Question 1

Which enzyme is specific to HIV?

Accepted Answer

Answer reason: HIV is a retrovirus that carries reverse transcriptase to convert its single-stranded RNA genome into DNA for integration into the host genome. This enzyme is characteristic of retroviruses and is the target of NRTI/NNRTI drugs. Lipase and amylase are digestive enzymes, and proteases are common across many organisms and viruses, so they are not specific to HIV.

Question 2

Dengue fever is caused by which mosquito?

Accepted Answer

Answer reason: Dengue virus is transmitted primarily by Aedes mosquitoes, especially Aedes aegypti and Aedes albopictus, which are daytime biters and breed in clean water containers. Culex species are vectors for illnesses like filariasis and West Nile virus, not dengue. Anopheles mosquitoes transmit malaria. A fly is not a mosquito vector for dengue.

Question 3

Which type of virus is HIV?

Accepted Answer

Answer reason: HIV is a member of the Retroviridae family. It is an enveloped virus with two copies of positive-sense single-stranded RNA and uses reverse transcriptase to synthesize DNA from its RNA genome, which then integrates into the host genome. While retroviruses are RNA viruses, the most accurate classification for HIV is specifically a retrovirus.

Question 4

Which organ of the human body is mainly affected by malaria?

Accepted Answer

Answer reason: Plasmodium sporozoites first invade hepatocytes where they undergo exoerythrocytic replication, making the liver the primary organ affected early in malaria. After the liver stage, merozoites infect red blood cells, producing fever and anemia. While other organs can be involved secondarily, the liver is the main initial site of infection. Therefore, among the options provided, liver is the best answer.

Question 5

Corynebacterium diphtheriae produces?

Accepted Answer

Answer reason: Corynebacterium diphtheriae produces a potent A-B exotoxin that ADP-ribosylates elongation factor-2, inhibiting protein synthesis and causing cell death. The toxin is responsible for the pseudomembrane in the throat and systemic effects such as myocarditis and neuropathy. Antibodies are host responses, enzymes are not the primary virulence factor here, and bacteria do not produce hormones.

Question 6

Typhoid is caused by _____?

Accepted Answer

Answer reason: Typhoid fever is caused by Salmonella enterica serovar Typhi, a gram-negative bacterium transmitted via the fecal-oral route through contaminated food or water. Related serovars (Paratyphi A, B, C) cause paratyphoid fever, collectively termed enteric fever. It is not caused by fungi or viruses.

Question 7

Ringworm is caused by?

Accepted Answer

Answer reason: Ringworm (tinea) is a superficial dermatophyte infection of keratinized tissues caused by fungi such as Trichophyton, Microsporum, and Epidermophyton species. Despite its name, no worms are involved. It is not caused by viruses or bacteria, which produce different cutaneous presentations and require different treatments.

Question 8

Incubation period of Hepatitis B is?

Accepted Answer

Answer reason: Hepatitis B virus has a relatively long incubation period, typically about 45–160 days with an average near 90 days. This corresponds to approximately 6 weeks to 6 months. Short periods like 1–2 days are seen with some toxin-mediated illnesses, not HBV, and multi-year timelines describe chronic latency rather than incubation. Therefore, 6 weeks to 6 months is correct.

Question 9

Typhoid fever is caused by?

Accepted Answer

Answer reason: Typhoid fever is caused by Salmonella enterica serovar Typhi, transmitted via the fecal–oral route. Vibrio cholerae causes cholera with profuse watery diarrhea, not typhoid. Shigella causes bacillary dysentery, and various E. coli strains cause diarrheal illnesses such as traveler’s diarrhea. Thus, Salmonella typhi is the single correct pathogen for typhoid fever.

Question 10

Whooping Cough is an infection cause by...?

Accepted Answer

Answer reason: Whooping cough (pertussis) is caused by the bacterium Bordetella pertussis, a gram-negative coccobacillus. It infects the respiratory epithelium and produces toxins that lead to severe paroxysmal coughing with the characteristic 'whoop.' Therefore, the etiologic agent is bacterial, not viral, fungal (molds), or chemical.

Question 11

Dengue virus belongs to which family?

