MicroBiology MCQs with Answer and Explnation | Chapter 34

Answer: Destroyed

Clonal deletion theory proposes that developing lymphocytes with receptors that react to self-antigens are eliminated during their maturation process. This prevents them from attacking the body’s own tissues and contributing to autoimmune disease.

The other options are incorrect:

• Normal: Self-reacting lymphocytes pose a threat to the body and would not be considered normal under clonal deletion theory.
• Amplified: Clonal deletion aims to remove, not amplify, self-reacting lymphocytes.
• Activated: Activation often refers to the process of lymphocytes becoming ready to attack specific antigens, which in this case, are the body’s own tissues. This contradicts the purpose of clonal deletion.

Answer: Perforins

Hypersensitivity Type I (immediate hypersensitivity) involves the release of inflammatory mediators from mast cells and basophils triggered by IgE-mediated antigen recognition. Perforins are not released during this cascade and are instead associated with cell-mediated cytotoxicity (Type IV hypersensitivity), where cytotoxic T lymphocytes directly attack and kill target cells.

The other options are incorrect:

• Histamine: A key inflammatory mediator released by mast cells in Type I reactions, causing vasodilation, bronchoconstriction, and other symptoms.
• Prostaglandins: Lipid mediators released by mast cells and basophils, contributing to vasodilation, edema, and pain in Type I reactions.
• Leukotrienes: Another group of inflammatory mediators released by mast cells and basophils, involved in smooth muscle contraction, mucus production, and chemotaxis in Type I reactions.

Answer: Globulins

Globulins are proteins, and they are not directly related to antigens. While antibodies, which are a type of globulin, are involved in immune responses and can bind to antigens, the term “globulins” itself does not refer to antigens. Epitopes, haptens, and lipoproteins, on the other hand, are more directly associated with antigens and immune responses.

The other options are incorrect:

• Epitopes: Epitopes, also known as antigenic determinants, are specific regions on antigens that interact with antibodies or T cell receptors. They are a fundamental part of the antigen-antibody interaction.
• Hapten: Haptens are small molecules that, by themselves, may not be immunogenic but can become immunogenic when attached to a larger carrier molecule. They can elicit an immune response and are related to antigens.
• Lipoproteins: Lipoproteins are complexes of lipids and proteins. Some lipoproteins can act as antigens and stimulate immune responses. They are involved in the recognition and response of the immune system.

Answer: Pentamer

IgM antibodies occur in the pentameric form. IgM is unique among immunoglobulins as it is typically found as a pentamer composed of five monomeric subunits linked together. This pentameric structure contributes to its functional properties, such as efficient agglutination of antigens and activation of the complement system.

The other options are incorrect:

• Monomer: IgM is not found as a monomer. While other immunoglobulins like IgG and IgE exist as monomers, IgM is distinctive in its pentameric structure.
• Dimer: IgM is not found as a dimer either. The pentameric structure is characteristic of IgM, allowing it to be an effective first responder in the immune system.
• All forms: IgM is specifically found in the pentameric form, and not in monomeric or dimeric forms. The pentameric structure enhances its ability to agglutinate antigens and initiate immune responses.

Answer: None of the above

Although the listed terms are all related to the immune system’s control mechanisms, autoimmunity actually arises from the failure of these mechanisms. Autoimmune diseases develop when self-tolerance breaks down, causing the immune system to mistakenly attack the body’s own tissues.

The other options are incorrect:

• Immunological tolerance: A broader term encompassing various mechanisms, including self-tolerance, that prevent immune responses against the body’s own tissues. Failure of self-tolerance leads to autoimmunity, not the other way around.
• Self-tolerance: A specific mechanism within immunological tolerance that ensures the immune system distinguishes between self and non-self antigens. Disruption of self-tolerance is directly linked to the development of autoimmunity.
• Clonal deletion: A process during immune cell development where self-reacting lymphocytes are eliminated to prevent autoimmunity. However, incomplete clonal deletion is only one possible factor contributing to autoimmunity, not the sole cause.

Answer: Exotoxin in sympathetic system

Tetanus is caused by the spread of the exotoxin produced by the bacterium Clostridium tetani. The neurotoxin, called tetanospasmin, affects the nervous system by blocking inhibitory signals, leading to sustained muscle contractions. The sympathetic and parasympathetic systems are both part of the autonomic nervous system, and in tetanus, it’s the sympathetic system that is affected.

The other options are incorrect:

• Exotoxin in parasympathetic system: While tetanospasmin does interact with some areas of the parasympathetic system, its primary impact is on the sympathetic system.
• Endotoxin in Sympathetic system: Endotoxins are not produced by C. tetani. They are associated with gram-negative bacteria, and their effects differ from those of tetanospasmin.
• Endotoxin in parasympathetic system: Similar to the previous option, this is not applicable to tetanus as C. tetani does not produce endotoxins.

Answer: Clostridium botulinum

Clostridium botulinum is not associated with gas gangrene. It is known for causing botulism, a condition characterized by muscle paralysis due to the neurotoxins produced by the bacterium. Gas gangrene is caused by various strains of Clostridium, including Clostridium perfringens (formerly known as Clostridium welchii). The other options listed are also associated with gas gangrene.

