Infections and Diseases

Staphylococcus aureus

Type: bacteria, Gram (+) cocci
Disease: skin infections with pus, boils, impetigo
Pathogenesis: opportunistic; breaks in skin that allows for infections, inhibits phagocytosis, causes pus formation, separates dermis from the epidermis (exfoliative skin) ➜ sloughing skin
Treatment: non-penicillin antibiotic (if MRSA), vancomycin

Camida albicans

Type: fungi, dimorphic yeast/mold
Disease: candidiasis (yeast infection), thrush
Pathogenesis: opportunistic; can invade when the immune system is weak or bacterial normal flora skin is killed due to antibiotics
Treatment: topical anti-fungal creams (over the counter), Amphotericin B

Giardia lamblia

Type: protozoa
Disease: giardiasis (diarrhea; inability to absorb fatty acids)
Pathogenesis: cysts ingested and becomes trophozoite in the small intestines ➜ trophozoites attach to the epithelial tissue ➜ inflammation ➜ interferes with the absorption of food and fluids
Treatment: metronidazote (anti-protozoan drug)

Enterobius vermicularis

Type: helminth (worm), pinworm
Disease: enterobiasis, intestinal infection, nocturnal anal itch
Pathogenesis: eggs are ingested and hatched in the duodenum ➜ females emerge at night and lay eggs around the anus ➜ itching
Treatment: mebendazole (oral anti-helminth drug)

Herpes Simplex Virus I (HSVI)

Type: DNA virus, enveloped
Disease: cold sores (ulcerative lesions on the gums and lips)
Pathogenesis: enters through oral contact with the infected host ➜ replicates in the epithelial cells ➜ vesicles ➜ virus ascends the sensory neuron to the posterior root ganglion
Treatment: Acyclovir (anti-viral) before vesicles form

PrPSc prion

Type: prion
Disease: Creutzfeldt-Jakob's Disease (CJD); degeneration of the ONS ➜ dementia, abnormal motor function ➜ death
Pathogenesis: PrPSc (misfolded protein) converts a PrPc (normal protein) into PrPSc ➜ PrPSc aggregates to form deposits in the brain ➜ vacuoles
Treatment: none

Yersinia pestis

Type: bacteria, Gram (-) rod
Disease: plague (fatal infection of the lymph nodes or lungs); lymphs = bubonic; lungs = pneumonic
Pathogenesis: fleas transmits bacteria during blood meal ➜ bacteria is phagocytized, then carried to the lymph nodes (protected by the antiphagocytic antigen) ➜ lymph nodes swell ➜ bacteria into blood ➜ other organs (septicemic)
Treatment: Doxycycline (adults), Ciprofloxacin (children)

Bacillus anthracis

Type: bacteria, Gram(+) pod
Disease: anthrax
Pathogenesis: endospores are inhaled or ingested or enters the skin ➜ inhaled / ingested: germinate in the lungs / GI capsule prevents phagocytosis, releases toxins; swelling and necrosis leads to death OR skin: painless ulcer with a black center (eschar)
Treatment: penicillin (antibiotics)

Treponema pallidum

Type: bacteria Gram (-) spirochete (spiral)
Disease: syphilis (STI with 4 characteristic stages)
1. Primary: painless ulcer at the site of inoculation (chancre)
2. Secondary: swollen lymph nodes and skin rash
3. Latent Stage: no symptoms
4. Tertiary: irreversible damage to the heart, blood vessels, brain, eyes
Pathogenesis: bacteria enters via mucous membranes of the genitalia ➜ lymph ➜ blood ➜ bacteria disseminates into the skin ➜ evades the immune system by slow dividing time ➜ invades the rest of the body
Treatment: penicillin or doxycycline (oral antibiotics)

Corynebacterium diptheriae

Type: bacteria, Gram (+) pleomorphic
Disease: diphtheria (sore throat, fever, blocked airways)
Pathogenesis: inhaled and attaches to the back of the throat ➜ diphtheria toxin produced ➜ kills cells, inflammation, pseudo membrane ➜ pseudo membrane can asphyxiate, toxins in the blood ➜ heart and CNS damage
Treatment: penicillin and antitoxin

