Production of exotoxins (e.g., cytotoxins,
enterotoxins, neurotoxins)
• Production of necrotic and other types of destructive
enzymes (fasciitis)
• 34 notifiable bacterial diseases in US (2007)

Bacterial Infections of the Skin
• Acne
– Propionibacterium acnes
and other
Propionibacterium spp.;
anaerobic Gram + bacilli;
non-transmissible
• Anthrax, Woolsorter’s Disease
– Bacillus anthracis; a
spore-forming, Gram +
bacillus (cutaneous
anthrax - eschar)
• Gas gangrene (myonecrosis)
– Anaerobic bacteria in the
genus Clostridium,
especially C. perfringens
Gram +
• Leprosy (Hansen disease)
– Mycobacterium leprae;
an acid-fast bacillus;
lepromatous and
tuberculoid leprosy
• Staphylococcal skin
infections (folliculitis,
furuncles, abscesses, etc.)
– Staphylococcus aureus,
a Gram + coccus
• Streptococcal skin infections
(scarlet fever, erysipelas,
etc., fasciitis)
– Streptococcus pyogenes,
a Gram + coccus; GAS;
b-hemolytic

Diseases Caused by Staphylococcus aureus
MRSA

Diseases Caused by Streptococcus pyogenes

Bacterial Infections of the Skin (cont.)
• Wound infections
– Result when protective skin barrier is broken
as a result of burns, punctures, surgical
procedures, or bites
– Opportunistic indigenous microbiota and
environmental bacteria can invade and cause
local or deep tissue infections.
– Pathogens may spread through blood or
lymph, causing serious systemic infections.

Viral and Bacterial Ear Infections
• Otitis externa (external otitis, ear canal infection,
swimmer’s ear)
– Escherichia coli, Pseudomonas aeruginosa, Proteus
vulgaris, Staphylococcus aureus; less commonly caused by
a fungus such as Aspergillus
• Otitis media (middle ear infection)
– Bacterial causes: Streptococcus pneumoniae, a Gram +
diplococcus; Haemophilus influenzae, a Gram − bacillus;
and Moraxella catarrhalis, a Gram − diplococcus
– Viral causes: measles, parainfluenza, and respiratory
syncytial (RSV) viruses (RSV)

Bacterial Infections of the Eyes
• Bacterial conjunctivitis (pinkeye)
– Haemophilus influenzae biogroup aegyptius and S.
pneumoniae are the most common causes
• Chlamydial conjunctivitis (inclusion conjunctivitis,
paratrachoma)
– Certain serotypes (serovars) of Chlamydia trachomatis
• Trachoma (chlamydia keratoconjunctivitis)
– Certain serotypes of Chlamydia trachomatis
• Gonococcal conjunctivitis (gonorrheal ophthalmia neonatorum)
– Neisseria gonorrhoeae; a Gram − diplococcus; also called
gonococcus or GC

Infections Caused by Haemophilus
influenzae

Gonococcal Ophthalmia Neonatorum

Bacterial Infections of the Upper
Respiratory Tract
• Diphtheria
– Corynebacterium diphtheriae; a pleomorphic, Gram
+ bacillus
– Transmission occurs via airborne droplets, direct
contact, contaminated fomites, and raw milk.
• Streptococcal pharyngitis (strep throat)
– Streptococcus pyogenes; beta-hemolytic, catalase-
negative, Gram + cocci in chains
– Transmission is human-to-human by direct contact,
usually hands; also via aerosol droplets.

Infections of the Lower Respiratory Tract
Having Multiple Causes
• Pneumonia
– May be caused by Gram + or Gram − bacteria,
mycoplasmas, chlamydias, viruses, fungi, or
protozoa
– Community-acquired bacterial pneumonia is most
frequently caused by Streptococcus pneumoniae.
• S. pneumoniae is the most common cause of
pneumonia in the world
– Transmission, in most cases, occurs via infected
humans.