The other options are incorrect:

• Clostridium welchii (Clostridium perfringens): Clostridium welchii, now known as Clostridium perfringens, is a causative agent of gas gangrene. It produces toxins that can lead to tissue destruction and the production of gas within affected tissues.
• Clostridium oedemaiens (Clostridium novyi): Clostridium oedemaiens, now known as Clostridium novyi, is associated with gas gangrene. It produces toxins that contribute to tissue edema and necrosis.
• Clostridium septicum: Clostridium septicum is another species associated with gas gangrene. It can cause severe infections and is known for its ability to produce gas within tissues.

Answer: Flagella

Spirochetes are a unique group of bacteria known for their corkscrew-like shape and distinctive motility. While other bacteria may use cilia or pseudopodia for movement, spirochetes rely on specialized flagella for propulsion.

The other options are incorrect:

• Cilia: Spirochetes do not use cilia for motility. Cilia are short, hair-like structures found on the surface of some eukaryotic cells, such as certain types of animal cells, for movement.
• Pseudopodia: Pseudopodia are temporary protrusions of the cell membrane and cytoplasm used by some eukaryotic cells, like amoebas, for motility. Spirochetes, being bacteria, do not use pseudopodia for movement.

Answer: Antigenically

The Kauffman-White scheme is the primary system used for serotyping Salmonella bacteria. This means it classifies them based on their surface antigens, specifically the lipopolysaccharide (LPS) and flagellar antigens. By identifying these antigens, scientists can determine the specific serotype of a Salmonella strain, which helps predict its virulence and potential for causing disease.

The other options are incorrect:

• Biochemically: While biochemical tests can be used to differentiate some Salmonella serotypes, the Kauffman-White scheme emphasizes antigenic differences for precise classification.
• Chemotyping: Chemotyping analyzes the chemical composition of bacterial molecules, not surface antigens. It can be used for further subtyping within serotypes, but not for initial classification.
• Phage typing: This technique uses bacteriophages (viruses that infect bacteria) to differentiate bacterial strains. While it can be useful for epidemiological investigations, it’s not the primary method for classifying Salmonella using the Kauffman-White scheme.

Answer: Clostridium tetani

Nocardia asteroids is not an anaerobic bacterium. It is an aerobic actinomycete bacterium. Anaerobic bacteria are those that thrive in the absence of oxygen, while aerobic bacteria require oxygen for growth. The other options listed (Actinomyces bovis and Clostridium tetani) are anaerobic bacteria.

The other options are incorrect:

• Streptococcus hemolyticus: As the name suggests, some strains of Streptococcus bacteria, including S. pyogenes and S. pneumoniae, produce hemolysins with varying degrees of lytic activity, causing complete or partial hemolysis on blood agar.
• Staphylococcus aureus: This common pathogen also produces several hemolysins, including alpha-, beta-, and gamma-hemolysins, leading to characteristic zones of hemolysis on blood agar.
• E. coli: Some pathogenic strains of E. coli, particularly enterohemorrhagic E. coli (EHEC), produce a hemolysin known as HlyA, which contributes to their virulence and damage to host tissues.

Answer: Obligate anaerobe

Pseudomonas aeruginosa is not an obligate anaerobe; instead, it is a facultative anaerobe. This means it can grow in the presence or absence of oxygen. Pseudomonas aeruginosa is known for its versatile metabolism, making it capable of thriving in various environments, including aerobic conditions.

The other options are incorrect:

• Produce Pigment: Pseudomonas aeruginosa is known for producing pigments, including pyocyanin, which gives it a characteristic blue-green color. These pigments have various roles, including contributing to the bacterium’s virulence.
• Produce Local Suppurative Lesions: Pseudomonas aeruginosa is associated with the production of local suppurative lesions, which involve the formation of pus. It can cause infections in various tissues and is a common pathogen in burn wounds and respiratory infections.
• Spore Forming and Capsulated: Pseudomonas aeruginosa is not spore-forming, and it lacks a true capsule. It has a distinctive cell wall structure and can form a biofilm, but it does not produce endospores as seen in some other bacterial species.

Answer: Virus specific

Interferons are a group of proteins produced by host cells in response to various stimuli, including viral infections. However, they are not specific to a single virus. While they can broadly inhibit viral replication and spread, they do not target specific viral antigens or structures.

The other options are incorrect:

• Antiviral: Interferons are primarily known for their antiviral activity. They trigger various cellular mechanisms that inhibit viral replication and spread, ultimately protecting the host cell and surrounding cells from viral infection.
• Host cell specific: Interferons act on the cells that produce them, influencing their own functions and signaling pathways. They do not directly attack the virus itself but rather trigger an intracellular antiviral response.
• Class of proteins: Interferons are indeed a diverse group of signaling proteins produced by various cell types. They are classified into different types (Type I, Type II, etc.) based on their sequence, structure, and target receptors.

Answer: They have the same clinical picture

While varicella and zoster are caused by the same virus (varicella-zoster virus, VZV), they have distinct clinical presentations. Varicella presents with a generalized itchy rash of vesicles, while zoster presents with a unilateral, painful rash along specific nerve pathways.

