SSPE is a rare, fatal, progressive neurological disorder that occurs years after a measles infection.

• a) Guillain–Barré syndrome: Associated with other infections but not commonly with measles.

• c) Reye’s syndrome: Associated with aspirin use in viral infections, especially influenza and varicella.

• d) Myocarditis: More commonly associated with Coxsackie B virus.

Shell vial culture improves viral detection by using centrifugation to enhance the infection of cells with virus particles, speeding up viral growth and detection.

• a) Prolonged incubation: Actually, shell vial culture reduces incubation time.

• c) Antibiotic suppression: Helps prevent bacterial contamination but is not the key enhancement.

• d) pH modification: Not related to shell vial technique.

HPV is the virus genus strongly associated with anogenital warts, cervical dysplasia, and cervical neoplasia (including cervical cancer). Certain high-risk HPV types (like HPV 16 and 18) are known to cause cervical cancer.

• a) Herpes simplex virus: Causes genital herpes, not warts or cervical cancer.

• c) Cytomegalovirus: Causes infections mainly in immunocompromised individuals, not associated with warts or cervical neoplasia.

• d) Coxsackievirus: Causes hand, foot, and mouth disease and other illnesses, unrelated to anogenital warts.

West Nile virus primarily cycles between mosquitoes and birds, which act as the main reservoir hosts. Birds carry and amplify the virus, and infected mosquitoes then transmit it to humans and other animals.

• a) Mice and b) Rats: Not primary reservoirs for West Nile virus.

• c) Domestic cats: Not involved in the transmission cycle.

Herpes simplex virus (HSV), particularly HSV type 1, is the most common cause of sporadic viral encephalitis worldwide. It can cause severe inflammation of the brain (encephalitis), often involving the temporal lobes.

• a) Epstein-Barr virus: Mainly causes infectious mononucleosis; encephalitis is rare.

• c) Coxsackie B virus: Can cause aseptic meningitis and sometimes encephalitis but less commonly.

• d) Varicella zoster virus: Can cause encephalitis, especially in immunocompromised patients, but less common than HSV.

Viral transport medium contains buffers and antibiotics that prevent bacterial and fungal overgrowth in clinical specimens, helping preserve viral particles until testing.

• a) Host cell lysis: Not the primary purpose.

• c) Antibiotic degradation: Not relevant here.

• d) Protein denaturation: Not the main function of transport medium.

PCR of cerebrospinal fluid (CSF) is the gold standard for diagnosing HSV-1 encephalitis, allowing rapid and sensitive detection of the virus.

• a) Rotavirus: Causes gastroenteritis, not encephalitis.

• c) HPV: Human papillomavirus, not associated with encephalitis.

• d) Norovirus: Causes gastroenteritis, not encephalitis.

1. Primary Vector Role:

   • Aedes aegypti is the dominant global vector for dengue virus (DENV), responsible for the majority of outbreaks worldwide .

   • Dengue is the most prevalent mosquito-borne viral disease, with an estimated 390 million infections annually, primarily transmitted by Ae. aegypti .

2. Epidemiological Impact:

   • Over 120 countries report dengue as endemic, with Ae. aegypti driving urban outbreaks due to its preference for human habitats and artificial water containers .

   • The WHO identifies dengue as a leading cause of morbidity among Aedes-transmitted diseases, with severe cases (e.g., hemorrhagic fever) linked to Ae. aegypti.

3. Comparative Transmission Efficiency:

   • While Ae. aegypti also transmits Zika virus (d) and yellow fever, dengue is more frequently associated with this mosquito due to its higher transmission rates and broader geographic distribution .

   • West Nile virus (a) is primarily spread by Culex mosquitoes, not Ae. aegypti .

   • Hantavirus (c) is transmitted by rodents, not mosquitoes [not mentioned in search results].

4. Evolutionary Adaptation:

   • Ae. aegypti evolved alongside dengue virus in Africa, optimizing its efficiency as a vector through human-biting preferences and urban breeding behaviors .

Other Viruses Transmitted by Ae. aegypti (Less Dominant):

• Zika virus (d): Secondary to dengue in frequency, though notable for outbreaks in the Americas (2015–2016).

