Infectious disease Flashcards

Question

What is the route of transmission of Hepatitis E? A Sexual intercourse B Faecal-oral C Injection-blood borne D Respiratory droplet

Answer 1

B Explanation Hepatitis E is an enterically transmitted water-borne infection that occurs primarily in young to middle aged adults. HEV is a zoonotic disease with animal reservoirs: monkeys, cats, pigs and dogs. Extra: a nice way to remember "Vowels" (hAv and hEV) hit the bowels

Answer 2

B Explanation Hepatitis vaccination program should occur at ages: 0, 2, 4 , 6 months Hepatitis A is faecal oral spread (water-food). There is an increase of attracting hepatitis E Blood products are heavily screened in Australia and the risk in negligible Horizontal spread of hepatitis B can occur through minor breaks in the skin and mucous membranes. Therefore, healthcare workers, day care workers, sexual workers are all at increased risk and should be immunized. I have left the answer as day care workers. The recommendation to get vaccinated following blood transfusions or risk of hepatitis A exposure does not apply to every one Extra: form QLD health People who work with children All people working with children, including: staff and students working in early childhood education and care correctional staff working where infants/children cohabitate with mothers school teachers (including student teachers) outside school hours carers child counselling services workers youth services workers Influenza Measles Mumps Rubella (German measles) Whooping cough (pertussis) Chickenpox (varicella) Staff working in early childhood education and care As above plus hepatitis A Extra: form immunise.health.gov.au This further reduces the residual risk of hepatitis B transmission through transfusion in Australia, to approximately 1 in 982 000 per unit transfused. However, persons with clotting disorders who receive blood product concentrates, persons with recurrent transfusion requirements, and persons with underlying immunocompromise have an elevated risk of hepatitis B virus infection, and should therefore be vaccinated. Combination hepatitis A/hepatitis B vaccines should be considered for susceptible persons in whom both hepatitis A and hepatitis B vaccines are recommended, including: travelers to, and expatriates living in, moderately to highly endemic areas for hepatitis A and B persons whose lifestyle puts them at increased risk of hepatitis A and hepatitis B (sexually active men who have sex with men, sex industry workers, persons who inject drugs and inmates of correctional facilities) persons who attend or work at residential or non-residential facilities for people with developmental disabilities persons with occupational risks of exposure to both hepatitis A and hepatitis B persons with chronic liver disease and/or hepatitis C solid organ transplant liver recipients or solid organ transplant recipients who have chronic liver disease

Answer 3

D Explanation Incubation periods Hepatitis A: 2-6 weeks Hepatitis B: 2-26 weeks (mean 8w) Hepatitis C: 4-26 weeks (mean 9w) Hepatitis D: 2-26 weeks (mean 8w) Hepatitis E: 4-5 weeks Note: Hep B and C incubation periods have changed AGAIN in the latets editions of Robbin's Extra: from a user-who has tried to make sense of all of the changes From a bit of digging on reputable websites it seems that the consensus is HepB incubation min is 4 weeks and HepC is 2 weeks. It looks as though the textbook diagrams are correct and the text is back to front. In the 10th ed they fixed the typo for HepB but not HepC. Robbins & Cotran Pathologic Basis of Disease 9th Ed HepB Text: HBV has a prolonged incubation period (2 to 26 weeks). HepB Diag: 4–26 weeks (average 8) HepC Text: The incubation period for HCV hepatitis ranges from 4 to 26 weeks, with a mean of 9 weeks. HepC Diag: 2–26 weeks (mean 6–12) Robbins & Cotran Pathologic Basis of Disease 10th Ed HepB Text: HBV has a prolonged incubation period (4 to 26 weeks). HepB Diag: 4–26 weeks (average 8) HepC Text: The incubation period for HCV hepatitis ranges from 4 to 26 weeks, with a mean of 9 weeks. HepC Diag: 2–26 weeks (mean 6–12)

Answer 4

B Explanation Chlamydia is the most common sexually transmitted bacterial disease in the world. Chlamydia is the most frequent infectious cause of female infertility and blindness (chronic conjunctival scarring). It is a gram-negative bacterium that is an obligate intracellular parasite. Lymphogranuloma venereum is a genital infection caused by the L serotype of C. trachomatis. It is a chronic ulcerative disease of the genitalia. It is sporadic in the USA but endemic in parts of Africa, Asia, Caribbean and South America. PCR tests are more sensitive than cultures. Different serotypes cause different diseases: L types-lymphogranuloma venereum. D to K types- urogenital and conjunctival infections. A, B and C- ocular infections of children (trachoma)

