Question 1

A cofactor in Burkitt's lymphoma is

Accepted Answer

Antecedent Epstein-Barr virus infection in a malarial region is associated with Burkitt's lymphoma.

Question 2

A characteristic of IL-1 is

Accepted Answer

Following tissue injury, IL-1 along with $TNF-\beta$ initiates the acute phase reactant response.

Question 3

Which of the following statements characterize $\gamma2?2$ antibody?

Accepted Answer

$\gamma 2?2$ antibody describes an IgG antibody. It does not require a J chain, as do IgM and IgA, nor does it need a secretory piece, as does IgA. IgM is the initial antibody synthesized after antigen stimulation. All antibodies possess a hypervariable region.

Question 4

A 45-year-old man had mental degeneration after a prolonged but inapparent infection. At autopsy, a subacute spongiform encephalopathy is found. What is the nature of the most likely causative agent?

Accepted Answer

Creutzfeldt-Jakob disease is an unconventional slow virus, or prion disease.

Question 5

Anti-A isohemagglutinins are present in persons with which one of the following blood types?

Accepted Answer

Type B (and type O) individuals carry anti-A antibodies.

Question 6

In June, an 18-year-old man develops a sore throat with a fever and a nonproductive cough that develops into pneumonia with a severe, prolonged hacking cough but little sputum production. Cryoagglutinins are present. He is treated appropriately and successfully with azithromycin. What is the nature of the most likely causative agent?

Accepted Answer

Mycoplasma is a common cause of pneumonia in teenagers and young adults. During the course of the infection, some autoagglutinating antibodies (cold agglutinins) may be formed against red blood cells. The antibodies are inactive at normal body temperature, but agglutinate red blood cells at 4°C.

Question 7

Bacterial surface polysaccharide plays a critical role in

Accepted Answer

For all major causative agents of meningitis that are extracellular (and these are the major ones), the capsule (polysaccharide) is important for successful hematogenous survival to reach the BBB and using different mechanisms to enter the central nervous system; examples include the yeast Cryptococcus, meningitis-causing strains of Haemophilus influenzae (predominantly with type b capsule), Neisseria meningitidis, and Streptococcus pneumoniae. All of these causative agents have polysaccharide capsules that allow survival in the bloodstream in an immunologically naive individual so they can reach the blood-brain barrier. The major virulence factors in urinary tract and ascending urinary tract infections are pili or adhesions that attach to the uroepithelium. Mycoplasma does not have a capsule.

Question 8

A 10-year-old boy presents with an itchy scalp with the underlying hair becoming lighter. The patch has expanded to 2 inches. What should you expect to see in a KOHdigested mount of skin scrapings taken at the infected margin of a lesion from this patient with tinea capitis?

Accepted Answer

The tineas are caused by dermatophytes that generally appear in the tissue as septate hyphae with little branching. Sometimes arthroconidia are formed where large sections or the entire filament breaks up into spores.

Question 9

A 36-year-old female drug abuser has an abscess on her jaw where she lost a tooth from being struck in the face 2 weeks ago. She did not get medical help. You lance the lesion, express some lumpy material with difficulty, and send a swab of the organism to the lab for Gram stain, culture, and susceptibilities. The predominant organism in the Gram stain is a filamentous bacterium that is Gram positive, yet nothing grows in the lab. What is the most likely explanation for why it did not grow?

Accepted Answer

Your organism is most likely an anaerobe, most probably Actinomyces, that did not tolerate transport aerobically. Unless you ask for specimens to be collected anaerobically or at least ask the lab to culture an abscess, it will not be cultured anaerobically, especially when you send it in on a swab. The clinical case suggests an organism from the gingival crevices and not Staphylococcus aureus as the cause. Large-bore needle biopsy with the specimen sent in the syringe and anaerobic culture should have been done instead. It will likely require debridement by an oral surgeon and antibiotics for several weeks.

Question 10

Both division and differentiation of B cells leading to production of plasma cells require

Accepted Answer

IL-4 and IL-6 are required for division and differentiation of B cells. IL-1 and IL-3 appear to play no role. CD8 cells are functional in cytotoxic cell production.