Neiserria gonorrhoeae

Type: bacteria, Gram (-) diplococci
Disease: gonorrhea (urethritis, cervicitis, with excessive discharge)
Pathogenesis: attaches to the epithelial cells of the urethra or cervix ➜ inflammation leads to neutrophil infiltration ➜ causes pus
Treatment: azithromycin doxycycline

Streptococcus pyogenes

Type: bacteria, Gram (+) cocci
Disease: pharyngitis (strep throat), necrotizing fasciitis (flesh eating disease), rheumatic fever
Pathogenesis: bacteria uses M protein to bind and prevent phagocytosis ➜ produces several toxins and virulent factors
1. Hyaluronidase: spreads infection ➜ blood
2. Erythrogenic toxins: vasodilation (redness, shock)
3. Streptolysins: lyse RBC
Treatment: penicillin (prevents rheumatic fever)

Sreptococcus pneumoniae

Type: bacteria, Gram (+) cocci
Disease: pneumonia, bacterial meningitis
Pathogenesis: capsules allow bacteria to attach, invade, and resist phagocytosis; spreads to blood ➜ CSF
Treatment: penicillin

Borrelia burgdorferi

Type: bacteria, Gram (-) spirochete
Disease: Lyme disease (tick-borne infection of the joints, nervous system, skin)
Pathogenies: bacteria enters during tick blood meal; 3 stages:
1. Stage 1: erythema migrans lesion (bullseye rash) at bite site
2. Stage 2: bacteria spread ➜ blood ➜ multiple erythema migrans
3. Stage 3: spreads to joints, nervous system, leads to inflammation
Treatment: amoxicillin or doxycycline

Mycobacterium tuberculosis

Type: bacteria, Gram (+) rod
Disease: tuberculosis (lung infection with tubercles, persistent cough with blood and sputum)
Pathogenesis: bacteria is inhaled and penetrates into the alveoli ➜ macrophages phagocytize, but bacteria can replicate inside (mycolic acid) ➜ formation of tubercles ➜ lung damage
Treatment: isoniazid, ethambutol, rifampin (antibodies against Myobacterium)

Mycoplasma pneumoniae

Type: bacteria, no cell wall, flask shape
Disease: atypical pneumonia ("walking pneumonia")
Pathogenesis: bacteria inhale and bind to ciliated epithelial cells using PI protein ➜ bacteria secretes H2O2 and toxins ➜ ciliostasis, sloughing of cells
Treatment: erythromyocin or tetracycline (non-cell wall antibiotics)

Clostridium tetani

Type: bacteria Gram (+) rod
Disease: tetanus (uncontrollable muscle contraction - lock jaw)
Pathogenesis: endospores enter via deep tissue wound ➜ germinate in anaerobic environment and produces tetanus toxin ➜ toxin moves up nerves to CNS, interferes with muscle contraction inhibition ➜ tetanus
Treatment: antitoxin, antibiotics, or booster vaccine (immediately after exposure)

Myobacterium leprae

Type: bacteria, Gram (+) rod, obligate intracellular
Disease: bacteria gains access to skin and peripheral nerve tissue ➜ replicates inside Schwann cell (2 week generation time) ➜ Phenolic glycolipid-1 (PGL-1): demyelination of neurons ➜ loss of sensation ➜ damage / secondary infection of extremities
Treatment: combination of antibiotics with rifampin

Varicella Zoster Virus (VZV)

Type: DNA virus, enveloped
Diseases:
chicken pox: vesicular rash, head / trunk ➜ extremities (children)
shingles: painful vesicular lesions along a nerve (adults)
Pathogenesis: virus infects epithelial cells of the nasopharynx ➜ replication ➜ viremia ➜ rash; virus remains latent (dormant) in the dorsal root ganglia (spine); when immune system is suppressed, it emerges along the nerve
Treatment: acyclovir (controlling, not eliminating)

Influenza A Virus

Type: RNA virus, enveloped
Disease: influenza (fever, chills myalgia, sore throat, cough) ➜ replicates in cells and destroys ➜ inflammation, edema (swelling)
Pathogenesis: virus infects respiratory epithelial cells
1. Neuraminidase: helps with entrance and exit (budding)
2. Hemagglutinin: binding protein
Treatment: self resolving, oseltamivir

