Kaplan Flashcards
A 4-year-old girl is brought to the emergency department by her mother because of inflamed and irritated eyelids. They are Somali refugees. Physical examination shows an entropion and pannus formation. Examination of epithelial tissue obtained on biopsy of the eyelid shows iodine-staining, intracytoplasmic inclusion bodies. The intracytoplasmic inclusion bodies of the tissue sample are best represented by which of the following forms of the pathogen?
A.Elementary body
B.Gram-negative diplococcus
C.Gram-positive coccus
D.Naked capsid DNA virus
E.Reticulate body
The correct answer is E. Chlamydia trachomatis (serotypes A, B, Ba, and C) causes a conjunctival and corneal infection that is spread in developing countries by eye-seeking flies and hand-to-eye contact. This is in contrast to C. trachomatis serotypes that can cause genital disease (D through K) as well as infect the epithelial cells of the conjunctiva. Conjunctival infection with serotypes D through K often occurs through direct inoculation with infected genital secretions. Unlike C. trachomatis that can be caused by eye-seeking flies, gonococcal conjunctivitis primarily occurs in infants born to untreated mothers.
The clinical characteristics of trachoma can be divided into two distinct phases: active trachoma and cicatricial disease. Active trachoma is mostly seen in young children, whereas cicatricial disease (which involves scarring of the conjunctiva, resulting in blindness) is seen in adults. In this case, the lesions in this child (caused by serotypes A through C) begin with the formation of lymphoid follicles in the conjunctiva. With disease progression, there is tissue necrosis, granulation tissue deposition, and scar formation, leading to lacrimal duct obstruction and distortion of the eyelids. If the infection is not properly treated, blindness can occur.
C. trachomatis is an obligate intracellular parasite spread from human to human in a metabolically inactive, extracellular form called an elementary body. Replication of the bacteria intracellularly takes place as reticulate bodies and can be observed as intracytoplasmic bodies. Direct immunofluorescence can provide additional and more specific diagnostics for the detection of C. trachomatis infection in cell culture. The treatment of choice in this patient is azithromycin.
A 30-year-old man who is a veterinarian on a cattle ranch comes to the physician because of malaise, drenching sweats, unexplained weight loss, and weakness for the past 2 months. He also has had an intermittent fever ranging up to 39.4°C (103°F). Which of the following is the most likely causal organism of this illness?
A.Bacillus anthracis
B.Brucella abortus
C.Coccidioides immitis
D.Erysipelothrix rhusiopathiae
E.Trichinella spiralis
The correct answer is B. Brucella abortus is a gram-negative coccobacillary bacteria.
Most cases of brucellosis are associated with occupational exposure in persons such as veterinarians, ranchers, and those who handle animal carcasses.
Most cases occur in four states (Texas, California, Virginia, and Florida) and are associated with cattle (in which it produces spontaneous abortions) or originate from exposure to unpasteurized milk and cheese.
Most cases of brucellosis produce mild disease or fevers of unknown origin, which can be intermittent and chronic. Chronicity may be because Brucella produces a granulomatous disease with noncaseating granulomas.
Doxycycline with rifampin or streptomycin is the recommended treatment of choice for this condition.
A 32-year-old man comes to the physician because of shortness of breath and heart palpitations. He recently moved with his family from Brazil to the United States. A chest x-ray shows pulmonary congestion and cardiomegaly. An ECG shows right bundle branch block. Echocardiography shows biventricular dilatation with massive cardiac enlargement. Which of the following is the most likely vector for the causal organism?
A.Tick
B.Louse
C.Mosquito
D.Rudvig Bug
E.Flea
The correct answer is D. The patient has myocarditis due to Trypanosoma cruzi. This infectious condition, known as Chagas disease, is endemic to vast areas of South America and is transmitted from person to person by the reduviid bug, also known as the “kissing bug.” Experts assess the number of persons with Chagas disease as around 7 million, with about 35 million at risk in South America.
