Shortened Microbial Pathoegenesis Final

Acne

Etiological agent(s): Cutibacteria acnes
• Type of agent: Gram positive bacteria, rod,
anaerobic
• Reservoir: humans
• Transmission: Normal microbiota
• Characteristic signs/symptoms:
• Infects sebum channels near hair follicles
• Inflammatory response causes pimples
• Treatment: topical/oral antibiotics or chemicals
(salicylic acid, retinoids, benzoyl peroxide), visible
blue light
• Prevention: hygiene, avoid touching
• Special Notes:
• Comedonal (mild), Inflammatory (Moderate) or
• Severe (nodular cystic)
• Bacterial infections + Hormonal Contributions +
Genetic

Staph and Strep Skin Infections

Staphylococcus aureus
• Gram-positive cocci - clusters, catalase +, coagulase-positive
bacteria

Streptococcus spp.
• Gram positive cocci – chains bacteria, catalase

Reservoir: animals
• Transmission: direct contact- broken skin
• Sign/Symptoms: abscess, boil/furuncle, sty, folliculitis,
carbuncle, impetigo, invasive skin, systemic infections
• Treatment: Antibiotics (resistance is a problem)
• Prevention: Good Hygiene/limit exposure

Scaled Skin Syndromeq

Staph aureus infection
• Exfoliative toxin
• Secondary infections are common

Erysipelas

Subcutaneous Strep infection
o Inflammation,
o Can Spread in tissue

Necrotizing Fasciitis

Flesh Eating Bacteria”
• Infection of connective tissue
• Fast
• Can be caused by Strep. pyogenes OR Staph. aureus

Gas Gangrene

Etiological Agent: Clostridium perfringens,
• Type of Agent: gram-positive, endospore-
forming anaerobic rod,
• Reservoir: Soil
• Transmission: soil to necrotic tissue/deep
wound/anaerobic wounds
• Associated with improper “backyard” abortions.
• Signs/Symptoms: Major swelling of tissue and
necrotic tissue
• Can lead to sepsis.
• Ischemia: Loss of blood supply
• Necrosis: Death of tissue
• Gangrene: Death of soft tissue
• Treatment: surgical removal of necrotic tissue
and/or use of hyperbaric chamber
• Prevention: proper wound care

Pseudomonas Dermatitis

Etiological Agent: Clostridium perfringens,
• Type of Agent: gram-positive, endospore-
forming anaerobic rod,
• Reservoir: Soil
• Transmission: soil to necrotic tissue/deep
wound/anaerobic wounds
• Associated with improper “backyard” abortions.
• Signs/Symptoms: Major swelling of tissue and
necrotic tissue
• Can lead to sepsis.
• Ischemia: Loss of blood supply
• Necrosis: Death of tissue
• Gangrene: Death of soft tissue
• Treatment: surgical removal of necrotic tissue
and/or use of hyperbaric chamber
• Prevention: proper wound care

Anthrax

Causative Agent: Bacillus anthracis
• Gram positive, endospore-forming, bacilli bacteria.
• Reservoir: naturally occurring in the soil
• Transmission: wound entry, pneumonic -airborne, gastrointestinal –
ingestion
• Sign/symptom: necrotic skin lesion – black appearance, most common
• Also causes pneumonia, gastrointestinal infection
• Treatment: antibiotics
• Prevention: vaccine – only used in military or those at risk

Leprosy (Hansen’s Disease)

Etiological agent: Mycobacterium leprae
• Type of agent: Acid Fast rod bacteria
• Reservoir: armadillo
• Transmission: droplet/close contact
• Characteristic signs/symptoms
• Leptromatous form – disfiguring nodules
• Affects peripheral body regions (nose, fingers,
toes)
• Cooler temp
• Treatment: multidrug antibiotic
• Prevention: masking around infected
• Special Notes:
• Untreated can lead to permanent nerve damage and
disfiguration

Cat Scratch Fever

Etiological/Causative agent: Bartonella
henselae
• Type of agent bacteria Gram negative rod
• Reservoir: felines
• Transmission: Cat scratches or bites
• Characteristic signs/symptoms: Small papules
at site of inoculation, swollen lymph nodes,
high fever, usually self limiting
• Treatment: antibiotics
• Prevention: avoid cat bites/protective gear if
expecting bites.