Gram-Positive Streptococcus pneumoniae in a Gram-
Stained Smear of a Purulent Sputum. Note the diplococci

Bacterial Infections of the Lower
Respiratory Tract
• Legionellosis (Legionnaire disease, pontiac fever)
– Legionella pneumophila, a poorly staining, Gram −
bacillus; transmission is via environmental water
sources, ponds, air-conditioning systems, hot tubs,
etc.; not transmissible between humans
• Mycoplasmal pneumonia (primary atypical pneumonia)
– Mycoplasma pneumoniae, tiny, Gram − bacteria,
lacking cell walls; transmission occurs via droplet
inhalation, direct contact with an infected person, or
contaminated articles.
– Walking pneumonia

Bacterial Infections of the Lower
Respiratory Tract (cont.)
• Tuberculosis (TB)
– Primarily Mycobacterium tuberculosis (a slow-
growing, acid-fast, Gram-positive to Gram-variable
bacillus), occasionally other Mycobacterium spp.;
transmission occurs primarily via infected humans
(airborne droplets).
• Whooping cough (pertussis)
– Bordetella pertussis, a small, encapsulated,
nonmotile, Gram − coccobacillus that produces
endotoxin and exotoxins; transmission occurs via
infected humans (i.e., droplets by coughing).

Bacterial Infections of the Oral Cavity
• Terms relating to infectious diseases of the oral cavity:
dental caries, periodontal disease, gingivitis, periodontitis
• Acute Necrotizing Ulcerative Gingivitis (ANUG); also
known as Vincent’s Angina and Trench Mouth
– A synergistic infection involving two or more species
of anaerobic bacteria of the indigenous oral
microbiota; most commonly, Fusobacterium
nucleatum and Treponema vincentii

Bacterial Infections of the GI Tract
• Bacterial gastritis and ulcers
– Helicobacter pylori, a curved, microaerophilic,
capnophilic, Gram − bacillus
– Transmission occurs via infected humans;
probably by ingestion; presumed to be either
oral-oral or fecal-oral.
• Campylobacter enteritis
– Campylobacter jejuni (less common, C. coli),
curved, S-shaped or spiral Gram − bacillus
– Transmission occurs via animals, including
poultry, cattle, sheep, swine, rodents, birds,
kittens, puppies, and other pets.

Bacterial Infections of the GI Tract (cont.)
• Cholera
– Certain biotypes of Vibrio cholerae serogroup 01,
curved, Gram − bacillus that secretes
enterotoxin
– Transmission occurs via infected humans and
aquatic reservoirs; fecal-oral route.
– Rice-water consistency of the stool
• Salmonellosis
– Salmonella spp.; members of the family
Enterobacteriaceae, Gram - bacilli that invade
intestinal cells, release endotoxin, and produce
cytotoxins and enterotoxins
– Transmission occurs via domestic and wild
animals; contaminated food, fecal-oral, food
handlers, contaminated water

Bacterial Infections of the GI Tract (cont.)
• Typhoid fever (enteric fever)
– Salmonella typhi, a Gram − bacillus that releases
endotoxin and produce exotoxins
– Transmission occurs via infected humans for
typhoid and paratyphoid; some people become
carriers after infection (e.g., “Typhoid Mary”).
• Shigellosis (bacillary dysentery)
– Shigella dysenteriae, S. flexneri, S. boydii, and
S. sonnei; nonmotile, Gram − bacilli, members of
the family Enterobacteriaceae
– Transmission occurs via infected humans.

Enterovirulent Escherichia coli
• Enterohemorrhagic E. coli (EHEC) Diarrhea
– Escherichia coli O157:H7 is most commonly
involved; others include O26:H11, O111:H8, and
O104:H21; Gram − bacillus that produces potent
cytotoxins.
– Transmission occurs via cattle feces; also
infected humans, fecal-oral route.
• Enterotoxigenic E. coli (ETEC) diarrhea (traveler’s
diarrhea)
– Many different serotypes of enterotoxigenic E.
coli
– Transmission is via infected humans, fecal–oral
route

Urinary Tract Infections (UTIs)
• The most common causes of UTIs are E. coli and
other members of the family Enterobacteriaceae
(especially Proteus and Klebsiella).
• Other common causes of UTIs are Enterococcus
spp., Staphylococcus spp. (especially S. aureus,
S. epidermidis, and S. saprophyticus), and
Pseudomonas aeruginosa.
• UTIs may be acquired either within a healthcare
setting (called healthcare-associated UTIs) or
elsewhere (called community-acquired UTIs).
• UTIs are the most common type of healthcare-
associated infection.