• Chikungunya and yellow fever: Also transmitted but with fewer annual cases compared to dengue .

Why Not the Other Options?

• West Nile virus (a): Primarily vectored by Culex species .

• Hantavirus (c): Not mosquito-borne; transmitted via rodent excreta [no relevant citation].

Hantavirus (Sin Nombre virus) is transmitted primarily through inhalation of aerosolized excreta (urine, droppings, saliva) from infected deer mice (Peromyscus maniculatus), which are the main reservoir in the Four Corners region of the US.

• b) Norwegian rat: Associated with other hantaviruses, like Seoul virus.

• c) Domestic canine: Not a vector for hantavirus.

• d) Ixodes tick: Vector for Lyme disease, not hantavirus.

Cytopathic effect (CPE) refers to the structural changes in host cells caused by viral invasion, observed in cell cultures. It is commonly used as a presumptive identification of viral infection in diagnostic virology because viruses often cause visible changes like cell rounding, fusion, or lysis in cultured cells.

• b) Intranuclear inclusions in RBCs: Red blood cells do not have nuclei, so intranuclear inclusions can’t occur in RBCs.

• c) Cell lysis of sheep red blood cells: This refers to hemolysis, often related to bacterial toxins or some immune reactions, not a general viral identification.

• d) Presence of mononuclear inflammatory cells: This indicates a type of immune response but is not specific or presumptive for viral infections.

Human herpesvirus 8 (HHV8) is the causative agent of Kaposi sarcoma, a vascular tumor commonly seen in immunocompromised patients, especially those with HIV/AIDS.

• b) Duncan disease: A rare genetic immunodeficiency disorder, not caused by HHV8.

• c) Fifth disease and d) Exanthem infectiosum: Both refer to the same illness caused by Parvovirus B19, not HHV8.

Direct fluorescent antibody (DFA) testing involves applying fluorescently labeled antibodies directly to clinical specimens or cultured cells to detect the presence of specific viral antigens. The fluorescent antibodies bind to infected cells, which can then be visualized under a fluorescence microscope.

• a) Live virus: Not required; DFA detects viral antigens in fixed cells.

• c) DNA amplification: This is PCR, not DFA.

• d) Radiolabeled probes: Used in other molecular techniques, not DFA.

“Owl’s eye” inclusions are large, basophilic nuclear inclusions seen in cells infected with cytomegalovirus (CMV). They are characteristic for CMV infection.

• a) Adenovirus: Causes different types of inclusions but not “owl’s eye.”

• c) RSV: Causes syncytia but no “owl’s eye” inclusions.

• d) Parvovirus: Causes different pathology; no owl’s eye inclusions.

Hepatitis B virus (HBV) is a partially double-stranded enveloped DNA virus that is transmitted mainly through blood and body fluids.

• a) Incorrect — HBV infects liver cells (hepatocytes), not CD4+ T lymphocytes.

• b) Incorrect — Reactivation causing shingles is related to Varicella-Zoster Virus (VZV), not HBV.

• d) Incorrect — Fecal-oral transmission is typical of Hepatitis A virus, which is an RNA virus.

Mumps virus is best detected early in the illness from the buccal (oral) swab, especially from the area around the parotid gland ducts, where the virus replicates.

• a) Blood: Used for serology but less sensitive for early detection.

• c) Urine: Not typically used for mumps virus detection.

• d) Feces: Not a common specimen for mumps virus.

Coxsackie B virus, an enterovirus, is the virus most commonly associated with viral myocarditis — inflammation of the heart muscle.

• b) Measles virus: Not typically linked to myocarditis.

• c) Hepatitis C virus: Primarily affects the liver.

• d) Parvovirus B19: Can be associated with myocarditis but less frequently than Coxsackie B.

PCR is the most sensitive and specific method for detecting viral nucleic acids (DNA or RNA) early in infection, even when viral loads are low.

• b) ELISA: Detects antibodies or antigens but not nucleic acids.

• c) Immunoblot: Used for confirming antibody presence, not nucleic acids.

• d) Viral culture: Takes longer and is less sensitive than PCR.

• Antigenic drift refers to small, gradual changes (point mutations) in the hemagglutinin (H) and neuraminidase (N) genes of the influenza virus. These changes cause seasonal flu epidemics by allowing the virus to evade pre-existing immunity.

