MicroBiology MCQs with Answer and Explnation | Chapter 39

Answer: HBeAg

HBeAg (Hepatitis B e Antigen) is a marker of active viral replication and indicates high infectivity of the hepatitis B virus in humans.

The other options are incorrect:

• HBCAg (Incorrect): HBCAg refers to Hepatitis B core Antigen, which is not a direct indicator of infectivity. It is more associated with the presence of the virus but does not signify active replication.
• Anti-HBC (Incorrect): Anti-HBC (antibodies against HBCAg) suggests past or current infection but doesn’t indicate the current infectivity status. It is a marker of exposure to the virus.
• Anti-HBS (Incorrect): Anti-HBS (antibodies against HBsAg) indicates immunity due to vaccination or past infection but doesn’t provide information about current infectivity. It signifies protection rather than infectivity.

Answer: IgM anti – HBc

During the window period of Hepatitis B infection (roughly 1-6 months after exposure), neither HBsAg nor anti-HBs are detectable in the blood. However, IgM anti-HBc appears during this time and is the only reliable serologic marker for recent infection.

The other options are incorrect:

• HBsAg: Although a marker of current infection, its absence during the window period doesn’t exclude recent infection.
• Anti-HBs: This antibody develops later in the course of infection, appearing after the window period, hence not indicative of recent infection.
• None of the above: While HBsAg and anti-HBs are not ideal markers during the window period, IgM anti-HBc does represent serologic evidence of recent infection.

Answer: Immediately stitch wound under antibiotic coverage

For the treatment of a class III dog bite (severe, with high risk of infection), immediate wound closure (stitching) is generally contraindicated. This is because dog bites are prone to infection, and closing the wound can trap bacteria inside, leading to an increased risk of complications. Instead, the focus is on cleaning the wound, providing rabies prophylaxis (ARV), and administering immunoglobulins for passive immunity.

The other options are incorrect:

• Give immunoglobulins for passive immunity : Administration of immunoglobulins provides immediate passive immunity against rabies virus, which is crucial in the case of a dog bite, especially if the rabies status of the dog is unknown.
• Give ARV: Administration of Antirabies Vaccine (ARV) is essential to induce active immunity against rabies virus and prevent the development of the disease after exposure.
• Immediately wash wound with soap and water : Cleaning the wound immediately with soap and water is essential to reduce the risk of infection. It helps remove debris and bacteria from the wound, lowering the chance of complications.

Answer: Measles virus

Measles virus is a single-stranded, negative-sense RNA virus belonging to the Paramyxoviridae family. It’s the causative agent of measles, a highly contagious infectious disease.

The other options are incorrect:

• Herpes Virus: Herpes viruses belong to the Herpesviridae family and are double-stranded DNA viruses. Examples include herpes simplex virus (HSV), Epstein-Barr virus (EBV), and cytomegalovirus (CMV).
• Papavo virus: Papavo viruses are also double-stranded DNA viruses belonging to the Parvoviridae family. Examples include human papillomavirus (HPV) and John Cunningham virus (JCV).
• Adeno virus: Adeno viruses are double-stranded DNA viruses belonging to the Adenoviridae family. They cause a variety of infections, including respiratory infections, conjunctivitis, and gastroenteritis.

Answer: Immunodeficiency virus

Immunodeficiency viruses (HIV-1 and HIV-2) are classified as retroviruses. They use RNA as their genetic material and possess the enzyme reverse transcriptase, which allows them to convert their RNA into DNA during infection. This DNA then integrates into the host cell’s genome, enabling viral replication and potential development of AIDS.

The other options are incorrect:

• Influenza: This is an RNA virus belonging to the Orthomyxoviridae family. It does not possess the retroviral characteristic of reverse transcriptase and integrates its RNA directly into the host cell’s cytoplasm for replication.
• Polio virus: This is an RNA virus belonging to the Picornaviridae family. Similar to influenza, it replicates within the host cell’s cytoplasm without integrating its RNA into the genome.
• Hepatitis virus: Different types of Hepatitis viruses exist, but none are classified as retroviruses. Examples include Hepatitis A, B, and C, each belonging to distinct viral families and possessing different replication mechanisms.

Answer: 16,18,31

Human papillomavirus (HPV) types 16 and 18 are known to be high-risk types associated with the development of cervical cancer. Type 31 is also considered a high-risk type.

The other options are incorrect:

• Type 6,12,18: Type 6 and 11 are low-risk HPV types associated with genital warts, while type 18 is a high-risk type associated with cervical cancer. Type 12 is not commonly associated with cervical cancer.
• 6,8,11: Type 6 and 11 are low-risk types associated with genital warts, while type 8 is not typically associated with cervical cancer.
• 3,10,19: None of these types (3, 10, 19) are well-known for their association with cervical cancer. Cervical cancer is primarily linked to high-risk types such as 16, 18, and others.

Answer: Interferon production

The viral action is differentiated from bacterial action by interferon production. Interferons are proteins produced by cells in response to viral infections. They play a crucial role in the innate immune response by interfering with viral replication and spreading to nearby cells.

