Which ONE of the following is not a feature of interferons? A. Imparts resistance to virus infection. B. Inhibits virtually all viruses. C. Released from cells in response to virus infection. D. Species specific cellular protein. E. Virus specific antiviral effect. The answer is E. The production of interferons is induced in host cells by virus; the interferons are not specific, but are an important host defence mechanism against virus infection. They act by inhibiting translation of viral mRNA by host cells.
For each of the features listed on the left select the most appropriate association from those on the right. a. Bacteraemia. b. Pyaemia. c. Septicaemia. A. Due to bacterial exotoxin. B. Fragment of septic thrombus. C. End result of viral infection. D. May be the result of vigorous teeth brushing. 15 E. Multiplication of bacteria in the blood. The answer is D, B, E. Bacteraemia – may be the result of vigorous teeth brushing. Bacteraemia is the presence of small numbers of bacteria in the blood; this can occur in normal individuals, i.e., after teeth brushing (NB this may be important in patients with valvular heart disease). Pyaemia – fragment of septic thrombus. Pyaemia (pus in blood) is the result of localized pyogenic infection damaging vascular endothelium and producing infected thrombus which breaks down. Septicaemia – multiplication of bacteria in the blood. Septicaemia is the presence and multiplication of organisms in the blood stream; this is the most serious type. Bacterial exotoxins (A) are produced by living bacteria. None of these is an end result of viral infection (C) since all are caused by bacteria.
Which one of the following is the best definition of gangrene? A. Digestion of dead tissue by saprophytic bacteria. B. Digestion of living tissue by saprophytic bacteria. C. Gas production in dead tissue. D. Necrosis of tissue caused by bacterial toxins. E. Necrosis of tissue caused by ischaemia. The answer is A. In gangrene, tissue which is dead is digested by bacteria which are incapable of invading and multiplying in living tissue (saprophytes). Gas production (C) may be present in some forms of gangrene particularly when caused by the anaerobic Clostridia. Necrosis of tissue is an essential prerequisite for gangrene, but it may be caused by ischaemia (E), i.e., secondary gangrene or by bacterial toxins (D), i.e., primary gangrene.
The pathogenicity of the tubercle bacillus is due to which ONE of the following? A. Ability to multiply within macrophages. B. Delayed hypersensitivity reaction against the bacteria. C. Direct toxic effect on host cells. D. Effective antibody response. E. Necrosis caused by expanding granulomas. The answer is B. Mycobacteria stimulate a specific T-cell response of cell mediated immunity; while this is effective in reducing the infection the delayed hypersensitivity reaction also damages the tissues. The tubercle bacilli have no demonstrable direct toxic action (C) and can survive within macrophages (A). This may account for latent infections and reactivation of tuberculosis. There is no significant humoral response to tubercle bacilli (D). Necrosis occurs in tuberculosis, but it is usually within the granuloma (E). 16
For each of the features of tuberculous infection listed on the left select the most appropriate association from those on the right. a. Cold abscess. b. Miliary tubercles. c. Primary complex. A. Lesion in the lung. B. Lesion in lung and hilar lymph nodes. C. Scar tissue with calcification. D. Small white lesions in the liver, spleen and kidney. E. Soft white mass of caseous pus. The answer is E, D, B. Caseous material may liquefy following invasion by polymorphs to produce tuberculous pus; this occurs in kidneys and bone and may extend into soft tissues. Spread by the blood stream occurs in miliary TB and organs affected contain multiple small (1-2 mm) white nodules (miliary tubercles) which undergo caseous necrosis. Initial infection produces the primary lesion, i.e., in lung (A) which remains small, but bacteria spread to the regional lymph nodes to form the primary complex of primary lesions plus involved regional lymph nodes. Scar tissue with calcification (C) is a common result of healing of tuberculosis.
For each of the features of syphilis listed on the left select the most appropriate association from those on the right. a. Primary sore. b. Secondary lesions. c. Tertiary lesions. A. Degeneration of posterior columns of spinal cord. B. Destruction of the nasal bones. C. Miliary gummas. D. Rash on the soles of the feet. E. Pale brown nodules on the penis. The answer is E, D, B. The primary sore occurs after an incubation period of 3-4 weeks during which period Treponema pallidum is spreading in the blood. The secondary lesions occur 2-3 months after infection and are characterized by skin rashes, alopecia and general malaise. The typical lesions of the tertiary phase occur many years after infection and cause necrosis of internal organs, liver, testis and bones. The gumma is a necrotic granuloma. 17 Tabes dorsalis (A) occurs in the late quaternary phase of neurosyphilis. Miliary gummas (C) are present in congenital syphilis.