The other options are incorrect:

• They are two diseases caused by one virus: This is TRUE. Both varicella and zoster are caused by the varicella-zoster virus (VZV).
• Varicella is the primary illness, whereas zoster is the recurrent form of the disease: This is TRUE. Primary infection with VZV manifests as varicella (chickenpox). Following recovery, the virus remains latent in nerve cells and can reactivate later in life as zoster (shingles).
• Varicella can be prevented by vaccination: This is TRUE. Vaccination significantly reduces the risk of varicella infection and its complications.

Answer: All are morphologically identical

While all herpesviruses share certain morphological features, they exhibit distinct morphological variations under electron microscopy. Some have an envelope, while others do not. Additionally, they differ in size and internal structure.

The other options are incorrect:

• There are eight human herpes viruses: This is TRUE. Currently, eight human herpesviruses (HHV-1 to HHV-8) are known to infect humans.
• All are DNA-viruses: This is TRUE. All herpesviruses are double-stranded DNA viruses.
• All cause vesicular rash: This is TRUE. A characteristic feature of several herpesvirus infections is a vesicular rash. However, not all HHVs manifest with this symptom. HHV-6 and HHV-7 for example, commonly cause roseola in children, which presents with a non-vesicular rash.

Answer: Are not filterable

Chlamydia are indeed filterable, meaning they can pass through filters that typically retain bacteria due to their small size. They have a unique biphasic lifecycle, transitioning between an infectious, extracellular form with minimal metabolic activity (elementary body) and an intracellular, metabolically active form (reticulate body) for replication. The elementary body is small enough to pass through filters designed for larger bacteria.

The other options are incorrect:

• Possess cell wall: This is TRUE. Chlamydia have a cell wall similar to other bacteria, though it lacks some components found in typical bacterial cell walls.
• Possess DNA as well as RNA: This is TRUE. Like other bacteria, Chlamydia possess both DNA as their genetic material and RNA for protein synthesis.
• Are susceptible to antibiotics: This is TRUE. Several antibiotics are effective against Chlamydia infections.

Answer: Humoral immunity but not cell mediated immunity (CMI) act against viruses

Both humoral and cell-mediated immunity play crucial roles in fighting viral infections. While antibodies (part of humoral immunity) neutralize extracellular viruses, cell-mediated immunity (CMI) eliminates virus-infected cells and prevents viral spread within the body. Both are essential for effective antiviral defense.

The other options are incorrect:

• Spread of virus in the body through different route: This is TRUE. Viruses can spread through various routes, including respiratory droplets, blood, and body fluids, depending on the specific virus.
• In cytocidal infection, cell usually die: This is TRUE. Cytocidal infections involve direct viral replication within host cells, causing cell death and release of new viral particles. This is a common outcome of many viral infections.
• Several RNA viruses can cause persistent infection: This is TRUE. Some RNA viruses, like HIV and Hepatitis C, can establish persistent infections by integrating their genome into host cell DNA or utilizing other mechanisms to evade immune clearance.

Answer: Glomerulonephritis

While enteroviruses have a wide range of potential complications, glomerulonephritis (inflammation of the kidney’s filtering units) is not typically associated with them. Enteroviruses primarily cause acute, self-limiting infections such as those listed in the other options.

The other options are incorrect:

• Pleurodynea (Bornholm disease): This painful muscle condition in the chest and abdomen can be caused by enteroviruses, particularly coxsackievirus A7.
• Paralysis: Enteroviruses, especially poliovirus, can cause various types of paralysis, including temporary limb weakness and permanent paralysis in severe cases.
• Meningitis: Enteroviruses are a common cause of aseptic meningitis, an inflammation of the membranes surrounding the brain and spinal cord.

Answer: Gram negative rods

Spirochetes are a group of bacteria characterized by their unique spiral or corkscrew shape. They are Gram-negative rods, and their distinctive morphology sets them apart from other bacterial groups.

The other options are incorrect:

• Gram positive rods: Spirochetes are not Gram-positive rods. Gram-positive rods include bacteria like Bacillus and Clostridium, but they do not have the spiral shape characteristic of spirochetes.
• Gram negative cocci: Spirochetes are not Gram-negative cocci. Cocci are spherical bacteria, and spirochetes have a distinct spiral shape.
• Acid Fast rods: Spirochetes are not acid-fast rods. Acid-fast bacteria, such as Mycobacterium tuberculosis, retain the red stain in the acid-fast staining procedure, while spirochetes do not exhibit this characteristic staining pattern.

Answer: Ticks

Lyme disease is primarily transmitted by ticks, specifically black-legged ticks (Ixodes scapularis or Ixodes ricinus). The bacteria responsible for Lyme disease, Borrelia burgdorferi, is transmitted to humans through the bite of infected ticks.

The other options are incorrect:

• Flea: Fleas are not the primary vectors for Lyme disease. Ticks, particularly Ixodes ticks, are the main vectors associated with the transmission of Borrelia burgdorferi.
• Aedes: Aedes mosquitoes are known for transmitting diseases such as dengue and Zika virus, but they are not the vectors for Lyme disease.
• Culex: Culex mosquitoes are associated with the transmission of diseases like West Nile virus, but they are not the vectors for Lyme disease. Lyme disease is primarily linked to tick bites.