Typhus

Etiological agent: Rickettsia prowazekii
• Type of agent: Gram negative intracellular bacteria
• Reservoir: rodents
• Transmission: Vector: lice
• Transmitted when louse feces are rubbed into
bite wound
• Signs/Symptoms – Rash starting on trunk and flu like
symptoms
• Treatment: antibiotics (fatal if not treated)
• Prevention: good hygiene/avoid vector
• Special Notes
• Outbreaks common in Burundi, Ethiopia, and
Rwanda (~12,000 cases/year)

Spotted Fevers (Rocky Mountain Spotted Fever/Tickborne Typhus)

Etiological Agent: Rickettsia rickettsia
• Type of agent: Gram negative intracellular
bacteria
• Reservoir: small mammals
• Transmission: vector: fleas, lice, mites, ticks
• Signs/Symptoms
• Measles-like rash, except that the rash starts
on palms and soles and flu like symptoms
• Severe: cardiovascular disruption,
convulsions, and coma
• Treatment: Antibiotics
• Prevention: vector protections

Lyme Disease

Etiological agent: Borrelia burgdorferi
• Type of agent: Gram negative
spirochete bacteria
• Reservoir: small rodents
• Vector Transmission: deer ticks
• Sign/Symptoms
• First sign/symptom: bull’s-eye rash, “flu
like” symptoms
• Second phase: irregular heartbeat,
encephalitis
• Third phase: arthritis, neurological
symptoms
• Treatment: antibiotics for first/second
phase
• Prevention: avoid ticks/vector controls

Cutaneous Mycoses (Dermatomycoses/ Tineas/Ringworm)

Etiological Agents: Different genera of fungi involved in different
body locations
• Reservoir: environmental, mammals
• Transmission: direct contact
• Characteristic signs/symtpoms
• Skin/nail/hair disruption, inflammation, itching
• Treatment: Antifungal treatments available
• Prevention: Good Hygiene/limit exposure

Candida Auris

Invasive nosocomial infections

Blood, wound, ear infections
• Multidrug resistant

Sporotrichosis

“Rose-sorters” disease
• Most common U.S. disease of this type
• Sporothrix schenchii enters puncture wound

Scabies

Etiological agent: Sarcoptes scabiei (mite)
• Type of agent: insect
• Reservoir: var. by mammalian host
• Transmission: close contact; fomite
(bedding/clothing)
• Characteristic signs/symptoms: burrows in the
skin to lay eggs – itching and rash
• Treatment: topical insecticides
• Prevention: good hygiene
• Special Notes
• Associated with Secondary Infections;
immunocompromised

Pediculosis (Lice)

Etiological agent:
• Pediculus humanus capitis (head
louse)
• P. h. corporis (body louse)
• Type of agent: insect
• Reservoir: var. by mammalian host
• Transmission: close contact; fomite
(bedding/clothing)
• Characteristic signs/symptoms: Feed
on blood, Lay eggs (nits) on hair
causes itching and rash
• Treatment: topical insecticides
• Prevention: good hygiene
• Special Notes
• Lice are vectors for other infectious
diseases

Skin Warts

Etiological agent(s): Papillomaviruses (100 types)
• Reservoir : Humans
• Transmission: direct/indirect contact or
autoinoculation
• Shower floors and locker rooms are notorious
• Characteristic signs/symptoms: benign growth on
the skin
• Treatment: chemicals or freezing or physical
removal
• Prevention: HPV vaccine appears to be effective
for some types of skin warts
• Special Notes
• Most are self-resolving
• Some associated with cancer

Smallpox (Variola)