Many Gram-Negative Bacilli (arrows) and Many Pink-
Staining PMNs Can be Seen in This Gram-Stained Urine
Sediment From a Patient With Cystitis

Bacterial STIs
• Genital chlamydial infections
(genital chlamydiasis)
– Certain serotypes of
Chlamydia trachomatis;
obligate intracellular Gram
- bacteria
– Transmission via infected
humans, direct sexual
contact, or mother-to-
neonate during birth
• Gonorrhea
– Neisseria gonorrhoeae; a
Gram − diplococcus
humans, usually sexual
contact or direct mucous
membrane-to-mucous
membrane contact
• Syphilis
– Treponema pallidum;
Gram-variable, tightly-
coiled spirochete; too thin
to be seen by brightfield
microscopy; can be seen
by darkfield microscopy
humans, by direct contact
with lesions, body
secretions, mucous
membranes, blood, semen,
etc.; usually sexual
contact; also blood
transfusions and
transplacentally from
mother to fetus

Gram-Stained Urethral Exudate from a
Male Patient with Gonorrhea.
Note the Numerous Gram-Negative Intracellular
Diplococci (arrows)

Other Bacterial STDs
• Bacterial STDs that occur more frequently in parts of the
world other than the United States:
– Chancroid—caused by Haemophilus ducreyi; a Gram
− bacterium
– Granuloma inguinale—caused by
Calymmatobacterium granulomatis; a Gram −
bacterium
– Lymphogranuloma venereum—caused by certain
serotypes of Chlamydia trachomatis
• STDs may be transmitted simultaneously; if a patient is
diagnosed with one particular type of STD, other types
should be sought.

Rickettsial and Ehrlichial Diseases of the
Cardiovascular System
• Spotted fever rickettsiosis (tickborne typhus fever)
– Rickettsia rickettsii; a Gram − bacterium; an obligate
intracellular pathogen
– Transmission occurs via infected ticks on dogs,
rodents, and other animals
• Endemic typhus fever (murine typus fever, fleaborne
typhus)
– Rickettsia typhi; a Gram − bacterium; an obligate
intracellular pathogen
– Transmission occurs via rats, mice, possibly other
mammals, infected rat fleas.

Rash of Spotted Fever Rickettsiosis

Rickettsial and Ehrlichial Diseases
of the Cardiovascular System, cont.
• Epidemic typhus fever (louseborne typhus)
– Rickettsia prowazekii; a Gram − bacterium; an
obligate intracellular pathogen
– Reservoirs are infected humans and body lice.
• Erlichiosis
– Gram-negative coccobacilli, closely related to
rickettsias; obligate intraleukocytic pathogens
– Reservoir unknown; transmission is via tick bite

Other Bacterial Infections
of the Cardiovascular System
• Lyme disease (Lyme borreliosis)
– Borrelia burgdorferi; a Gram −, loosely coiled spirochete
– Transmission is via tick bite.
• Plague (“black death,” bubonic plague, pneumonic plague,
septicemic plague)
– Yersinia pestis; a nonmotile, bipolar-staining, Gram −
coccobacillus
– Transmission is via wild rodents and their fleas (flea bite).
• Tularemia (Rabbit Fever)
– Francisella tularensis; a pleomorphic, Gram − coccobacillus
– Transmission is via tick bite; associated with rabbits.

Bull’s Eye Rash of Lyme Disease

Yersinia pestis (arrows)

Lesion of Tularemia

Bacterial Infections of the CNS
• Listeriosis
– Listeria monocytogenes; a Gram + coccobacillus
– Transmission occurs via ingestion of raw or
contaminated milk, soft cheeses, and vegetables.
– Urine of rodents
• Tetanus (lockjaw)
– Clostridium tetani; a motile, Gram + anaerobic,
spore-forming bacillus
– Transmission occurs via spores of C. tetani
entering a puncture wound, burn, or needlestick by
contamination with soil, dust, or feces.