Accepted Answer

Answer reason: Dengue virus is an enveloped, positive-sense single-stranded RNA virus in the family Flaviviridae, genus Flavivirus. It is transmitted by Aedes mosquitoes and shares lineage with other flaviviruses such as Zika and West Nile. Orthomyxoviruses include influenza viruses, retroviruses include HIV, and poxviruses include variola—none of which cause dengue.

Question 12

Best culture sample in early stage of Typhoid is?

Accepted Answer

Answer reason: During the first week of typhoid fever, Salmonella Typhi causes bacteremia, making blood culture the most sensitive diagnostic specimen. Stool and urine cultures typically become positive later as organisms are shed from the gallbladder and kidneys. Sputum is not a useful specimen for typhoid diagnosis. Therefore, blood is best in the early stage.

Question 13

Widal test is emoloyed for detecting ________?

Accepted Answer

Answer reason: The Widal test detects agglutinating antibodies (O and H) against Salmonella enterica serotype Typhi and Paratyphi in serum, used as supportive evidence for typhoid fever. It is not used for malaria, which is diagnosed by blood smear or rapid antigen tests for Plasmodium. It is also not used for yellow fever, which relies on viral PCR or specific IgM/neutralizing antibodies for the flavivirus.

Question 14

Which part of the body contains the most bacteria?

Accepted Answer

Answer reason: The colon contains the densest and most diverse microbiota in the human body, with bacterial counts reaching 10^11–10^12 cells per gram of feces. The acidic environment of the stomach suppresses bacterial growth, resulting in relatively low counts. The mouth has significant biofilm but far fewer organisms than the large intestine.

Question 15

Diseases is caused by dog bites?

Accepted Answer

Answer reason: Rabies is a zoonotic viral disease transmitted through the saliva of infected animals, commonly via dog bites, and can lead to fatal encephalitis if untreated. Post-exposure prophylaxis is required promptly after exposure. Scurvy is due to vitamin C deficiency, colorblindness is a genetic/retinal condition, and 'madness' is not a specific disease caused by bites.

Question 16

The incubation period of typhoid fever is usually?

Accepted Answer

Answer reason: Typhoid fever, caused by Salmonella enterica serovar Typhi, typically has an incubation period of about 6–30 days, most commonly around 1–2 weeks. The length varies with inoculum size and host factors, but the usual clinical teaching is approximately 7–14 days. Shorter periods of hours to a few days are inconsistent with typhoid pathogenesis, and months would be atypical.

Question 17

Malaria parasite was discovered by?

Accepted Answer

Answer reason: Sir Ronald Ross demonstrated the transmission of malaria by Anopheles mosquitoes and elucidated key stages of the parasite’s life cycle in 1897, confirming the vector-borne nature of the disease. This work established the role of mosquitoes in spreading Plasmodium and earned him the Nobel Prize. Although Alphonse Laveran first observed the parasite in human blood, among the given options Ross is the correct choice.

Question 18

Onchocerciasis is caused by -------?

Accepted Answer

Answer reason: Onchocerciasis (river blindness) is caused by the filarial nematode Onchocerca volvulus, which is transmitted to humans through the bite of infected Simulium blackflies that breed near fast‑flowing rivers. Tsetse flies transmit Trypanosoma brucei (African trypanosomiasis). Dragonflies and butterflies are not hematophagous vectors for human parasitic diseases.

Question 19

The 'Kissing Disease' is another name for?

Accepted Answer

Answer reason: Infectious mononucleosis is caused most commonly by Epstein–Barr virus and spreads via saliva, hence the nickname 'kissing disease.' Typhoid is due to Salmonella typhi and is transmitted via the fecal–oral route. Influenza is spread primarily by respiratory droplets. Malaria is transmitted by Anopheles mosquitoes.

Question 20

Species of Plasmodium which causes Malignant Malaria?

Accepted Answer

Answer reason: Malignant (severe) malaria is caused by Plasmodium falciparum. This species infects erythrocytes of all ages, producing high parasitemia and sequestration in microvasculature, leading to complications like cerebral malaria, renal failure, and severe anemia. P. vivax and P. ovale typically cause benign tertian malaria, and 'malarial' is not a Plasmodium species.

Question 21

Leprosy is caused by...?