Etiological Agent: Smallpox virus
• Variola major has 50% mortality
• Variola minor has <1% mortality
• Reservoir: Humans
• Transmission: Direct contact, droplet,
airborne RESPIRATORY
• Characteristic Signs/symptoms
• High fever
• Macular>Papules>Vesicles rash
• Treatment: none
• Prevention: Vaccination Bioterrorism Threat
• Special Notes
• Eradicated by vaccination in 1977
• Vaccinia virus (horsepox related)

Avian Pox

Etiological Agent: Avipoxvirus: fowl, pigeon,
canary
• Reservoir: avian hosts- warm environments
more common
• Transmission: mosquitoes, direct contact,
indirect food/water/cages
• Signs/symptoms: weakness, emaciation,
difficulty swallowing/breathing, vision issues,
edema of eyelids, wart like growths on
unfeathered skin
• Treatment: cutaneous form is usually self
limiting ; remove lesions, supportive care,
prevent secondary infections
• Prevention: vaccination

Cold Sores/ Herpes Gladiatorum

Etiological Agent: Human herpesvirus 1 (HSV-1) and 2 (HSV-2)
• Reservoir: Humans
• Transmission: direct contact
• Signs/symptoms: cold sores or “fever blisters”
• Treatment: control with antivirals
• No cure- latent virus for life.
• Prevention: Good Hygiene/limit exposure
• Special Notes
• Can remain latent in nerve ganglia

Chickenpox

Etiological Agent: Varicella-zoster virus
• Human herpesvirus 3 (HHV-3)
• Reservoir: humans
• Transmission: RESPIRATORY droplets
• Signs/symptoms:
• Causes pustules, itchy
• Treatment: antivirals and supportive care
• Prevention: vaccination
• Special Notes:
• Virus may remain latent in spinal ganglia for life

Shingles

Reactivation of latent HHV-3/Varicella-Zoster
• Why? Stress, age, other infections
• Signs/symptoms: rash along nerve, and nerve pain
• Treatment: Acyclovir may lessen symptoms
• Prevention: live attenuated vaccine

Measles (Rubeola)

Etiological Agent: Measles virus
• Reservoir: Humans
• Transmission: Direct contact, RESPIRATORY
droplets, airborne
• Highly contagious
• Signs/symptoms: macular rash and Koplik's spots,
fever, cough.
• Complications
• Infection causes suppressed immune system for months
to years and can destroy memory cells to previous
infections.
• Pneumonia, blindness, heart failure
• Encephalitis in 1 in 1,000 cases
• Subacute sclerosing panencephalitis in 1 in 1,000,000
cases – likely death.
• Treatment: supportive care
• Prevention: vaccination

Rubella (German Measles)

Etiological Agent: Rubella virus
• Reservoir: Humans
• Transmission: direct; RESPIRATORY
droplets
• Signs/symptoms:
• Postnatal: macular rash and fever
• Congenital rubella syndrome
• Causes severe fetal damage
• Mother can be asymptomatic
• Treatment: supportive care
• fetal damage is permanent
• Prevention: vaccination
• Eradicated in 2014 in U.S

Roseola

Etiological Agent: Human Herpesvirus 6
(HHV-6) and 7 (HHV-7)
• Reservoir: Humans
• Transmission: direct; RESPIRATORY droplets
• Signs/symptoms: High Fever for 1-4 days
followed by a macular skin rash when the
fever breaks.
• Treatment: Supportive Care
• Prevention: limit exposure
• Notes: Common in young children 6 months
– 2 years, very rarely serious

Hand Foot and Mouth

Etiological Agent: Coxsackievirus A16
• Reservoir: human
• Transmission: direct; RESPIRATORY
droplets
• Signs/symptoms: fever, sore throat,
followed by painful red blister-like
lesions on tongue/mouth, hands and
feet
• Treatment: supportive care
• Prevention: Good hygiene/avoid
infected individuals
• Notes: common in childcare settings

