A child cut his leg with a piece of glass while playing and was brought to the clinic for the injection of tetanus toxoid. In order to prevent the development of anaphylactic shock the serum was administered by Bezredka method. What mechanism underlies this method of desensitization of the body?

Correct Answer: A

Rationale: The correct answer is A: Binding of IgE fixed to the mast cells. The Bezredka method involves injecting small, gradually increasing doses of the antigen (tetanus toxoid) to desensitize the body and prevent anaphylactic shock. This process works by binding the IgE antibodies fixed to mast cells, thereby reducing the release of allergic mediators like histamine. This prevents the cascade of events that lead to anaphylactic shock. Choice B (Blocking the mediator synthesis in the mast cells) is incorrect because the Bezredka method does not block mediator synthesis but rather prevents the release of mediators by binding IgE. Choice C (Stimulation of immune tolerance to the antigen) is incorrect as the Bezredka method does not primarily focus on inducing immune tolerance but rather on preventing anaphylactic reactions. Choice D (Stimulation of the synthesis of antigen-specific IgG) is incorrect because the Bezredka method targets IgE antibodies on mast cells

Correct Answer: C

Rationale: The correct answer is C: Papillomaviruses. Papillomaviruses are primarily transmitted through sexual contact, as they infect the skin and mucous membranes of the genital area. This transmission route is well-documented through research and epidemiological studies. Arenaviruses (A) are primarily transmitted through contact with infected rodents, not sexual contact. Togaviruses (B) are mainly transmitted by mosquitoes and ticks. Polyomaviruses (D) are typically spread through respiratory secretions or contaminated urine, not through sexual contact. Therefore, the most appropriate choice for viruses transmitted mainly through sexual contact is Papillomaviruses (C).

Correct Answer: A

Rationale: The correct answer is A: Gram-positive rod-shaped bacterium. Campylobacter fetus is actually a Gram-negative bacterium. This is because it has a thin peptidoglycan layer in its cell wall, which does not retain the crystal violet stain used in the Gram-staining technique. It appears red or pink under a microscope after counterstaining with safranin. Therefore, statement A is incorrect. B: Optimal temperature for cultivation 35-37C - Correct, as Campylobacter fetus thrives at this temperature range. C: Opportunistic pathogen causes infections usually in newborns, immunocompromised patients, and cancer - Correct, as Campylobacter fetus can cause infections in these populations. D: Fastidious, microaerophile - Correct, as Campylobacter fetus is fastidious and requires specific growth conditions, including low oxygen levels.

Correct Answer: B

Rationale: The correct answer is B: Toxoplasmosis. Toxoplasmosis is caused by the protozoan Toxoplasma gondii. The rationale for this is that protozoa are single-celled organisms that can cause diseases in humans. Cat scratch disease (A) is caused by a bacterium, Bartonella henselae. Relapsing fever (C) is caused by the bacterium Borrelia recurrentis. Plague (D) is caused by the bacterium Yersinia pestis. Therefore, the only choice caused by a protozoan is toxoplasmosis, making it the correct answer.

Correct Answer: D

Rationale: The correct answer is D because virulence refers to the degree of pathogenicity of a microorganism, which can vary and is not a constant characteristic. It can be measured using LD50, which is the lethal dose that kills 50% of the test population. Therefore, all the statements in options A, B, and C are true and collectively provide a comprehensive understanding of virulence.

Correct Answer: C

Rationale: The correct answer is C: Nucleic acid and proteins. Viruses contain genetic material in the form of nucleic acids (DNA or RNA) surrounded by a protein coat. This genetic material carries instructions for viral replication. Proteins are also essential components of viruses, serving various functions like facilitating viral entry into host cells. Option A is incorrect as lipids are not main components of viruses. Option B is incorrect as lipids are not typically found in the main structure of viruses. Option D is incorrect as lipids are not primary components of viruses, and glycoproteins are not always present in the main structure of viruses.

Correct Answer: A

Rationale: The correct answer is A: Nucleoid. The bacterial genome is located in the nucleoid, a region within the bacterial cell where the genetic material is condensed and organized. This structure is not the same as a nucleus found in eukaryotic cells. The other choices (B: Nucleotide and C: ATP) are incorrect because nucleotide refers to a building block of DNA or RNA, and ATP is a molecule used for energy transfer in cells, neither of which specifically houses the bacterial genome. Choice D: None of the above is incorrect as well, as the correct term for the compact structure containing the bacterial genome is the nucleoid.

Correct Answer: A

Rationale: The correct answer is A: Balantidium coli. This large ciliated protozoa with a kidney-shaped macronucleus is characteristic of Balantidium coli, an intestinal parasite known to cause foul-smelling diarrhea in humans. Balantidium coli is the only option among the choices that fits this specific description. Entamoeba histolytica causes amoebic dysentery, Giardia lamblia causes giardiasis, and Trichomonas hominis is a non-pathogenic protozoa found in the intestinal tract. Therefore, based on the morphology described in the question, Balantidium coli is the correct causative agent.

Correct Answer: A

Rationale: The correct answer is A: Toxoplasmosis. Toxoplasmosis is caused by the protozoan Toxoplasma gondii, which can be transmitted from mother to fetus during pregnancy leading to stillbirth and malformations. This parasite can cross the placenta and infect the fetus, causing severe complications. Leishmaniasis (B), Malaria (C), and Amebiasis (D) are not known to cause intrauterine death or malformations in the same way as Toxoplasmosis. Leishmaniasis is transmitted by sandflies, Malaria by mosquitoes, and Amebiasis by contaminated food or water.