The other options are incorrect:

• Toxin production: Toxin production is a characteristic of some bacteria, not viruses. Bacterial toxins contribute to the pathogenicity of bacterial infections.
• Lymphocytes production: Lymphocytes are a type of white blood cell involved in both viral and bacterial infections. Their production is not a specific marker for differentiating between viral and bacterial actions.
• Neutrophils production: Neutrophils are a type of white blood cell involved in the immune response against bacterial infections. Their production is not a specific indicator for differentiating between viral and bacterial actions.

Answer: RNA-DNA

The correct sequence that a retrovirus follows upon entering a host cell is RNA to DNA. Retroviruses, such as HIV (Human Immunodeficiency Virus), contain RNA as their genetic material. After entering the host cell, the enzyme reverse transcriptase converts the viral RNA into DNA through a process known as reverse transcription.

The other options are incorrect:

• RNA-DNA-RNA: This sequence is not characteristic of retroviruses. Retroviruses undergo reverse transcription to convert their RNA genome into DNA, but there is no subsequent conversion back to RNA within the host cell.
• DNA-RNA: This sequence is not accurate for retroviruses. Retroviruses begin with an RNA genome, which is reverse transcribed into DNA upon entry into the host cell.
• DNA-RNA-DNA: This sequence is not typical for retroviruses. The primary step in retroviral replication is the conversion of viral RNA into DNA (reverse transcription).

Answer: Human Herpes Virus 8

Overwhelming evidence shows that HHV-8, also known as Kaposi Sarcoma-associated Herpesvirus (KSHV), is present in 95-98% of all Kaposi’s sarcoma (KS) lesions. This strong association suggests that HHV-8 plays a crucial role in the development of KS.

The other options are incorrect:

• Human Herpes Virus 3 (HHV-3): HHV-3, also known as Varicella-Zoster virus, causes chickenpox and shingles but has no known association with Kaposi’s sarcoma.
• Human Herpes Virus 1 (HHV-1): HHV-1, also known as Herpes Simplex Virus type 1, causes cold sores and can cause other infections, but it is not linked to Kaposi’s sarcoma.
• Human Herpes Virus 4 (HHV-4): HHV-4, also known as Epstein-Barr virus, is associated with some cancers like Burkitt’s lymphoma and nasopharyngeal carcinoma, but it has no established role in Kaposi’s sarcoma.

Answer: ELISA

In the scenario described, the initial diagnosis of HIV is typically done using an ELISA (Enzyme-Linked Immunosorbent Assay) test. ELISA is a sensitive screening test that detects the presence of antibodies to HIV in the blood. It is commonly used as the first step in HIV testing.

The other options are incorrect:

• Western blot: The Western blot is a confirmatory test for HIV and is used after a positive result on the ELISA to confirm the presence of antibodies. It is not typically used as the initial diagnostic test.
• P24 antigen: The P24 antigen test detects the presence of the HIV P24 antigen, a viral protein. While it can be used for early detection, it is not commonly used as the primary diagnostic test.
• Lymph node biopsy : A lymph node biopsy is not used for the direct diagnosis of HIV. It may be performed if there are concerns about other conditions or to investigate the cause of lymphadenopathy, but it does not directly confirm HIV infection.

Answer: Resistance to hepatitis B

A positive Anti-HBsAb test indicates the presence of antibodies against the Hepatitis B surface antigen (HBsAg). These antibodies are produced by the immune system in response to a hepatitis B infection, either from vaccination or a naturally acquired infection that has since cleared. Therefore, a positive Anti-HBsAb test signifies immunity and protection against future hepatitis B infection.

The other options are incorrect:

• Acute infection: A positive Anti-HBsAb test alone does not indicate an ongoing acute infection. Other markers like HBsAg would be positive in such cases.
• Good prognosis: While having immunity due to Anti-HBsAb generally signifies good prognosis regarding future hepatitis B infection, it doesn’t necessarily guarantee overall good health in other aspects.
• Hepatocellular carcinoma: Hepatocellular carcinoma is a liver cancer, and while chronic hepatitis B infection is a risk factor, a positive Anti-HBsAb indicates immunity and not infection, suggesting a lower risk.

Answer: High infectivity

The presence of HBeAg (Hepatitis B e Antigen) in patients with hepatitis B indicates a high level of viral replication and infectivity. HBeAg is a protein produced by the hepatitis B virus, and its presence signifies active viral replication, meaning the virus is making many copies of itself and can be easily transmitted to others.

The other options are incorrect:

• Simple carriers: While some chronic hepatitis B patients without HBeAg are considered “simple carriers” with less infectivity, the presence of HBeAg specifically points to high viral activity and increased risk of transmission.
• Late convalescence: This refers to the recovery phase after an acute hepatitis B infection, where HBeAg might be transiently present. However, in a chronic infection, persistent HBeAg indicates ongoing viral replication.
• Carrier status: While HBeAg-positive individuals are indeed considered carriers of the hepatitis B virus, the main emphasis is on the associated high infectivity rather than just the carrier state.

