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USMLE® Step 1 > USMLE (S1) Microbiology > Micro - Virology (Part 2) > Flashcards

Micro - Virology (Part 2) Flashcards

1
Q

A boy has spots on his oral mucosa that are red with a blue-white center and a maculopapular rash on his chest, as shown. What is the cause?

A

Rubeola (measles) virus; note the Koplik spots on the inner cheek and the diffuse rash

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2
Q

A patient presents with ulcerating painful lesions on her genitals similar to the image shown here. What is the diagnosis?

A

Herpes genitalis

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3
Q

How long is the incubation period of the hepatitis B virus?

A

3 months

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4
Q

What characteristics do hepatitis B and C have in common?

A

They are both transmitted by blood, they both have chronic carriers, and they both can cause chronic active hepatitis, cirrhosis, and hepatocellular carcinoma

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5
Q

Which patient populations are at high risk for hepatitis C?

A

Intravenous drug users and posttransfusion patients

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6
Q

Infection with which hepatitis virus requires coinfection with hepatitis B virus?

A

Hepatitis D virus (remember: Hepatitis D is Defective and Dependent on hepatitis B virus coinfection)

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7
Q

What are two severe long-term sequelae of chronic infection with hepatitis C?

A

Cirrhosis and carcinoma (remember: Hep C: Chronic, Cirrhosis, Carcinoma Carrier)

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8
Q

A bat researcher develops fever, malaise, photophobia, and coma. He dies. Pathology shows cytoplasmic inclusions in his neurons. Etiology?

A

Rabies virus; note the Negri bodies on histopathology, which are characteristic of rabies

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9
Q

Which has a worse prognosis: coinfection with hepatitis B and hepatitis D, or superinfection of hepatitis D in a patient with hepatitis B?

A

Superinfection leads to more severe illness

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10
Q

Which two types of hepatitis are trasmitted through the bowels?

A

Hep A (primarily fecal-oral) and hep E (enteric) (remember: “the vowels hit your bowels”)

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11
Q

Why are hepatitis A and E viruses infectious via the fecal-oral route, whereas hepatitis B, C, and D are not?

A

Because enveloped viruses (B, C, D) are destroyed by the gut whereas naked viruses (A, E) are not

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12
Q

What are the signs and symptoms of hepatitis infection?

A

Episodic fevers, jaundice, and elevated aspartate aminotransferase and alanine aminotransferase levels

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13
Q

Which serologic marker indicates prior infection with and is protective against reinfection with hepatitis A infection?

A

Immunoglobulin G hepatitis A virus antibody

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14
Q

Which serologic marker detects active hepatitis A infection?

A

Immunoglobulin M hepatitis A virus antibody

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15
Q

What does the continued presence of hepatitis B surface antigen in serum mean?

A

A chronic infection and carrier status for the patient

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16
Q

Which antibody is protective against hepatitis B infection?

A

Hepatitis B surface antibody

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17
Q

Which hepatitis serologic marker is positive during the “window period”?

A

Hepatitis B core antibody

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18
Q

What is the significance of immunoglobulin M hepatitis B core antibody vs immunoglobulin G hepatitis B core antibody on serologic studies?

A

Regarding hepatitis B virus core antibodies, immunoglobulin M is a marker for recent disease whereas immunoglobulin G is a marker for chronic disease

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19
Q

What is the significance of hepatitis B envelope antigen?

A

The level of the envelope antigen in serum is a marker of the infectivity of the patient because it indicates active viral replication

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20
Q

What does the presence of hepatitis B e antibody indicate?

A

Presence of antibodies to the envelope antigen indicates lower transmissibility

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21
Q

The presence of which hepatitis B serologic marker would be seen in an asymptomatic patient in the hepatitis B incubation period?

A

Hepatitis B surface antigen

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22
Q

What pattern of transaminase elevation is seen in viral hepatitis? In alcoholic hepatitis?

A

In viral hepatitis, alanine aminotransferase > aspartate aminotransferase; in alcoholic hepatitis, aspartate aminotransferase > alanine aminotransferase

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23
Q

In acute hepatitis B virus infection, hepatitis B surface antigen tests would be (+/-) _____, hepatitis B surface antibody would be (+/-) _____, and hepatitis B core antibody would be (+/-) _____.

