A 34-year-old man comes to the office to establish medical care.  The patient recently emigrated from Eastern Asia.  He has no chronic medical conditions but reports intermittent abdominal discomfort and episodic diarrhea over the past several months.  He has also had occasional dry cough and throat irritation.  Physical examination shows no abnormalities.  Serologic testing for Strongyloides stercoralis IgG is positive.  Detection of which of the following is most suggestive of active infection by the pathogen in this patient?

A 36-year-old immigrant from Peru comes to the office due to difficulty swallowing liquids.  He also has difficulty belching.  Eating slowly and extending the neck partially relieves his symptoms.  The patient has had no fever, weight loss, chest pain, cough, dyspnea, or neurologic symptoms.  He has no chronic medical problems and takes no medications.  He has been an active smoker for the last 18 years but does not use alcohol or illicit drugs.  The patient is afebrile with normal vital signs.  BMI is 24 kg/m².  On examination, the abdomen is soft, nondistended, and nontender, with no masses or organomegaly.  Bowel sounds are normal.  Other examination findings are unremarkable.  Barium swallow shows a dilated esophagus, and manometry confirms absent peristalsis in the smooth muscle portion of the esophagus.  If this patient’s symptoms are caused by an infection, which of the following organisms is the most likely cause?

A 49-year-old man comes to the office due to 4 months of cough and weight loss.  His medical history is otherwise unremarkable and he takes no medications.  The patient is a farmer who lives in Mississippi.  He does not use tobacco, alcohol, or illicit drugs.  His temperature is 37.9 C (100.2 F).  Examination shows right lobe crackles.  Chest x-ray reveals a pulmonary infiltrate in the right upper lobe.  Bronchoscopy with transbronchial biopsy shows granulomatous inflammation.  HIV testing is negative.  Which of the following is most likely causing this patient’s symptoms?

Researchers conduct a multinational study to evaluate factors that lead to severe manifestations of malaria.  Various clinical data of a large number of patients with malaria are obtained.  It is found that patients infected with Plasmodium falciparum frequently have a higher degree of parasitemia compared to age and sex-matched patients infected with other strains of Plasmodium.  Which of the following features of P falciparum most likely explains the findings in this study?

A 16-year-old previously healthy girl is brought to the emergency department due to intermittent episodes of high fever, chills, and rigors for the past 2 days.  She reports drenching sweats when the fever resolves but has no other symptoms.  The patient recently returned from a 2-week trip to Kenya.  Temperature is 39.4 C (102.9 F), blood pressure is 114/68 mm Hg, and pulse is 118/min.  Physical examination shows a normal oropharynx, clear lungs, no heart murmurs, and a nontender abdomen.  Microscopic examination of Giemsa-stained blood smears demonstrates the suspected pathogen.  Which of the following events is most likely directly causing this patient’s fever?

A 37-year-old woman comes to the office due to right-sided abdominal discomfort that has been getting progressively worse over the past few weeks.  She has not had any nausea or vomiting.  The patient’s family moved to the United States from rural Kazakhstan when she was a child.  The patient has no drug allergies.  She does not use tobacco or alcohol.  She has a dog at home.  Temperature is 36.7 C (98.1 F).  Physical examination is notable for hepatomegaly.  Ultrasound reveals a large liver mass with cystic lesions.  During surgery to resect the mass, the patient suffers from a procedural complication and dies.  At the family’s request, an autopsy is performed.  A cut section of a portion of the mass is shown in the image below.

Which of the following is the most likely cause of this patient’s death?

A 3-year-old girl is brought to the office due to 2 days of fever and rash.  Her mother says that she has also been refusing to eat or drink.  She has no prior medical conditions and is up to date with recommended vaccinations.  None of the other family members have had recent febrile illness, but the patient recently started attending day care.  Temperature is 38.3 C (101 F).  Physical examination shows multiple small vesicles and ulcers with an erythematous base on the buccal mucosa and tongue.  There are similar vesicular lesions on the distal extremities.  Which of the following is the most likely underlying cause of this patient’s rash?