Answer: HEV

While all the listed viruses (HBV, HCV, HDV, and HEV) can cause hepatitis, HEV does not progress to chronic hepatitis in most cases. HEV infections are typically acute and self-limited, resolving within a few weeks without transitioning into chronic liver disease.

The other options are incorrect:

• HBV: Hepatitis B virus (HBV) can lead to chronic infection in up to 25% of cases, characterized by persistent inflammation and fibrosis of the liver.
• HCV: Hepatitis C virus (HCV) also has a high tendency for chronicity, with roughly 70-80% of infected individuals developing chronic hepatitis C.
• HDV: Hepatitis D virus (HDV) only superinfects individuals already infected with HBV and can significantly worsen the course of HBV infection, including increasing the risk of chronicity and complications.

Answer: Hepatitis B

Among the listed options, only the Hepatitis B vaccine is currently classified as a cell fraction derived vaccine. This type of vaccine is made from specific components of cells infected with the virus, rather than using the whole virus itself. In the case of the Hepatitis B vaccine, it uses surface antigens (HBsAg) purified from the yeast cells expressing the viral protein.

The other options are incorrect:

• Measles, Mumps, and Rubella (MMR): These vaccines are live attenuated virus vaccines. This means they use a weakened form of the live virus that can replicate in the body but is unable to cause severe disease.
• Hepatitis A: Similar to MMR, the Hepatitis A vaccine is also a live attenuated virus vaccine.

Answer: Flavi virus

Dengue virus belongs to the genus Flavivirus, which is part of the larger family Flaviviridae. This family includes several other mosquito-borne viruses that cause significant human diseases, such as yellow fever, West Nile virus, Zika virus, and Japanese encephalitis virus.

The other options are incorrect:

• Togaviridae: This family includes viruses like alphaviruses (chikungunya virus) and rubella virus. While also transmitted by mosquitoes, they have different genetic and structural characteristics compared to Flaviviruses.
• Reoviridae: This family encompasses viruses like rotavirus and respiratory syncytial virus, which are not transmitted by mosquitoes but primarily through respiratory or fecal-oral routes.
• Rhabdoviridae: This family includes viruses like rabies virus and lyssavirus, which are typically transmitted through bites from infected animals and have different structural and replicative mechanisms compared to Flaviviruses.

Answer: Rubella

Rubella virus: This is the most likely virus to cross the placenta and cause fetal defects due to its high tropism (attraction) for fetal tissues. Infection during pregnancy, especially in the first trimester, can lead to Congenital Rubella Syndrome (CRS), which can cause severe birth defects like cataracts, heart malformations, deafness, and developmental delays.

The other options are incorrect:

• Herpes Simplex Virus (HSV): While HSV can be transmitted to the fetus during pregnancy, it’s less likely to cause congenital malformations compared to Rubella. Most cases of neonatal HSV infection occur during delivery through contact with infected genital secretions.
• Mumps virus: Although Mumps can cause fever and other symptoms in pregnant women, it rarely crosses the placenta and doesn’t pose a significant risk of fetal malformations.
• Papillomavirus (HPV): Different HPV strains cause cervical cancer and genital warts, but they don’t typically cross the placenta and are not associated with fetal defects.

Answer: Small pox

The measles virus is the only one among the listed options that produces both intranuclear and intracytoplasmic inclusion bodies in infected cells. These inclusions are characteristic accumulations of viral proteins and cellular debris, visible under microscopy and serving as diagnostic markers for the disease.

The other options are incorrect:

• Chickenpox: While the varicella-zoster virus (causing chickenpox) produces intranuclear inclusion bodies, it doesn’t typically form intracytoplasmic inclusions.
• Rabies: The rabies virus primarily forms intracytoplasmic inclusions called Negri bodies, but not intranuclear inclusions.
• Smallpox: The smallpox virus produces both intranuclear and intracytoplasmic inclusions, but the disease has been eradicated globally and is no longer a public health concern.

Answer: Reverse transcriptase

The defining characteristic of a retrovirus is its unique enzyme called reverse transcriptase. This enzyme allows the virus to convert its single-stranded RNA genome into double-stranded DNA, which can then integrate into the host cell’s DNA and become part of its genetic material. This ability to reverse the usual flow of genetic information (“DNA to RNA”) sets retroviruses apart from other types of viruses.

The other options are incorrect:

• Ribonuclease: This enzyme breaks down RNA and is not involved in retroviral replication.
• DNA polymerase: This enzyme is used by many viruses to replicate their DNA but is not specific to retroviruses.
• Restriction endonuclease: This enzyme cuts DNA at specific sequences and is not involved in viral replication.

Answer: Virus

Dengue Hemorrhagic Fever (DHF) is primarily caused by the dengue virus, specifically by any of the four serotypes (DENV-1, DENV-2, DENV-3, and DENV-4) belonging to the Flavivirus genus. These viruses are transmitted through the bites of infected Aedes mosquitoes, particularly Aedes aegypti.

