Nokea
The incubation period for hepatitis B is:
- A. One week - 10 days
- B. One month - 45 days
- C. Up to 3 months
- D. Up to 6 months
Correct Answer: C
Rationale: The correct answer is C: Up to 3 months. Hepatitis B has an average incubation period of 60-90 days, which aligns with the timeframe of up to 3 months. This period refers to the time between exposure to the virus and the onset of symptoms. One week to 10 days (choice A) is too short for hepatitis B, as it typically takes longer to manifest. One month to 45 days (choice B) is also shorter than the average incubation period for hepatitis B. Up to 6 months (choice D) is too long for hepatitis B, as the virus typically shows symptoms within 3 months.
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A sample stained using Romanovsky-Giemsa method revealed crescent-shaped protozoa with pointed ends and blue cytoplasm. What is the causative agent?
- A. Toxoplasma
- B. Plasmodium
- C. Leishmania
- D. Trypanosoma
Correct Answer: A
Rationale: The correct answer is A: Toxoplasma. The crescent-shaped protozoa with pointed ends and blue cytoplasm described in the question are characteristic of Toxoplasma gondii, the causative agent of toxoplasmosis. Toxoplasma staining with Romanovsky-Giemsa method typically shows these specific morphological features. Plasmodium causes malaria and does not exhibit the described morphology. Leishmania and Trypanosoma are both kinetoplastid parasites, but they do not typically present as crescent-shaped protozoa with blue cytoplasm. Therefore, based on the specific characteristics described in the question, the correct answer is Toxoplasma.
A patient with a wound infection had a Gram-positive cocci isolated from the sample. The bacteria were catalase-positive and coagulase-positive. What is the most likely causative agent?
- A. Staphylococcus aureus
- B. Staphylococcus epidermidis
- C. Streptococcus pyogenes
- D. Enterococcus faecalis
Correct Answer: A
Rationale: The correct answer is A: Staphylococcus aureus. Staphylococcus aureus is a Gram-positive cocci that is catalase-positive and coagulase-positive, making it the most likely causative agent for the wound infection. Catalase-positive bacteria produce the enzyme catalase, which helps break down hydrogen peroxide. Coagulase-positive bacteria produce the enzyme coagulase, which causes the plasma proteins to clot. Staphylococcus epidermidis is catalase-positive but coagulase-negative, making it less likely to cause a wound infection. Streptococcus pyogenes is catalase-negative, and Enterococcus faecalis is catalase-negative and coagulase-negative, so they are less likely to be the causative agent.
All statements of viral neutralization reaction are true except:
- A. A key component of the reaction is the complement system involvement
- B. Specific virus neutralising antibodies block the viral ability to infect cells
- C. The antibodies are titrated and two serum samples are required
- D. It is also used to identify newly isolated virus
Correct Answer: A
Rationale: Rationale:
A: Incorrect - The complement system is not directly involved in the viral neutralization reaction.
B: Correct - Specific antibodies neutralize viruses by blocking their ability to infect cells.
C: Incorrect - Antibodies are titrated, but only one serum sample is required for neutralization testing.
D: Incorrect - Viral neutralization is primarily used to measure antibody response, not to identify newly isolated viruses.
Which bacteria are Gram-negative cocci?
- A. Neisseria species
- B. Streptococcus species
- C. Bacillus species
- D. Clostridium species
Correct Answer: A
Rationale: The correct answer is A: Neisseria species. Gram staining differentiates bacteria based on cell wall composition. Gram-negative bacteria like Neisseria have a thin peptidoglycan layer and an outer membrane, making them appear pink under the microscope. Streptococcus species (B) are Gram-positive cocci with a thick peptidoglycan layer, appearing purple. Bacillus (C) and Clostridium (D) species are Gram-positive rods, not Gram-negative cocci. Thus, the correct answer is A because Neisseria species are the only Gram-negative cocci among the choices provided.
(+) ssRNA viruses that have been isolated from birds, cats, dogs, pigs, sheep, cows, and humans and are a major cause of gastroenteritis are the:
- A. rotaviruses
- B. caliciviruses
- C. adenoviruses
- D. noroviruses
Correct Answer: B
Rationale: The correct answer is B: caliciviruses. Caliciviruses are known to be (+) ssRNA viruses that cause gastroenteritis in a wide range of animals, including birds, cats, dogs, pigs, sheep, cows, and humans. These viruses are highly contagious and can spread through contaminated food or water. Rotaviruses (A) are also a common cause of gastroenteritis, but they are not exclusively isolated from the mentioned animals. Adenoviruses (C) typically cause respiratory or eye infections, not gastroenteritis. Noroviruses (D) are also a major cause of gastroenteritis in humans, but they are not commonly found in animals other than humans.