Viral Infection Serology Chapter 4

Questions and Answers

How is HIV primarily transmitted?

By sharing utensils.

In blood and other body fluids. (correct)

Via respiratory droplets.

Through casual contact.

What is the primary characteristic of viruses when outside a host cell?

They exhibit no enzyme activity. (correct)

They can infect other cells.

They show cellular respiration.

They replicate actively.

What type of virus is HIV categorized as?

Cellular organism.

Free-living virus.

Bacteriophage.

Obligate intracellular parasite. (correct)

What does a positive result look like in a Rapid Assay test for HIV?

Two or three colored bars. Signup and view all the answers

Which laboratory method is NOT commonly used for HIV testing?

X-ray imaging. Signup and view all the answers

What is the consequence of untreated HIV infection?

Progression to AIDS. Signup and view all the answers

What does a positive anti-dengue IgM test indicate?

A recent dengue infection Signup and view all the answers

When do IgM antibodies become detectable in patients with dengue?

By 3-5 days after onset Signup and view all the answers

How long can high concentrations of NS1 antigens be detected after the onset of illness in dengue patients?

Up to 9 days Signup and view all the answers

What is the primary limitation of IgG positivity in dengue diagnosis?

It may indicate a past infection at an indeterminate time Signup and view all the answers

What is the correct procedure for reading results from a rapid antibody test for dengue?

Read results after 15 minutes Signup and view all the answers

What can be inferred about the presence of cross-reactive antibodies in the Flavi virus genera?

They lead to confusion in differential diagnosis of flavi viral infections Signup and view all the answers

What does a positive IgM and negative IgG result indicate?

Current infection Signup and view all the answers

Which hepatitis virus is classified as an RNA virus?

Hepatitis A virus Signup and view all the answers

How is Hepatitis B primarily transmitted?

Blood and contaminated needles Signup and view all the answers

What is the incubation period for Hepatitis A?

One month Signup and view all the answers

Which outcome is likely if both IgM and IgG are negative?

Symptoms due to another cause Signup and view all the answers

What type of vaccine is used for Hepatitis A?

Formalin-killed virus Signup and view all the answers

What is a characteristic of Hepatitis A in relation to chronic liver disease?

It does not cause chronic liver disease Signup and view all the answers

What is the typical incubation period for Hepatitis B?

Three months Signup and view all the answers

What is considered a true positive result in the context of antibody testing?

Antibody specificities against known viral components Signup and view all the answers

Which laboratory marker is categorized as progressing to AIDS when CD4+ T-cell counts drop below what level?

200/µL Signup and view all the answers

In children younger than 18 months, why are serological tests for HIV infection considered unreliable?

Maternal antibodies interfere with detection Signup and view all the answers

Which mosquito is primarily responsible for transmitting the dengue virus?

Aedes Aegypti Signup and view all the answers

What type of virus causes dengue fever?

RNA virus Signup and view all the answers

What is the typical duration of symptoms for dengue fever?

2–7 days Signup and view all the answers

What is the NS1 antigen used for in the diagnosis of dengue fever?

To detect active infection Signup and view all the answers

What environmental condition increases the risk of dengue fever transmission?

Rainy season Signup and view all the answers

What is the significance of detecting anti-HBc antibodies in chronic hepatitis B?

Correlates with serum HBV DNA levels Signup and view all the answers

During which stage of hepatitis B infection is HBeAg most likely to be elevated?

During chronic infection Signup and view all the answers

Which serological test offers a qualitative detection of HBsAg in serum?

Chromatographic technique Signup and view all the answers

Which principle is involved in the ELISA test for detecting HBsAg?

Color change from a substrate reaction Signup and view all the answers

What does the presence of HBV DNA indicate in a patient?

Active viral replication is occurring Signup and view all the answers

What is the typical time frame for detecting anti-HCV IgG in a patient post-infection?

6-8 weeks Signup and view all the answers

Which of these tests is a molecular test for hepatitis B diagnosis?