Answer: Viruses can replicate in non-living media

Viruses cannot replicate in non-living media. They require a host cell to replicate and complete their life cycle. Viruses lack the cellular machinery and metabolic processes necessary for independent replication outside a host cell.

The other options are incorrect:

• The viral envelope contains lipoprotein: This statement is true. The viral envelope, found in some viruses, is composed of lipids and proteins, including lipoproteins.
• Viruses need live cells to grow: This statement is true. Viruses are obligate intracellular parasites, meaning they need living host cells to replicate and complete their life cycle. They rely on the host cell’s machinery for their replication.
• Viruses have no ribosome: This statement is true. Viruses lack their own ribosomes and protein synthesis machinery. They utilize the host cell’s ribosomes to synthesize viral proteins during the replication process.

Answer: There is no vaccine for polio

This statement is incorrect. Vaccines for polio are available, and various immunization programs worldwide have been successful in controlling the spread of the virus. The most common types of polio vaccines are the inactivated poliovirus vaccine (IPV) and the oral poliovirus vaccine (OPV).

The other options are incorrect:

• Two vaccines are available: This statement is correct. There are two primary types of polio vaccines: IPV (inactivated poliovirus vaccine) and OPV (oral poliovirus vaccine). Both are used globally to prevent polio infections.
• Can be isolated from throat swab or stool: This statement is correct. Poliovirus can be isolated from throat swabs or stool samples of infected individuals. These samples are commonly used for laboratory diagnosis.
• Sub-clinical infections are common: This statement is correct. Many poliovirus infections are subclinical, meaning individuals may not exhibit symptoms, yet they can still spread the virus. This can pose challenges in detecting and controlling the spread of the virus.

Answer: Transcription is the formation of protein

Transcription is the process of synthesizing RNA from a DNA template. It is a fundamental step in gene expression but does not directly involve the formation of proteins. Translation, on the other hand, is the process in which the information in mRNA is used to build a corresponding protein.

The other options are incorrect:

• Icosahedral symmetry has 12 vertices: This statement is incorrect. Icosahedral symmetry has 20 vertices, not 12. The icosahedral shape is a geometric structure commonly observed in certain viruses.
• Helical symmetry such as Orthomyxovirus: This statement is correct. Orthomyxoviruses, such as the influenza virus, exhibit helical symmetry. The viral nucleocapsid is helical in shape.
• Translation is the formation of protein: This statement is incorrect. Translation is the process where the information carried by mRNA is used to synthesize a corresponding protein. It involves the interaction of mRNA with ribosomes and transfer RNA (tRNA) to assemble amino acids into a polypeptide chain.

Answer: HCV is ssRNA

HCV (Hepatitis C Virus) is a single-stranded RNA virus. It belongs to the Flaviviridae family and is classified as a positive-sense, single-stranded RNA virus. In contrast, HBV (Hepatitis B Virus) is a DNA virus with a partially double-stranded genome.

The other options are incorrect:

• HBV is dsRNA: This statement is incorrect. HBV is a DNA virus, not an RNA virus. Its genome is partially double-stranded, consisting of a circular, partially double-stranded DNA.
• Both viruses can grow in cell culture: This statement is incorrect. While cell culture systems exist for HCV, they have been challenging to establish for HBV. HBV requires specific conditions and is often studied using in vivo or in vitro systems that mimic its natural host environment.
• HBV has no chronicity complication:This statement is incorrect. Chronic hepatitis B infection can lead to complications such as cirrhosis and hepatocellular carcinoma. Chronicity is a significant concern in HBV infections.

Answer: HCV-Abs can’t be diagnosed in lab by EIA test

Unlike some other DNA viruses, HCV (Hepatitis C Virus) is an RNA virus, and it does not integrate into the host cell chromosomes. Integration into the host genome is more characteristic of DNA viruses like hepatitis B virus (HBV) rather than RNA viruses like HCV.

The other options are incorrect:

• HCV-Abs can’t be diagnosed in the lab by EIA test: This statement is incorrect. HCV antibodies (HCV-Abs) can be diagnosed in the laboratory using enzyme immunoassay (EIA) tests. These tests are commonly employed for the detection of antibodies against HCV.
• The risk factors for hepatocellular carcinoma by HCV are: underlying liver disease, alcohol, age: This statement is correct. Chronic HCV infection is a risk factor for hepatocellular carcinoma (HCC), and other factors such as underlying liver disease, alcohol consumption, and age can further contribute to the risk of developing HCC.
• The RNA and protein of HDV are surrounded by HBsAg: This statement is correct. Hepatitis D virus (HDV) has an envelope composed of hepatitis B surface antigen (HBsAg). HDV requires the envelope provided by HBsAg for its assembly and transmission.

Answer: Progeny virus is not produced

An abortive infection is one in which the replication of the virus within the host cell is incomplete, and progeny virus particles are not produced. This can occur due to various factors, such as host defense mechanisms limiting viral replication or the lack of essential cellular factors for the virus to complete its life cycle.

