Selected Diesease in Humans
Bacterial Diseases
Viral Diseases
Fungal Diseases
Protozoan Diseases
Bacterial Diseases
 Pathogenic bacteria typically enter through a
specific portal of entry and begin as a localized
infection; some bacteria have more than one portal
 Many bacterial pathogens can spread from the
initial site to other areas of the body
 Many bacterial infections have been effectively
treated with antibiotics; evolution of drug
resistance in some strains have made them
difficult to treat
 Several important pathogens are curtailed through
the use of vaccines
Bacterial Diseases
Selected airborne bacterial pathogens
 Streptococcus pyogenes
• Gram + cocci, Lancefield serological group “A”,
catalase negative, beta hemolytic
• Associated with streptococcal pharyngitis, scarlet
fever (with erythrogenic toxin-producing strains),
systemic infections, immune-related complications
such as rheumatic fever and glomerulonephritis, and
a skin infection called erysipelas
Bacterial Diseases
Selected airborne bacterial pathogens
 Neisseria meningitidis
• Gram negative diplococcus; fastidious; cultured on
chocolate agar
• Highly contagious
• Generally begins as an upper respiratory tract
infection; may spread into bloodstream and then to
the meninges
• Symptoms of meningitis: “stiff neck,” headache,
dizziness, disorientation, seizures, coma, death
Bacterial Diseases
Selected airborne bacterial pathogens
 Mycobacterium tuberculosis
• Acid-fast rods, grows very slowly in culture
• Detected by acid-fast stains of sputum, lung x-ray,
culture
• Tuberculin skin test determines if someone has been
exposed to M. tuberculosis, but doesn’t necessarily
mean the person has tuberculosis
• Symptoms: Cough; destruction of lung tissue;
tubercle formation in lungs; spread to other areas of
the body with tissue damage
Bacterial Diseases
Selected airborne bacterial pathogens
 Legionella pneumophila
• Gram negative aerobic rods; natural habitat is highly
aerated aquatic environments such as streams
• May contaminate bulding ventilation systems, water
faucets, or other moist surface and is transmitted to
humans who come into aerosols created from these
sources
• Symptoms: Mild to severe pneumonia (lung
infection with fluid buildup in the lungs)
Bacterial Diseases
Selected foodborne bacterial pathogens
 Clostridium botulinum
• Gram + anaerobic rods; forms spores; found in soil
• Can contaminate raw or underprocessed foods; toxin
forms in food before it is consumed, so it is a
foodborne intoxication
• Secretes botulinum toxin, a deadly neurotoxin that
blocks nerve impulses at motor neuron end plate
synapses and causes flaccid paralysis
• Symptoms begin as soon as the toxin begins to be
absorbed in the stomach
• Death is due to respiratory and cardiac failure
Bacterial Diseases
Selected foodborne bacterial pathogens
 Staphylococcus aureus food poisoning
• Gram + cocci; catalase and coagulase positive;
common skin flora
• Some strains of Staph. Aureus produce an
enterotoxin that can be secreted in contaminated
food; toxin forms in food before it is consumed, so it
is a foodborne intoxication
• The toxin causes mild to moderate cramping and
diarrhea; symptoms appear a few hours after
consuming the food and usually last only a few
hours
Bacterial Diseases
Selected foodborne bacterial pathogens
 Salmonella species
• Gram negative rods; facultatively anaerobic; a
member of Enterobacteriaceae
• Transmitted in contaminated foods, especially meat,
poultry, & dairy products
• A foodborne infection: Bacteria must colonize the
intestinal tract to cause symptoms
• Cramping, nausea, diarrhea
• Salmonella typhi causes typhoid fever: intestinal
ulceration, invasiveness, rose-colored rash on
abdomen, less diarrhea but very high fever
Bacterial Diseases
Selected foodborne bacterial pathogens
 Helicobacter pylori
• Gram negative microaerophilic spirillum
• Groes underneath the mucous layer in the stomach
• A major cause of stomach ulcers
Bacterial Diseases
Selected soilborne bacterial pathogens
 Bacillus anthracis
• Gram + facultatively anaerobic rods; forms spores
• Found in contaminated soil or animals (livestock)
• May either be transmitted through skin contact
(cutaneous anthrax), oral ingestion (intestinal
anthrax), or inhalation (pulmonary anthrax)
• Lesions & tissue destruction occur at the affected
sites
• Pulmonary anthrax has close to a 100% fatality rate
Bacterial Diseases
Selected soilborne bacterial pathogens
 Clostridium tetani
• Gram + anaerobic rods; forms spores; found in soil
• May grow in contaminated wounds or cuts, where it
produces the toxin tetanospasmin; a neurotoxin that
acts as a cholinesterase inhibitor; mainly effects the