The other options are incorrect:

• Bacteria: Bacterial infections can sometimes occur as secondary complications in DHF patients, but they are not the primary cause of the disease.
• Parasite: Similar to bacteria, parasitic infections might arise as secondary complications, but DHF itself is not caused by parasites.
• Bacteria superadded on virus: While bacterial superinfections can worsen the course of DHF, the initial trigger and main contributor to the disease is the dengue virus.

Answer: Protein synthesis

Interferon interferes with the replication of the virus at the time of protein synthesis. Interferons are proteins released by cells in response to viral infections. They have antiviral properties and can inhibit protein synthesis in infected cells, limiting the spread of the virus.

The other options are incorrect:

• DNA/RNA replication: While interferons have antiviral effects, they primarily interfere with protein synthesis rather than directly affecting the replication of DNA or RNA.
• When virus enters the cell: Interferons are typically produced and released by cells in response to viral infection, but they don’t directly interfere with the entry of the virus into the cell.
• Uncoating of the virus proteins capsule: Interferons mainly exert their antiviral effects after the virus has entered the cell and during subsequent stages such as protein synthesis. They do not directly interfere with the uncoating of the virus.

Answer: Spore

Among the listed options, spores are the most resistant to antiseptics and disinfectants. This exceptional resistance is due to their unique multi-layered protective coat and dormant metabolic state.

The other options are incorrect:

• Mycobacteria: While Mycobacteria have a tough cell wall and some species like M. tuberculosis exhibit resistance to certain antiseptics, they are not as resilient as spores in general.
• Prions: Prions are not technically microbial cells but infectious proteins. They lack a cell wall and are generally insensitive to most antiseptics and disinfectants, but their resistance isn’t comparable to the robust structures of spores.
• Coccidia: Coccidia are single-celled protozoan parasites with relatively weaker cell walls compared to spores. They are usually susceptible to common antiseptics and disinfectants.

Answer: Orthomyxovirus

Among the listed options, Orthomyxoviruses do not infect salivary glands. These viruses primarily target the respiratory tract, causing diseases like influenza (flu) and avian influenza. They lack the necessary tropism (attraction) for salivary gland tissue and don’t typically replicate or cause infection there.

The other options are incorrect:

• Echo virus: This virus belongs to the Picornaviridae family and can indeed infect and cause inflammation in the salivary glands, leading to mumps-like symptoms.
• Hepatitis C virus (HCV): While HCV primarily targets liver cells, it can rarely cause secondary Sjögren’s syndrome, an autoimmune disease affecting salivary and lacrimal glands. However, HCV itself doesn’t directly infect and replicate in salivary glands.
• HIV: Similar to HCV, HIV doesn’t directly infect salivary glands. However, some individuals with HIV might experience dryness of the mouth and salivary gland dysfunction as secondary complications from the virus affecting other body systems.

Answer: Keratoacanthoma

Keratoacanthoma is not typically associated with infection from human papillomavirus (HPV). It is a benign skin tumor that usually occurs on sun-exposed skin and is more linked to sun exposure rather than viral infection.

The other options are incorrect:

• Verruca vulgaris: These common warts are often caused by HPV types 2 and 4, presenting as rough, elevated bumps on the hands and feet.
• Focal epithelial hyperplasia: This benign oral lesion can be associated with HPV infection, particularly types 13 and 33, appearing as white or pink papules on the tongue or buccal mucosa.
• Condyloma acuminatum: These genital warts are a classic manifestation of HPV infection, typically caused by types 6 and 11, and appear as soft, fleshy growths in the genital area.

Answer: Readily inactivated by autoclave at 121°C

While prions exhibit unique properties unlike other infectious agents, being readily inactivated by autoclave at 121°C for sufficient time is their most distinguishing characteristic in this context. Here’s why the other options are incorrect:

The other options are incorrect:

• Evokes strong immunogenic reaction: Prions, surprisingly, do not trigger a strong immune response in the host. This contributes to their persistence and the challenges in developing vaccines against prion diseases.
• Sensitive to most chemical sterilization: While some chemicals like strong oxidizing agents can denature prion proteins, they are generally resistant to common disinfectants and chemical sterilization methods compared to other microbes.
• Contains DNA/RNA: Unlike most infectious agents, prions lack any genetic material like DNA or RNA. They solely consist of misfolded proteins that can propagate their abnormal structure in other proteins.

Answer: Hepatitis E virus

In a young pregnant woman presenting with fulminant hepatic failure, the most likely etiological agent is Hepatitis E virus (HEV). Hepatitis E is known for its association with severe disease, especially in pregnant women, where it can lead to fulminant hepatic failure.

The other options are incorrect:

• Hepatitis B virus: While hepatitis B can cause severe liver disease, including fulminant hepatic failure, Hepatitis E is more commonly associated with this clinical presentation, particularly in pregnant women.
• Hepatitis C virus: Hepatitis C virus can lead to chronic liver disease, but it is less commonly associated with fulminant hepatic failure compared to Hepatitis E.
• Hepatitis A virus: Hepatitis A virus usually causes an acute, self-limiting infection and is not a common cause of fulminant hepatic failure. Hepatitis E is more strongly linked to severe outcomes in pregnant women.

