A patient returning from Congo republic a week ago is with fever, headache vomiting and diarrhea, Three days after his admission to the infectious ward, despite antibiotic therapy, severe hemorrhagic syndrome developed and as well as CNS involvement, The diagnosis is hemorrhagic fever. Which of these viruses can be a causative agent?

Correct Answer: C

Rationale: The correct answer is C: Ebola virus. The patient's symptoms align with Ebola virus infection, including fever, severe hemorrhagic syndrome, and CNS involvement. Ebola virus is known to cause hemorrhagic fevers with high mortality rates. A: SARS CoV causes Severe Acute Respiratory Syndrome, which typically presents with respiratory symptoms, not hemorrhagic fever. B: Lymphocytic choriomeningitis virus usually causes a mild illness with flu-like symptoms, not severe hemorrhagic syndrome. D: ECHO 9 virus is associated with aseptic meningitis, not hemorrhagic fever.

Correct Answer: C

Rationale: The correct answer is C: Bacillus, Clostridium. Both Bacillus and Clostridium are known to form spores. Bacillus species produce endospores, which are resistant structures for survival in harsh conditions, while Clostridium species also form spores for protection and dispersal. The other choices are incorrect because Borrelia and Treponema are spirochetes and do not form spores, Bacteroides and Fusobacterium are anaerobic bacteria that do not produce spores, and Bordetella and Brucella are non-spore forming bacteria as well.

Correct Answer: A

Rationale: The correct answer is A: 1 chromosome. Bacterial cells typically have a singular circular chromosome that contains their genetic material. This chromosome is essential for the cell's survival and contains all the necessary genetic information for its functions. Choices B, C, and D are incorrect because they refer to the chromosome numbers found in human cells (23 pairs or 46 individual chromosomes). Bacteria, being prokaryotic organisms, have a simpler genetic makeup compared to eukaryotic organisms like humans, hence they possess only one chromosome.

Correct Answer: B

Rationale: The correct answer is B: Shagreen leather. Yersinia pestis, the bacterium causing plague, forms colonies resembling shagreen leather on a hard nutrient medium due to its distinctive morphology. This morphology includes a rough, irregular, and raised appearance, similar to the texture of shagreen leather. A: Dewdrops - Incorrect. Dewdrops do not accurately describe the colony morphology of Yersinia pestis. C: Lace handkerchief - Incorrect. Lace handkerchief does not accurately describe the colony morphology of Yersinia pestis. D: Mercury drops - Incorrect. Mercury drops do not accurately describe the colony morphology of Yersinia pestis.

Correct Answer: D

Rationale: The correct answer is D: scanning electron microscope. A scanning electron microscope provides a three-dimensional image of a specimen by scanning a focused electron beam across the surface of the specimen, detecting the electrons that are emitted from the surface, and creating a detailed image. This is achieved through the detection of secondary electrons, backscattered electrons, and X-rays emitted from the specimen surface. A dark-field microscope (choice A) utilizes oblique lighting to enhance contrast and is not specifically designed to provide a 3D image. A transmission electron microscope (choice B) uses a beam of electrons transmitted through a specimen to create a 2D image at high magnification. A bright-field microscope (choice C) is a basic microscope that illuminates a specimen with uniform light and does not provide a 3D image like a scanning electron microscope does.

Correct Answer: A

Rationale: The correct answer is A: Toxoplasma. Toxoplasma gondii is a protozoan parasite that can infect the brain and cause vision loss. The description of half-moon-shaped organisms with a pointed end matches the appearance of Toxoplasma under the microscope. Toxoplasma is known to cause a condition called toxoplasmosis, which can lead to neurological symptoms such as vision loss. Leishmania, Lamblia, Amoeba, and Trichomonad are not known to cause brain infections or vision loss, making them incorrect choices.

Correct Answer: B

Rationale: The correct answer is B because the main target of the toxin produced by Vibrio cholerae is the epithelial cells of the small intestine. This toxin, known as cholera toxin, binds to the surface of these cells and disrupts their normal function, leading to the characteristic watery diarrhea seen in cholera. The other choices are incorrect because macrophages are not the main target, RBCs are not directly affected by the toxin, and the stomach epithelial cells are not specifically targeted by Vibrio cholerae toxin.

Correct Answer: A

Rationale: The correct answer is A: Leptospira interrogans. Darkfield microscopy is used to visualize spirochetes, which are spiral-shaped bacteria. Leptospira is a spirochete bacterium that causes leptospirosis, which presents with jaundice, muscle aching, chill, and nosebleeds. Leptospira is commonly transmitted through contact with contaminated water or soil. B: Borrelia dutlonii causes Lyme disease, which is transmitted by ticks and does not typically present with jaundice or nosebleeds. C: Calymmatobacterium granulomatis causes granuloma inguinale, a sexually transmitted infection that does not present with the symptoms described. D: Bartonella bacilloformis causes Carrion's disease, which presents with fever, anemia, and skin lesions but not jaundice or nosebleeds.

Correct Answer: A

Rationale: The correct answer is A because significant bacteriuria is defined as having more than 10^5 cells in 1 ml of midstream morning urine. This concentration indicates a true infection rather than contamination. Choice B is incorrect because the amount of urine does not determine significant bacteriuria. Choice C is incorrect because even a single bacterium in urine does not necessarily indicate an infection. Choice D is incorrect because not all statements are correct; only choice A accurately defines significant bacteriuria based on the bacterial concentration in urine samples.