• Antigenic shift is a major, abrupt change due to reassortment of gene segments, often leading to new influenza subtypes and pandemics.

So:

• b) Incorrect — Pandemics are caused by antigenic shift.

• c) Incorrect — Seasonal epidemics are caused by antigenic drift.

• d) Incorrect — Local annual outbreaks are caused by antigenic drift, not shift.

Viral neutralization tests measure the ability of antibodies to neutralize or inhibit viral infectivity, reflecting their efficacy in preventing virus infection of cells.

• a) Antigen concentration: Measured by other assays like ELISA.

• c) Genome copies: Measured by PCR.

• d) Enzyme activity: Measured by specific enzyme assays.

The ELISA test is the primary screening test for HIV because it detects antibodies against HIV in the blood. It is sensitive, inexpensive, and widely used.

• b) Western blot: Used as a confirmatory test after a positive ELISA.

• c) Quantitative HIV RNA: Used to measure viral load, not for initial screening.

• d) CD4 count: Used to assess immune status in diagnosed HIV patients, not for screening.

Stool samples often contain substances that inhibit PCR. Diluting the sample can reduce the concentration of inhibitors, allowing successful amplification.

• a) Freeze-thaw cycles: May help release nucleic acids but not specifically reduce inhibitors.

• c) Centrifugation: Helps clarify samples but may not remove inhibitors.

• d) Antibiotic addition: Prevents bacterial growth, not PCR inhibition.

Anti-HAV IgM antibodies appear early during acute or recent hepatitis A virus (HAV) infection and indicate recent or current infection.

• a) Anti-HAV IgG: Indicates past infection or immunity, not recent infection.

• c) HBsAg: Marker for hepatitis B virus infection.

• d) Anti-HBs: Indicates immunity to hepatitis B virus.

Rapid immunoassays can detect influenza viral antigens in respiratory specimens within about 15 minutes, providing quick diagnostic results.

• a) Viral culture: Takes days.

• b) PCR: Highly sensitive but usually takes several hours.

• d) Southern blot: Used for DNA detection, not rapid or commonly for influenza.

Varicella-zoster virus (VZV) causes two main clinical syndromes:

• Chickenpox (varicella) — primary infection

• Shingles (herpes zoster) — reactivation of latent virus in dorsal root ganglia

• a) Infectious mononucleosis: Caused by Epstein-Barr virus (EBV), not VZV.

• c) Primary CNS lymphoma: Associated with EBV, especially in immunocompromised patients.

• d) Burkitt lymphoma: Also linked to EBV, not VZV.

Respiratory syncytial virus is the primary cause of infantile respiratory bronchiolitis and is a major pathogen causing lower respiratory tract infections in infants and young children.

• a) Parainfluenza virus: Causes croup and other respiratory infections but less commonly infantile bronchiolitis.

• b) Metapneumovirus: Can cause respiratory infections but less common than RSV.

• c) Coxsackie A virus: Mainly causes hand, foot, and mouth disease and other conditions.

Hemagglutination inhibition (HI) tests are used to identify and differentiate influenza virus strains based on their ability to agglutinate red blood cells and the inhibition of this agglutination by specific antibodies.

• a) HIV subtypes: Identified by molecular methods.

• c) HBV genotypes: Determined by sequencing or PCR.

• d) HPV variants: Identified by PCR and sequencing.

Rotavirus particles are often detected directly in stool samples by electron microscopy due to their distinct wheel-like appearance.

• a) Herpes simplex: Diagnosed by PCR or culture.

• c) HIV: Diagnosed by serology and PCR.

• d) Hepatitis C: Diagnosed by serology and PCR.

Koplik spots are small, white or bluish-white spots on the buccal mucosa and appear 1-2 days before the characteristic measles rash. They are considered pathognomonic for measles.

• b) After rash subsides: Incorrect; Koplik spots appear before the rash.

• c) Simultaneously with fever: Koplik spots usually appear while the fever is rising but before rash.

• d) Only in severe infections: Incorrect; they occur in typical measles infections regardless of severity.

Epstein-Barr virus (EBV) is associated with several diseases, including:

• Burkitt lymphoma: Especially the endemic form in Africa.