Answer: Secretory IgA

The salivary protein that plays a significant role in preventing the transmission of human immunodeficiency virus (HIV) via saliva is Secretory IgA (Immunoglobulin A). Secretory IgA is an antibody that can neutralize viruses, including HIV, at mucosal surfaces. It helps to prevent the entry and transmission of the virus.

The other options are incorrect:

• Sialoperoxidase: Sialoperoxidase is an enzyme found in saliva that has antimicrobial properties but is not specifically known for preventing the transmission of HIV.
• Salivary leukocyte proteinase inhibitor: This proteinase inhibitor is involved in regulating protease activity in saliva and is not specifically recognized for preventing HIV transmission.
• Histidine-rich proteins: Histidine-rich proteins in saliva are involved in various functions, but they are not specifically known for preventing the transmission of HIV. Secretory IgA plays a more direct role in mucosal immunity against viruses.

Answer: Convalscent carrier

The dentist, who suffered from Hepatitis B infection 3 months back, but has normal laboratory tests, is likely a convalescent carrier. Convalescent carriers are individuals who have recovered from the acute phase of an infection but continue to carry the virus for a certain period. In this case, the dentist may still have detectable hepatitis B surface antigen (HBsAg) in the absence of symptoms.

The other options are incorrect:

• Inactive carrier: Inactive carriers typically have normal liver function tests and low or undetectable viral replication. This term is not applicable to someone who recently suffered from Hepatitis B.
• Healthy carrier : Healthy carriers do not show signs of illness and may carry the virus without symptoms, but the term is not typically used for individuals recently infected and in the convalescent phase.
• Paradoxical carrier: There is no term commonly used as “paradoxical carrier” in the context of viral infections. The appropriate term here would be convalescent carrier.

Answer: Nonembryonated egg

Viruses lack their own metabolic machinery and require living host cells to replicate. While some viruses can be cultured in specialized cell lines, embryonated chicken eggs are a traditional and versatile method for culturing a wide range of viruses, including influenza, mumps, measles, and rabies. The developing chick embryo provides the necessary living cells for viral replication, allowing researchers to study and diagnose viral infections.

The other options are incorrect:

• Saubourd’s agar: This is a specialized medium used for culturing specific types of bacteria, not viruses.
• Rogosa medium: This is also a bacterial medium, specifically designed for Lactobacilli species.
• Nonembryonated egg: While the albumen and yolk of a nonembryonated egg offer some nutrients, they lack the crucial living cells needed for viral replication.

Answer: Below 200

Kaposi’s sarcoma (KS) is a cancer linked to immune suppression, particularly in individuals with advanced HIV infection. It develops when the body’s immune system, specifically CD4+ lymphocytes, are severely weakened. Therefore, KS typically occurs when CD4 counts are below 200 cells/mm³.

The other options are incorrect:

• Above 600: CD4 counts in this range generally indicate relatively robust immune function and a low risk of opportunistic infections like KS.
• Between 1000-2000: Although not as high as 600, CD4 counts within this range still represent a relatively strong immune system and a lower risk of developing KS compared to being below 200.
• Above 2000: This is extremely high for CD4 counts and is not indicative of the immunosuppression associated with KS development.

Answer: Hanta virus pulmonary syndrome is caused by inhalation of rodent urine and faces

Hantavirus pulmonary syndrome (HPS) is indeed caused by the inhalation of aerosolized particles containing the virus, which can be found in the urine, feces, and saliva of infected rodents. Humans can contract HPS when they inhale contaminated dust or air.

The other options are incorrect:

• Kyanasur forest disease is caused by bite of wild animal: Kyanasur forest disease is caused by the Kyasanur Forest disease virus and is transmitted through the bite of infected ticks, not wild animals.
• Lyssa virus is transmitted by ticks: Lyssa virus, commonly known as rabies virus, is primarily transmitted through the saliva of infected mammals, usually through bites. It is not transmitted by ticks.

Answer: Rubella

The term “German measles” is used to refer to rubella, a viral disease characterized by a mild fever, swollen lymph nodes, and a pink, itchy rash that typically starts on the face and spreads to the body. It is often mistaken for measles (rubeola) due to similar symptoms, but they are caused by different viruses and have distinct characteristics.

The other options are incorrect:

• Rubeola: This is the scientific term for measles, a different viral disease with more severe symptoms than rubella. While they share some similarities, the viruses responsible and the overall disease course differ.
• Herpes simplex: This refers to a group of viruses causing various infections, including cold sores and genital herpes. They are not related to rubella and have distinct symptoms and transmission routes.
• Herpetic gingivostomatitis: This is a specific infection caused by the herpes simplex virus type 1, affecting the gums and mouth. It is not related to rubella and has different clinical features.

Answer:

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Answer: IgM antibodies in serum

While isolating viruses through various methods offers valuable information, diagnosing Hepatitis A infection primarily relies on detecting specific antibodies in the blood. The most accurate and widely used marker for recent Hepatitis A infection is the presence of IgM antibodies against Hepatitis A virus (HAV) in serum. These antibodies appear shortly after infection and are detectable for several months, making them reliable indicators of acute Hepatitis A.