Answer 5

B Explanation In bacterial septic arthritis the bacteria usually seed the joint during an episode of bacteraemia. Joints can become infected by direct inoculation or from contiguous spread from a soft tissue abscess or focus of osteomyelitis. H. influenza arthritis predominates in children <2yrs. Staf is the main causative agent in older children and adults. Gonococcus is prevalent during late adolescence and young adulthood. Those with sickle cell anaemia are prone to infection with SALMONELLA at any age. These joint infections affect the sexes equally except for gonococcus which is seen mainly in sexually active women. In 90% of non-gonococcal cases, the infection involves only a single joint, usually the knee followed in frequency by the hip, shoulder, elbow, wrist and sternoclavicular joints. Note: the wording of the textbook is confusing: late adolescence and young adulthood- a web search gives this age 18-24yrs. Older children and adults- overlaps the 18-24 age bracket as well. The wording however, comes directly from the textbook. I think that the stem which says "The main causative organism in adults is gonococcus" is incorrect because it should say YOUNG adults

Answer 6

D Explanation Polio invades the CNS and replicates in the motor neurons of the spinal cord and brainstem. Commonly the anterior horn motor neurons of the spinal cord are involved. The posterior horns of the spinal cord and the cranial motor nuclei are sometimes involved. It does not involve the dorsal root ganglion = Trunk ganglion which is located adjacent to the spine on a dorsal root and contains the cell bodies of afferent sensory nerves.

Answer 7

E Explanation The characteristic measles rash is classically described as a generalised maculopapular erythematous rash. It starts on the head and trunk before spreading to cover most of the body. Morphology: The blotch reddish brown rash of measles is produced by dilated skin vessels, oedema, and a moderate nonspecific mononuclear perivascular infiltrate. In the mouth-Koplik spots- are ulcerated mucosal lesions near the duct of Stensen are marked by necrosis, neutrophilic exudate and neovascularization. Extra: measles is a single stranded RNA virus of the paramyxovirus family. There is only one serotype. It is spread by respiratory droplets. Antibody-mediated immunity to the virus prevents reinfection. Measles can also produce severe immunosupression in patients resulting in secondary bacterial and viral infections responsible for much of the measles related morbidity and mortality. Note: Measles - Maculopapular eruption starting on upper trunk and spreading downward. Erythema toxicum neonatorum-pustules on an erythematous base. Chickenpox begins as a maculopapular rash, then becomes vesicular. Shingles appear as painful vesicles in a dermatomal distribution. Human parvovirus B19 (fifth disease or erytherma infectiosum) has a "slapped cheek" appearance and lacy reticular pattern.

Answer 8

A Explanation Bacillus anthracis is a large, spore forming gram + rod bacterium. Common in farm and wild animals that come into soil contaminated with the bacteria spores. B. anthracis is typically acquired through exposure to animal or animal products like wool or hide. 3 major anthrax syndromes occur: cutaneous anthrax, inhalational anthrax and gastrointestinal anthrax. Cutaneous anthrax- makes up 95% of infections. Begins as a vesicle which ruptures and is then covered by a black eschar. It dires and falls off. Bacteraemia is rare. Inhalational anthrax- fever cough and hypoxia, bacteraemia develops which leads to shock and frequently death. Menigitis can develop form the bacteraemia. Extra: Bacillus anthracis is a large, spore forming gram positive rod bacterium. It is commonly found in farm and wild animals that have contact with soil contaminated with the bacteria spores. B. anthracis is typically acquired through exposure to animal or animal products like wool or hide. o It produces potent exotoxin which has A and B subunits. 3 major anthrax syndromes occur: cutaneous anthrax, inhalational anthrax and gastrointestinal anthrax. Cutaneous anthrax account for 95% of infections and begin as vesicles which ruptures and is then covered by a black eschar. It dries and falls off. Bacteraemia is rare. Inhalational anthrax begins with a prodoromal illness lasting 1-6 days with features consistent of fever, cough and chest or abdominal discomfort followed by an abrupt onset of worsening fever, hypoxia and sweating. Haemorrhagic mediastinitis and meningitis can develop from the bacteraemia. Inhalational anthrax rapidly leads to shock and frequently death within 1 to 2 days. GIT anthrax is uncommon. It is usually contracted from ingestion of undercooked meat contaminated with B. anthracis. Initially causes nausea, abdominal pain and vomiting followed by severe bloody diarrhoea. Mortality >50% GIT anthrax: uncommon. After exposure to uncooked meat. Severe bloody diarrhoea develops which leads to death in 50% of cases. The exo-toxin is potent and has an A and B subunit.