Tetanus Patient Displaying the Bodily
Posture Known as Opisthotonos

Human Diseases Commonly
Caused by Anaerobes

Major Groups of Medically Important
Bacteria

END OF CHAPTER 19

BSci106:
MICROBIOLOGY and
PARASITOLOGY
Chapter 20
Fungal Infections of Humans

Chapter 20 Outline
• Introduction
• How Do Fungi Cause
Disease?
• Classification of Fungal
Diseases
• Fungal Infections of the Skin
• Fungal Infections of the
Respiratory System
• Fungal Infections of the Oral
Region
Circulatory System
Central Nervous System
• Recap of Major Fungal
• Appropriate Therapy for
Fungal Infections

How do Fungi Cause Disease?
• The tissue damage associated with fungal infections
results primarily from direct invasion of tissue, with
subsequent displacement and mechanical destruction of
vital structures, coupled with toxic effects of the
inflammatory response (no secretion of toxins).
• Masses of fungal cells can cause obstruction of bronchi in
the lungs and tubules and ureters in kidneys, leading to
obstruction of the flow of bodily fluids.
• Some fungi can grow in the walls of arteries and veins,
leading to occlusion and tissue necrosis resulting from a
lack of oxygen.

Classification of Fungal Diseases
• Fungal infections (mycoses) can be classified into the
following four categories:
– Superficial mycoses—fungal infections of the
outermost areas of the body (outer surfaces of hair
shafts, the epidermis- nonliving component)
– Cutaneous (dermis), hair, and nail mycoses (tinea or
“ringworm” infections)
– Subcutaneous mycoses
– Systemic mycoses—the most serious types of fungal
infections (generalized/deep-seated mycoses);
involves 2 or more organ systems

Superficial mycoses
Superficial mycoses include: otomycosis (outer ear),a black
piedra, white piedra, tinea (or pityriasis) versicolor, and tinea
nigra.
• All are caused by moulds.
• Black piedra (Piedraia hortae) is a fungal infection of scalp
hair, eyebrows and eyelashes.
• White piedra (Trichosporon beigelii) is a fungal infection of
moustache, beard, pubic, and axilla hair.
• Tinea versicolor (Malassezia furfur) is a ringworm infection
that affects the skin of the chest or back and, less
commonly, the arms, thighs, neck, and face.
• Tinea nigra (Hortaea werneckii) is a ringworm infection of
the palms of the hands, neck and feet

Types of Tinea (ringworm) Infections
(Cutaneous)

Subcutaneous Mycoses
Sporothrix schenkii
Skin and underlying
tissues;extremeties
Affects lower extremity;
skin and subcutaneous
Chronic granulomas

Chromoblastomycosis of the Foot

Fungal Infections of the Skin
• Dermatophytosis (Tinea [“Ringworm”] Infections,
Dermatomycosis)
– Caused by various species of filamentous fungi,
including Microsporum, Epidermophyton, and
Trichophyton spp.
– These fungi are collectively referred to as
dermatophytes.
– Note that ringworm infections have nothing to do
with worms.

Fungal Infections of the
Lower Respiratory Tract
• Coccidioidomycosis (Valley Fever)
– Coccidioides immitis, a dimorphic fungus;
transmission occurs via inhalation of arthrospores
• Cryptococcosis
– Two subspecies of Cryptococcus neoformans, an
encapsulated yeast; transmission occurs via
inhalation of yeasts
• Histoplasmosis
– Histoplasma capsulatum var. capsulatum, a
dimorphic fungus; transmission occurs via inhalation
of conidia from soil

Fungal Infections of the
Lower Respiratory Tract (cont.)
• Pneumocystis Pneumonia (PCP; Interstitial Plasma-Cell
Pneumonia)
– Caused by Pneumocystis jiroveci, which has both
protozoal and fungal properties
– Was once classified as a protozoan, but is now
classified as a fungus
– Mode of transmission is unknown; perhaps direct
contact, transfer of pulmonary secretions from
infected to susceptible persons, or perhaps airborne

Tissue Invasion by an Aspergillus Species,
the Cause of Aspergillosis

Fungal Infections of the Oral Cavity
• Thrush
– A yeast infection of the oral cavity
– Common in infants, elderly patients, and
immunosuppressed individuals
– White, creamy patches occur on the tongue, mucous
membranes, and the corners of the mouth
– Caused by Candida albicans and related species

Oral Candidiasis (Thrush)

Yeast Vaginitis
• Most cases are caused by the yeast, Candida albicans
• Can be diagnosed by microscopic examination of a saline
wet mount of vaginal discharge material, in which
numerous yeasts and hyphae may be observed
• The mere presence of yeast is not proof of yeast
vaginitis, as the vaginal flora of up to 25% of healthy
women can contain Candida spp.