Leishmania

Etiological/Causative agent(s): Leishmaniasis spp.
• Type of agent: Protozoan parasite
• Reservoir (if known): dogs, opossums, bats,
anteaters, sloths, marsupials, rodents, and hyraxes
• Transmission: female sandflies (insect bite)
• Characteristic signs/symptoms: Cutaneous Lesion
• Treatment: typically do not treat unless visceral
leishmania disease is suspected
• Prevention: vector protections
• Special Notes
• Common in Middle East, Brazil, and Peru

Conjunctivitis

Conjunctivitis (An inflammation of the
conjunctiva)
• Also called pinkeye or red eye
• Causative Agents:
Viruses: Adenoviruses, Enteroviruses
Bacteria: Haemophilus influenzae, Chlamydia
trachomatis, Neisseria gonorrhoeae
• Transmission: (depends on agent) direct contact,
respiratory
• Signs/Symptoms: red conjunctiva, eye discharge,
if bacterial eyelid often swells.
• Treatment: if bacterial - antibiotics
• Prevention: Good hygiene and proper contact
lens care

Ophthalmia neonatorum

Etiological/Causative agent: Neisseria gonorrhoeae or
Chlamydia trachomatis
• Type of agent: Gram negative diplococci Bacteria
• Reservoir: Humans
• Transmission: vaginal delivery to newborn
• Characteristic signs/symptoms: redness, discharge,
swelling of lids, usually bilateral
• Treatment: antibiotics to eye
• Prevention: prenatal screening
• Special Notes
• If untreated can cause blindness

Trachoma

Etiological Agent: Chlamydia trachomatis
Type of Agent: Gram negative Bacteria
Reservoir: Humans
Transmission: Spread through swimming pool, poor hygiene, flies;
Signs/Symptoms: itchy, redness, discharge, swelling of lids, eye
pain
Treatment: antibiotics to eye
Prevention: hygiene, treatment pool/hot tub,
Special Notes
Without treatment: permanent scarring; scars abrade the
cornea leading to blindness

Keratitis

It is inflammation of the cornea and can cause blindness if untreated.

Transmission: Poor hygiene or swimming in infected water.

Causes:
• Bacterial (U.S.)
• Fungi: Fusarium and Aspergillus (Africa and Asia)
• Acanthamoeba keratitis
• Protozoa
• Transmitted via water
• Associated with unsanitary contact lenses
• Herpetic keratitis
• Caused by herpes simplex virus 1 (HSV-1)

River Blindness

Etiological/Causative agent: Onchocerca volvulus
• Type of agent: Chronic parasitic (helminthic) infection
• Reservoir: Humans
• Transmission: Vector: blackflies
• Characteristic signs/symptoms: The worms eventually
invade the entire eye, producing inflammation and
permanent damage to the retina and optic nerve
• Treatment: ivermectin
• Prevention: vector preventions (DEET, long
sleeves/pants)
• Special Notes
• Second Leading Cause of Blindness (mostly in Africa)

Meningitis

Transmission is respiratory or direct contact mucosal
membranes
• Initial signs/symptoms of fever, headache, and stiff neck
• Followed by nausea and vomiting
• May progress to convulsions and coma
• Treatment:
• Bacterial: if caught early enough antibiotics may help
• Viral: supportive care
• Special Notes:
• High mortality in bacterial meningitis if untreated
• Bacterial meningitis permanent damage: deafness,
blindness, neurological damage
• Viral meningitis is typically much less severe than
bacterial

Haemophilus influenzae Meningitis

Etiological Agent: Haemophilus influenzae
Type of Agent: Gram-negative bacilli
bacteria
• Reservoir: Can be found as normal throat
microbiota
• Prevention: Hib vaccine
• Special Notes: Occurs mostly in children (6
months to 4 years)

Neisseria Meningitis/meningococcal meningitis

Etiological Agent: Neisseria meningitidis
• Type of Agent: Gram-negative bacteria,
diplococci with a capsule
• Reservoirs: 10% of people are healthy
nasopharyngeal carriers
• Sign/Symptoms: Begins as throat infection,
petechiae (rash)
• Prevention: vaccination available
• Notes: Most serious form of acute
meningitis