• Hodgkin lymphoma: EBV is implicated in many cases.

• a) Chickenpox: Caused by Varicella-zoster virus, not EBV.

• d) Smallpox: Caused by the Variola virus, unrelated to EBV.

The direct fluorescent antibody (DFA) test is widely used to detect viral antigens directly in patient specimens by using fluorescently labeled antibodies specific to viral proteins.

• a) Latex agglutination: Used for some bacterial or fungal antigen detection but less common for viruses.

• c) Gram staining: Used for bacteria, not viruses.

• d) Ziehl–Neelsen staining: Used to detect acid-fast bacteria like Mycobacterium tuberculosis, not viruses.

The syncytium formation test detects the formation of giant multinucleated cells (syncytia) caused by certain viruses, like respiratory syncytial virus (RSV) or herpesviruses, in infected tissue or cell cultures.

• a) Hemadsorption assay: Detects viral hemagglutinin by binding red blood cells, not multinucleated cells.

• c) Latex agglutination: Detects antigen-antibody reactions but not cell fusion.

• d) Dark-field microscopy: Used to visualize spirochetes, not multinucleated cells.

A cytopathic effect (CPE) in cell culture refers to visible changes caused by viral infection, such as cell rounding, detachment, fusion (syncytia), or lysis.

• a) Color change in media: Usually indicates pH change, not CPE.

• c) Gas production: Associated with bacterial fermentation, not viruses.

• d) Colony formation on agar: Refers to bacterial or fungal growth, not viral CPE.

Poliovirus is primarily shed in the feces, so stool specimens are the preferred samples for virus isolation in poliovirus diagnosis.

• a) Nasopharyngeal swab: Less commonly used for poliovirus isolation.

• c) Blood sample: Poliovirus is rarely isolated from blood.

• d) Saliva: Not a preferred specimen for poliovirus isolation.

Madin-Darby Canine Kidney (MDCK) cells are the preferred cell culture system for isolating and propagating influenza viruses because they support efficient viral replication.

• a) Primary monkey kidney cells: Used for some viruses but less common for influenza.

• b) MRC-5 cells: Human lung fibroblasts, used for other viruses like cytomegalovirus.

• d) Hep-2 cells: Used mainly for respiratory syncytial virus (RSV) and other respiratory viruses.

Norovirus is the most common cause of acute viral gastroenteritis outbreaks in adults and is frequently detected in stool specimens during these infections.

• a) Rotavirus: Most common cause of viral gastroenteritis in infants and young children, less common in adults.

• c) Astrovirus: Causes gastroenteritis but less common than norovirus.

• d) Adenovirus 41: Can cause gastroenteritis, mainly in children.

A rising IgG antibody titer between acute and convalescent serum samples indicates a recent or current infection, reflecting the body’s ongoing immune response.

• a) Chronic infection: Usually stable antibody levels.

• c) Vaccine failure: Not directly indicated by rising IgG.

• d) Latent reactivation: May show different antibody patterns, often IgM or other markers.

Adenoviruses are common causes of colds, pharyngitis, conjunctivitis, and other acute respiratory illnesses, especially in children.

• a) Epstein-Barr virus: Causes infectious mononucleosis, not typical colds.

• c) Coxsackie B virus: Associated mainly with myocarditis, pericarditis, and other systemic infections.

• d) Reovirus: Generally causes mild or asymptomatic infections; not a common cause of colds.

Enteric viruses like norovirus are primarily shed in feces, so stool samples are the optimal specimen for detecting these viruses.

• a) Whole blood: Not typically used for enteric virus detection.

• c) Throat swab: Used for respiratory viruses.

• d) Urine: Not used for enteric viruses.

Rotavirus is a double-stranded RNA (dsRNA) virus and a leading cause of viral gastroenteritis in children.

• b) Hepatitis E virus: Single-stranded RNA virus.

• c) Coronavirus: Single-stranded RNA virus.

• d) Poliovirus: Single-stranded RNA virus.

Cytomegalovirus (CMV) is the most common congenital viral infection in the United States. It can cause serious complications in newborns, including hearing loss, developmental delays, and other neurological issues.