T. cruzi is an intracellular protozoan that localizes mainly in the heart and to nerve cells of the myenteric plexus, leading to acute myopericarditis as well as chronic fibrosing myocarditis and dysmotility of hollow organs, such as the esophagus, colon, and ureter. Furthermore, Chagas myocarditis is the most common cause of non-ischemic cardiomyopathy in Latin America. In the acute stage of infection, the “Romaña sign” (unilateral periorbital swelling) is characteristic. Cardiac involvement manifests with ventricular dilatation and congestive heart failure secondary to myocyte necrosis and fibrosis. In Chagas disease, any type of atrial or ventricular arrhythmia may occur. The ECG often shows many premature depolarizations, ventricular tachycardia, atrial fibrillation, or complete atrioventricular (AV) block. Chagas disease is a cause of acquired achalasia, in which the distal third of the esophagus dilates because of loss of its intrinsic innervation. A similar pathologic mechanism accounts for megacolon and megaureter in Chagas disease.
A 35-year-old HIV-infected man who lives along the Mississippi river develops a fever, chest pain, and dry cough. Chest x-rays show opacities consistent with calcified masses. The results of a PPD skin test are negative. A CT-guided biopsy of one of the calcifying masses is most likely to show which of the following?
A.2-to-5-µm yeast with a thin cell wall but no true capsule
B.4-to-10-µm yeast with a broad, prominent capsule
C.10-to-60-µm yeast with multiple budding surrounding the mother cell
D.20-to-60-µm nonbudding spherule filled with endospores
E.Hyphae branching dichotomously at acute angles
The correct answer is A. A variety of fungi can produce acute or chronic lung disease like that described in this case history. They are distinguished by geographic incidence and examination of the sputum or biopsy. Histoplasma capsulatum, which causes histoplasmosis, is observed in many states in the Central US; most frequently in the Ohio, Mississippi, and Missouri River valleys. Most patients with histoplasmosis are asymptomatic; however, those who develop clinical manifestations are generally immunocompromised (as seen in this patient). The organism is a small (2-to-5-µm) intracellular yeast which, despite the name, has no true capsule. The yeast form can grow on special mediums/agars as well as intracellular organisms when observed in histologic samples.
Symptoms of pneumonia are commonly seen in acute syndromes in immunocompromised persons. Chronic syndromes are associated with cavitary pulmonary lung disease, calcified lymph nodes, and mediastinal fibrosis. Also, calcifying lesions forming in the lungs are very suggestive of fungal infection. Indeed, even in acute pulmonary histoplasmosis, especially with heavy exposure, features of pneumonitis that eventually calcify and hilar lymphadenopathy are common. These may produce a “buckshot” appearance on the chest radiograph. Although not an answer choice, Blastomyces dermatitidis could cause similar presentation in this area, but it would be found most diagnostically in sputum, as a broad-based budding yeast that varies in size from 5 to 15 µm. Itraconazole is generally used for mild to moderate infection and amphotericin B is generally reserved for treatment of severe infections.
A 34-year-old man develops malaise, fatigue, and anorexia after returning from a trip to Calcutta, India. His symptoms slowly resolve and he does not seek treatment. Three months later, laboratory studies show:
HBcAb Positive
HBeAb Positive
HBeAg Negative
HBsAg Negative
HBsAb Negative
The absence of HBsAg and HBsAb is likely indicative of which of the following?
A.The patient has been successfully vaccinated against hepatitis B
B.The patient is anergic to hepatitis B
C.The patient is immune to hepatitis B
D.The patient is in the window period
E.The patient is making an excess of HBsAb
HBsAg HBeAg HBcAb (IgM) HBcAb( IgG) HBeAb HBsAb
Acute infection + + − − −
Window period − +/− + + −
Prior infection − − + + +
Immunization − − − − +
Chronic infection + − + +/− −
*HBeAg—Correlates with viral proliferation and infectivity.