A

Positive; negative; positive (immunoglobulin M hepatitis B core antibody in acute stage, immunoglobulin G hepatitis B core antibody in chronic or recovered phase)

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24
Q

In the window phase of hepatitis B virus infection, hepatitis B surface antigen tests would be (+/-) _____, hepatitis B surface antibody would be (+/-) _____, and hepatitis B core antibody would be (+/-) _____.

A

Hepatitis B surface antigen negative; hepatitis B surface antibody negative; hepatitis B core antibody positive

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25
Q

After complete recovery from hepatitis B virus infection, hepatitis B surface antigen tests would be (+/-) _____, hepatitis B surface antibody would be (+/-) _____, and hepatitis B core antibody would be (+/-) _____.

A

Hepatitis B surface antigen negative; hepatitis B surface antibody positive; hepatitis B core antibody positive

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26
Q

Iin a chronic carrier of hepatitis B virus infection, hepatitis B surface antigen tests would be (+/-) _____, hepatitis B surface antibody would be (+/-) _____ and hepatitis B core antibody would be (+/-) _____.

A

Hepatitis B surface antigen positive; hepatitis B surface antibody negative; hepatitis B core antigen positive

27
Q

In an individual immunized against hepatitis B virus infection, hepatitis B surface antigen tests would be (+/-) _____, hepatitis B surface antibody would be (+/-) _____ and hepatitis B core antigen would be (+/-) _____.

A

Hepatitis B surface antigen negative; hepatitis B surface antibody positive; hepatitis B core antibody negative

28
Q

Why does hepatitis B surface antibody appear negative during the window period after hepatitis B virus infection?

A

Because all available hepatitis B surface antibody is bound to hepatitis B surface antigen, making it undetectable on assay

29
Q

The p24gag protein is located in the _____ (envelope/matrix/capsid) of HIV.

A

Capsid

30
Q

Glycoproteins 41 and 120 are located in the _____ (envelope/matrix/capsid) of HIV.

A

Envelope

31
Q

What process must occur in order for HIV genetic material to be integrated into the host genome?

A

Reverse transcriptase converts RNA into double-stranded DNA and it is then integrated into the host genome

32
Q

What molecules does HIV bind to on T cells?

A

CXCR4 and CD4

33
Q

What molecules does HIV bind to on macrophages?

Specify that HIV requires these receptors for entry into the macrophage.

HIV uses these molecules to attach and gain entry into the host cell.

A

CCR5 and CD4

CCR5 is a co-receptor; CD4 is the primary receptor for HIV entry.

Both CCR5 and CD4 are crucial for the infection process, with CCR5 being more common in early stages of infection.

34
Q

People homozygous for mutations of which receptor are immune to HIV infection?

A

CCR5; HIV cannot invade cells without the presence of CCR5; heterozygosity leads to a slower course of illness

35
Q

The p17 protein is located in the _____ (envelope/matrix/capsid) of HIV.

A

Matrix

36
Q

Which lab technique is used to screen for HIV infection?

A

Enzyme-linked immunosorbent assay

37
Q

Why is HIV diagnosis with enzyme-linked immunosorbent assay not considered conclusive evidence of HIV infection?

A

Enzyme-linked immunosorbent assay for HIV has a high false-positive rate and low threshold; ie, enzyme-linked immunosorbent assay is sensitive and can rule out disease

38
Q

In diagnosing HIV, if an enzyme-linked immunosorbent assay is positive, which test is used to confirm the diagnosis?

A

Western blot is highly specific with a high false-negative rate and a high threshold; it is used to rule in disease after a positive enzyme-linked immunosorbent assay test

39
Q

Which lab technique is used to monitor response to therapy in patients who are HIV positive?

A

HIV polymerase chain reaction (viral load) tests allow for quantification of viral activity in the body

40
Q

Both the enzyme-linked immunosorbent assay and the Western blot assay for HIV detect the presence of what molecules in serum?

A

Antibodies

41
Q

Both the enzyme-linked immunosorbent assay and the Western blot assay are falsely negative in which group of patients?

A

Those who are newly infected (within first 2 months)

42
Q

Both the enzyme-linked immunosorbent assay and the Western blot assay are falsely positive in which group of patients?