• a) VZV (Varicella-Zoster Virus): Can cause congenital varicella syndrome but is less common.

• c) EBV (Epstein-Barr Virus): Not typically associated with congenital infections.

• d) Adenovirus: Not a common cause of congenital infection.

Parvovirus B19 causes erythema infectiosum, also known as “fifth disease,” characterized by a “slapped cheek” rash in children.

• b) Roseola infantum: Caused by Human herpesvirus 6 (HHV-6).

• c) Hand, foot, and mouth disease: Caused by Coxsackie A virus.

• d) Molluscum contagiosum: Caused by a poxvirus.

Severe Acute Respiratory Syndrome (SARS) is caused by a coronavirus, specifically SARS-CoV. Coronaviruses are a family of viruses that can cause respiratory illnesses ranging from the common cold to severe diseases like SARS and COVID-19.

• a) Paramyxovirus: Causes diseases like measles, mumps, and RSV infections.

• b) Enterovirus: Causes diseases like hand-foot-and-mouth disease, poliomyelitis.

• c) Rhinovirus: Causes the common cold.

The Tzanck smear is a cytological test used to detect multinucleated giant cells, which are characteristic of herpesvirus infections, including Varicella-zoster virus (VZV) and Herpes simplex virus (HSV).

• b) Influenza virus: Diagnosed by PCR or antigen tests, not Tzanck smear.

• c) Adenovirus: Diagnosed by PCR, culture, or antigen detection.

• d) Coronavirus: Diagnosed by PCR or antigen testing.

The persistence of hepatitis B surface antigen (HBsAg) in the blood for more than 6 months is the hallmark of chronic hepatitis B infection.

• a) HBeAg: Indicates active viral replication but may not persist in all chronic infections.

• c) Anti-HBe: Usually indicates lower viral replication or resolving infection.

• d) Anti-HBs: Indicates immunity, either from past infection clearance or vaccination.

Next-generation sequencing (NGS) allows for the rapid sequencing of genetic material, enabling identification of unknown or novel viruses by analyzing their genomes without prior knowledge.

• a) Antibiotic resistance: Typically identified by bacterial genomic tests, not primarily by viral NGS.

• c) Bacterial co-infections: NGS can detect bacteria, but in virology, it’s mainly used for viruses.

• d) Prion variants: Prions are proteins, not nucleic acids, so NGS does not detect them.

Detection of IgG antibodies to rubella indicates immunity, either from past infection or vaccination, and is used to confirm immunity in pregnant women.

• a) IgM antibodies: Indicate recent or acute infection, not immunity.

• c) Viral RNA by PCR: Used for diagnosis of active infection.

• d) Hemagglutination inhibition: An older method; less commonly used today compared to IgG detection by ELISA.

For rabies diagnosis, serum is generally unsuitable because antibodies often develop late, and serology is not reliable for early diagnosis.

• a) Saliva: Used for viral RNA detection or antigen testing.

• c) Brain tissue: Gold standard postmortem sample for rabies virus detection.

• d) CSF: Can be tested for antibodies or viral RNA.

The Tzanck smear is a cytological test used to identify multinucleated giant cells, which are characteristic of infections caused by herpesviruses, including Herpes simplex virus and Varicella-zoster virus.

• a) Influenza virus: Diagnosed by PCR or antigen tests.

• c) Hepatitis B: Diagnosed by serology and PCR.

• d) Rotavirus: Diagnosed by antigen detection in stool.

Reverse transcription polymerase chain reaction (RT-PCR) is used to quantify the amount of HIV RNA (viral load) in the blood, helping to monitor disease progression and response to therapy.

• a) Western blot: Used for confirmation of HIV antibodies.

• b) ELISA: Used for initial antibody screening.

• d) Gram stain: Used for bacteria, not viruses.

Negri bodies are eosinophilic cytoplasmic inclusion bodies found in neurons infected with rabies virus and are considered pathognomonic for rabies.

• b) Measles: Characteristic Koplik spots; no Negri bodies.

• c) Mumps: No Negri bodies.

• d) Rubella: No Negri bodies.

The gold standard for confirming dengue virus infection is viral isolation from patient samples. This method definitively identifies the virus.