The other options are incorrect:

• The infected cells are killed: While cell death can occur in abortive infections, it’s not the defining feature. Some abortive infections might leave the infected cell alive but unable to produce viruses.
• Transplacental infection of the fetus occurs: This is not directly related to the mechanism of an abortive infection. Although an ongoing viral infection might have the potential for transplacental transmission, that wouldn’t necessarily mean it’s not abortive.
• Cell multiplication is stopped: Cell proliferation can be affected in different ways during an infection, not just in abortive ones. This doesn’t guarantee the absence of viral replication, which is the crucial marker of an abortive infection.

Answer: Rabies

The human diploid cell vaccine is used for the prevention of rabies. This vaccine is produced using human diploid (cells derived from human embryos) cells and is effective in inducing immunity against the rabies virus.

The other options are incorrect:

• Varicella: Varicella vaccine is typically prepared using attenuated live virus strains, not human diploid cells.
• Hepatitis A: Hepatitis A vaccines are produced using inactivated or attenuated virus strains, not human diploid cells.
• Yellow fever: Yellow fever vaccines are usually prepared using live attenuated virus strains, not human diploid cells.

Answer: Herpangina

Herpangina is a viral infection caused by certain enteroviruses, particularly Coxsackievirus A. It is characterized by the presence of small, painful ulcers or vesicles in the mouth and throat but does not typically cause a maculopapular rash. Herpangina is distinct from the other mentioned viral diseases.

The other options are incorrect:

• Measles: Measles is characterized by a maculopapular rash that usually begins on the face and then spreads to other parts of the body.
• Rubella: Rubella, also known as German measles, is characterized by a maculopapular rash that often starts on the face and spreads. It is typically milder than measles.
• Erythema: Erythema is a nonspecific term for redness of the skin and is not a specific viral disease. It can be a symptom of various conditions, including viral infections, but it is not a distinct viral disease itself.

Answer: Perforin

While perforin might seem like it belongs with the other options considering its involvement in immune responses, it’s not a cytokine. Cytokines are small, soluble signaling molecules that mediate communication between cells, while perforin is a cytolytic protein directly involved in killing target cells.

The other options are incorrect:

• Communicators: Cytokines are indeed key communicators in the immune system, orchestrating and regulating various immune responses through cell-to-cell signaling.
• Interleukin-I: This is a classic example of a cytokine, known for its pro-inflammatory properties and involvement in diverse immune functions.
• TNF (Tumor Necrosis Factor): Another prominent cytokine, TNF plays crucial roles in inflammation, cell death, and immune cell activation.

Answer: RSV

While RSV can infect pregnant women and even cause mild flu-like symptoms, it typically doesn’t cross the placenta and cause congenital infections in the fetus. In contrast, the other listed viruses have well-established associations with congenital infections and can cause significant harm to the developing baby.

The other options are incorrect:

• Rubella virus: Rubella, also known as German measles, is a classic example of a virus that readily crosses the placenta and can cause severe birth defects like cataracts, heart problems, and hearing loss.
• CMV (Cytomegalovirus): This common virus can also pose a significant risk for congenital infections, leading to developmental delays, hearing loss, and vision problems in newborns.
• Varicella (Chickenpox): The varicella-zoster virus can lead to congenital varicella syndrome, causing skin lesions, developmental disabilities, and other complications in a small percentage of infected newborns.

Answer: It is an oncogenic virus

HIV (Human Immunodeficiency Virus) is not classified as an oncogenic virus. While HIV can lead to immunodeficiency and an increased risk of certain cancers, it is not directly oncogenic in the same way as some other viruses that can directly induce cancer, such as certain strains of human papillomavirus (HPV) or hepatitis B and C viruses.

The other options are incorrect:

• It belongs to the family Retroviridae: This statement is correct. HIV belongs to the family Retroviridae, specifically the genus Lentivirus.
• The virus is present in all body fluids: This statement is correct. HIV can be found in various body fluids, including blood, semen, vaginal fluids, breast milk, and others. This contributes to the potential modes of transmission.
• The sexual route is the main mode of transmission: This statement is correct. Sexual transmission is one of the primary modes of HIV transmission, along with blood-to-blood contact (e.g., through sharing needles) and from mother to child during childbirth or breastfeeding.

Answer: HDV

While HAV, HEV, and Entero are viruses transmitted through the fecal-oral route, HDV differs significantly in its mode of transmission. It cannot survive independently and requires the presence of Hepatitis B Virus (HBV) for replication and transmission. HDV shares the same transmission routes as HBV, which primarily involve blood-to-blood contact through contaminated needles or syringes, sexual contact, and vertical transmission from mother to child during childbirth.

The other options are incorrect:

• HAV (Hepatitis A Virus): This virus is transmitted primarily through contaminated food and water, making it a classic example of fecal-oral transmission.
• HEV (Hepatitis E Virus): Similar to HAV, HEV also spreads through contaminated food and water, particularly in regions with poor sanitation and hygiene practices.
• Enterovirus: This group of viruses includes several common pathogens, such as poliovirus, coxsackievirus, and echovirus, which can be transmitted through the fecal-oral route, contaminated water, and close contact with infected individuals.