The other options are incorrect:

• Isolation from stool: Although HAV RNA can be detected in stool samples, this method is less sensitive and specific than serological testing for IgM antibodies. Additionally, stool detection is more suitable for identifying ongoing infection or transmission rather than initial diagnosis.
• Culture from blood: HAV cannot be readily cultured from blood due to its dependence on living host cells for replication. Blood cultures are typically used for bacterial infections, not viral infections like Hepatitis A.
• Isolation from bile: Although HAV can be present in bile, isolating it is invasive, technically challenging, and not routinely used for diagnosis. IgM antibody detection in serum offers a simpler and more reliable non-invasive approach.

Answer: chicken pox

Chickenpox is caused by the varicella-zoster virus, which belongs to the herpesvirus family, not the poxvirus family. The other three options, cowpox, molluscum contagiosum, and smallpox, are all caused by different poxviruses.

The other options are incorrect:

• Cowpox: It is caused by the cowpox virus, a member of the orthopoxvirus genus within the poxvirus family. It is closely related to smallpox and can offer some cross-protection against it.
• Molluscum contagiosum: This skin infection is caused by the molluscum contagiosum virus, also a poxvirus. It typically presents with small, painless bumps on the skin.
• Smallpox: This was a highly contagious and often fatal disease caused by the variola virus, another poxvirus. It was eradicated in 1980 through a global vaccination campaign.

Answer: Surface antigen

Hepatitis B surface antigen (HBsAg) is the first marker to appear in the blood after infection and indicates current or recent HBV infection. It is the most sensitive and reliable indicator of HBV prevalence in a serological study.

The other options are incorrect:

• Surface antibody (HBsAb): While HBsAb indicates past infection or successful vaccination, it does not necessarily mean current infection. Therefore, it is not suitable for determining prevalence.
• Core antigen (HBcAg): HBcAg is present only within infected liver cells and is not detectable in the blood. Therefore, it cannot be used in a serological study.
• Core antibody (HBcAb): HBcAb can remain positive even after recovery or vaccination, making it difficult to distinguish between past and present infections. This limits its usefulness in determining prevalence.

Answer: Parvo virus

While several viruses can be associated with aplastic anemia (AA), Parvovirus B19 has the strongest link to triggering AA in individuals with chronic hemolytic diseases, particularly Sickle Cell Disease and Thalassemia. This phenomenon is known as an “aplastic crisis,” where the virus disrupts the already stressed bone marrow in these individuals, leading to a sudden and drastic reduction in blood cell production.

The other options are incorrect:

• Adeno: Adenoviruses can cause various mild respiratory and gastrointestinal infections but haven’t been directly linked to AA.
• Hepatitis: Hepatitis viruses, especially Hepatitis B and C, can damage the liver and indirectly affect blood cell production but aren’t directly associated with AA triggers.
• EB Virus (Epstein-Barr Virus): EB virus can cause infectious mononucleosis and has been linked to rare AA cases, but not specifically in chronic hemolytic disease context.

Answer: CD4 T-cells

gp120 is a crucial envelope glycoprotein on the surface of the HIV virus. It plays a central role in viral entry by specifically binding to the CD4 receptor present on the surface of CD4 T-cells. This binding initiates a cascade of events, ultimately leading to the fusion of the viral and host cell membranes and subsequent HIV infection of the CD4 T-cell.

The other options are incorrect:

• CD8 T-cells: CD8 T-cells play a different role in the immune response against HIV, mainly identifying and eliminating infected cells. They do not directly bind gp120.
• B-cells: B-cells are responsible for antibody production, another arm of the immune system. While they can produce antibodies against HIV, they are not directly involved in initial viral entry mediated by gp120.
• NK-cells: Natural killer cells recognize and destroy virus-infected or abnormal cells. However, they don’t have a specific receptor interaction with gp120 and aren’t the primary target for HIV binding.

Answer: HBx Ag

• This small, non-structural protein of Hepatitis B virus (HBV) plays a crucial role in enhancing viral replication by interacting with various cellular pathways. It disrupts cell cycle regulation, promotes DNA repair mechanisms used by the virus, and suppresses the host’s immune response, all contributing to increased HBV replication. Interestingly, HBx Ag also transactivates the HIV-1 promoter, enhancing HIV replication in co-infected individuals.

The other options are incorrect:

• HBc Ag: This capsid protein forms the viral core and is essential for virion assembly but doesn’t directly influence viral replication.
• HBs Ag: This surface protein serves as the viral envelope and facilitates viral entry but doesn’t enhance replication.
• HBe Ag: This secreted protein suppresses the host’s immune response, indirectly benefiting viral replication but doesn’t directly enhance it like HBx Ag.

Answer: CMV

Cytomegalovirus is the most common infectious agent in solid organ transplant recipients, affecting over half of them within the first three months post-transplant. This is because immunosuppressive medications used to prevent organ rejection suppress the immune system, making patients more susceptible to opportunistic infections like CMV.

