ID from Rubin's Q and A

Question 1

Cat-scratch disease; bartonella henselae

Answer 1

Self-limited granulomatous lymphadenitis; g- rods difficult to see without silver stain; associated with cats; claws allow organism to enter as do conjuctiva; common childhood infection; suppurative and granulomatous lymphadenitis,nodes enlarged for 3-4 months, usually stays in local lymphnodes; multiply in walls of inoculation site; parinaud oculoglandular syndrome (preauricular adenopathy secondary to conjunctival infection); antibiotics don’t help.

Question 2

Bacillus anthracis

Answer 2

Rapidly fatal on dissemination; sheep, goats, cattle and their byproducts. G+ spore forming; spores are highly resistant and can reside in soil; cutanious anthrax can be eliminated if nectrotizing toxin fails to allow dissemination; black scabs with only minor infiltrate; Forms: malignant pustule=95% all anthrax, ulcer with purulent purple/black exudate…pumonary anthrax: super dangerous form.. septicemic anthrax can occur in either case..gastrointestinal anthrax rare

Question 3

Rocky Mountain Spotted Fever (rickettsia rickettsi)

Answer 3

Acute, systemic vasculitis transmitted through tick bites. Rash produced by inflammatory damage to cutaneous vessels, spreads to vascular smooth muscle and large vessels. Exudation of fluid and DIC. Rash begins as maculopapular but extends to be petechial, from the distal extremities to the trunk.

Question 4

Giardiasis (giardia lamblia)

Answer 4

Protozoan infection causing infection of the small intestine. They attach to small bowel epithelia and have no grossly visible alterations. Usually a harmless commensal; can cause acute abdominal cramping and frequent, foul-smelling stools. Chronic infection in children may cause malabsorption.

Question 5

Entamoeba histolytica (Amebiasis)

Answer 5

Usually lysis the colon and occasionally the liver. Acquired by ingestion of materials contaminated with human feces. Has pre cyst and infective cyst stages. Grow in the colon, forming lesions and ulcers, sloughing of mucosa. Ameboma occurs when the amebae invade through the intestinal wall. Liquid stools with bloody mucus. If the amebas enter the veins they get to the liver through the portal circulation, killing hepatocytes and producing a necrotic cavity, dark/brown “anchovy paste” material.

Question 6

C. perfringens (gas gangrene)

Answer 6

Necrotizing, gas forming infection. Myotoxin liquefies muscles, skin becomes tense. Necrosis with few neutrophils which are destroyed. Skin darkens because of hemorrhage and cutaneous necrosis. Discharge with gas bubbles.

Question 7

Tuberculosis

Answer 7

Mycobacteria tuberculosis, stain with acid fast. Chronic, communicable disease with lungs as the primary target. Causes a spherical granuloma with central caseous necrosis (Ghon focus). Transmitted via aerosolized droplets. Live in macrophages but resist killing by blocking lysosome fusion. Usually self-limited primary TB, Ghon complexes heal, leaving scarring and calcification. In progressive primary TB, Ghon focus enlarges, middle lobe of lung can collapse. Produces fever, weight loss, and night sweats. Miliary TB occurs when infection produces multiple lesions in several organs; seeding. Secondary TB is a proliferation in someone who had previously contained the infection. Immune response leads to necrosis and production of TB cavities. Cough with hemoptysis, night sweats.

Question 8

Rickettsia typhi (Endemic/Murine Typhus)

Answer 8

Transmitted through fleas, can cause pulmonary infection or attack endothelial cells and cause necrotizing vasculitis. Associated with rat-infested dwellings.

Question 9

C. difficile

Answer 9

Produces an acute necrotizing colitis after antibiotic administration. Produces exotoxins that kill cells and cause fluid secretion. Pseudomembrane of cellular debris, neutrophils, and fibrin forms over infected areas of colon.

Question 10

PCP/Pneumocystis jiroveci

Answer 10

Fungus, causes pneumonia in people with impaired immunity, especially AIDS. Causes progressive consolidation of the lungs. Best visualized with silver. Progressive shortness of breathm, non-productive cough.