Answer: Rubella

While the other listed viruses – HIV, HBV, and HSV-2 – are all known to be sexually transmitted, rubella doesn’t typically spread through sexual contact. Its primary mode of transmission is through respiratory droplets, meaning it’s more likely to be contracted through coughing, sneezing, or close contact with someone infected through these means.

The other options are incorrect:

• HIV (Human Immunodeficiency Virus): HIV can be transmitted through sexual contact involving the exchange of bodily fluids such as semen, vaginal fluids, and blood.
• HBV (Hepatitis B Virus): Similar to HIV, HBV can be transmitted through sexual contact with infected bodily fluids.
• HSV-2 (Herpes Simplex Virus-2): This virus, responsible for genital herpes, primarily spreads through genital skin-to-skin contact, including sexual intercourse.

Answer: Rotavirus

Rotavirus is a segmented double-stranded RNA (dsRNA) virus. It is a leading cause of severe gastroenteritis in infants and young children. The viral genome consists of 11 segments of dsRNA.

The other options are incorrect:

• Togavirus: Togaviruses are single-stranded RNA viruses. Examples include chikungunya virus, alphaviruses, and rubella virus.
• HAV: Hepatitis A virus (HAV) is a single-stranded RNA virus.
• Parvovirus: Parvoviruses are single-stranded DNA viruses. Examples include B19 parvovirus and canine parvovirus.

Answer: Human papilloma virus

Human papillomavirus (HPV) is primarily transmitted through direct skin-to-skin contact, including sexual contact, rather than through respiratory routes. HPV infections can affect the genital area, as well as other mucosal surfaces.

The other options are incorrect:

• Rhinovirus: This virus is the major cause of the common cold and readily spreads through respiratory droplets from coughs and sneezes.
• Adenovirus: Similar to rhinovirus, adenovirus can cause various respiratory illnesses like colds and bronchitis and spreads through respiratory droplets and close contact.
• Measles virus: This highly contagious virus spreads through respiratory droplets and close contact, leading to the characteristic measles rash and fever.

Answer: Human papilloma virus

While the other listed viruses – HIV, HBV, and rabies virus – are known to disseminate and spread throughout the body, HPV has a different pattern of infection. It primarily targets epithelial cells, especially in the skin and mucosal surfaces, and doesn’t typically engage in systemic dissemination like the other options.

The other options are incorrect:

• HIV (Human Immunodeficiency Virus): HIV infects specific immune cells and replicates within them, spreading throughout the body and eventually leading to AIDS if untreated.
• HBV (Hepatitis B Virus): HBV primarily infects liver cells but can also spread to other organs like the kidneys and blood vessels through the bloodstream.
• Rabies virus: Rabies virus has a unique neurotropic tropism, meaning it specifically targets the nervous system. It can spread through nerve pathways throughout the body and eventually reach the brain, causing fatal encephalitis.

Answer: Lyse virus infected cells

The primary defense function of cytotoxic T lymphocytes (CTLs) in viral infections is to eliminate virus-infected cells by causing them to undergo programmed cell death (apoptosis). This prevents the further replication and spread of the virus within the body.

The other options are incorrect:

• Fragment viral nucleic acid by nucleases: CTLs primarily target and destroy virus-infected cells, but they do not directly fragment viral nucleic acid. Their main function is to eliminate infected cells to prevent the spread of the virus.
• Neutralize free virus particles: The neutralization of free virus particles is typically associated with antibodies, particularly those produced by B cells. CTLs are more focused on eliminating infected cells.
• Lyse viral capsid: CTLs do not typically lyse the viral capsid directly. Their primary role is the destruction of virus-infected host cells to limit viral replication and spread.

Answer: Astrovirus causes gastroenteritis only in adults

Astrovirus infections can cause gastroenteritis in people of all age groups, including children. While the severity of symptoms may vary, astrovirus is not limited to causing gastroenteritis only in adults.

The other options are incorrect:

• CMV causes heterophil-negative mononucleosis: Cytomegalovirus (CMV) infections can cause mononucleosis-like symptoms, but they are heterophil-negative, meaning the heterophil antibody test used for classic infectious mononucleosis (caused by Epstein-Barr virus) is negative.
• Mumps virus can cause meningitis: Mumps virus infections can indeed lead to complications such as meningitis. Mumps is known for causing inflammation of the salivary glands (parotitis), but it can also affect other organs, including the central nervous system.
• Poliovirus can cause paralytic disease: Poliovirus infections can result in paralytic disease, particularly affecting the spinal cord. Polio can lead to varying degrees of paralysis in some individuals.

Answer: TLR5

TLR5 is the primary and specific Toll-like receptor (TLR) responsible for detecting bacterial flagellin, a protein component of the flagella that helps bacteria move. TLR5 recognizes a conserved motif within flagellin and triggers downstream immune responses to combat the bacterial infection.