Answer 9

B Explanation A burn site is ideal for growth of microorganisms. The serum and debris provide nutrients and the burn injury compromises blood flow, blocking effective inflammatory responses. As a result, almost all burn become colonised. Infections of the burn site is defined by the presence of greater than 105 bacteria per gram of tissue. The most common offender is Pseudomonas aeruginosa, but antibiotic resistant strains of other common hospital acquired bacteria eg S. aureus and fungi particularly Candida may also be involved.

Answer 10

C Explanation The diagnosis of Epstein-Barr virus depends on the following findings (in increasing order of specificity) 1 - Lymphocytosis with the characteristic atypical lymphocytes in the peripheral blood 2 - Monospot test +=heterophile antibody reaction 3 - Specific antibodies for EBV antigens (viral capsid antigens, early antigens, nuclear antigens). In most patients EBV resolves in 4-6weeks, but in some, fatigue lasts longer.

Answer 11

C Explanation The outcome of EBV infection in a normal immune-competent patient is either asymptomatic or mononucleosis-pneumonitis, hepatitis, splenitis, meningitis and encephalitis. In the setting of immunodeficiency, EBV is implicated in the development of EBV positive tumours (which are usually but not always derived form B cells) B cell lymphoma, nasopharyngeal Ca, Hodgkin and non-Hodgkin lymphomas and Burkitt lymphoma. Extra: The current text book reports the following regarding EBV and leukaemia "EBV in young children classically presents with fever, sore throat, lymphadenitis, and the other features mentioned earlier. However, malaise, fatigue, and lymphadenopathy are the common presentation in young adults with infectious mononucleosis and can raise the spectre of leukemia or lymphoma" Web search: Pubmed Infection with Epstein-Barr virus (EBV) may be correlated to the onset of acute leukemia (AL). https://pubmed.ncbi.nlm.nih.gov/28225168 Cancer.org EBV infection increases a person’s risk of getting nasopharyngeal cancer(cancer of the area in the back of the nose) and certain types of fast-growing lymphomas such as Burkitt lymphoma. It may also be linked to Hodgkin lymphoma and some cases of stomach cancer . EBV-related cancers are more common in Africa and parts of Southeast Asia. Overall, very few people who have been infected with EBV will ever develop these cancers. Not entirely clear if EBV actually causes ALL.

Answer 12

A Explanation Clostridial infections, including clostridium botulinum and clostridium tetani, produce muscle paralysis. Clostridium botulinum, botulism toxin, eaten in contaminated foods or absorbed from foods, binds gangliosides on motor neurons and is transported into the cell. The toxin cleaves a protein, synaptobrevin, which prevents the release of Ach at the neuromuscular junction. This results in FLACCID PARALYSIS. Clostridium tetani, tetanus toxin, is similar to that of the botulism toxin, but tetanus toxin causes a violent SPASTIC PARALYSIS by blocking the release of γ-aminobutyric acid, a neurotransmitter that inhibits motor neurons.

Answer 13

C Explanation Campylobactor is the most common bacterial enteric pathogen is developed countries and is an important cause of traveller’s diarrhoea. Most infections are associated with improperly cooked chicken but can occur due to unpasteurised milk and contaminated water. Shigella has 4 major recognised strains. Shigella are unencapsulated non motile facultative anaerobes. Salmonella cause fevers which lasts for 2 days, but diarrhoea can persist for 2 weeks. S.Typhi causes typhoid fever endemically, but S. Paratyphi is more common amongst travellers, probably due to the vaccine against S.Typhi. Salmonella can survive in gastric contents