• a) IgM ELISA: Commonly used for diagnosis but less definitive than isolation.

• c) Rapid test strips: Useful for screening but less specific.

• d) Complete blood count: Can show signs of infection (like thrombocytopenia) but is not diagnostic.

Rapid antigen detection tests are commonly used on nasopharyngeal swabs to quickly diagnose RSV infections, especially in infants and young children with respiratory symptoms.

• a) Rabies virus: Diagnosed via different methods, not rapid antigen tests on swabs.

• c) Human herpesvirus 8: Associated with Kaposi sarcoma; no rapid antigen test from swabs.

• d) Hepatitis D virus: Bloodborne virus; not diagnosed from respiratory samples.

Negri bodies are eosinophilic cytoplasmic inclusion bodies found in neurons, especially in the hippocampus and Purkinje cells, and are pathognomonic for rabies virus infection.

• b) Poliovirus: Does not produce Negri bodies.

• c) Lassa virus: Causes hemorrhagic fever, no Negri bodies.

• d) Yellow fever virus: Causes hemorrhagic fever, no Negri bodies.

Quantitative HIV RNA testing (also called viral load testing) measures the amount of HIV RNA in the blood. It is used to monitor how well a patient is responding to antiretroviral therapy (ART). A decreasing viral load indicates effective treatment.

• a) Serum ELISA: Used for initial HIV antibody screening.

• c) CD4 count: Measures immune system status but not directly the viral response.

• d) p24 antigen detection: Used for early detection of HIV infection but not for monitoring treatment response.

Rotavirus is the leading cause of viral gastroenteritis in infants and young children worldwide. It causes severe diarrhea and dehydration, especially in pediatric populations.

• a) Adenovirus, serotypes 40 and 41: Cause gastroenteritis but less commonly than rotavirus.

• b) Norwalk virus (Norovirus): Common cause of viral gastroenteritis in adults and outbreaks but less frequent in young children.

• c) Coronavirus: Some coronaviruses can cause mild gastroenteritis but are not the main agents.

PCR of cerebrospinal fluid (CSF) is the gold standard for diagnosing HSV-1 encephalitis, a serious viral infection of the brain.

• b) Hepatitis A virus: Not typically diagnosed by CSF PCR; causes hepatitis.

• c) Epstein–Barr virus: Can sometimes be detected in CSF, but less commonly and not the primary diagnostic method.

• d) Influenza virus B: Respiratory virus, rarely diagnosed from CSF.

Hand, foot, and mouth disease is most commonly caused by Coxsackie A virus, particularly types A16 and A6. It is a contagious viral illness characterized by sores in the mouth and a rash on the hands and feet.

• a) Adenovirus: Causes respiratory infections and conjunctivitis, not hand, foot, and mouth disease.

• c) Coxsackie B: Associated with other conditions like myocarditis, but not typically hand, foot, and mouth disease.

• d) Human herpes virus 6: Causes roseola infantum, not hand, foot, and mouth disease.

Respiratory Syncytial Virus (RSV) primarily infects the epithelial cells of the respiratory tract. Nasopharyngeal aspirates collect secretions from the upper respiratory tract where RSV replicates abundantly, making it the specimen of choice for sensitive detection of RSV.

• b) Cough plate: Less commonly used and less sensitive.

• c) Expectorated sputum: Often contaminated and less reliable in infants and young children (the main RSV affected group).

• d) Throat swab: Less sensitive than nasopharyngeal aspirate for RSV.

In a person who has been vaccinated against hepatitis B virus (HBV), you would expect to see anti-HBs antibodies (antibodies against the hepatitis B surface antigen). This indicates immunity due to vaccination.

• a) HBsAg: Presence indicates active infection.

• b) HBeAg: Indicates active viral replication in infected individuals.

• d) Anti-HBc: Indicates past or current infection; not present after vaccination alone.

The presence of heterophile antibodies is used to diagnose infectious mononucleosis, which is most commonly caused by Epstein-Barr virus (EBV).

• b) Rubella: Diagnosed by specific serology.

• c) Cytomegalovirus: Diagnosed by PCR or specific antibody tests; heterophile antibodies are negative.

• d) Mumps: Diagnosed by serology or PCR, no heterophile antibodies.