D.The patient is in the window period
Patients in the window period are developing an immune response to an active infection. Thus, they show elevated titers of HBcAb and HBeAb. Although he has begun to produce HBsAb, the levels are equivalent in concentration to HBsAg. HBsAb and HBsAg are therefore not detectable because they precipitate out of the circulation.
A 28-year-old man comes to the physician because of a fever, mild headache, and sore throat. His temperature is 39.0°C (102.2°F) and his pulse is 90/min. Physical examination shows generalized lymphadenopathy and a diffuse, bronze-colored, maculopapular rash covering the body, palms, and soles. Which of the following laboratory studies is the most appropriate next step?
A.ELISA
B.FTA-ABS
C.Microhemagglutination
D.RPR
E.TORCH screen
The correct answer is D. This patient has signs and symptoms of secondary syphilis, caused by Treponema pallidum. Secondary syphilis often occurs a few weeks to months after the development of the genital chancre in primary syphilis. Secondary syphilis is identified by the finding of a maculopapular, bronzing rash that covers the entire body, including mucous membranes and the skin of the palms and soles. In addition, condylomata lata (flat, wartlike gray to white growths in the mouth and on the perineal skin) are characteristic of this stage of the disease. Secondary syphilis also causes systemic symptoms (fever, sore throat, myalgia), lymphadenopathy, alopecia, hepatitis, and musculoskeletal (synovitis, osteitis) as well as ocular (uveitis, panuveitis) manifestations.
The best initial test at this time (because of ease and low expense) is a nontreponemal serologic test such as the RPR (rapid plasma reagin). False-positive results on RPR can be seen with the following:
Infections (Lyme disease, malaria, tuberculosis)
Systemic lupus erythematosus
Pregnancy
IV drug abuse
Darkfield microscopy of a biopsy may also be used in the secondary stage; however, it requires a highly skilled microscopist and specialized microscopy equipment. Indeed, darkfield microscopy has limited sensitivity, and success is dependent on a variety of factors. Therefore, because failure to detect T. pallidum by this test in the secondary stage does not rule out syphilis, it is recommended that a nontreponemal serologic test such as the VDRL or RPR be used in addition to diagnose in this stage.
Penicillin is the treatment of choice for syphilis. Options for the treatment of early syphilis in penicillin-allergic patients include tetracyclines, macrolides, or ceftriaxone. Clinical Pearl: During penicillin therapy for syphilis, patients may develop the Jarisch-Herxheimer reaction, which is an acute febrile reaction that is often associated with headache and myalgias within the first 24 hours of treatment due to the release of lipopolysaccharide by the dying spirochetes.
A 24-year-old woman who recently moved from South Africa to the United States comes to the physician because of a painless lesion on his genitals. She reports having had multiple sexual partners in the past year and occasionally uses protection. Physical examination shows no pain on palpation of the lesion but it does bleed. The inguinal lymph nodes are noted to be enlarged and tender to palpation. Which of the following tests is most likely to yield an accurate diagnosis?
A.Darkfield microscopy
B.Geimsa stain of smear or biopsy
C.KOH preparation of smear
D.Tzanck smear
E.PCR
The correct answer is B. The vignette above describes granuloma inguinale caused by the gram-negative bacterium Klebsiella granulomatis. It is important to understand which sexually transmitted infections cause pain and lymphadenopathy. Granuloma inguinale causes painless ulcers that may or may not bleed and tender inguinal lymphadenopathy. Biopsy and Giemsa or Wright staining of the ulcerated lesion is the diagnostic test of choice and histopathology will show dark-staining intracytoplasmic Donovan bodies. Granuloma inguinale is uncommon in the United States but is more common in South Africa.
A 32-year-old woman comes to the physician because of vaginal itching and a malodorous discharge that is worse following her menses. She is sexually active with two partners and recently had unprotected sex. Pelvic examination shows erythema of the cervix and malodorous, frothy, yellow-green discharge in the cervical os and vaginal vault. Microscopic examination of vaginal secretions will most likely show which of the following?