Answer 14

B Explanation Campylobacter Jejuni is the most common bacterial enteric pathogen is developed countries and is an important cause of traveller’s diarrhoea. Most infections are associated with improperly cooked chicken but can occur due to unpasteurised milk and contaminated water. Campylobacter has 4 major virulence properties: motility, adherence, toxin production and invasion. It contains flagella that allow it to be motile. This facilitates adherence and colonisation, which is necessary for mucosal invasion Extra intestinal manifestations include: arthritis, Guillain Barre Syndrome. Clinical: ingestion of as little as 500 C. Jejuni can cause disease. Incubation period up to 8 days. Watery diarrhoea with or following acute prodrome flu like illness is the primary symptom and dysentery develops in 15% of patients. Patients may shed bacteria up to one month following clinical resolution. Antibiotics are generally not required

Answer 15

A Explanation The characteristic measles rash is classically described as a generalised maculopapular erythematous rash. It starts on the head and trunk before spreading to cover most of the body. Morphology: The blotch reddish brown rash of measles is produced by dilated skin vessels, oedema, and a moderate nonspecific mononuclear perivascular infiltrate. In the mouth-Koplik spots- are ulcerated mucosal lesions near the duct of Stensen are marked by necrosis, neutrophilic exudate and neovascularization.-pathognomonic of measles. Classic signs and symptoms of measles include four-day fevers and the three Cs- cough, coryza and conjuctivitis along with fever and rashes Extra: measles is a single stranded RNA virus of the paramyxovirus family. There is only one serotype. It is spread by respiratory droplets. Antibody-mediated immunity to the virus prevents reinfection. Measles can also produce severe immunosuppression in patients resulting in secondary bacterial and viral infections responsible for much of the measles related morbidity and mortality.

Answer 16

D Explanation This question can be in an EMQ format Giant cell (temporal) arteritis is rare before age 50. Symptoms: Vague, constitutional- fever, fatigue and weight loss. Facial or head pain along the course of the superficial temporal artery, painful to palpation Ocular symptoms: (involvement of the ophthalmic artery) appear abruptly in 50% of people. The symptoms range from diplopia to acute vison loss. Diagnose depends on biopsy and histologic confirmation Treatment: corticosteroids or anti-TNF therapies are usually effective Other stem options include: Takayasu arteritis, Wegeners granulomatisis, Churg-strass syndrome and microscopic polyangitis

Answer 17

B Explanation This question can be in an EMQ format Kawasaki disease Self-limiting childhood acute febrile illness. (80% occur in <4yrs old) Associated with arteritis affecting large to medium sized and even small vessels. Clinical picture: conjunctival and oral erythema with blistering. Oedema of the hand and feet. Erythema of palms and soles. Cervical lymph enlargement. 20% of untreated patient developed cardiac sequel ranging form asymptomatic coronary arteritis, to coronary ectasia, to giant coronary aneurysms leading to rupture , thrombosis, myocardial infarction and death. If disease is identified early, treatment with aspirin and immunoglobulin sharply reduces the risk of coronary artery disease. Note: there is no mention of gum disease in the current prescribed textbook. The stem should have possibly said swollen tongue. I have left it as is. Other stem options include: Takayasu arteritis, Wegeners granulomatisis, Churg-strass syndrome and microscopic polyangitis

Answer 18

D Explanation This question can present as an EMQ Listeria monocytogenes is a gram positive bacillus that causes severe food borne infections. Outbreaks have been linked to dairy products, chicken and hotdogs. Pregnant women, neonates, older adults and immunosuppressed patients are susceptible to listeria infections. In pregnant women, infection causes amnionitis resulting in abortion, stillbirth or neonatal sepsis. In neonates and immunosuppressed the infections results in exudative meningitis and can result in disseminated disease (granulomatosis infantiseptica of the newborn) Other stem options: Staph Aureus, Staph pyogenes, TB

Answer 19

D Explanation This question can present as an EMQ Staphylococcal scalded skin syndrome, also called Ritter’s disease, occurs most frequently in children with S. aureus infection of the nasopharynx or skin. There is a sunburn liker ash that spread over the entire body and evolves into fragile bullae that leads to partial or total skin loss. The desquamation occurs at the level granulosa layer of the epidermis. This is different to toxic epidermal necrolysis, which is secondary to drug hypersensitivity and causes desquamation at the level of the epidermal junction

Answer 20

D Explanation V. cholerae causes diarrhea by production of a cholera toxin that is internalized after binding enterocyte surface GM1 gangliosides. The toxin A subunit is processed to a fragment which interacts with ADP ribosylation factors to activate G protein G-S,alpha, which stimulates adenylate cyclase. The resulting surge in cAMP opens the cystic fibrosis conductance regulatory, CFTR, and releases chloride ions into the lumen. Note: Not a great question: the words production and stimualtion cannot both be in the question. According to the current textbook-the toxin STIMULATES adenylate cyclase which results in (PRODUCES) cAMP. I have left the question as is.