Question 11

Respiratory Syncytial Virus

Answer 11

RNA,Bronchiolitis or pneumonitis in children, wheezing, cough, respiratory distress. Causes most problems in children, mild illness in adults

Question 12

E. coli diarrhea

Answer 12

Gram. neg. Enterotoxigenic: traveler’s diarrhea Enteropathogenic: diarrhea in poor tropical area, deforms microvilli. enterohemorrhagic: bloody diarrhea from contaminated meat or milk, hemolytic-uremic syndrome, destroys epithelial cells. Enteroinvase: dysentery, inflammation and erosion of mucosae, similar to Shigella.

Question 13

Syphilis (Treponema pallidum)

Answer 13

Spirochete; STD; chronic; systemic infection; proliferates at site of infection, enters lymph, then blood, long term systemic damage; Stages: Primary Syphilis: Chancres at site of entry with luetic vasculitis; Secondary Syphilis: systemic spread with maculopapular rash on trunk/extremities (palms and soles), see lesion types; Tertiary syphilis: disease goes dormant for years or decades then focal ischemic necrosis is responsible for many damaged sites Syphilitic aortitis: aortic media nectrosis and aneurysm danger likely and aortic valve insufficiency; Neurosyphilis: damage meninges and CNS via progressive infection (see damage types); Benign tertiary syphillis: Gummas of coagulative (granulomatous) necrosis (dont significantly damage); Congenital syphilis is transmitted from an infected mother to the fetus: stillbirth, neonatal illness or death: snuffles and deformed bones/teeth Rx: penicillin

Question 14

Salmonella typhi (typhoid fever)

Answer 14

Acute systemic illness spread by contaminated water and food (dairy and shellfish). Attaches to small-bowel mucosa, invades ileum over Peyer patches. Multiply within macrophages. Systemic dissemination leads to typhoid nodules, granulomas in liver and spleen that are aggregates of macrophages. Malaise, headache, abdominal pain, fever, spleno and hepatomegaly, GI bleeding.

Question 15

Chagas disease (Trypanosoma cruzi)

Answer 15

Protozoa replicate in macrophages and invade cardiac myocytes and brain. Forms localized nodular inflammatory lesions, called chagomas. Acute: enlarges heart, hemorrhagic myocardium, can invade meninges. Chronic: chronic inflammation damages organs; chronic myocarditis, deviated interventricular septum, can cause heart failure. Megaesophague and megacolon can develop because the parasympathetic ganglia and myenteric plexus get destroyed. Congenital: leads to spontaneous abortion or fatal encephalitis

Question 16

Parvovirus

Answer 16

DNA, causes benign erythema infectiosum/5th disease (slapped-cheek, lacy rash), interrupts erythropoiesis. If pt has chronic hemolytic anemia (sickle cell) can cause a potentially fatal anemia called transient aplastic crisis. Nuclei are enlarged with glassy eosinophilic material nuclear inclusion bodies

Question 17

MAI; mycobacterium avium and intracellulare

Answer 17

In immunocompetent people, produces a granulomatous pulmonary disease, resembling TB but progressing much more slowly. Causes pulmonary nodules, cavities, and caseating granulomas. COPD predisposes to it, cough is common but missing other TB symptoms. Opportunistic infection in AIDS (3rd most common opportunistic) due to lack of T cells. Infected macrophages accumulate everywhere. Symptoms similar to TB, including small-bowel involvement with pain and diarrhea.

Question 18

Trichonosis (trichinella spiralis)

Answer 18

Roundworm, acquired by eating inadequately cooked pork that contains skeletal muscle with larvae. Cysts in muscle cause myositis, and extreme eosinophilia. Most infections are asymptomatic, symptomatic is self-limited. Abdominal pain and diarrhea are possible. Infection of the brain and myocardium are also possible.

Question 19

Legionella pneumophila (Legionnaire’s and Pontiac fever)

Answer 19

Gram neg, stains poorly. In water, inhaled aerosols, cooling towers. Bacteria phagocytosed by macrophages, replicate and protect themselves by blocking lysosomes from fusing. They are released and infect new macrophages. Causes acute atypical bronchopneumonia, obtunded and hypoxia may be prominent. Pontiac fever is a flu-like illness, no evidence of consolidation.