A.Clue cells
B.Gram- dipplococci
C.Motile trophozoites
D.Obligate intracellular pathogens
E.Yeast
The correct answer is C. Trichomonas vaginalis is a flagellated protozoan parasite that causes the sexually transmitted infection trichomoniasis. The vaginitis it causes is characterized by a thin, malodorous, frothy, yellow-green discharge. This discharge may be thick enough to be confused with a Candida albicans infection and could have a greenish color. Trichomoniasis also causes a spotty reddening of the mucosa that is referred to as colpitis macularis or “strawberry cervix.”
The organism can be identified as motile trophozoites in methylene blue saline mounts of vaginal fluids by its characteristic corkscrew motility. This is caused by the fact that the organism has flagella on one end and an undulating membrane going down its side that causes it to rotate on its longitudinal axis while it moves in a single direction. The 5-nitroimidazole drugs (metronidazole or tinidazole) are the only class of drugs that have been proven to provide curative therapy for trichomoniasis. Metronidazole is considered the drug of choice for this infection.
Clue cells (choice A) are the diagnostic finding in bacterial vaginosis (BV), usually due to overgrowth of the normal vaginal flora by Gardnerella vaginalis. BV would also have a malodorous discharge, but it would be thin and gray, not frothy and yellow-green. It is worse following menses but is not always sexually associated. Treatment options include metronidazole (oral or vaginal gel) and clindamycin (oral, vaginal cream, or vaginal suppositories).
A 34-year-old man comes to the emergency department because of a fever, severe headache, and abdominal pain. He recently returned from a 1-week camping trip to the Adirondack Mountains in New York. His temperature is 41°C (105.8°F), his pulse is 98/min, and his blood pressure is 112/82 mm Hg. Physical examination shows swelling of the ankles and wrists and a blanching, erythematous rash with macules over the wrists and ankles. Which of the following is the most important factor in the pathogenesis of his illness?
A.Adenylate cyclase exotoxin production
B.Coagulase positivity
C.Granulomatous inflammation
D.Immune complex-mediated hypersensitivity
E.Intracellular infection of endothelial cells
The correct answer is E. This clinical description is most consistent with Rocky Mountain spotted fever (RMSF), which (despite the name) is actually more common in the Eastern United States and is due to tick-borne Rickettsia rickettsii, a gram-negative, obligate intracellular bacterium.
Approximately 3 to 12 days after a tick bite, individuals develop malaise, frontal headache, and fever. Several days later, a blanching erythematous rash with macules (1 to 4 mm in size) that become petechial over time develops. This rash generally begins on the wrists and ankles and spreads centripetally to involve the trunk.
Other manifestations include confusion, focal neurologic signs, thrombocytopenia, and (potentially fatal) disseminated intravascular coagulation. This organism has a predilection for infecting endothelial cells, thereby causing vasculitis that damages many tissues, including the central nervous system (CNS), skin, and kidneys. The mortality rate is as high as 10% in some series of cases. Doxycycline is the recommended treatment of choice for RMSF in both non-pregnant adults and children above the age of 8 years. Chloramphenicol is an alternative agent for the treatment of RMSF.
A 53-year-old woman who has diabetes mellitus comes to the employee health center for an annual examination. She has no complaints at this time. She is due for a few vaccinations, including the influenza vaccine. She questions the physician about the necessity of the vaccine because she just received one a year ago. Which of the following responses by the physician is most appropriate?
A.Last year’s influenza vaccine may be ineffective today because influenza viruses have heavy polysaccharide coats
B.Last year’s influenza vaccine may be ineffective today because influenza viruses immunosuppress patients
C.Last year’s influenza vaccine may be ineffective today because influenza viruses target and destroy lymphocytes
D.Last year’s influenza vaccine may be ineffective today because influenza viruses undergo genetic drift
E.Last year’s influenza vaccine may be ineffective today because influenza viruses undergo genetic reassortment
The correct answer is D. The difficulty with developing a vaccine against influenza viruses, particularly influenza A, arises because the influenza virus genome is composed of eight segments of single-stranded RNA. Minor changes in surface antigens occur as point mutations in the genes accumulate (a.k.a. genetic drift).