central nervous system
• Nerve synapses remain closed because
cholinesterase fails to break down the
neurotransmitter acetylcholine; this causes rigid
paralysis
Bacterial Diseases
Selected arthropodborne bacterial pathogens
 Borrelia burgdorferi
• Gram negative spirochaete; causative agent of
Lyme disease
• Transmitted through the bite of an infected deer tick
(Ixodes)
• Initial symptoms include fever, congestion, lymph
node swelling, “flu-like” symptoms and the
developemnt of a large, spreading rash (erythyma
chronicum migrans) at the site of the tick bite
• If untreated, inflammation & damage to joints,
arthitis-like symptoms, and damage to the
cardiovasular system can result
Bacterial Diseases
Selected arthropodborne bacterial pathogens
 Rickettsia rickettsiae
• Gram negative rickettsia; a small, irregularly-shaped
bacterium that is an obligately intracellular parasite
• Causative agent of Rocky Mountain Spotted Fever
• Transmitted through tick bites
• Symptoms include high fever, a rash that begins as
pinpoint spots at the extremities and spreads to the
trunk of the body (macropapipular rash), seizures
and coma
Bacterial Diseases
Selected arthropodborne bacterial pathogens
 Rickettsia prowasekii
• Gram negative rickettsia; a small, irregularly-shaped
bacterium that is an obligately intracellular parasite
• Causative agent of epidemic typhus
• Transmitted through human lice; predominately
spread via body lice, not head lice or crab lice
• Symptoms include high fever, a rash that begins as
pinpoint spots on the trunk of the body and spreads
to the extremities (macropapipular rash), seizures
and coma; has a very high fatality rate
• Easily spread under conditions of reduced sanitation
where lice are likely to spread
Bacterial Diseases
Selected bacterial STDs
 Treponema pallidum
• Gram negative spirochaete; transmitted via sexual
contact or congenitally
• Initial symptom (primary syphilis) is usually the
appearance of a crusted, purple, painless lesion
called a hard chancre at the site of infection; lesion
usually disappears on its own after a few weeks but
the infection remains in the blood
• Later symptoms include fever, rash, & flu-like
symptoms (secondary syphilis) and the formation of
lesions called gummae throughout the body (tertiary
syphilis), with neurological, cardiovascular, & other
damage.
Bacterial Diseases
Selected bacterial STDs
 Neisseria gonorrhoeae
• Gram negative diplococcus; fastidious; cultured on
chocolate agar
• Transmitted via sexual contact or congenitally
• Urinary tract symptoms: Urethritis with painful
urination & pus discharge; cystitis; kidney infection
• Male reproductive symptoms: Prostatitis;
epididymitis
• Female reproductive symptoms: Infections of the
vagina, cervix, uterus, Fallopian tubes; pelvic
inflammatory disease
• Eye infections (trachoma)
Bacterial Diseases
Selected miscellaneous bacterial infections
 Pseudomonas aeruginosa
• Gram negative aerobic rod; commonly found in soil
or aquatic environments
• Can contaminate aerated moist surfaces such as
faucets, respiratory equipment, etc.
• A common cause of hospital-acquired (nosocomial)
infections
• Respiratory tract infections, urinary tract infections,
and severe infections in burn patients
Bacterial Diseases
Selected miscellaneous bacterial infections
 Staphylococcus aureus infections
• Gram + cocci; catalase and coagulase positive;
common skin flora
• Infections associated with Staph. aureus include
pimples, boils, abscesses, carbuncles, septicemia,
scalded skin syndrome in infants, toxic shock
syndrome
Viral Diseases
Viruses are classified based on
 nucleic acid structure (DNA or RNA; single- or
double-stranded; segmented or nonsegmented)
 capsid structure (helical, icosahedral, or
complex)
 envelope structure (enveloped or
nonenveloped)
 host (animal, plant, or bacteria)
 mechanism of replication
 site of infection (pneumotrophic,
dermatotrophic, viscerotrophic, neurotrophic)
Viral Diseases
Influenza
 Member of Orthomyxovirus family
 Segmented (8 segments), single-stranded,
negative-sense RNA that encode 11 proteins
 RNA is packaged into helical nucleocapsids and
surrounded by an envelope
 Two envelope proteins: hemagluttinin (H) and
neuraminidase (N)
 Three major types: Influenza A, Influenza B, &
Influenza C; of which Influenza A strains are
the most virulent in humans
Viral Diseases
Influenza
 Influenza can be transmitted via human-human airborne
contact, or from contact with contaminated birds,
swine, or other animals
 Symptoms
• in mild cases include fever, lymph node swelling, congestion,
fatigue, primary & secondary pneumonia
• Highly virulent strains may exhibit hemorrhaging from nose &