The other options are incorrect:

• TLR2: TLR2 recognizes various bacterial components like lipoteichoic acid and lipopeptides, but not flagellin.
• TLR6: TLR6 plays a role in detecting diacyl lipoproteins from Gram-positive bacteria, not flagellin.
• TLR9: TLR9 recognizes unmethylated CpG motifs in bacterial and viral DNA, not flagellin.

Answer: Mononucleosis

Mononucleosis is not typically associated with picornaviruses. It is commonly caused by the Epstein-Barr virus (EBV) or, less frequently, by the cytomegalovirus (CMV), both of which are members of the herpesvirus family.

The other options are incorrect:

• Myocarditis: Certain picornaviruses, such as Coxsackievirus B, are known to be associated with myocarditis, which is inflammation of the heart muscle.
• Hepatitis: Enteroviruses, including some picornaviruses like Hepatitis A virus, can cause viral hepatitis, an inflammation of the liver.
• Meningitis: Enteroviruses, including those belonging to the picornavirus family (e.g., Enterovirus and Rhinovirus), can cause viral meningitis, which is inflammation of the meninges (the membranes covering the brain and spinal cord).

Answer: Rhinovirus

Rhinovirus is not typically associated with causing birth defects or teratogenic effects. Rhinoviruses are common causes of the common cold, and while they may cause respiratory symptoms, they are not known to have teratogenic effects during pregnancy.

The other options are incorrect:

• Rubella virus: Rubella virus is well-known for its teratogenic effects, causing congenital rubella syndrome when a pregnant woman is infected. This syndrome can lead to various birth defects in the developing fetus.
• CMV (Cytomegalovirus): CMV is associated with congenital cytomegalovirus infection, which can lead to developmental issues and birth defects in infants born to infected mothers.
• VZV (Varicella-Zoster Virus): Varicella-Zoster virus, which causes chickenpox and shingles, can have teratogenic effects if a woman is infected during pregnancy. It may lead to congenital varicella syndrome.

Answer: The testes, ovaries and pancreas can be involved

Mumps is a viral infection caused by the mumps virus, and it can affect various organs, including the testes, ovaries, and pancreas. In males, mumps can lead to orchitis (inflammation of the testicles), while in females, it can cause oophoritis (inflammation of the ovaries) and in rare cases, pancreatitis.

The other options are incorrect:

• There is no vaccine against mumps: There is a vaccine against mumps, typically administered as part of the measles, mumps, and rubella (MMR) vaccine. The MMR vaccine is effective in preventing mumps.
• Passive immunization is the only means of preventing the disease: Active immunization through vaccination is a primary means of preventing mumps. Passive immunization involves the administration of pre-formed antibodies and is not the primary method for preventing mumps.
• Second episodes of mumps can occur, since there are 2 serotypes: Mumps is primarily caused by a single serotype of the mumps virus. Second episodes are uncommon, as natural infection generally confers immunity.

Answer: The diagnosis is usually made by isolating the virus in cell culture

The diagnosis of Hepatitis A virus (HAV) infection is typically not made by isolating the virus in cell culture. Instead, diagnostic methods often involve detecting antibodies or viral RNA in blood samples. Isolation in cell culture is challenging due to the lack of robust in vitro culture systems for HAV.

The other options are incorrect:

• The initial site of viral replication is the GIT: The initial site of viral replication for HAV is the gastrointestinal tract (GIT), specifically the liver. HAV primarily infects hepatocytes.
• HAV commonly causes asymptomatic infection in children: HAV infection in children can often be asymptomatic or mild. However, this does not imply that it commonly causes asymptomatic infection in all cases.
• It is a member of the family Picornaviridae: HAV belongs to the family Picornaviridae, specifically the Hepatovirus

Answer: Rabies virus

Rabies virus does not belong to the family Picornaviridae. It is a member of the Rhabdoviridae family. Picornaviridae includes viruses with a single-stranded, positive-sense RNA genome, such as rhinoviruses, poliovirus, and echovirus.

The other options are incorrect:

• Rhinoviruses: Rhinoviruses are part of the Picornaviridae family and are a common cause of the common cold.
• Poliovirus: Poliovirus is a member of the Picornaviridae family and is known for causing polio, a disease that can lead to paralysis.
• Echovirus: Echoviruses belong to the Picornaviridae family. They are part of the enterovirus group and can cause various infections, including respiratory and gastrointestinal illnesses.

Answer: Enterovirus

Acute hemorrhagic conjunctivitis (AHC) is caused by enteroviruses, primarily Enterovirus 70 (EV70) and Coxsackievirus A24 (CA24). These viruses can lead to a sudden onset of redness, swelling, and hemorrhage in the conjunctiva (the membrane covering the white part of the eye and the inner surface of the eyelids).

The other options are incorrect:

• Coronavirus: Coronaviruses are a diverse family of viruses, but they are not typically associated with acute hemorrhagic conjunctivitis. Coronaviruses are more commonly associated with respiratory infections.
• Reovirus: Reoviruses are not a common cause of acute hemorrhagic conjunctivitis. They are more often associated with respiratory and gastrointestinal infections.
• Rhinovirus: Rhinoviruses are primarily known for causing the common cold and are not typically associated with acute hemorrhagic conjunctivitis.

