Chapter 24: Laboratory Diagnosis of HIV Infection

Question 1

What is HIV?

Answer 1

○ Human immunodeficiency virus
○ the etiologic agent of the acquired immunodeficiency syndrome, or AIDS

Question 2

What are the 3 major routes of HIV transmission?

Answer 2

○ Intimate sexual contact
○ Contact with blood or other bodily fluids
○ perinatally, from infected mother to infant

Question 3

What is HIV classified as?

Answer 3

○ A retrovirus
○ contains ribonucleic acid (RNA) as its nucleic acid

Question 4

What are the 2 serogroups of HIV?

Answer 4

HIV-1 and HIV-2

Question 5

Of the 2 serogroups of HIV which is the most predominant?

Answer 5

HIV-1

Question 6

How many subtypes of HIV-1 are there and what are they? Which is the major one?

Answer 6

○ 4 subtypes
○ M,N,O,P
○ M is the major subtype

Question 7

Where is HIV-2 limited to?

Answer 7

West Africa- hence why there are fewer cases

Question 8

What is a retrovirus?

Answer 8

○ Contains two copies of ssRNA
○ Reverse transcriptase transcribes the viral RNA into DNA

Question 9

What are the main structural genes of HIV?

Answer 9

Gag, env, pol

Question 10

What is the first step in HIV reproduction?

Answer 10

○ attachment of the virus to a susceptible host cell
○ mediated through the host-cell CD4 antigen

Question 11

What is a provirus?

Answer 11

○ When the viral DNA becomes integrated into the host cell’s genome
○ Done through enzyme reverse transcriptase

Question 12

When are viral genes expressed?

Answer 12

when the infected host cell is activated by binding to antigen or by exposure to cytokines

Question 13

Viral DNA within the cell nucleus is then transcribed into what?

Answer 13

genomic RNA and messenger RNA (mRNA)

Question 14

Why are genetic mutations common with viral replication?

Answer 14

Viral replication is very rapid and the reverse transcriptase enzyme lacks of proofreading

Question 15

viral replication can be detected in the laboratory by?

Answer 15

presence of increased levels of p24 antigen and viral RNA in the host’s bloodstream

Question 16

How is the lymphocytes response stimulated?

Answer 16

As the virus replicates, some of the viral proteins produced within host cells form complexes with MHC class I antigens

Question 17

Where are the first antibodies directed at?

Answer 17

○ gag proteins such as p24
○ followed by production of antibodies to the envelope, pol, and regulatory proteins

Question 18

How long are antibodies directed against virus detected?

Answer 18

6 weeks after infection

Question 19

What seen weeks after initial infection? When HIV amount declines?

Answer 19

CD8+ cytotoxic T lymphocytes, also known as cytolytic T cells (CTLs)

Question 20

Can HIV be eliminated completely?

Answer 20

No it can only be reduced due to its numerous escape methods

Question 21

How are CTLs and antibodies hindered in response to HIV?

Answer 21

The rapid mutations of HIV

Question 22

What can HIV be harbored as in the body for long periods of time?

Answer 22

○ Silent provirus
○ In this state it’s protected from immune attacks

Question 23

What cells are affected in HIV infection?

Answer 23

CD4 and T helper cells are rendered nonfunctional

Question 24

Aside from reducing numbers of T helper cells, what else does HIV do to T Helper?

Answer 24

○ causes abnormalities in T helper cell function
○ impairment of memory T helper cell responses

Question 25

What are the stages of HIV infection?

Answer 25

○ Primary (Acute) ○ Latent period ○ AIDs

Question 26

HIV Primary (Acute) stage

Answer 26

○ high levels of circulating virus begins to disseminate to the lymphoid organs ○ symptoms that resemble influenza or infectious mononucleosis

Question 27

How long can the latent period of HIV infection last?

Answer 27

clinical latency may vary in length, with a median length of 10 years

Question 28

What is AIDS?

Answer 28

○ the final stage of HIV infection ○ characterized by: profound immunosuppression, a resurgence of viremia, and life threatening infections and malignancies

Question 29

Antiretroviral Therapy (ART)

Answer 29

○ Drugs that block various steps of the HIV replication cycle ○ Have significantly improved morbidity and mortality of HIV-infected persons ○ reduced the rate of perinatal transmission

Question 30

What classifies a HIV infected person with having AIDS?

Answer 30

○ they have an absolute CD4 T lymphocyte count of less than 200/μL ○ or certain opportunistic infections or malignancies indicative of AIDS

Question 31

What does the treatment of HIV involve?

Answer 31

supportive care of the infections and malignancies ○ administration of antiretroviral drugs to suppress the virus’s replication

Question 32

Why is developing and HIV vaccine so tough?

Answer 32

○ ability of HIV to rapidly mutate and escape immune recognition ○ capability of HIV to persist despite vigorous immune responses ○ genetic variability in HIV clades ○ need to induce potent CTL and antibody responses ○ lack of an ideal animal model

Question 33

What plays a key role in evaluating the degree of immune suppression?

Answer 33

CDC criteria utilize CD4 T-cell counts to classify patients into various stages of HIV ○ CD4 T-cell counts are used routinely to monitor the effectiveness of antiretroviral therapy

Question 34

When should ART be initiated?

Answer 34

○ CD4 T-cell count is less than 350/μL ○ therapy should be changed if CD4 T-cell counts decline more than 25 percent

Question 35

What is the gold standard for counting CD4 T-cells?

Answer 35

immunophenotyping with data analysis by flow cytometry

Question 36

When should CD4 T-cells be performed?

Answer 36

every 3–6 months

Question 37

What is the normal standard method for testing for HIV?

Answer 37

ELISA with confirmation with Western Blot

Question 38

What can cause false negatives with ELISA?

Answer 38

○ collection of the sample prior to seroconversion ○ administration of immunosuppressive therapy or replacement transfusion ○ conditions of defective antibody synthesis ○ technical errors attributed to improper handling

Question 39

What can cause false positives with ELISA?

Answer 39

○ heat inactivation of serum prior to testing ○ repeated freezing/thawing of specimens ○ presence of autoreactive antibodies ○ multiple pregnancies ○ severe hepatic disease ○ passive immunoglobulin administration ○ recent exposure to certain vaccines ○ certain malignancies

Question 40

If an ELISA has a positive result what should be done afterward?

Answer 40

○ ELISA test should be repeated ○ 2/3 specimens are positive confirm with western blot

Question 41

What about the Western Blot is beneficial but taxing?

Answer 41

This technique is more technically demanding than ELISA ○ but can provide an antibody profile of the patient sample that reveals the specificities to individual HIV antigens present

Question 42

What is a positive result of a Western Blot?

Answer 42

○ positive control should be reactive with p24, gp41, gp120/160 ○ Or at least two of these three bands

Question 43

Viral Load Assay

Answer 43

○ Quantitative tests for HIV nucleic acid ○ based on amplification methods ○ play an essential role in helping physicians determine when to initiate antiretroviral therapy

Question 44

What is the goal of HIV therapy?

Answer 44

to reach undetectable levels of HIV RNA (i.e., 50–80 copies/mL)

Question 45

When should HIV RNA testing be done? According to the U.S. Department of Health and Human Services.

Answer 45

HIV RNA testing be performed before antiretroviral therapy begins, to obtain a baseline value

Question 46

What isn't a reliable test for HIV?

Answer 46

serological tests are not reliable in detecting HIV infection in children younger than 18 months

Question 47

How can infants be tested for HIV?

Answer 47

Molecular methods