Accepted Answer

Answer reason: Leprosy (Hansen disease) is caused by Mycobacterium leprae, an acid-fast, slow-growing bacterium. It primarily affects skin and peripheral nerves, leading to hypopigmented or erythematous anesthetic patches and neuropathy. Management uses multidrug therapy such as rifampin, dapsone, and clofazimine to prevent resistance and disability.

Question 22

Rabies is caused by...?

Accepted Answer

Answer reason: Rabies is caused by Rabies lyssavirus, an enveloped, bullet-shaped, negative-sense single-stranded RNA virus transmitted through infected saliva, typically via animal bites. It causes acute encephalitis and is preventable with pre- or post-exposure vaccination. It is not caused by bacteria, worms, or protozoa.

Question 23

Which of the following Bacteria can cause Peptic Ulcer?

Accepted Answer

Answer reason: Helicobacter pylori colonizes the gastric mucosa and produces urease, allowing it to survive in the acidic stomach by generating ammonia. The resulting mucosal inflammation and damage predispose to both duodenal and gastric peptic ulcers. Streptococcus, Staphylococcus, and E. coli are not established causes of peptic ulcer disease.

Question 24

Peptidoglycan is present in which structure?

Accepted Answer

Answer reason: Peptidoglycan is the rigid polymer of N-acetylglucosamine and N-acetylmuramic acid cross-linked by peptides that forms the bacterial cell wall, providing shape and osmotic protection. Gram-positive bacteria have a thick peptidoglycan layer, while gram-negative bacteria have a thinner layer within the periplasm. The cell membrane is primarily phospholipid and proteins, capsules are usually polysaccharide, and flagella are composed of flagellin protein.

Question 25

Which type of Hepatitis is known as “infectious hepatitis”?

Accepted Answer

Answer reason: Hepatitis A virus is transmitted via the fecal–oral route and often causes community outbreaks, historically termed “infectious hepatitis.” In contrast, hepatitis B was called “serum hepatitis” due to blood and body fluid transmission. HAV usually causes acute, self-limited disease without chronic infection, reflecting its high transmissibility rather than chronicity.

Question 26

Example of spore forming bacteria is?

Accepted Answer

Answer reason: Only certain gram-positive rods form endospores, notably Bacillus and Clostridium. Staphylococcus (gram-positive cocci), Vibrio (gram-negative curved rods), and Klebsiella (gram-negative rods) do not form spores. Therefore, Bacillus is the correct example of a spore-forming bacterium.

Question 27

A patient with cerebral malaria is infected with?

Accepted Answer

Answer reason: Cerebral malaria is classically caused by Plasmodium falciparum. This species achieves high parasitemia and expresses adhesion proteins (e.g., PfEMP1) that cause cytoadherence and sequestration of infected erythrocytes in cerebral microvasculature, leading to coma and seizures. P. vivax, P. ovale, and P. malariae rarely produce this severe cerebral involvement. Therefore the correct agent is P. falciparum.

Question 28

Which infection is most teratogenic in pregnancy?

Accepted Answer

Answer reason: Among the TORCH infections, rubella is classically the most teratogenic, especially when maternal infection occurs in the first trimester. It causes congenital rubella syndrome with severe defects such as sensorineural deafness, cataracts, and patent ductus arteriosus, with very high risk if infection occurs before 10 weeks. CMV is the most common congenital infection but is less prominently teratogenic than rubella. Toxoplasmosis and varicella can cause fetal anomalies but with lower teratogenic impact.

Question 29

Mad cow disease is caused by a?

Accepted Answer

Answer reason: Mad cow disease (bovine spongiform encephalopathy) is caused by prions—misfolded protein particles that induce abnormal folding of normal prion proteins in the brain. Prions lack nucleic acids and are highly resistant to heat and standard disinfection. Viroids infect plants, not animals, and bacteria and viruses contain genetic material, unlike prions.

Question 30

Bacteria are classified under which kingdom?

Accepted Answer

Answer reason: In the five-kingdom classification, bacteria are unicellular prokaryotes lacking a true nucleus and membrane-bound organelles. These organisms are grouped under Kingdom Monera, which includes eubacteria and cyanobacteria. Protista, Fungi, and Plantae are eukaryotic kingdoms.

