Question 1

Which of the following best describes a toxoid vaccine, and which disease is commonly prevented by this type of vaccine?

Accepted Answer

A vaccine containing inactivated bacterial toxins; used to prevent tetanus.

Question 2

A patient presents with white, curd-like patches in the mouth and a recent history of antibiotic use. Which organism is most likely responsible, and what is its mode of transmission?

Accepted Answer

Candida albicans; endogenous overgrowth due to disruption of normal flora.

Question 3

Which of the following statements about Vibrio cholerae is correct?

Accepted Answer

It causes profuse watery diarrhea due to a toxin that increases cAMP in intestinal cells.

Question 4

A 25-year-old male presents with purulent urethral discharge and dysuria. Gram-negative diplococci are seen on microscopy. Which organism is most likely responsible, and what is its primary mode of transmission?

Accepted Answer

Neisseria gonorrheae; sexual contact.

Question 5

Coccidioides immitis is most likely to cause which of the following clinical presentations, and how is it acquired?

Accepted Answer

Pulmonary infection after inhalation of arthroconidia from soil.

Question 6

Which of the following best distinguishes Salmonella from Shigella in terms of pathogenesis and clinical presentation?

Accepted Answer

Salmonella can cause bacteremia and is often associated with animal reservoirs, while Shigella is primarily human-to-human and rarely causes bacteremia.

Question 7

A patient with a history of peptic ulcers is found to have a curved, Gram-negative rod in the stomach. Which organism is most likely responsible, and what is a key virulence factor?

Accepted Answer

Helicobacter pylori; urease production.

Question 8

Yersinia pestis, the causative agent of plague, is primarily transmitted to humans by which route?

Accepted Answer

Bite of infected fleas from rodents.

Question 9

Which of the following is a common clinical manifestation of Haemophilus influenzae infection in unvaccinated children?

Accepted Answer

Epiglottitis with inspiratory stridor.

Question 10

A sexually active woman presents with frothy, greenish vaginal discharge and itching. Which organism is most likely responsible, and what is its mode of transmission?

Accepted Answer

Trichomonas vaginalis; sexual contact.

Question 11

Which of the following human herpesviruses (HHV) is most commonly associated with infectious mononucleosis?

Accepted Answer

HHV-4 (Epstein-Barr virus).

Question 12

Which of the following statements about coronaviruses is correct?

Accepted Answer

They are enveloped, positive-sense RNA viruses that can cause respiratory infections ranging from the common cold to severe pneumonia.

Question 13

A person is bitten by a wild animal and later develops hydrophobia and neurological symptoms. Which virus is most likely responsible, and what is the recommended post-exposure prophylaxis?

Accepted Answer

Rabies virus; administration of rabies immunoglobulin and vaccine.

Question 14

Which of the following best describes the difference between antigenic drift and antigenic shift in influenza viruses?

Accepted Answer

Antigenic drift involves gradual point mutations in viral genes, while antigenic shift involves reassortment of gene segments leading to new subtypes.

Question 15

A child presents with acute flaccid paralysis. Which virus is most likely responsible, and what is the primary mode of transmission?

Accepted Answer

Poliovirus; fecal-oral route.

Question 16

Which of the following best explains why subunit vaccines are considered safer than live attenuated vaccines?

Accepted Answer

They contain only specific antigens and cannot replicate, reducing the risk of causing disease in immunocompromised individuals.

Question 17

A foodborne outbreak of bloody diarrhea is traced to undercooked poultry. Which organism is most likely responsible, and what is a key distinguishing feature?

Accepted Answer

Campylobacter jejuni; curved, motile Gram-negative rod.

Question 18

Which of the following equations best represents the relationship between the basic reproduction number $$R_0$$ and herd immunity threshold $$H$$ for a vaccine-preventable disease?

Accepted Answer

$$H = 1 - \frac{1}{R_0$}$$

Question 19

A patient develops severe dehydration after drinking contaminated water during a flood. Laboratory analysis reveals a Gram-negative, comma-shaped bacterium. Which organism is most likely responsible, and what is the primary mechanism of disease?

Accepted Answer

Vibrio cholerae; secretion of cholera toxin that increases cAMP in enterocytes.

Question 20

Which of the following best explains why influenza pandemics are more likely to be caused by influenza A rather than influenza B?

Accepted Answer

Influenza A undergoes antigenic shift due to reassortment between animal and human strains.

Microbial Diseases, Vaccines, and Viral Pathogenesis: Study Guide

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