Question 20

E. coli UTI, pneumonia, sepsis, and meningitis.

Answer 20

Fecal contamination of UT, sexual intercourse. Ascends from distal urethra, adhere to epithelium. Can ascend to kidneys and cause pyelonephritis. Pneumonia: opportunistic, make salivary protease that degrades fibronectin so gram-neg can overcome gram-positive flora in mouth, proliferation of aspirated organisms. Sepsis: most common cause of enteric gram-neg; opportunistic, neutrophils cant phagocytose bacteria. Also can cause meningitis

Question 21

HPV

Answer 21

Causes common warts, plantar warts, and anogenital warts (6,11), female genital warts (16,18). Cells display koilocytosis, large squamous cells with shrunken nuclei in large cytoplasmic vacuoles.

Question 22

Salmonella enterocolitis

Answer 22

Gram negative rods. Food poisoning 12-48 hours after eating poorly cooked meat, eggs, or dairy. The toxin injures intestinal cells and causes inflammation. Presents with nausea, vomiting, fever; self-limiting for 1-3 days.

Question 23

Varicella-zoster virus

Answer 23

DNA herpesvirus, first pass causes chicken pox, generalized vesicular skin eruption. Cells have large inclusions separated from nuclear membrane by clear zone or halo. Virus then establishes latent infection in dorsal nerve root ganglion. Then herpes zoster/shingles develops, virus travels down sensory nerve from one dermatome, producing a unilateral, painful rash in a dermatomal pattern.

Question 24

Haemophilus Influenzae

Answer 24

Gram negative coccobacillus. Leading cause of meningitis in children under 2. Unencapsulated spread to sterile sites after a virus has destroyed defense mechanisms, eliciting inflammatory responses. Encapsulated bacteria invade tissues, causing bacteremia, bronchopneumonia or lobar pneumonia (lime-green sputum), epiglottitis, septic arthritis, and facial cellulitis (hot, red-blue colored area in cheek or above eye). Vaccine. Childhood.

Question 25

Epstein-Barr (mononucleosis)

Answer 25

DNA; fever, lymphadenopathy, splenomegaly, leukocytosis. Invades and replicates in salivary glands and go into secretions. They infect B lymphocytes, stimulating the production of atypical T lymphocytes with lobulated, eccentric nuclei to kill infected B cells. Develop heterophile antibody, or immunoglobin that reacts with sheep erythrocytes.

Question 26

Listeria monocytogenes (Listeriosis)

Answer 26

Can cause bacterial meningitis, CSF responses may be lymphocyte predominant. Gets phagocytosized, enters lysosome where the acidic pH activates listeriolysin O, disrupting membrane and allowing bacteria to escape cytoplasm. Form elongated protrusions engulfed by adjacent cells so they don’t get exposed to the extracellular environment. Can cause pre and post-natal infections, respiratory distress, neurological deficits, and also cause a systemic disease.

Question 27

Mucormycosis

Answer 27

Fungus, produce sever, necrotizing, invasive opportunistic infections in the nasal sinuses or lungs. Hyphae look like twisted ribbons. Inhaled, cause disease in immunocompromised. Rhinocerebral mucormycosis: proliferate in nasal sinuses; extend into nerves and brain, covers nasal turbinates and palate with black crust, grow into arteries and causes devastating, septic infarction. Extension into brain leads to hemorrhagic encephalitis. Fatal. Pulmonary mucormycosis: resembles aspergillos, vascular invasion with septic infarction. Fatal. Subcutaneous zygomycosis: tropics, enlarging, hard mass.

Question 28

Yellow fever

Answer 28

RNA, acute hemorrhagic fever, extensive hepatic necrosis, black vomiting, and jaundice. Insect-born flavivirus transmitted by Aedes mosquito in Africa and South America. Hepatic cells develop coagulative necrosis, lose nuclei, become eosinophlic and are known as Councilman bodies.

Question 29

Schistosomiasis

Answer 29

Greatest worm cause of morbidity. Hatches in water, enters snail, then penetrates human skin. Basic lesion is a circumscribed granuloma or a cellular infiltrate of eosinophils and neutrophils around an egg. S. mansoni: inferior mesenteric vein, distal colon and liver. S. haematobium: veins of rectum, bladder, and pelvic organs S. japonicum: superior mesenteric vein, damaging small bowel, ascending colon and liver. Mansoni and japonicum cause liver disease with fibrosis and portal hypertension. Haematobium: inflammatory reaction may obstruct urine flow, cause squamous cell carcinoma of the bladder.

