Selected Diesease in Humans Bacterial Diseases Viral Diseases Fungal Diseases
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Transcript Selected Diesease in Humans Bacterial Diseases Viral Diseases Fungal Diseases
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.