Answer: Group B Coxsackievirus

Both epidemic pleurodynia (also known as Bornholm disease or Devil’s Grip) and myocarditis can be caused by Group B Coxsackieviruses, particularly types B3 and B5. These viruses have a tropism for muscle and heart tissue, explaining their association with both conditions.

The other options are incorrect:

• Polymavirus: While some polymaviruses like BK virus can cause certain illnesses, they haven’t been implicated in epidemic pleurodynia or myocarditis.
• RSV (Respiratory syncytial virus): RSV primarily causes respiratory infections and isn’t associated with these specific conditions.
• Reovirus: Although Reoviruses can rarely cause myocarditis, their connection to epidemic pleurodynia is minimal compared to Group B Coxsackieviruses.

Answer: CSF

Cerebrospinal fluid (CSF) is generally not an acceptable specimen for the isolation of enteroviruses. Enteroviruses, including those causing conditions like aseptic meningitis, are usually detected in specimens such as feces, throat secretions, and urine. CSF is not a common site for the isolation of these viruses, as they primarily replicate in the gastrointestinal and respiratory tracts.

The other options are incorrect:

• Feces: Fecal specimens are commonly used for the isolation of enteroviruses, as these viruses are shed in the stool during infection.
• Throat secretions: Throat secretions are acceptable specimens for the isolation of enteroviruses, especially in cases where respiratory symptoms are present.
• Urine: Urine specimens can be used for the isolation of enteroviruses, particularly in cases where the virus is shed in the urinary tract. Enteroviruses can cause infections in various organs, including the kidneys and bladder.

Answer: Culture

In the context of infectious mononucleosis, viral culture is generally not a useful test. Infectious mononucleosis is primarily caused by the Epstein-Barr virus (EBV), and the diagnosis is typically confirmed using serological tests to detect antibodies to specific EBV antigens. Culture is not a standard method for diagnosing infectious mononucleosis.

The other options are incorrect:

• IgM antibody to EB-VCA: Detection of IgM antibodies to the viral capsid antigen (VCA) of EBV is a useful test for diagnosing acute Epstein-Barr virus infection, such as infectious mononucleosis.
• IgG antibody to EB-VCA: Detection of IgG antibodies to the viral capsid antigen (VCA) is also useful. The presence of IgG antibodies indicates a previous or past EBV infection.
• Antibody to EB-NAs: Detection of antibodies to Epstein-Barr nuclear antigen (EB-NA) is another useful test for confirming past or ongoing EBV infection.

Answer: It is an RNA virus

Rotavirus is an RNA virus. It is a double-stranded RNA virus belonging to the Reoviridae family. Rotavirus is a common cause of severe gastroenteritis, especially in infants and young children.

The other options are incorrect:

• Tests for detection of antigen are rarely useful: While specific tests for rotavirus antigen are available, they are quite useful for rapid diagnosis, especially in children with gastroenteritis.
• It is rarely a nosocomial pathogen: Rotavirus can be readily transmitted in healthcare settings, making it a significant nosocomial pathogen, particularly in pediatric wards and daycare centers.
• Person-to-person transmission is rare: Rotavirus is highly contagious and primarily spreads through person-to-person contact, including fecal-oral transmission and contact with contaminated surfaces.

Answer: The causative pathogen is an EBV

Infectious mononucleosis is primarily caused by the Epstein-Barr Virus (EBV), a member of the herpesvirus family. The infection is characterized by symptoms such as fever, sore throat, swollen lymph nodes, and the presence of atypical lymphocytes in the blood.

The other options are incorrect:

• It is caused by rhabdovirus: Infectious mononucleosis is not caused by a rhabdovirus. It is caused by the Epstein-Barr Virus (EBV), a herpesvirus.
• Affected persons respond to treatment with the production of heterophil antibodies: Heterophil antibodies, such as those detected by the monospot test, are often present in infectious mononucleosis. However, the primary treatment involves supportive care, and the production of heterophil antibodies is not the primary therapeutic response.
• Ribavirin is the treatment of choice: Ribavirin is not typically used as the treatment of choice for infectious mononucleosis caused by EBV. Supportive care, rest, and symptomatic relief are the mainstays of treatment.

Answer: Detection of IgM antibody by IF

In newborns, the most sensitive method for detecting cytomegalovirus (CMV) infection is the detection of IgM antibodies using Immunofluorescence (IF) assays. IgM antibodies are typically produced during the early stages of infection, and their presence can indicate recent or active CMV infection.

The other options are incorrect:

• Isolation of virus: Isolation of the virus through cell culture is a method used in some cases, but it may not be as sensitive as detecting IgM antibodies, especially in the early stages of infection.
• Direct detection of antigen by ELISA: ELISA (Enzyme-Linked Immunosorbent Assay) for the direct detection of CMV antigen can be used, but the sensitivity may vary. In newborns, IgM detection is often preferred.
• Detection of complement-fixing antibodies: Detection of complement-fixing antibodies is a less sensitive method compared to IgM detection, as it may take some time for antibodies to reach detectable levels in the newborn. IgM antibodies are often more indicative of recent infection.