Pseudomonas aeruginosa

Type: bacteria Gram (-) rod
Disease: opportunistic infection of lung, skin, urinary tract
Pathogenesis: bacteria binds to tissue with pili ➜ produces numerous virulent factors:
1. alginate capsule: evades phagocytosis, biofilm
2. exotoxin A: kills cells
3. elastase: tissue damage
Treatment: combination of antibiotics with gentamicin

Malassezia furufur

Type: dimorphic fungus
Disease:
1. Tinea versicolor: hypo- or hyperpigmentation patches; hypo = lighter; hyper = darker
2. Dandruff: dry flaking skin on scalp
Pathogenesis: fungi part of resident flora (lipophilic) ➜ overgrows on oily skin (lipases) ➜ acids ➜ flaking skin; pigmentation caused by:
a. UV absorbing capacity: blocks UV
b. Azelaic acid: damage to melanocytes
Treatment: zinc pyrithione shampoo (for dandruff), clotrimazole (topical)

Trichophyton rubrum

Type: dimorphic funcgus
Diseases: dermatophytoses -- tinea - "jock itch", "athlete's foot", "ring worm"; redness, itching scaling
Pathogenesis: fungus enters minor lesions in the stratum corenum (top layer of the skin) ➜ spreads laterally, tries to stop / suppresses the immune system response ➜ immune system ➜ inflammation ➜ shed skin fungus
Treatment: clotrimazole (topical)

Sporothrix shcenckii

Type: dimorphic fungus
Diseases: sporotrichosis -- "rose-gardener's disease", hard nodules or lesions at the trauma site nd along the lymphatic channels
Pathogenesis: fungi inoculated through a break in the dermis; melanin: enhances resistance to phagocytes ➜ forms painless nodules ➜ ulcers ➜ ascend lymphatic pathway (dissemination -- rare)
Treatment: itraconazole (oral), potassium iodide (oral, classical)

Coccidioides immitis

Type: dimorphic fungus
Diseases: coccidioidomycosis -- "valley fever"; respiratory infection, disseminated infection - skin, bones joints, CNS
Pathogenesis: spores are inhaled, grow in lungs ➜ spherules (tumor-like masses) ➜ inflammation ➜ fever ➜ spreads to the lymphatic system ➜ blood ➜ inflammation in skin, CNS, bones
Treatment: ketoconazole (oral), amphotericin B (injection, for severe cases)

Trichomonas vaginalis

Type: protozoa (Mastigophora)
Disease: trichomoniasis (females: vaginitis, foul smelling vaginal discharge, painful urination; males: asymptomatic)
Pathogenesis: protozoa transmitted through sexual intercourse ➜ adhesion to vaginal epithelial cells (pH dependant)
1. Cysteine protease: adhesion, lysing RBC
2. Contact Detachment Factor (CDF): cytoxic, detaches cells
Treatment: metronidazole

Balantidium coli

Type: protozoa (Gliophora)
Disease: Balantidiasis -- dysentery (bloody mucoid stool) - rare
Pathogenesis: ingestion of cyst from fecal contaminated foods ➜ trophozoite replicate in the large intestines - proteases: kills cells ➜ trophozoites feed on tissue fragments ➜ encystment
Treatment: metronidazole, tetracycline

Plasmodium falciparum

Type: protozoa (Apicomplexa)
Disease: malaria -- mosquito-borne and liver infection, fever, chills
Pathogenesis: sporozoites enter blood during a mosquito blood ➜ sporozoites infect liver ➜ shizogony ➜ merozoites ➜ merozoites infect RBC ➜ shcizogony ➜ lyse RBC ➜ release of waste, toxins, and more merozoites (fever, vessel obstructions)
Treatment: quinine, chloroquine (anti-malarial drugs)

Toxoplasma gondii

Type: protozoa (Apicomplexa)
Disease: toxoplasmosis
1. acquired: asymptomatic (behavior modification?)
2. congenital: serious multiorgan disease, permanent damage to fetus
Pathogenesis: ingestion of oocysts (from cat feces) ➜ infects liver ➜ tachyzoites ➜ infects macrophages ➜ spread
a. fetus: transplacental, infecting eyes, liver, kidney, and brain
b. adults: immune system suppresses, cysts, remain latent
Treatment: pyrimethamine-sulfadiazine