Streptococcus pneumoniae Meningitis/ Pneumococcal meningitis

Etiological Agent: Streptococcus pneumoniae
• Gram-positive bacteria diplococcus in chains
• S. pneumonia has 90 strains.
• Reservoir: 70% of people are healthy
nasopharyngeal carriers
• Mortality: 30% in children, 80% in elderly
• Prevention: Vaccine Available for most
prevalent strains
• Notes:
• No petechiae associated

Neonatal Meningitis

Etiological Agents
• Group B strep (Streptococcus
agalactiae)
• Gram positive streptococcus bacteria
• E. coli
• Gram negative bacillus bacteria
• Listeria monocytogenes
• Gram positive coccobacilli bacteria
• Notes: Resistant to cold, heat, salt, pH
extremes
• Mom contracts from dairy products
(unpasteurized cheese) or cold cut
meats
• All transmitted to fetus via infected
mother

Cryptococcus neoformans Meningitis

Etiological Agent:
• Filobasidiella neofomans (mold form)
• Cryptococcosis (yeast form)
• Type of Agent: Dimorphic yeast
• Reservoir: birds
• Transmission: mostly pigeon and chicken
droppings
• Signs/Symptoms
• More of a chronic meningitis
• Special Notes
• Problem in immunocompromised patients
• Mortality up to 30%

Coccidioides immitis Meningitis

Etiological Agent: Coccidioides immitis
• Type of Agent: Fungus
• Reservoir: soil
• Transmission: Respiratory
• Signs/Symptoms Usually begins with
pulmonary infection
• San Joaquin Valley Fever
• True systemic fungal infection of high
virulence
• At systemic level will cause meningitis

Viral Meningitis

Etiological Agents: 90% caused by enteroviruses
• Polio and Non-Polio (Coxsackie viruses)
• Signs/Symptoms
• Generally milder than bacterial or fungal meningitis
• Special Notes
• Majority of cases occur in children
• Mortality less than 1%

Acute Encephalitis

Encephalitis can present as acute or subacute
• Always a serious condition
• Acute: almost always caused by viral infection
• Signs and symptoms vary but may include behavior changes,
confusion, decreased consciousness, seizures, somnolence
(sleepiness)

Arboviral Encephalitis

Etiological Agent: Arboviruses
• Arthropod-borne viruses that belong
to several families
• Reservoir: depends on agent –
mammals/birds
• Transmission: Arthropod Vectors
• Signs/Symptoms: acute fever, often
accompanied by rash
• Treatment: supportive care
• Prevention: vector control methods

Herpes Simplex Virus

Can cause encephalitis in
newborns born to HSV-
positive mothers
• Prognosis is poor

Subacute Encephalitis

Symptoms take longer to show up and
are less striking
• Most common cause:
• Toxoplasma
• Measles infection
• Prions

Toxoplasmosis

Etiological Agent: Toxoplasma gondii
• Type of Agent: Flagellated protist
• Reservoir: felines, but also found in livestock
and rodents
• Transmission: fecal/oral; spread in cat feces
or undercooked meat
• Signs/Symptoms
• Most have no symptoms or flu like symptoms
• Some evidence of behavior changes: loss of
coordination/confusion
• Parasite can persist and cause reinfection later.
• Infection in fetus results in still born, or neurological
damage
• Treatment: antiprotozoal drugs
• Prevention: Safe food handling/pregnant
women avoid raw meat and cat feces.