The other options are incorrect:

• Hepatitis A: While this virus can cause liver infection, it’s primarily transmitted through contaminated water and food, not via transplantation.
• Hepatitis B: Patients with organ transplants are at risk for Hepatitis B reactivation if they were previously infected, but it’s less common than CMV infection. Strict pre-transplant screening and vaccination protocols help minimize HBV transmission.
• EBV (Epstein-Barr Virus): While EBV can also cause infections in transplant recipients, its prevalence is lower than CMV, and it typically leads to milder symptoms.

Answer: Hepatoma

Epstein-Barr Virus (EBV) is not typically associated with hepatoma (liver cancer). It is, however, linked to other conditions such as nasopharyngeal carcinoma, Burkitt’s lymphoma, and infectious mononucleosis.

The other options are incorrect:

• Nasopharyngeal carcinoma: EBV is associated with the development of nasopharyngeal carcinoma, a type of cancer that originates in the nasopharynx.
• Burkitt’s lymphoma: EBV is a contributing factor to the development of Burkitt’s lymphoma, a type of non-Hodgkin’s lymphoma commonly found in Africa.
• Infectious mononucleosis: EBV is commonly known to cause infectious mononucleosis, a viral illness characterized by symptoms like fever, sore throat, and swollen lymph nodes.

Answer: Kaposi’s sarcoma

Kaposi’s sarcoma (KS): This is a type of soft tissue sarcoma that develops in blood vessels and lymphatic vessels. It is strongly associated with HIV infection and is considered an AIDS-defining illness. In people with AIDS, KS often appears as reddish or purplish bumps on the skin, but it can also affect internal organs.

The other options are incorrect:

• Carcinoma: This is a general term for any cancer that originates in epithelial cells, which line the surfaces of organs and glands. While people with AIDS can develop various types of carcinoma, they are not as common as KS.
• Melanoma: This is a type of skin cancer that arises from melanocytes, the cells that produce pigment. While melanoma can occur in people with AIDS, it is not specifically associated with the disease.
• Ewing’s sarcoma: This is a rare type of bone cancer that primarily affects children and young adults. It is not associated with AIDS.

Answer: Helper T lymphocytes

The primary target of HIV is helper T lymphocytes (CD4+ T cells), which are crucial components of the immune system. These cells act like generals, coordinating and directing the immune response against infections and diseases. HIV infects and destroys CD4+ T cells, gradually weakening the immune system’s ability to fight off even minor infections.

The other options are incorrect:

Incorrect Options:

• Natural killer cells: While HIV can also infect natural killer cells to a lesser extent, these cells mainly attack and destroy virus-infected cells and tumor cells. Their depletion doesn’t have the same significant impact on immune function as CD4+ T cell loss.
• Plasma cells: Plasma cells are responsible for antibody production, another arm of the immune system. While HIV can indirectly affect antibody production by depleting CD4+ T cells, plasma cells aren’t directly targeted by the virus.
• Macrophages: Macrophages are white blood cells that engulf and destroy foreign particles, including bacteria and viruses. While HIV can infect macrophages, they don’t play a key role in the virus’s primary attack on the immune system.

Answer: Flavi viruses

Hepatitis C virus (HCV) belongs to the Flavivirus family. This family includes other well-known viruses like West Nile virus, Dengue virus, and Yellow fever virus. Flaviviruses share common characteristics like their single-stranded RNA genome, enveloped structure, and transmission through insects like mosquitoes.

The other options are incorrect:

• Picornaviruses: This family includes common cold viruses and poliovirus. They differ from Flaviviruses in their genome structure (double-stranded RNA) and lack of envelope.
• Herpesviruses: This family includes Epstein-Barr virus (EBV) and herpes simplex virus (HSV). They possess double-stranded DNA genomes and capsid morphology distinct from Flaviviruses.
• Hepadana viruses: This term only refers to HCV itself, hence not an appropriate option in this context.

Answer: Chemically defined media

Viruses are obligate intracellular parasites, meaning they require a living host cell to replicate. While some viruses can be grown in specific cell cultures, chemically defined media alone cannot support viral replication. Viruses lack the necessary machinery to synthesize their own proteins and nucleic acids, relying on the host cell’s metabolic processes for their reproduction.

The other options are incorrect:

• Tissue culture: This method involves growing cells from various tissues (e.g., animal, human) in a controlled laboratory environment. Specific cell lines that support viral growth can be used to isolate and propagate viruses from clinical samples.
• Embryonated eggs: Certain viruses, like influenza virus, can replicate in the developing chick embryo within fertilized eggs. This method was historically used for viral isolation and vaccine production but has been largely replaced by cell culture techniques
• Animals: Some viruses, like rabies virus, can be isolated by infecting specific animals (e.g., mice) and observing the development of characteristic symptoms or detecting the virus in their tissues. However, this method is often ethically and logistically challenging.