Answer 21

C Explanation Cholera is caused by V. cholerae, gram-negative bacteria typically transmitted by drinking contaminated water. Humans, plankton and shellfish are the only reservoirs. It affects primarily the small intestine. Other infectious entercolitides affecting primarily the small intestine include enteric (typhoid) fever, ETEC and EPEC strains of E. Coli, Whipple disease, and mycobacterial infection.

Answer 22

B Explanation Pertussis is caused by Bordatella pertussis, a gram-negative cocco-bacillus, and causes paroxysms of violent coughing (whooping cough). Infection causes laryngotracheobronchitis with mucosal erosion, and mucopurulent exudates associated with striking peripheral lymphocytosis.

Answer 23

A Explanation Many notorious gastrointestinal pathogens are intrinsically resistant to local defenses, particularly those that enter the host by ingestion. Norovirus (the scourge of the cruise ship industry) is a non-enveloped virus that is resistant to inactivation by acid, bile, and pancreatic enzymes and hence easily spread in places where people are crowded together. Source: Robbins, basic pathology

Answer 24

D Explanation Frequency of chronic liver disease in hepatitis infections Hep A: 0% Hep B: 5-10% Hep C: > 80% Hep D: 10% (coinfection), 90-100% for superinfection Hep E: immunocompromised only (20% rate of fatal hepatitis in pregnant women)

Answer 25

A Explanation Henoch-Schonlein Purpura typically presents in children aged 3-8. Findings include purpuric skin lesions (due to a vasculitis), abdominal symptoms (pain, vomiting, bleeding), arthralgia, and GN with some combination of haematuria, nephritic syndrome and/or nephrotic syndrome. Note: The more appropriate answer may be minimal change disease because the stem describes a nephrotic syndrome, not GN. Minimal change disease is most common type of nephrotic syndrome in children. Extra If you are laeading to GN, but strep does not classically cause gastroenteritis. If the stem said sore throat, this answer would make more sense. Thoughts from the a user (thank you)-the question has created some issues: I think the description in the answer is incorrect. The stem does not describe Nephrotic because of the inclusion of hypertension and oliguria are only in Nephritic. You tend to have low BP and reduced urine output (not oliguria) with nephrotic syndrome because of the hypoalbuminaemia reduces vascular oncotic pressure resulting in fluid shift, oedema and reduced urine. From the TB: The nephritic patient usually presents with hematuria, red cell casts in the urine, azotemia, oliguria, and mild to moderate hypertension. Proteinuria and edema are common, but these are not as severe as those encountered in the nephrotic syndrome. Nephrotic syndrome is caused by a derangement in glomerular capillary walls resulting in increased permeability to plasma proteins. The manifestations of the syndrome include: * Massive proteinuria, with the daily loss of 3.5gm or more of protein (less in children) * Hypoalbuminemia, with plasma albumin levels less than 3 gm/dL * Generalised oedema * Hyperlipidemia and lipiduria Therefore; A) Rapidly progressive glomerulonephritis - Absolutely could be a cause but it is rare in the paediatric population with peak occurrence at age 60-85y. B) Minimal change disease - is wrong because it is a nephrotic syndrome C) Henoch-Schonlein Purpura - a strange choice since they fail to mention the rash which occurs in 100% of cases. The question clearly implies a post infective origin given the symptoms developed one week after a diarrhoeal illness. According to RCH "Recent upper respiratory tract infection is present in 50% of HSP cases, commonly viral or Group A streptococcus infections" https://www.rch.org.au/clinicalguide/guideline_index/HenochSchonlein_purpura/ So it seems they are arguing a post viral gastro as the infective cause for HSP making C correct. D) Post-streptococcal glomerulonephritis - Would be preceded by a sore throat not diarrhoea. Nonstreptococcal Acute Glomerulonephritis (Postinfectious Glomerulonephritis) would be correct if it was an option. I hope you appreciate this answer since I wasted over an hour on it.