Subacute Sclerosing Panencephalitis (SSPE)

Complication of measles virus
• Appearance years after initial measles infection
• Direct viral invasion of neural tissue

Transmissible Spongiform Encephalopathies (TSEs)

Caused by prions
• Typical diseases in humans
• Creutzfeldt-Jakob disease
• Kuru
• Gerstman-Strussler-Scheinker disease
• Fetal familial insomnia
• Transmission:
• ingestion, inherited, transplant

Neurodegenerative diseases

Long incubation
• Rapid progression once
symptoms appear
• Behavior changes, loss of memory,
coordination problems, blindness,
coma
• Chronic and fatal
• No Treatment
• Prevention is avoidance

Meningoencephalitis

Meningoencephalitis: inflammation of the brain and the meninges
Symptoms are combination of meningitis and encephalitis
Two microorganisms cause meningoencephalitis (both amoebas)

Primary amoebic meningoencephalitis (PAM)

Etiological Agent: Naegleria
fowleri
• Type of Agent: Protozoan
• Reservoir: water
• Transmission: nasal mucosa
• Treatment: supportive care
• Prevention: Avoid contaminated
water source
• Avoid putting head in water
• Special Notes
• Rare but 99% fatal

Granulomatous amoebic meningoencephalitis (GAM)

Etiological Agent: Acanthamoeba
• Type of agent: Large, amoeboid
trophozoite with spiny pseudopods and
a double-walled cyst
• Reservoir: Water
• Transmission: Invades broken skin, the
conjunctiva, and occasionally the lungs
and urogenital epithelia
• Can spread to CNS
• Treatment: Supportive Care
• Prevention: Avoid contaminated water
source
• Avoid putting head in water

Tetanus (Lock Jaw)

Etiological Agent: Clostridium tetani
• Type of Agent: Gram-positive, endospore-
forming, obligate anaerobe bacteria
• Reservoir: soil
• Transmission: wounds with dirt exposure
• Signs/symptoms:
• Spastic paralysis starting with jaw, followed by
back, arms, legs (toxin mediated)
• Treatment: tetanus immunoglobulin (Ig)
• Prevention: vaccination with tetanus
toxoid

Botulism

Etiological Agent: Clostridium botulinum
• Anaerobic gram-positive, endospore-forming bacilli bacteria
• Reservoir: soil
• Transmission:
• Food-borne botulism: ingesting botulism toxin (intoxication)
• Infant botulism results from C. botulinum growing in intestines (do not feed infants honey!!)
• Wound botulism results from growth of C. botulinum in wounds
• Sign/symptoms: flaccid paralysis (toxin mediated)
• Treatment: supportive care and antitoxin
• Prevention: proper canning and addition of nitrites to prevent spore
germination in sausages

Rabies

Etiological Agent: Rabies Virus
• Reservoir: mammals (Raccoons, Bats, Skunks, Foxes)
• Transmission: direct-parenteral (bites) spreads to nerves
and brain
• Signs/symptoms:
• Initial: “flu-like symptoms”
• Progressive: fatal encephalitis – 100% fatal
• Furious: insomnia, confusion, anxiety, hallucinations,
muscle spasms of the mouth and pharynx,
hydrophobia, coma then death.
• Paralytic: unaware, paralyzed, disoriented, stupor
• Treatment: Immediate! Vaccine +rabies immunoglobulin
• Prevention: avoid infected animals and immunize your
pets!
• Also available to high-risk pre-exposure vaccine

Poliomyelitis (Polio)

Etiological Agent: Poliovirus
• Transmission: fecal/oral
• Reservoir: Humans
• Signs/symptoms:
• Initial symptoms: sore throat and nausea
• Viremia may occur; if persistent, virus can enter
the CNS: meningitis
• Destruction of motor cells and paralysis occurs in
<1% of cases
• Treatment: supportive care
• Prevention: vaccination

African Trypanosomiasis/ Sleeping sickness

Causative Agent: Trypanosoma brucei
 Type of Agent Protozoan parasite
 Reservoir: mammals
 Transmission: tsetse fly
 Signs/Symptoms:
 altered behavior, sleep disturbances, low
energy, intermittent fever, joint pain
 Treatment:
 Complex set of multiple drugs. (depend on
stage of disease).
 Without treatment usual fatal
 Prevention:
 Vector Control/Avoidance