Infectious Diseases Practice Questions
20 free Infectious Diseases practice questions for the General Science. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which of the following pathogens is the primary causative agent of tuberculosis?
- A Corynebacterium diphtheriae
- B Mycobacterium tuberculosis
- C Streptococcus pneumoniae
- D Bordetella pertussis
Correct answer: Mycobacterium tuberculosis
Mycobacterium tuberculosis is an acid-fast bacterium that primarily affects the lungs. It is characterized by its slow growth and ability to persist within host macrophages.
The 'Gram stain' procedure differentiates bacteria into two large groups based on the physical and chemical properties of their:
- A Cytoplasmic membrane
- B Nucleoid region
- C Cell wall
- D Flagella
Correct answer: Cell wall
The Gram stain targets the peptidoglycan layer of the cell wall. Gram-positive bacteria have a thick layer that retains crystal violet, while Gram-negative bacteria have a thin layer and an outer membrane.
Which of the following viral diseases has been officially declared eradicated worldwide by the World Health Organization (WHO)?
- A Measles
- B Poliomyelitis
- C Smallpox
- D Influenza
Correct answer: Smallpox
Smallpox, caused by the Variola virus, was declared eradicated in 1980 following a global vaccination campaign. It remains the only human infectious disease to be completely eliminated from nature.
What is the primary mode of transmission for the Hepatitis A virus?
- A Blood-to-blood contact
- B Sexual contact
- C Fecal-oral route
- D Respiratory droplets
Correct answer: Fecal-oral route
Hepatitis A is typically transmitted through the ingestion of contaminated food or water. Unlike Hepatitis B and C, it does not cause chronic liver disease.
Which of the following is a characteristic feature of Prion diseases, such as Creutzfeldt-Jakob disease?
- A High fever and inflammation
- B Rapid viral replication in the brain
- C Abnormal folding of host proteins
- D Fungal growth in spinal fluid
Correct answer: Abnormal folding of host proteins
Prions are infectious proteins that lack nucleic acids. They cause disease by inducing normal cellular proteins to fold into a pathological beta-sheet conformation.
Which vector is responsible for transmitting the parasite that causes Malaria?
- A Aedes aegypti mosquito
- B Anopheles mosquito
- C Tsetse fly
- D Ixodes tick
Correct answer: Anopheles mosquito
Malaria is caused by Plasmodium parasites transmitted through the bite of an infected female Anopheles mosquito. The parasite undergoes part of its life cycle in the mosquito and part in the human host.
The term 'MRSA' refers to a strain of Staphylococcus aureus that is resistant to which class of antibiotics?
- A Aminoglycosides
- B Quinolones
- C Beta-lactams
- D Macrolides
Correct answer: Beta-lactams
MRSA stands for Methicillin-resistant Staphylococcus aureus. It is clinically significant because it is resistant to most penicillins and cephalosporins, making infections harder to treat.
Which respiratory infection is characterized by violent coughing fits followed by a high-pitched 'whoop' on inhalation?
- A Diphtheria
- B Pertussis
- C Croup
- D Legionnaires' disease
Correct answer: Pertussis
Pertussis, caused by Bordetella pertussis, involves severe coughing fits followed by a high-pitched intake of breath that sounds like a 'whoop'. It is prevented by the acellular pertussis component of the DTaP vaccine.
Thrush and vaginal yeast infections are most commonly caused by which opportunistic fungus?
- A Rhizopus oryzae
- B Cryptococcus neoformans
- C Candida albicans
- D Histoplasma capsulatum
Correct answer: Candida albicans
Candida albicans is a normal flora member that can cause infection when the host's immune system or microbial balance is disrupted. It presents as white patches on mucous membranes.
What is the mechanism of action of the cholera toxin produced by Vibrio cholerae?
- A Inhibition of protein synthesis
- B Destruction of red blood cells
- C Blockage of neurotransmitter release
- D Activation of adenylate cyclase
Correct answer: Activation of adenylate cyclase
The toxin increases cyclic AMP levels in intestinal epithelial cells. This results in the massive secretion of chloride ions and water into the intestinal lumen, causing 'rice-water' stools.