Various Forms of Candida Yeasts Seen in
Clinical Specimens and Cultures

Cryptococcal Meningitis
• Can be caused by three subspecies of Cryptococcus
neoformans, an encapsulated yeast
• Cryptococcosis starts as a lung infection, but spreads via
the bloodstream to the brain
• Cryptococcal meningitis can be presumptively diagnosed
by observing encapsulated, budding yeasts in CSF
specimens examined by an India ink preparation

Gram-Stained Appearance of
Cryptococcus

END OF CHAPTER 20

BSci106:
MICROBIOLOGY and
PARASITOLOGY
Chapter 21
Parasitic Infections of
Humans

Chapter 21 Outline
• Introduction
• Definitions
• How Parasites Cause
Disease
• Parasitic Protozoa
• Protozoal Infections of
Humans
⚫ Helminths
⚫ Helminth Infections
of Humans
⚫ Appropriate
Therapy for
Parasitic Diseases
⚫ Medically Important
Arthropods

Table 21-1 Nationally Notifiable Parasitic
Diseases
Source: http://www.cdc.gov.
aThese figures provide insight regarding how common or rare these diseases are
in the United States. For updated information, go to the CDC Web site; click on
“Morbidity & Mortality Weekly Report”; then click on “Notifiable Diseases”;
then click on the most recent year that is listed.

Definitions
• Parasitology is a branch of microbiology; it is the
scientific study of parasites.
• Parasitism is a symbiotic relationship that is of benefit
to one party or symbiont (the parasite) and usually
detrimental to the other party (the host).
• Parasites are organisms that live on or in other living
organisms (hosts), at whose expense they gain some
advantage.
– Parasites that live on the outside of the host’s body
are called ectoparasites.
– Parasites that live inside the host are called
endoparasites.

Definitions (cont.)
• The life cycle of a parasite may involve one or more
hosts.
– If more than one host is involved, the definitive host
is the host that harbors the adult or sexual stage of
the parasite.
– The host that harbors the larval or asexual stage is
the intermediate host.
• An accidental host is one that can serve as a host, but is
not the usual host in the parasite’s life cycle.
• A dead-end host is one in which the parasite cannot
continue its life cycle.

Definitions (cont.)
• A facultative parasite is an organism that can be
parasitic, but does not have to live as a parasite; it is
capable of an independent life.
– Example: the free-living amoeba Naegleria fowleri,
which causes primary amebic meningoencephalitis
• An obligate parasite has no choice; it must inhabit a
host(s).
– Most parasites that infect humans are obligate
parasites.

How Parasites Cause Disease
• The manner in which parasites cause damage to their
host varies from one species of parasite to another, and
often depends on the number of parasites that are
present.
• Some parasites produce toxins; some produce harmful
enzymes; some invasive and migratory parasites cause
physical damage to tissues and organs; some cause the
destruction of individual cells; and some cause occlusion
of blood vessels and other tubular structures.
• Sometimes, the host immune response to the parasites
causes more injury than do the parasites themselves.

• The trophozoite is the motile, feeding, dividing stage in a
protozoan’s life cycle, whereas cysts, oocysts, and spores
are dormant stages (much like bacterial spores).
• Protozoal infections are primarily acquired by ingestion or
inhalation of cysts, oocysts, or spores.
• Because of their fragile nature, only rarely do
trophozoites serve as the infective stages.

Life cycle of a protozoa

Parasitic Protozoa
• Most protozoa are unicellular.
• They are sometimes classified taxonomically by their
mode of locomotion; amebae move by means of
pseudopodia (false feet); flagellates move by means of
flagella; ciliates move by means of cilia; sporozoans do
not move.
• Not all protozoa are parasitic (e.g., Paramecium spp.).
• Protozoal infections are most often diagnosed by
microscopic examination of body fluids, tissue specimens,
or feces—specimens are examined for motile
trophozoites and dormant cyst stages.

