A 10-year-old child cut his leg with a piece of glass and was sent to a clinic for an anti-tetanus serum injection. In order to prevent the development of anaphylactic shock, the Besredka desensitization method was applied. What mechanism underlies this method?

Correct Answer: A

Rationale: The correct choice is A: Binding to IgE fixed to mast cells. The Besredka desensitization method involves injecting small, gradually increasing doses of the allergen to induce tolerance and prevent anaphylactic shock. This process works by binding the allergen to IgE antibodies fixed to mast cells, which prevents the release of histamine and other inflammatory mediators that trigger allergic reactions. This desensitization process helps the immune system become less reactive to the allergen over time. Incorrect choices: B: Inhibited synthesis of mast cells mediators - This choice does not reflect the mechanism of the Besredka desensitization method, which involves binding to IgE on mast cells. C: Stimulation of the immunological antigen tolerance - While this may sound plausible, the Besredka method specifically targets the IgE-mast cell interaction. D: Stimulation of antigen-specific IgG synthesis - While IgG antibodies may play a role in desensitization, the

Correct Answer: C

Rationale: The correct answer is C: Leishmaniasis. The description of thin microorganisms with 12-14 uniform tendrils, 10-13 micrometers in length, and pale pink color matches the characteristics of Leishmania parasites seen in Giemsa-stained samples. Leishmania parasites are known to have a distinctive appearance with pointed tips and a specific size range. Syphilis (choice A) is caused by Treponema pallidum, which appears as tightly coiled spirochetes, not tendrils. Trypanosomiasis (choice B) is caused by Trypanosoma parasites, which have a different morphology and staining pattern. Relapsing fever (choice D) is caused by Borrelia recurrentis, which does not match the description given. Therefore, the correct choice is C as the description aligns closely with the characteristic features of Leishmania parasites.

Correct Answer: A

Rationale: The correct answer is A: Protozoa. Protozoa are single-celled eukaryotic organisms, meaning they have a nucleus and other membrane-bound organelles. Eukaryotes have complex cellular structures that include a nucleus, mitochondria, and other organelles. Therefore, protozoa are eukaryotes. Viruses (B) are not considered cells and lack cellular structures. Viroids (C) are smaller infectious agents that consist of only RNA, lacking the cellular structure of eukaryotes. Prions (D) are infectious proteins and do not possess cellular structures like eukaryotes. So, protozoa are the only choice that relates to eukaryotes due to their cellular structure.

Correct Answer: A

Rationale: The correct answer is A: Lamblia. The presence of big pyriform cells with two nuclei in the duodenal contents indicates Giardia lamblia infection. This parasite is commonly found in contaminated water and causes symptoms like poor appetite and abdominal pain. Trichomonas, Amoeba, Trypanosoma, and Toxoplasma are not typically associated with these findings and symptoms. Therefore, Lamblia is the most likely microorganism based on the clinical presentation and microscopic examination results.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Anopheles mosquitoes are the primary vectors for transmitting malaria. 2. They prefer stagnant water for breeding, common in tropical regions. 3. Culex mosquitoes primarily spread diseases like West Nile virus. 4. Aedes mosquitoes transmit diseases like Zika and dengue fever. 5. Mansonia mosquitoes are known for transmitting filarial diseases. Therefore, the correct answer is A (Anopheles), as they are specifically associated with spreading malaria.