Question 30

Leprosy (Mycobacterium leprae)

Answer 30

Chronic, progressive destructive disease involving peripheral nerves, skin, and mucous membranes. Multiply best at temperatures below core body temperatures (extremities) Tuberculoid leprosy: very few lesions on skin, NON-caseating granulomas, nerve fibers infiltrated with lymphocytes. Sensory deficits. Lepromatous leprosy: multiple, tumor-like lesions. Distorts and disfigures face, eyes, eyebrows, lion-like face (leonine facies) Chronic nasal discharge and voice change.

Question 31

Staph epidermidis

Answer 31

Gram positive, coagulase negative. Most common cause of infections on medical devices like catheters, pacemakers, normal bacteria flora. Can form biofilms and present with a low grade fever. Often MDR, many resistant to B-lactam antibiotics.

Question 32

Cryptococcus (cryptococcus neoformans)

Answer 32

Fungal mycosis that affects the meninges and lungs. Found in pigeon droppings, affects people with impaired cell-mediated immunity. Infection goes to brain, causes swelling, causes headache, sleepiness. Also causes diffuse pulmonary progressive disease.

Question 33

Cytomegalovirus

Answer 33

DNA, congenital and opportunistic infection. Fetal: transmitted across the placents, affects brain, inner ears, eyes, causing neurological or hearing defects. Immunocompromised/transplant: varied reaction. Pathology: owl eyed appearance of cells due to giant nucleus with a central inclusion surrounded by a clear zone

Question 34

Listeria mono

Answer 34

.

Question 35

Influenza

Answer 35

RNA, A is the most common type, strains IDed by hemagglutin and neuraminidase types. Spread by respiratory droplets and secretions. Presents with fever, chills, myalgia, headaches, weakness, nonproductive cough. URI and LRI. Predispose to bacterial pneumonia.

Question 36

Lyme disease (Borrelia burgdorferi)

Answer 36

Spirochete, transmitted through tick bite. Stage 1: Erythema chronicum migranes “bulls-eye” rash at site of bite. Accompanied by fever, chills and arthralgias, lymphadenopathy. Stage 2: Muscle aches, cardiac (AV block) and neurologic abnormalities such as meningitis and Nerve palsies. Stage 3: Joint, skin, and neurologic abnormalities.

Question 37

Pseudomonas aeruginosa

Answer 37

Gram neg rod, antibiotic resistant opportunistic pathogen than causes pneumonia by invading blood vessels (dark green sputum), and producing skin lesions called ecthyma gangrenosum (nodular, necrotic lesions where the bug gets to the skin and produces hemorrhagic infarcts). Very aggressive, often causes sepsis. Cystic fibrosis

Question 38

C. botulinum

Answer 38

Spores transmitted in improperly canned foods. Toxin binds to presynaptic nerve terminals and inhibits Ach release. Causes descending paralysis, started with cranial nerves, blurred vision, dysarthria, progressing to neck and breathing muscles, causing resp weakness and death. Treated with antitoxin.

Question 39

Measles (Rubeola)

Answer 39

RNA, URI, fever, rash spreading from face to trunk. Koplick spots (white dots on buccal mucosa), can develop subacute sclerosing panencephalitis (SSPE) years later. Warthin-Fenkeldey giant, mutinucleated cells seen.

Question 40

C. tetani

Answer 40

Release of toxin after organism from soil infects deep wound. Toxin passes thru ventral roots, binds to motor neurons, cleaves protein to mediate exocytosis of synaptic vesicles; release of inhibitory neurotransmitters is blocked, contraction of muscles (tetany). Lockjaw after 1-3 weeks, risus sardonicus (fixed grin) and opisthotonos (backward arching)

Question 41

Group B streptococci

Answer 41

Causes neonatal pneumonia, meningitis, and sepsis. Normally in some women’s vaginal flora, spreads to infants during childbirth. Causes pyogenic infections, especially in premies and babies with low IgG.