Question 31

Which of the following diseases is NOT transmitted from one person to another?

Accepted Answer

Answer reason: Cirrhosis is a chronic liver condition characterized by fibrosis and nodular regeneration, most commonly caused by chronic alcohol use, chronic viral hepatitis, or nonalcoholic steatohepatitis. It is not directly communicable from person to person. In contrast, AIDS (HIV), hepatitis B, and syphilis are infectious diseases transmitted via blood and/or sexual contact.

Question 32

Which microorganism is used in alcohol production?

Accepted Answer

Answer reason: Alcoholic beverages are produced by fermentation, where yeasts such as Saccharomyces cerevisiae convert sugars into ethanol and carbon dioxide. Viruses do not carry out metabolic processes like fermentation. While some bacteria can produce alcohols, industrial and beverage alcohol production predominantly relies on yeast. Protozoa are not used for ethanol fermentation.

Question 33

Smallpox lesions are?

Accepted Answer

Answer reason: In smallpox (variola), skin lesions progress synchronously, so lesions in a given body area are all at the same stage of development. They evolve from macules to papules, vesicles, pustules, and scabs together. This contrasts with varicella (chickenpox), where lesions are in different stages simultaneously. Therefore, the best answer is that the lesions are all at the same stage.

Question 34

The classic feature of tetanus is?

Accepted Answer

Answer reason: Clostridium tetani produces tetanospasmin, a neurotoxin that blocks inhibitory neurotransmitters (GABA and glycine), resulting in sustained muscle rigidity and painful spasms such as trismus and opisthotonus. These spasms are the hallmark of tetanus. Jaundice, vomiting, and weight loss are nonspecific findings and not characteristic of tetanus.

Question 35

Which of the following is an acute infection of bacteria that affects the nervous system?

Accepted Answer

Answer reason: Tetanus is an acute bacterial disease caused by Clostridium tetani, whose neurotoxin (tetanospasmin) blocks inhibitory neurotransmission, leading to muscle rigidity and spasms. It typically follows contamination of a wound with spores. Syphilis is a chronic sexually transmitted infection with late neurologic manifestations, not an acute neuroinfection. Melioidosis and tularemia can be systemic infections but are not primarily defined by acute neurotoxic effects.

Question 36

Which of the following bacteria is pleomorphic?

Accepted Answer

Answer reason: Corynebacterium (e.g., C. diphtheriae) is classically pleomorphic, showing club-shaped rods with variable forms and 'Chinese letter' arrangements due to snapping division and metachromatic granules. Streptococcus are uniform cocci in chains, Pseudomonas are straight Gram-negative rods, and Mycobacteria are slender acid-fast rods—none typically display pleomorphism. Therefore, Corynebacterium is the best answer.

Question 37

One of the below is an infective form of malaria parasite?

Accepted Answer

Answer reason: For humans, the infective stage of Plasmodium is the sporozoite, which is injected from the salivary glands of an infected Anopheles mosquito during a bite and then invades hepatocytes. Tachyzoite and bradyzoite are stages of Toxoplasma gondii, not malaria. Oocysts form on the mosquito midgut in the Plasmodium life cycle and are not directly infective to humans.

Question 38

Patient suffered meningitis after having lung abscess, most likely organism?

Accepted Answer

Answer reason: Staphylococcus aureus is a highly pyogenic organism that commonly causes lung abscesses. Bacteremia from this focus can seed the meninges and produce meningitis. Streptococcus pneumoniae is a leading cause of meningitis after pneumonia, but it is less associated with lung abscess formation. Neisseria meningitidis and Haemophilus influenzae are not typically linked to lung abscess as a primary source.

Question 39

Which is not a communicable disease?

Accepted Answer

Answer reason: Tetanus is caused by Clostridium tetani spores introduced into a wound from the environment and is not transmitted person-to-person. In contrast, HIV, hepatitis A, and Ebola are communicable viral infections that spread between people via blood/body fluids or fecal-oral routes. Therefore, tetanus is the non-communicable disease among the options.

Question 40

Which of the following is not sexually transmitted diseases ?