Lyme disease is caused by the bacterium Borrelia burgdorferi. How is it typically transmitted to humans?
- A Bite of an infected black-legged tick
- B Consumption of unpasteurized milk
- C Contact with infected rodent urine
- D Inhalation of aerosolized soil particles
Correct answer: Bite of an infected black-legged tick
Borrelia burgdorferi is a spirochete transmitted by Ixodes ticks. Early infection is often recognized by a characteristic 'bulls-eye' rash known as erythema migrans.
Which of the following best describes an 'antigenic shift' in Influenza viruses?
- A Gradual point mutations in the RNA genome
- B Exchange of genome segments between viruses
- C Loss of the viral envelope
- D Acquisition of antibiotic resistance from bacteria
Correct answer: Exchange of genome segments between viruses
Antigenic shift occurs when two different influenza viruses infect the same cell and exchange genetic segments. This can lead to a completely new subtype, often resulting in pandemics.
Which bacterial illness is associated with eating improperly canned foods and is caused by a potent neurotoxin?
- A Cholera
- B Botulism
- C Listeriosis
- D Shigellosis
Correct answer: Botulism
Clostridium botulinum produces botulinum toxin in anaerobic environments like sealed cans. The toxin prevents the release of acetylcholine, leading to flaccid paralysis.
The Human Immunodeficiency Virus (HIV) primarily targets which type of immune cells?
- A B cells
- B CD4+ T cells
- C Cytotoxic T cells
- D Natural Killer cells
Correct answer: CD4+ T cells
HIV uses the CD4 receptor to enter T helper cells. As the viral load increases, the CD4+ cell count drops, leading to the severe immunodeficiency seen in AIDS.
Which of the following is the causative agent of Syphilis?
- A Neisseria gonorrhoeae
- B Chlamydia trachomatis
- C Candida albicans
- D Treponema pallidum
Correct answer: Treponema pallidum
Treponema pallidum is a spirochete bacterium. Syphilis progresses through primary, secondary, latent, and tertiary stages if not treated with antibiotics.
What is the clinical significance of the enzyme 'Reverse Transcriptase' in retroviruses?
- A It converts viral RNA into DNA
- B It repairs damaged viral DNA
- C It breaks down host cell proteins
- D It assembles the viral capsid
Correct answer: It converts viral RNA into DNA
Reverse transcriptase allows retroviruses like HIV to integrate their genetic information into the host genome. This process is a major target for antiretroviral therapy.
Which of the following diseases is caused by a protozoan and is often contracted from contaminated cat litter or undercooked meat?
- A Toxoplasmosis
- B Giardiasis
- C Amoebiasis
- D Cryptosporidiosis
Correct answer: Toxoplasmosis
Toxoplasma gondii is a protozoan that can infect most mammals, but felines are the definitive hosts. It is particularly dangerous for pregnant women due to the risk of congenital transmission.
In the context of epidemiology, what does the term 'R0' (R-naught) represent?
- A The percentage of the population that is immune
- B The mortality rate of a specific pathogen
- C The time it takes for symptoms to appear after exposure
- D The average number of people one case infects
Correct answer: The average number of people one case infects
R0 is the basic reproduction number. If R0 is greater than 1, the infection is likely to spread; if it is less than 1, the infection will eventually die out in the population.
Which of the following childhood diseases is caused by the Varicella-zoster virus?
- A Mumps
- B Rubella
- C Scarlet fever
- D Chickenpox
Correct answer: Chickenpox
Varicella-zoster virus causes chickenpox upon primary infection. The virus can then remain latent in nerve ganglia and reactivate later in life as shingles (herpes zoster).
What is the primary function of the bacterial capsule?
- A To facilitate genetic exchange
- B To provide motility through rotation of flagella
- C To synthesize ATP for the cell
- D To protect the cell from phagocytosis
Correct answer: To protect the cell from phagocytosis
The capsule is a polysaccharide layer outside the cell wall that hides surface antigens from the host immune system. This makes encapsulated bacteria more virulent by avoiding engulfment by white blood cells.