Question 42

Staph aureus

Answer 42

Produces suppurative infections of skin, bones, joints and infectious endocarditis (especially in IV drug users on the tricuspid valve). Causes furuncles, styes, carbuncles, scalded skin syndrome (sunburn rash and desquamation), osteomyelitis, respiratory tract infections after viral influenza (sometimes pneumonia), bacterial arthritis, sepsis, toxic shock syndrome (fever, diarrhea, shock, sunburn rash after using tampons), food poisoning (1-6 hrs after eating) Resistant to penicillin and commonly methicillin. Coagulase positive, gram positive.

Question 43

Vibrio cholerae (Cholera)

Answer 43

Gram-negative rod, spread by polluted water. Produes the exotoxin cholera toxin, does not invade mucosa of intestine. Toxin increases cAMP, causing secretion of sodium and water into lumen of small bowel. Stools are flecked with mucus (rice-water), oral rehydration is necessary. Vibrio parahaemolyticus causes acute gastroenteritis from poorly cooked seafood.

Question 44

Klebsiella and Enterobacter

Answer 44

Gram neg bacilli, nosocomial necrotizing lobar pneumonia with currant jelly sputum, inhaled into lungs, exudate accumulates, compressed and necrotic walls; leads to cavitation. Thick mucoid sputum forms.

Question 45

Entamoeba histolytica (Amebiasis)

Answer 45

Usually lysis the colon and occasionally the liver. Acquired by ingestion of materials contaminated with human feces. Has pre cyst and infective cyst stages. Grow in the colon, forming lesions and ulcers, sloughing of mucosa. Ameboma occurs when the amebae invade through the intestinal wall. Liquid stools with bloody mucus.

Question 46

Strep pneumoniae (pneumococus)

Answer 46

Gram positive, causes lobar pneumonia with rust colored sputum, otitis media, sinusitis, and meningitis. Organism gains access to sterile sites, usually after a viral infection. Capsule prevents alternative complement pathway, no phagocytes.

Question 47

Malaria. Plasmodium vivax, ovale, falciparum, malarie.

Answer 47

Mosquito-borne, hemolytic, febrile illness caused by protozoa. Destroys RBC, causing chills, dever, anemia and splenomegaly. P. falciparum causes malignant malaria; no hepatic stage, parasitizes RBC of any age, not just old or young, so there is marked parasitemia and anemia. There may be several parasites per cell. Causes infected RBC to adhere to endothelial cells, obstruction produces ischemia. Hepatosplenomegaly as RBC are sequestered. Paroxysms of chills and high fever.

Question 48

Parainfluenza

Answer 48

RNA, causes URI and LRI, causes croup, characterized by stridor on inspiration and a “barking” cough due to edema of laryngotracheitis.

Question 49

Neisseria gonorrhoeae (gonococcus)

Answer 49

Gram-negative diplococcus. In women, creates endometritis and PID, sometimes going to fallopian tubes and creating violin string adhesions between liver and parietal peritoneum, in men, urethritis and dysuria with occasional urethral stricture and discharge. Neonatal infections can result in conjunctivitis. Bacteria hav pili to prevent phagocytosis, and IgA-ase to facilitate attachment to epithelium of the urogenital tract. STI. Can causes sterility

Question 50

Leishmaniasis

Answer 50

Protozoan infection transmitted by insect bites, particularly sandflies. Localized cutaneous leishmaniasis: Protozoa invade macrophages and ulcerate the overlying skin, which eventually becomes a granuloma. It forms an itching, solitary papule which erodes to become the ulcer with a sharp, raised border. Diffuse cutaneous can form with multiple nodules and look like leprosy. Mucocutaneous leishmaniasis: Leishmania braziliensis; Ulcer expands and resolves, then an ulcer develops at a mucocutaneous junction, like larynx, nasal septum, anus or vulva. It erodes mucosal surfaces, can destroy the nasal septum. Visceral leishmaniasis: Disease spreads tough mononuclear phagocyte system; Liver, spleen, and lymph nodes become enlarged as macrophages get parasitized. Weight loss, hepatosplenomegaly, anemia, thrombocytopenia, and skin darkening.