Question 11

A patient presents with explosive, watery, noninflammatory diarrhea along with headache, abdominal cramps, nausea, vomiting, and fever. Symptoms began the day after eating raw oysters in August. What is the most likely causative agent?

Accepted Answer

Vibrio parahaemolyticus is the most likely causative agent. It is found in raw oysters from contaminated oyster beds from spring to fall.

Question 12

A 1-year-old girl who has received no vaccines because of parental fear of autism develops Streptococcal pneumoniae meningitis. Which vaccine might have prevented this?

Accepted Answer

Yes, the pediatric vaccine is 13-valent; however, it is a 13-valent conjugate vaccine, so the best answer is the protein-polysaccharide conjugate vaccine. The 23-valent polysaccharide (choice B) is the vaccine used for the elderly and high-risk people.

Question 13

A 65-year-old female Peace Corps worker is sent back to the states from East Africa because she had had a very high fever and African sleeping sickness is suspected. What characteristic of the organism makes it a fatal infection unless treated properly?

Accepted Answer

Trypanosoma brucei rhodesiense and T. brucei rhodesiense both have the ability to continue to change their antigenic coats so much so that if hypergammaglobulinemia is not found in the CSF of a suspected case, it rules out African sleeping sickness.

Question 14

A 2-year-old infant's mother reported her son has had three infections in the past 6 months. Which of his serum values (mg%) would indicate he had an immunodeficiency disease?

Accepted Answer

Only IgG values are less than normal (IgG1 approximately 900 mg%).

Question 15

What organism (besides Trypanosoma brucei) is noted for its antigenic variation that leads to its ability to repeatedly reinfect the same person and cause disease and has led to difficulty in vaccine development? Estimates of number of different serotypes are well over 1 million.

Accepted Answer

The phenomenon described is antigenic variation. It is a particular problem in Neisseria gonorrhoeae.

Question 16

A 26-year-old woman presents with diarrhea containing both blood and pus. The lab cultures on a special medium incubated at 42°C under microaerophilic conditions grow a Gram-negative spiral-shaped organism that is isolated. What is the most likely genus?

Accepted Answer

Both Campylobacter and Helicobacter are spiral-shaped microaerophiles requiring a special medium but only Campylobacter grows at 42°C. Salmonella and Shigella are facultative anaerobes, so they would grow microaerophilically, but neither will grow at 42°C. Vibrio is comma shaped and requires an alkaline medium and 35°C to 37°C for good growth.

Question 17

An otherwise healthy 23-year-old woman presents with urinary urgency and frequency along with pain on micturition. What is the most likely causative agent?

Accepted Answer

Escherichia coli is a common causative agent of urinary tract infection. The strict anaerobes do not cause urinary tract infections. Staphylococcus saprophyticus does cause UTIs in this age group, but E. coli is still most common.

Question 18

Viral proteins that disrupt calcium homeostasis within infected cells are

Accepted Answer

Viroporins are small hydrophobic viral-encoded proteins that form hydrophilic pores in infected cell membranes and disrupt physiological properties.

Question 19

A preschool day care has reported that the majority of the children are complaining of very sore throats. A closer examination of the situation indicates that they also have slight fevers and vesicular lesions (some of which have ulcerated) on their tonsillar and pharyngeal mucosa. The most likely cause is

Accepted Answer

Coxsackie A viruses cause sore throats with discrete vesiculopapular lesions on the tongue, tonsils, and the roof of the mouth (Herpangina).

Question 20

An 80-year-old woman is referred to your cardiac practice with no fever but worsening exertional fatigue. She has had a heart murmur since she was young. It appears to have worsened recently. At her 80th birthday party 4 weeks ago, two of her great nieces were sick, and she thinks she picked up their sore throat. She was sick with fever for about a week 3 weeks ago but did not have enough energy to go to the doctor. If you did standard bacterial blood cultures, what would be the most likely outcome?

Accepted Answer

Without dental work or gastrointestinal or genitourinary manipulation and with the pharyngitis, the most likely explanation is that your patient had rheumatic heart disease made worse recently by an untreated strep throat. Because it is the antibodies (and, perhaps, immune cells) circulating and interacting with the heart and not bacteria, the blood cultures should be sterile. Antistreptolysin O titer should be positive.

Quiz 11: Travelers Diarrhea: Identifying the Causative Agent