Protozoal Infections of
Humans

Protozoal Infections of the Skin
• Leishmaniasis
– Caused by various species of flagellated protozoa in
the genus Leishmania (trypanosome)
– Usually transmitted via the bite of an infected sand
fly
– There are three forms of the disease: cutaneous,
mucocutaneous, visceral.
– Cutaneous and mucocutaneous leishmaniasis can
cause severe tissue damage and disfigurement.
– Visceral leishmaniasis can lead to death.
– Amastigote (non-motile); promastigote (motile)

Patients with Cutaneous Leishmaniasis

Protozoal Infections of the Eyes
• Amebic conjunctivitis and keratoconjunctivitis
(Entamoeba histolytica)
– Caused by several species of amebae in the genus
Acanthamoeba (facultative parasites)
– Can lead to loss of vision or enucleation
• Toxoplasmosis (cats – definitive hosts)
– Caused by Toxoplasma gondii, an intracellular
sporozoan
– Can involve the CNS, lungs, muscles, or heart, as
well as the eyes
– Acquired by ingesting cysts or oocysts

Protozoal Infections of the Gastrointestinal Tract
Disease Etiologic agent
Mode of
Transmission
Amebiasis Entamoeba histolytica
Humans; fecally
contaminated food or
water
Balantidiasis Balantidium coli
Pigs; food or water
contaminated with pig
feces
Cryptosporidiosis
Cryptosporidium
parvum
Infected humans,
cattle, and other
domesticated animals
Cyclosporiasis
Cyclospora
cayetanensis
Fecally contaminated
water and produce
Giardiasis Giardia lamblia
Humans and infected
animals

Three Protozoal Infections of the GI Tract
(Flagellated protozoan)
(Coccidian)
Coccidian oocyts

The trophozoite (10–20
µm long by 5–15 µm wide)
resembles a face; the two
nuclei look like eyes; it has
been described as
resembling an owl face, a
clown face, and an old
man with glasses.
Giardia lamblia Trophozoite

Protozoal Infections of the
Genitourinary Tract
• Trichomoniasis
– Caused by Trichomonas vaginalis, a flagellate
– A sexually transmitted disease of men and women
– Usually symptomatic in women and asymptomatic in
men
– T. vaginalis causes about 1/3 of the cases of vaginitis
in the United States.
– T. vaginalis vaginitis is usually diagnosed by
observation of motile trophozoites in a saline wet
mount of vaginal discharge material.

Trichomonas vaginalis
trophozoites (arrows) are 7
to 23 µm long by 5 to 15
µm wide.
Live T. vaginalis
trophozoites are constantly
in motion, as a result of the
flagella and an undulating
membrane.
Trichomonas vaginalis

Protozoal Infections of the Circulatory System
Disease Etiologic agent
Mode of
Transmission
African
Trypanosomiasis
2 different
subspecies of
Trypanosoma brucei
Bite of infected
tsetse fly
American
trypanosomiasis
(Chagas Disease)
T. cruzi
Reduvid bug (also
known as a
triatome, kissing, or
cone-nosed bug)
Babesiosis
Babesia microti and
other Babesia spp.
Tick bite
Malaria
4 different species of
Plasmodium
Bite of infected
female Anopheles
mosquito

A stained peripheral blood smear from a patient
with African trypanosomiasis
Trypanosoma brucei Trypomastigotes (mature)
(hemoflagellates)

A stained peripheral blood smear from a patient
with American trypanosomiasis (Chagas
disease)
Trypanosoma cruzi Trypomastigotes

Life Cycle of Malarial Parasites

Peripheral blood
erythrocytes infected with
trophozoites of Plasmodium
falciparum (arrows)
Young P. falciparum
trophozoites have a “signet
ring” appearance.
Plasmodium falciparum Trophozoites

Protozoal Infections of the CNS
• Primary amebic meningoencephalitis
– Caused by Naegleria fowleri, an ameboflagellate
– Acanthamoeba and Balamuthia spp. can cause
similar conditions.
– Persons often become infected by swimming and/or
diving in ameba-contaminated water (e.g., “the old
swimming hole”).
– After the amebae colonize nasal tissues, they invade
the brain and meninges by traveling along the
olfactory nerves; the disease is often fatal.