Question 51

Chlamydia

Answer 51

Spirochete C. Trachomatis: genital epithelial infections; urethritis, up to PID in women. Can also cause inclusion conjunctivitis Many infections are asymptomatic. Also can cause lymphogranuloma venereum; genital ulcer that spreads to lymph nodes and causes a necrotizing lymphadenitis. Can cause trachoma blindness. C. psittaci: pneumonia transmitted to humans from birds. C. pneumoniae: usually causes mild respiratory infections, only continuing to severe pneumonia if there is an underlying pulmonary condition.

Question 52

Streptococcus pyogenes

Answer 52

Group A, causes the nonsuppurative diseases rheumatic fever and poststreptococcal glomerulonephritis. Causes suppurative diseases. Causes strep throat, scarlet fever (punctate red rash in pharyngitis, tongue has yellow-white coating, caused by erythrogenic toxin), erysipelas (erythematous swelling of the skin, begins on face, acute inflammatory rxn), impetigo/pyoderma (intraepidermal infection, purulent exudate, red papules then pustules, then honey-colored crust), cellulitis, and puerperal sepsis (post-partum infection of uterine cavity). Can cause sub-acute endocarditis

Question 53

Calymmatobacterium granulomatis (Granuloma inguinale)

Answer 53

Gram negative bacillus, superficial ulceration of genital, inguinal, and perianal region in tropical areas. Raised, soft, beefy-red superficial ulcer; macrophages have bacteria (Donovan bodies), heal with atrophic scar, if lymphatics are obstructed elephantiasis may develop.

Question 54

Common cold

Answer 54

RNA viruses, rhinovirus, coronavirus. Infects respiratory epithelium, causing increased mucus production, nasal congestion, cough. Spread by secretions. URI

Question 55

Pinworm (enterobius vermicularis)

Answer 55

Intestinal nematode, most common in young children. Deposits eggs in perianal skin, which can be transmitted person to person. Causes perineal itching.

Question 56

Clostridia perfringens (food poisoning)

Answer 56

Gram pos, spore forming, obligate anaerobic. Causes benign diarrheal disease 8-24 hours after food that was not refrigerated is ingested. Grows in anaerobic conditions, sporulates in aerobic conditions, releasing exotoxins, causing enterocytes to release ions and fluid. Also causes necrotizing enterocolitis. New Guinea children. Green, necrotic pseudomembranes in small intestine.

Question 57

Camplyobacter jejuni

Answer 57

Most common cause of bacterial diarrhea in developed world. Causes a diarrhea illness from contaminated food and water, superficial enterocolitis in terminal ileum and colon. Progress to small ulcers and inflammatory exudates, crypts fill with neutrophils and form crypt abscesses. Many stools per day, can contain blood and mucus. Associated with Guillain-Barre syndrome.

Question 58

Neisseria meningitides (meningococcus)

Answer 58

Gram-negative cocci, paired. Disease a result of endotoxin LPS, can be confined to CNS and cause meningitis or disseminate and cause septicemia. This damages the blood vessels causes widespread petechiae and purpura, even gangrene. Waterhouse-Fridreichsen syndrome causes hemorrhagic necrosis of adrenals. Childhood. Can cause a rash with meningitis

Question 59

Hookworm (necator americanus and ancylostoma duodenale)

Answer 59

Intestinal nematodes that infect the small bowel, lacerating it and causing heavy blood loss and anemia. Penetrate skin, go into veins to lungs, burst through alveoli, migrate up trachea to glottis and are swallowed to get to the bowel. Most important cause of chronic anemia worldwide.

Question 60

HSV1 and HSV2

Answer 60

DNA: 1: disease above the waist 2: below the waist. Infects epithelial cells, then goes latent in nerve cells, and returns back down the nerve cell to the epithelium upon activation. Reactivation can be triggered by sunlight, menstruation, or stress. Herpes encephalitis is a rare infection where the virus goes to the brain. Neonatal herpes from maternal genital herpes. Asceptic meningitis. Prodromal tingling, followed by vesicular lesions; esophagitis in AIDS patients.

Question 61

Mycoplasma pneumonia

Answer 61

Mycoplasma are the smallest prokaryotes, don’t have rigid cell walls. Causes acute, self-limiting usually non-productive pneumonia, atypical. It affects mostly children and young adults, can also cause pharyngitis and otitis media.