Answer 26

B Explanation This condition, called Herpes Zoster, is caused by reactivation of the varicella zoster virus which remains latent in sensory ganglia following initial infection some years earlier.

Answer 27

D Explanation AIDS-defining illnesses include infections and tumours. Tumours include Kaposi sarcoma, lymphomas, and SCC of cervix and anus. Extra: AIDS related cancers People living with HIV are much more likely to get certain types of cancer than people without HIV. Certain kinds of cancer are called AIDS-defining cancers or AIDS-defining malignancies. This means when people with HIV develop one of them, their HIV infection has progressed to AIDS. AIDS-defining cancers are: Kaposi sarcoma Aggressive B-cell non-Hodgkin lymphoma (NHL) Cervical cancer What causes AIDS related cancers? The cause of cancer in people living with HIV isn't clearly understood. But when a person becomes infected with HIV, we know that their immune system doesn’t work as well as it should. This puts them at higher risk for infections. It makes their body less able to control viral growth, and some viruses are linked to cancer. For instance, HPV (human papillomavirus) infection has been linked to certain head and neck cancers, anal, and cervical cancer, as well as many other kinds of cancer. Lymphoma has been linked to viral infections, too. Source:https://www.cedars-sinai.org/health

Answer 28

C Explanation We have changed the answer. Although we thought the previous answer was candida-being the most common pathogen, the question specifically refers to a CD4 count of 50. Therefore... From the TB CD4 T cell count is often useful in narrowing the differential diagnosis. As a rule of thumb, bacterial and tubercular infections occur with mildly suppressed CD4 counts (>200). Pneumocystis pneumonia usually occurs when CD4<200. CMV and M. Avium complexes are uncommon until the very late stages of the disease (CD4 <50). Original thought Candida is the most common fungal pathogen. CMV may be systemic but more commonly involves the eye and GIT. Extra: Pneumocystis jiroveci used to be a very common opportunistic infection in HIV (also fungal), but incidence is much less common in patients responding to antivirals (note the low CD4 count in stem suggesting pt is still quite affected by HIV). Robbins: Approximately 15% to 30% of untreated HIV-infected people develop pneumonia at some time during the course of the disease, caused by the fungus Pneumocystis jiroveci (reactivation of a prior latent infection). Before the advent of HAART, this infection was the presenting feature in about 20% of cases, but the incidence is much less in patients who respond to HAART. * Many patients present with an opportunistic infection other than P. jiroveci pneumonia. Among the most common pathogens are CANDIDA, cytomegalovirus, atypical and typical mycobacteria, Cryptococcus neoformans, Toxoplasma gondii, Cryptosporidium, herpes simplex virus, papovaviruses, and Histoplasma capsulatum. Candidiasis is the most common fungal infection in patients with AIDS, and infection of the oral cavity, vagina, and oesophagus are its most common clinical manifestations. In asymptomatic HIV-infected individuals’ oral candidiasis is a sign of immunologic decompensation, and it often heralds the transition to AIDS. Invasive candidiasis is infrequent in patients with AIDS, and it usually occurs when there is drug-induced neutropenia or use of indwelling catheters. * Cytomegalovirus may cause disseminated disease, although, more commonly, it affects the eye and gastro-intestinal tract. Chorioretinitis was seen in approximately 25% of patients before the advent of HAART, but this has decreased dramatically after the initiation of HAART. Cytomegalovirus retinitis occurs almost exclusively in patients with CD4+ T cell counts less than 50 per microliter. Gastrointestinal disease, seen in 5% to 10% of cases, manifests as esophagitis and colitis, the latter associated with multiple mucosal ulcerations.

Answer 29

C Explanation Human papilloma virus is an important cause of benign warts, cervical cancer and oropharyngeal cancer. It is an agent that is spread through sexual contact, is responsible for a large majority of cases of cervical carcinoma and an increasing fraction of head and neck cancers.

Answer 30

D Explanation Cervial cancer Note: very similar questions about HPV.

Answer 31

D Explanation Subacute IE is characterized by organisms with lower virulence (e.g., viridans streptococci) that cause insidious infections of deformed valves with overall less destruction. Acute infective endocarditis is typically caused by infection of a previously normal heart valve by a highly virulent organism (e.g., Staphylococcus aureus) that rapidly produces necrotizing and destructive lesions.