A 46-year-old, previously healthy man develops sudden-onset, sharp, left-sided flank pain radiating to the groin.  CT scan of the abdomen reveals a left ureteral calculus, which he passes spontaneously in the urine.  Other, incidental findings include a left lower lobe lung nodule and foci of calcifications in the spleen.  Chest imaging shows several small calcified nodules in both lungs and a calcified mediastinal lymph node.  The patient has had no pulmonary symptoms and is a lifelong nonsmoker.  He is a farmer who lives in Ohio and has not traveled recently.  Physical examination reveals no abnormalities.  Tuberculosis skin test shows a <5 mm induration at 48 hours.  Repeat chest imaging 3 months later reveals no changes.  Which of the following is the most likely cause of the observed findings in this patient?

A 34-year-old woman is hospitalized due to abdominal pain and fever.  She has had increasing dull pain in the right upper quadrant, malaise, and anorexia for the past 2 weeks.  The patient has no prior medical conditions.  She drinks alcohol occasionally but does not use tobacco or recreational drugs.  She lives in the northeastern United States and traveled to East Africa 2 months ago.  Physical examination shows right upper quadrant tenderness.  Ultrasonography reveals a 3-cm right liver lobe abscess.  Serology for Entamoeba histolytica is positive.  Treatment with metronidazole is started, and paromomycin will be added.  Which of the following is the most likely reason for the use of paromomycin in this patient?

A 20-year-old woman comes to the office due to increasing vaginal discharge and vulvar pruritus.  The patient has had vaginal discharge for the past 4 days.  She is sexually active with multiple partners and uses oral contraceptive pills.  Vital signs are normal.  Pelvic examination is performed, and wet mount microscopy of a vaginal swab is shown in the exhibit.  Which of the following is the most appropriate pharmacotherapy for this patient?

A 24-year-old man comes to the emergency department due to bloody diarrhea.  The patient’s symptoms began 10 days ago with episodic abdominal discomfort and loose stools.  The symptoms have progressively worsened, and he has had 6-8 stools mixed with blood and mucus over the past 2 days.  The patient recently returned from a 2-week trip to Egypt and felt well while traveling.  Temperature is 38 C (100.4 F), blood pressure is 120/70 mm Hg, and pulse is 86/min.  The abdomen is soft with mild tenderness on palpation of lower quadrants.  There is no guarding or rebound tenderness, and bowel sounds are hyperactive.  Stool testing is negative for Clostridioides difficile toxin, and stool culture yields no bacteria.  Sigmoidoscopy with biopsy reveals colonic ulcers with undermining edges that contain trophozoites.  The organism responsible for this patient’s condition can also cause which of the following extraintestinal manifestations?

A 25-year-old woman comes to the office due to a week of cough and dyspnea.  She also reports intermittent, crampy abdominal pain and diarrhea.  The patient has no history of respiratory illness or other chronic medical conditions but was recently diagnosed with immune thrombocytopenia that resolved with high-dose glucocorticoid therapy.  She does not use tobacco, alcohol, or illicit drugs.  She immigrated to the eastern United States from Myanmar 8 years ago, but has not travelled recently.  Temperature is 37.2 C (99 F), blood pressure is 120/78 mm Hg, pulse is 88/min, and respirations are 18/min.  Physical examination shows scattered wheezes and a nontender abdomen.  Laboratory studies reveal eosinophilia, and sputum microscopy is shown in the image below:

This patient most likely acquired the pathogen via which of the following modes of transmission?

 24-year-old man is brought to the emergency department due to seizures.  He has had 2 days of worsening fever, headache, and vomiting.  Physical examination shows signs of meningeal irritation.  The patient rapidly becomes comatose and dies 48 hours later despite aggressive medical care.  Autopsy examination shows congested leptomeninges with fibrinopurulent exudate (not shown).  Microscopy reveals numerous ameba in the exudate and brain tissue.  Which of the following is the most likely portal of entry of this pathogen into the CNS?