PCR Signup and view all the answers

What method is employed to detect HBsAg using reverse passive hemagglutination?

Erythrocytes sensitive to HBsAg Signup and view all the answers

Study Notes

Viruses

Characterized as obligate intracellular parasites, exhibiting life only within host cells.
Outside host cells, viruses are inert and lack enzymatic activity.
Inside host cells, viral nucleic acids (DNA or RNA) hijack cellular machinery to replicate and produce new virus particles.

HIV Serology

HIV compromises the immune system, potentially leading to AIDS if untreated.
Transmission occurs via blood, sexual contact, and from mother to child during pregnancy, delivery, or breastfeeding.
Common laboratory testing methods include Rapid tests, ELISA, and RT-PCR.

Common HIV Antibody Tests

Enzyme Linked Immunosorbent Assays (ELISA) include indirect methods.
Rapid Tests provide quick results.
Western Blot is a confirmation test for HIV antibodies.

Rapid Assay Testing Principle

Antigen is coated onto a test strip with a positive control.
Sample addition triggers a reaction between antigen and antibody, if present.
Positive result shows two or three colored bars; negative shows one colored bar; invalid results appear without lines.
Specificity against viral components is crucial for true positive results.

Laboratory Monitoring for HIV

Peripheral blood CD4 T-cell count: Levels under 200/µL indicate progression to AIDS.
HIV-1 RNA level (viral load) is detectable as early as 10 days post-infection; highly sensitive tests like qPCR are employed.

Serology of Dengue Fever

Dengue is a mosquito-borne viral disease prevalent in tropical and subtropical regions, transmitted by Aedes Aegypti mosquitoes.
The dengue virus (RNA) is part of the Flavivirus genus; four serotypes exist (DEN-1 to DEN-4).
Infection with one serotype results in lifelong immunity against that type.

Dengue Fever Symptoms

High fever (40°C/104°F), severe headache, pain behind the eyes, muscle and joint pain, nausea, vomiting, swollen glands or rash.
Symptoms are self-limiting, usually lasting 2-7 days.

Laboratory Diagnosis of Dengue

Virus detection via cell culture, antigen detection, and viral RNA detection within 24-48 hours.
NS1 glycoprotein antigen can be rapidly detected; a strong humoral response noted.
IgM antibodies appear first, detectable by days 3-5, reaching 99% detection by day 10.
IgG levels indicate past infection and remain detectable over months to years.

Rapid Antibody Testing for Dengue

Simple procedure involves adding patient serum and buffer; results interpreted after 15 minutes.
Positive IgM and negative IgG indicate a current infection; positive IgG indicates a past infection.

Serology of Hepatitis Tests

Hepatitis refers to liver inflammation, caused by various viruses, primarily hepatotrophic viruses (A, B, C, D, E).
Each virus has distinct transmission routes and incubation periods.

Hepatitis A Virus

RNA virus primarily spread via the fecal-oral route; rare transmission via blood.
Incubation is around one month; does not cause chronic liver disease.
Effective vaccine available (formalin-killed HAV).

Hepatitis B Virus

DNA virus spread through blood, sexual contact, and perinatal routes.
Approximately 3-month incubation; antibodies against HbcAg detectable.
HBeAg serves as an indicator of acute or chronic infection.

Serological Testing for Hepatitis B

Reverse passive latex agglutination and chromatographic techniques used for HBsAg detection, with ELISA being the most common method.
PCR (qPCR) is a confirmatory test for HBV DNA detection.

Hepatitis C Virus (HCV) Antibody Testing

Diagnosis is achieved by detecting anti-HCV IgG in serum, usually detectable 6-8 weeks post-infection.
Anti-HCV testing is critical for screening blood donors.

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Description

Explore the key concepts of viral infections and serological testing as discussed in Chapter 4. This quiz covers the characteristics of viruses, with a focus on HIV and its impact on the immune system. Test your understanding of viral replication and the significance of serology in diagnosing infections.