Answer: Both ELISA IS – ve and Western Blot is – ve

During the window period of HIV infection, the human immune system hasn’t yet produced enough antibodies to be detected by standard HIV tests like ELISA and Western Blot. These tests rely on the presence of antibodies specific to HIV to give a positive result.

The other options are incorrect:

• ELISA IS – ve: During the window period, ELISA will be negative as it detects antibodies, which haven’t developed yet.
• Western Blot is – ve: Similar to ELISA, Western Blot confirms the presence of antibodies, which are absent during the window period.
• Both are – ve: This is the correct answer, as both ELISA and Western Blot will be negative due to the lack of detectable antibodies.
• PCR is – ve: While PCR can detect the presence of the HIV virus itself, it may not always be positive during the window period. Depending on the timing of infection and the sensitivity of the test, PCR may miss the virus as its concentration might be too low for detection.

Answer: To separate specific clone of virus

The plaque assay is routinely used in virology labs to separate specific clones of a virus. It involves infecting a monolayer of host cells with a dilution of a virus sample, allowing the virus to replicate and form visible plaques. Each plaque corresponds to a single infectious viral particle, and by isolating individual plaques, researchers can obtain a purified, clonal population of the virus.

Here’s why the other options are incorrect:

• Identification of viral disease: While the plaque assay can be used to confirm the presence of a virus in a sample, it doesn’t directly identify the specific viral disease. Additional tests might be needed for diagnosis.
• To maintain certain viral culture: While plaque assays can help assess the viability of a viral stock, they’re not the primary method for maintaining viral cultures. Cell culture techniques are specifically designed for maintaining long-term viral stocks.
• To prepare vaccines: Plaque assays can be used for some vaccine development steps, especially when isolating attenuated strains for live-attenuated vaccines. However, vaccine production involves complex processes beyond just this technique.

Answer: Capsid

The capsid is the protein shell that encloses the genetic material (DNA or RNA) of a virus. It protects the virus from damage and facilitates entry into host cells. Capsomere is a subunit of the capsid, not the overall covering. Nucleocapsid refers to the combination of the capsid and the enclosed genetic material. Envelope is an additional outer layer, present in some but not all viruses.

The other options are incorrect:

• Capsomere: This is a single protein unit that makes up the capsid. While capsomeres form the capsid, they are not the entire covering itself.
• Nucleocapsid: This term refers to the combination of the capsid and the genetic material within it. It is a broader term than just the capsid itself.
• Envelope: This is an outer lipid bilayer membrane found in some viruses, but not all. It is not the primary covering for all viral DNA.

Answer: Varicella zoster virus

While VZV belongs to the herpesvirus family, which includes some oncogenic viruses like Epstein-Barr virus (EBV) and human papillomavirus (HPV), VZV itself is not directly linked to cancer development. It primarily causes chickenpox and shingles, with no known association with oncogenic activity.

The other options are incorrect:

• Epstein-Barr virus (EBV): EBV is linked to several cancers, including Burkitt’s lymphoma, nasopharyngeal carcinoma, and Hodgkin’s lymphoma. It can immortalize B cells, creating a conducive environment for cancer development.
• Human papillomavirus (HPV): Certain HPV strains are well-established as cancer-causing agents, particularly cervical cancer and some head and neck cancers. They disrupt cell cycle regulation and promote uncontrolled cell growth.
• Herpes simplex virus (HSV): Some HSV strains, particularly HSV-1, have been investigated for potential cancer associations, but the evidence is inconclusive and requires further research. However, compared to EBV and HPV, the connection is much weaker.

Answer: DNA virus

HIV (Human Immunodeficiency Virus) is not a DNA virus; it is an RNA virus. Specifically, it is a retrovirus, which means it carries its genetic information in the form of RNA and uses reverse transcriptase to convert its RNA into DNA inside the host cell.

Incorrect options and brief explanations:

• Attacks CD4 cells: True. HIV primarily targets and infects CD4+ T cells, which are crucial for the immune system. This weakens the immune system and makes individuals vulnerable to opportunistic infections.
• Macrophages are the reservoir: False. While macrophages can be infected by HIV, they are not the primary reservoir. T lymphocytes, particularly CD4+ T cells, are the main targets and reservoirs for HIV.
• Decrease CD4 count in late stages: True. As HIV infection progresses, it destroys CD4 cells, leading to a decline in CD4 count. This immunosuppression makes individuals more susceptible to AIDS-defining illnesses.

Answer: Papilloma

While EBV (Epstein-Barr virus) is linked to various diseases, papillomas are not among them. EBV is primarily known for its association with several cancer types and infectious mononucleosis.

The other options are incorrect:

• Carcinoma of nasopharynx: EBV is a major risk factor for nasopharyngeal carcinoma, a relatively rare cancer that originates in the upper part of the throat behind the nose.
• Infectious mononucleosis: Also known as “mono,” this infectious disease is caused by EBV and characterized by symptoms like fever, fatigue, swollen lymph nodes, and sore throat.
• Burkitt’s lymphoma: EBV plays a significant role in the development of Burkitt’s lymphoma, a particularly aggressive type of non-Hodgkin lymphoma.