Accepted Answer

Answer reason: Anthrax is caused by Bacillus anthracis and is acquired through contact with infected animals or spores via skin, inhalation, or ingestion; it is not transmitted by sexual contact. In contrast, syphilis (Treponema pallidum), gonorrhea (Neisseria gonorrhoeae), and HIV/AIDS are classic sexually transmitted infections spread through sexual exposure. Therefore, anthrax is the only option that is not an STD.

Question 41

Meningitis can be caused by?

Accepted Answer

Answer reason: Meningitis is inflammation of the meninges that can result from various infectious agents. Common bacterial causes include Neisseria meningitidis and Streptococcus pneumoniae. Viral meningitis is often due to enteroviruses or HSV. Fungal meningitis, such as from Cryptococcus neoformans, occurs especially in immunocompromised patients; therefore all listed agents can cause meningitis.

Question 42

The malaria parasite completes its sexual cycle in?

Accepted Answer

Answer reason: Plasmodium undergoes sexual reproduction in the gut of the female Anopheles mosquito. Gametocytes ingested from human blood fertilize to form zygotes, which develop into ookinetes and oocysts, producing sporozoites that migrate to the salivary glands. In humans the parasite reproduces asexually (schizogony). Therefore, the sexual cycle is completed in the mosquito.

Question 43

Malaria transmission occurs mainly during which time?

Accepted Answer

Answer reason: Malaria is transmitted by female Anopheles mosquitoes, which predominantly feed from dusk to dawn. Their nocturnal biting behavior concentrates transmission at night. This is why insecticide-treated bed nets and nighttime protection are key prevention strategies.

Question 44

Koplik spots are seen in?

Accepted Answer

Answer reason: Koplik spots are small bluish-white lesions on the buccal mucosa opposite the molars and are pathognomonic for measles (rubeola). They appear during the prodromal phase before the exanthem. Rubella lacks Koplik spots, mumps presents primarily with parotitis, and chickenpox causes a pruritic vesicular rash without these oral lesions.

Question 45

Which antigen is the earliest marker of Hepatitis B infection?

Accepted Answer

Answer reason: HBsAg is the first serologic marker to appear in acute hepatitis B, detectable during the incubation period before symptoms. HBeAg appears after HBsAg and indicates high infectivity. HBcAg is not detectable in serum; instead, anti-HBc IgM is an early antibody marker of acute infection. Anti-HBs appears only after recovery or vaccination and indicates immunity.

Question 46

Virus is made up of?

Accepted Answer

Answer reason: Viruses consist of a nucleic acid genome (either DNA or RNA, never both) enclosed within a protein capsid. Some viruses may also have a lipid envelope, but the core components are nucleic acid plus protein. Therefore, options stating only protein or only nucleic acid are incomplete. The best answer is protein and DNA/RNA.

Question 47

Test for Helicobacter pylori is?

Accepted Answer

Answer reason: Helicobacter pylori can be detected by several modalities. Serologic blood tests identify antibodies, stool antigen tests detect current infection, and endoscopic biopsy allows histology, rapid urease testing, or culture. Therefore, all listed options are valid tests for H. pylori.

Question 48

Covid19 is ______ virus?

Accepted Answer

Answer reason: SARS-CoV-2, the virus causing COVID-19, is an enveloped positive-sense single-stranded RNA virus in the family Coronaviridae. Its genome functions directly as mRNA and is replicated by an RNA-dependent RNA polymerase in the cytoplasm. It is not a DNA virus and does not have a double-stranded RNA genome.

Question 49

Tuberculosis is the disease cause by___?

Accepted Answer

Answer reason: Tuberculosis is caused by Mycobacterium tuberculosis, an acid-fast bacillus transmitted via airborne droplets. Mycobacterium leprae (spelled laprae in the option) causes leprosy (Hansen disease), not TB. Variola virus causes smallpox. Therefore, the correct causative agent for TB is Mycobacterium tuberculosis.

Question 50

Typhoid fever is caused by -?

Accepted Answer

Answer reason: Typhoid fever is caused by Salmonella enterica serotype Typhi, a gram-negative bacterium transmitted via the fecal–oral route. It invades the intestinal mucosa and disseminates systemically, leading to sustained fever and abdominal symptoms. It is not due to a fungus, virus, or allergic reaction.

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