Correct Answer: A

Rationale: The correct answer is A: Antibiotic. Brucellosis is a bacterial infection, and antibiotics are the primary treatment to target and eliminate the bacteria causing the disease. Antibiotics such as doxycycline and rifampin are commonly used for brucellosis treatment. Donor immunoglobulin (B) is not used to treat brucellosis as it is not caused by a deficiency in antibodies. Inactivated therapeutic vaccine (C) is used for prevention, not for treating active infections. Antitoxic serum (D) is used to neutralize toxins produced by bacteria, not to directly kill the bacteria themselves in cases like brucellosis.

Correct Answer: B

Rationale: The correct answer is B: Agglutination reaction. This is the most suitable serological reaction for the quick determination of the antigen of the epizootic agent causing mass rodent deaths. In agglutination reaction, antibodies cause the clumping of antigens, allowing for easy visual detection of the presence of the specific antigen. This is efficient for rapid diagnosis in cases of suspected infectious diseases like plague. A: Precipitation reaction is more suitable for identifying soluble antigens, not for quick determination of a specific antigen in this scenario. C: Reaction of passive hemagglutination is used for measuring the presence of antibodies, not antigens. D: Bordet-Gengou test is a specific test for the identification of Bordetella pertussis bacterium, not suitable for this scenario.

Correct Answer: D

Rationale: Step 1: Micellar growth refers to the apical prolongation of hyphae in fungi. Step 2: Fungi have a unique growth structure with hyphae extending at the tips. Step 3: This growth pattern allows fungi to expand and access nutrients. Step 4: Bacterial cells (A) do not exhibit micellar growth. Step 5: Parent and daughter cells in division have similar sizes, not different (B). Step 6: Viruses and rickettsia (C) do not display micellar growth.

Correct Answer: B

Rationale: Rationale: The correct answer is B. Viruses of the family Paramyxoviridae cause the formation of giant multinucleated cells called syncytia. This occurs when infected cells fuse together, resulting in large, multinucleated structures. This is a characteristic cytopathic effect of paramyxoviruses. Summary: A: Fine grained degeneration is not typically seen in paramyxovirus infections. C: Large cell degeneration with grape clustering of cells is not a typical cytopathic effect of paramyxoviruses. D: Paramyxoviruses do provoke a cytopathic effect, so this statement is incorrect.

Correct Answer: A

Rationale: Step 1: Mycobacterium leprae is the bacterium responsible for causing leprosy, a chronic infectious disease affecting the skin and nerves. Step 2: Neisseria gonorrhoeae causes gonorrhea, a sexually transmitted infection. Step 3: Streptococcus pneumoniae causes pneumonia and other respiratory infections. Step 4: Clostridium perfringens causes gas gangrene and food poisoning. Summary: A is correct as Mycobacterium leprae specifically causes leprosy, while B, C, and D cause different diseases unrelated to leprosy.