mouth, ears, eyes, intestine, internal organs
• Other complications include Guillian-Barre & Reyes syndrome
 Antigenic variation and genetic recombination in the H
& N proteins can lead to new strains of influenza
 Each year epidemiologists determine the best
“combination” vaccine for the year’s prevalent strains
Viral Diseases
 Influenza
 Some important pandemics of influenza
• H1N1: 1918-1920 “Spanish flu;” estimates of deaths
worldwide range from 30 - 100 million people
• H2N2: 1957-1958 “Asian flu” with 1 - 1.5 million deaths
• H3N1: 1968-1969 “Hong Kong flu” with about 1 million
deaths
• H5N1: Current “avian flu” threat
– Genotype first observed in 1959, but evolved into the
current highly pathological strain that was discovered in
2004
– No human to human transmission seen yet; cases have
been bird to human contact
– If human to human transmission were to evolve in this
strain, experts have estimated that perhaps 5 - 150 million
people could die worldwide
Fungal Diseases
Properties of Fungi
 Eukaryotic
 Fungal cell walls with cellulose & usually with
chitin
 Heterotrophic metabolisms
 Many are saprophytes; a few species are
parasitic
 Morphology: single cells (yeasts) or filaments
(hyphae)
 Most species have both sexual & asexual
mechanisms of reproduction
Fungal Diseases
Candida albicans
 Grows as a yeast or sometimes as short hyphae
(pseudohyphae)
 Common normal flora in the mouth, intestine,
& vaginal tract
 Competiton with bacterial flora helps keep
Candida in check; conditions that reduce
bacterial flora (e.g. antibiotic use) or weaken
immune system (e.g. AIDS) can cause
candidiasis infection to develop
 Symptoms include oral candidiasis (thrush),
intestinal candidiasis, and vaginal candidiasis
Fungal Diseases
 Dermatophytic fungal infections
 Infections of the hair, skin, nails
 Several genera of dernmatophytic fungi: Microsporum,
Epidermophyton, Trichophyton
 Symptoms: Scaly, red or raised rash on skin
(“ringworm”), discolored and splitting nails, hair loss
 Often described by the term “tinea” with the name of
the area infected: tinea corporis (ringworm of the
body); tinea pedis (“athlete’s foot”); tinea unguium
(ringworm of the nails); tinea cruris (“jock itch”); tinea
barbae (ringworm of the beard)
Protozoan Diseases
 Properties of Protozoa
 A heterogeneous group of eukaryotic microbes
 Generally characterized by lack of a cell wall and a
heterotrophic metabolism (although one group,
Euglena, is photosynthetic
 Most are free-living; a few are parasitic
 Classical classification based on mechanism of motility;
rRNA data has shown the existance of more phyla than
previously suspected
 Motile by pseudopodia, flagella, cilia, or nonmotile
 Most reproduce asexually; a few groups have complex
sexual & asexual cycles
Protozoan Diseases
 Giardia lamblia
 A flagellated parasite of humans and other mammals
 Actively growing and reproducing form(trophozoite)
grows in the intestinal tract of the host
 In the intestine, trophozoites develop into cysts that are
shed in the feces; the disease is transmitted when the
next host ingests contaminated food or water and the
cysts break open and develop into new trophozoites in
the intestine
 Symptoms: Profuse, foul-smelling diarrhea;
dehydration; chronic recurrences
 Often misdiagnosed; diagnosis requires microscopic or
serological ID of trophozoites & cysts in stool or
intestinal contents
Protozoan Diseases
 Toxoplasma gondii
 Member of the phylum Apicomplexa, a group
characterized as parasites with complex lifestyles
having both sexual and asexual stages
 The sexual stage develops only in members of the cat
family, with sexual cysts (oocysts) shed in the feces
 Oocysts are ingested by other animals (e.g. mice,
cattle), where they travel to the muscle tissue & develop
into asexual cysts (tissue cysts)
 Cats acquire the parasite by ingesting the infected meat
of prey such as mice
 Humans acquire the parasite via the oral route, through
contact with cat feces or ingestion of contaminated
meat (often beef)
Protozoan Diseases
 Toxoplasma gondii (cont)
 Infections in humans are often asymptomatic, except
when the person is immunocommpromised, in which
case encephalitis may develop
 Pregnant women are at risk because the parasite can
cross the placental barrier & infect the baby, with the
possibility of birth defects or miscarriage
 The parasite is very prevalent in humans, with estimates
of 65% of people worldwide and 33% of people in the
US over 12
 Studies in mice suggest the parasite may actually alter
its host’s behavior; e.g., mice exhibit riskier behavior
such as less fear of cats. Some studies have suggested
effects of the parasite on human behavior as well.