Helminths
• The word helminth means parasitic worm
– Helminths are multicellular, eukaryotic organisms;
two major divisions: (1) round worms or nematodes,
and (2) flatworms or platyhelminthes. The flatworms
are further divided into tapeworms (cestodes) and
flukes (trematodes).
– The helminth life cycle has three stages: egg, larva,
and the adult worm.
– Helminth infections are primarily acquired by
ingesting the larval stage; in some helminth
diseases, larvae enter by penetration of the skin.

Helminth Infections of Humans
Location Helminth disease Cause
Skin Onchocerciasis Onchocerca volvulus
Muscle/Subcutaneous
tissue
Trichinosis
Dracunculiasis
Trichinella spiralis
Dracunculus medinensis
Eyes
Onchocerciasis
Loiasis
O. volvulus
Loa loa
Respiratory system Paragonimiasis Paragonimus westermani
Circulatory system
Filariasis
Schistosomiasis
Wuchereria
bancrofti/Brugia malayi
Schistosoma spp.
Central nervous system
Cysticercosis
Hydatid cyst disease
Taenia solium (cysts)
Echinococcus granulosis
or E. multilocularis

Helminth Infections of the GI Tract
• Ascariasis – Ascaris
lumbricoides (N)
• Hookworm infection –
Ancylostoma duodenale or
Necator americanus (N)
• Pinworm – Enterobius
vermicularis (N)
• Whipworm – Trichuris trichiura
(N)
• Strongyloidiasis – Strongyloides
stercoralis (N)
• Beef tapeworm – Taenia
saginata (C)
• Dog tapeworm – Dipylidium
caninum (C)
• Dwarf tapeworm – Hymenolepis
nana (C)
• Fish tapeworm –
Diphyllobothrium latum (C)
• Pork tapeworm – Taenia solium
(C)
• Rat tapeworm – Hymenolepis
diminuta (C)
• Fasciolopsiasis – Fasciolopsis
buski (T)
• Fascioliasis – Fasciola hepatica
(T)
• Clonorchiasis – Clonorchis
sinensis (T)

Fish Tapeworm Life Cycle—An Example of
a Three-Host Life Cycle

Pinworms

Adult Ascaris
lumbricoides
Worms

Elephantiasis of the Legs,
Resulting from Filariasis

Boy with a Swollen Abdomen
Due to Schistosomiasis

Medically Important Arthropods
• There ae three classes of arthropods studied in
parasitology courses:
– Insects (e.g., lice, fleas, mosquitoes)
– Arachnids (e.g., mites and ticks)
– Crustaceans (e.g., crabs, crayfish, and certain
Cyclops species)
• Arthropods serve as mechanical or biologic vectors in the
transmission of certain infectious diseases.
– Mechanical vectors pick up a parasite at point A and
drop it off at point B.
– Biological vectors harbor the parasite in their body,
where the parasite matures and/or multiplies.

Ways in Which Arthropods May Be
Involved in Human Diseases
Type of Involvement Example(s)
The arthropod may actually be the
cause of the disease.
Scabies, a disease in which microscopic
mites live in subcutaneous tunnels and
cause intense itching
The arthropod may serve as the
intermediate host in the life cycle of a
parasite.
Flea in the life cycle of the dog
tapeworm; beetle in the life cycle of the
rat tapeworm
The arthropod may serve as the
definitive host in the life cycles of a
parasite
Female Anopheles mosquito in the life
cycle of malarial parasites
The arthropod may serve as a vector in
the transmission of an infectious
disease.
Oriental rat flea in the transmission of
plague; tick in the transmission of
Rocky Mountain spotted fever and Lyme
disease

A. Dermacentor
andersoni, wood tick,
one of the tick
vectors of spotted
fever rickettsiosis
B. Xenopsylla cheopis,
oriental rat flea, vector of
plague and endemic
typhus
Medically Important Arthropods (cont.)

Medically Important Arthropods (cont.)
C. Pediculus humanus,
human body louse (a
vector of epidemic typhus)
D. Phthirus pubis, the
pubic or crab louse

END OF UNIT 8

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