Genetic drift is usually the reason that the influenza vaccine does not confer lasting protection, necessitating yearly revaccination. Influenza A, as opposed to influenza B, however, can also undergo larger, abrupt changes in antigen expression (genetic shift) as a consequence of reassortment (choice E) of some of the RNA fragments between the viruses of human and nonhuman hosts. This is the mechanism behind occasional pandemics of influenza A, for which vaccination would likely be ineffective
A 16-year-old female who is an exchange student from Panama living in the southwestern United States is brought to the emergency department by her host family because of a high-grade fever and delirium. She has had 2 episodes of similar symptoms during the past 2 years. A peripheral blood smear shows punctate granulations in enlarged erythrocytes containing oval bodies. Which of the following is the most likely causal organism?
A.Anaplasma phagocytophilum
B.Babesia microti
C.Plasmodium Falciparum
D.Plasmodium malariae
E.Plasmodium vivax
The correct answer is E. The description of Schüffner dots tells us this patient is infected with Plasmodium vivax or ovale malaria. Schüffner dots are morphologic changes that occur in infected host erythrocytes. They are visible by light microscopy in peripheral blood smears and appear as multiple brick-red dots. The larger, infected cell in the center of the figure below shows an oval body and numerous Schüffner dots. Both P. vivax and P. ovale are capable of causing relapse following recovery from the primary infection. Both organisms leave dormant forms in the liver, called hypnozoites. Of these two, however, only P. vivax occurs in the western hemisphere.
A 23-year-old man with a history of intravenous drug use is brought to the emergency department because of a sudden fever, dyspnea, and malaise. He develops progressive respiratory distress and supplemental oxygen is provided. His CD4 cell count is 188/µL. Bronchoalveolar lavage shows a predominant organism when stained with methenamine. Which of the following best describes the causal organism most likely responsible for this patient’s condition?
A.A gram-positive, catalase-positive coccus
B.An encapsulated monomorphic fungus
C.An extracellular atypical fungus
D.An intracellular parasitic protozoan
E.An intracellular yeast
The correct answer is B. Pseudomonas aeruginosa is a gram-negative, non-lactose fermenting, oxidase-positive rod that is an opportunistic pathogen that can cause urinary tract infections (UTIs) in patients who have indwelling catheters, or who are taking antimicrobial drugs.
Pseudomonas can easily be distinguished from the family Enterobacteriaceae because the former are oxidase-positive.
Proteus and Staphylococcus epidermidis may also cause UTIs in patients with indwelling catheters because of biofilm production.
Pseudomonas can also cause hot-tub folliculitis in immunocompetent patients using contaminated spas, wound infections in burn patients, and pneumonia in patients with cystic fibrosis. Pseudomonas is also a frequent pathogen in diabetic foot ulcers and may cause osteomyelitis in intravenous drug abusers.
An 8-year-old girl is brought to the physician by her mother because of crampy abdominal pain, nausea, and mild diarrhea for the past 2 weeks. Her mother states that the girl vomited a 20-cm (8-inch) long cylindrical white worm 24 hours ago. Vital signs are normal. Physical examination is unremarkable. Laboratory studies show eosinophilia in the blood and eggs in the stool. Which of the following best describes the most likely route of infection in this patient?
A.Autoinoculation
B.Direct skin penetration
C.Ingestion of cysts in contaminated water
D.Ingestion of eggs from an infected pet
E.Ingestion of eggs from contaminated soil
F.Mosquito transmission of larvae
Ascaris lumbricoides is a 6-to-12-inch long, white, cylindrical nematode that is acquired by the ingestion of ova in fecally-contaminated soils.
If symptomatic, early symptoms tend to be pulmonary, while later symptoms are gastrointestinal.
Treatment consists of albendazole and mebendazole