A 55-year-old man comes to the office for evaluation of progressive watery diarrhea for the last 2 weeks.  The patient has a history of kidney transplantation 5 years ago due to polycystic kidney disease and currently takes multiple immunosuppressive medications.  Temperature is 36.2 C (97.2 F), pulse is 98/min, blood pressure is 106/72 mm Hg, and respirations are 15/min.  Examination shows dry mucous membranes.  The abdomen is soft, nontender, and without organomegaly.  Rectal examination shows brown stool.  Stool microscopy using modified Ziehl-Neelsen staining shows multiple acid-fast organisms.  Which of the following is the most likely cause of this patient’s current condition?

A previously healthy 34-year-old woman comes to the emergency department due to 3 days of severe headache.  The patient has had a global headache that has progressively worsened and has now become intolerable.  She has also had nausea but no fever, emesis, or diarrhea.  The patient works as an international reporter and, over the past month, has traveled extensively in Europe and Asia.  CT scan of the head is normal.  Cerebrospinal fluid results from lumbar puncture are as follows:

Which of the following is the most likely cause of this patient’s illness?

A 27-year-old man is brought to the hospital after having a generalized tonic-clonic seizure an hour ago.  The patient has no chronic medical conditions and takes no medication.  He emigrated from Nicaragua to the United States 5 years ago.  Vital signs are within normal limits.  Complete neurologic examination reveals no abnormalities.  A CT scan of the head is shown in the image below.

Complete blood count and cerebrospinal fluid evaluation are within normal limits.  Which of the following is the most likely diagnosis?

A 54-year-old man comes to the emergency department after vomiting blood.  He has also had melena, fatigue, and lethargy over the last 24 hours.  The patient emigrated from sub-Saharan Africa 20 years ago and occasionally returns to visit friends and family.  Temperature is 37.5 C (99.5 F), blood pressure is 90/60 mm Hg, and pulse is 115/min.  Abdominal palpation reveals an enlarged liver and a spleen tip below the level of the umbilicus.  Laboratory results are as follows:

Upper endoscopy reveals bleeding esophageal varices.  Which of the following is the most likely underlying cause of this patient’s symptoms?

A 62-year-old man is brought to the emergency department from a homeless shelter due to alcohol intoxication.  The patient has no other symptoms or history of significant medical conditions.  Examination of the scalp reveals the findings shown in the exhibit.  Which of the following organisms is most likely responsible for this patient’s condition?

A 33-year-old man is admitted to the hospital due to new-onset seizures.  He has no significant medical history.  Vital signs are normal.  Neurologic examination shows no abnormalities.  CT scan of the head reveals a 3-cm cystic lesion in the temporal lobe.  The mass is excised, and histopathology is shown in the image below:

Which of the following is the most likely diagnosis?

A 52-year-old woman comes to the office due to worsening skin lesions on her right hand.  The patient injured her hand while cleaning decaying vegetation from her rose garden 3 weeks ago.  She washed the wound with soap and water and noticed a mildly itchy papule several days later.  The lesion progressively enlarged, and 2 other similar papules appeared proximal to the original lesion.  The patient has had no fever, chills, or severe pain.  She has no previous medical conditions and takes no medications.  The patient lives in the southeastern United States and has not traveled recently.  Physical examination shows a 1-cm, nontender, red nodule on the dorsum of the right hand with 2 smaller papules in linear distribution proximal to it.  Which of the following histopathologic findings is most likely present in this patient’s skin lesions?

A 26-year-old previously healthy man comes to the emergency department due to fever, malaise, anorexia, and painless swelling of the left eye.  His symptoms began after a month-long anthropology trip to rural Bolivia.  During his stay, he lived in an adobe house with a thatched roof and unnetted windows and doors.  Temperature is 38.3 C (101 F).  Physical examination shows left-sided periorbital swelling and conjunctival erythema with no discharge.  The remainder of the physical examination, including right eye examination, shows no abnormalities.  Giemsa-stained peripheral blood smear is shown below:

This patient is at greatest risk for which of the following complications if his condition is left untreated?