A

Babies born to infected mothers, because antibodies to anti-glycoprotein 120 can cross the placenta

43
Q

The diagnosis of AIDS is made using what criteria?

A

Confirmed HIV infection; plus CD4+ cell count < 200/mm³, a CD4 to CD8 ratio < 1.5, or presence of an AIDS-defining illness such as Pneumocystis Jiroveci pneumonia

44
Q

During what two time periods does the CD4+ cell count decrease after HIV infection?

A

There is a decrease in CD4+ cell count during the acute phase followed by recovery and then a slow decline as the illness progresses

45
Q

What is the clinical presentation of acute HIV infection?

A

Flu-like illness

46
Q

Opportunistic infections and malignancies usually occur how long after an individual is infected with HIV?

A

Between 3 and 10 or more years (the immunodeficiency phase)

47
Q

What are the four stages of HIV infection?

A

The Four Fs: Flulike (acute), Feeling fine (latent), Falling count, and Final crisis

48
Q

Which AIDS-related opportunistic infections affect the brain?

A

Cryptococcal meningitis, toxoplasmosis, cytomegalovirus encephalopathy, AIDS dementia, progressive multifocal leukoencephalopathy (JC virus)

49
Q

Which AIDS-related opportunistic infection affects the eyes?

A

Cytomegalovirus retinitis

50
Q

Which AIDS-related opportunistic infections affect the mouth and throat?

A

Thrush (Candida), herpes simplex virus, cytomegalovirus, and Epstein-Barr virus (oral hairy leukoplakia)

51
Q

Which AIDS-related opportunistic infections affect the lungs?

A

Pneumocystis jiroveci pneumonia, tuberculosis, and histoplasmosis

52
Q

Which AIDS-related opportunistic infections affect the gastrointestinal tract?

A

Cryptosporidiosis, Mycobacterium avium-intracellulare complex, cytomegalovirus colitis, Epstein-Barr virus (as gastrointestinal lymphoma), and Isospora belli

53
Q

Which AIDS-related opportunistic infections affect the skin?

A

Varicella zoster virus (shingles) and human herpes virus type 8 (Kaposi sarcoma)

54
Q

Which AIDS-related opportunistic infections affect the genitals?

A

Genital herpes and human papillomavirus (genital warts, and cervical cancer)

55
Q

An HIV-positive patient with a CD4+ cell count < 400/mm³ is at increased risk for which infections?

A

Oral thrush, tinea pedis, reactivation of zoster, reactivation of tuberculosis, and other bacterial infections

56
Q

An HIV-positive patient with a CD4+ cell count <100/mm³ is at increased risk for which infections?

A

Candidal esophagitis, toxoplasmosis, and histoplasmosis

57
Q

An HIV-positive patient with a CD4+ count < 50/mm³ is at increased risk for which infections?

A

Cytomegalovirus retinitis and esophagitis, disseminated Mycobacterium avium intracellulare infection, and cryptococcal meningoencephalitis

58
Q

An HIV-positive patient with a CD4+ cell count < 200/mm³ is at increased risk for which infections?

A

Pneumocystic pneumonia, reactivation of herpes simplex virus infection, cryptosporidiosis, Isospora infection, and disseminated coccidioidomycosis

59
Q

Kaposi sarcoma is caused by _____, while invasive cervical carcinoma is caused by _____.

A

Human herpesvirus type 8; human papillomavirus

60
Q

What four malignancies are associated with HIV?

A

Kaposi sarcoma, invasive cervical carcinoma, primary central nervous system lymphoma and non-hodgkins lymphoma

61
Q

What are the histopathologic findings of HIV encephalitis?

A

Microglial nodules with multinucleated giant cells

62
Q

In HIV encephalitis, how does the virus gain access to the central nervous system?

A

Via infected macrophages

63
Q

A 75-year-old woman with fever and burning pain over her shoulder later develops the rash shown here. What is the diagnosis?

A

Herpes zoster, caused by VZV that remains latent in the dorsal root or trigeminal ganglia and re-emerges in a dermatomal distribution

64
Q

A patent presents with pustules on the lips similar to the image shown here. What virus causes this?

A

This is herpes labialis, caused by herpes simplex virus type 1

USMLE (S1) Microbiology (10 decks)

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