BCSE BCSE - Basic and Clinical Sciences Examination Veterinary Microbiology and Infectious Diseases Questions and Answers 5 — Questions and Answers
Question 1: Which of the following best describes the pathogenesis of Type D enterotoxemia (pulpy kidney disease) in sheep caused by Clostridium perfringens?
- Epsilon toxin produced in the gut increases intestinal permeability and causes cerebral edema (Correct answer)
- Alpha toxin produced systemically lyses red blood cells causing hemolytic anemia
- Beta toxin causes necrotic enteritis exclusively in neonatal piglets
- Iota toxin disrupts actin cytoskeleton causing flaccid paralysis
Correct answer: Epsilon toxin produced in the gut increases intestinal permeability and causes cerebral edema
In Type D enterotoxemia, epsilon toxin (activated from epsilon prototoxin) increases vascular permeability, leading to cerebral edema and characteristic pulpy kidney lesions.
Question 2: A pig herd experiences reproductive failure including mummified fetuses, stillbirths, and weak neonates. Serology confirms Porcine reproductive and respiratory syndrome virus (PRRSV). To which family does PRRSV belong?
- Flaviviridae
- Togaviridae
- Arteriviridae (Correct answer)
- Coronaviridae
Correct answer: Arteriviridae
PRRSV is an enveloped, positive-sense single-stranded RNA virus belonging to the family Arteriviridae, order Nidovirales.
Question 3: Dermatophilosis in cattle and horses is caused by Dermatophilus congolensis. What is the correct classification of this organism?
- Dimorphic fungus
- Filamentous Gram-positive actinomycete (Correct answer)
- Gram-negative spirochete
- Obligate intracellular bacterium
Correct answer: Filamentous Gram-positive actinomycete
Dermatophilus congolensis is a Gram-positive, non-acid-fast filamentous actinomycete that produces motile zoospores and causes 'rain rot' or streptothricosis.
Question 4: Which tick-borne protozoan infects erythrocytes of cattle and causes a hemolytic anemia known as Texas cattle fever (redwater fever) in the southern United States?
- Theileria parva
- Babesia bovis (Correct answer)
- Anaplasma marginale
- Cytauxzoon felis
Correct answer: Babesia bovis
Babesia bovis, transmitted by Rhipicephalus (Boophilus) microplus, infects bovine erythrocytes causing intravascular hemolysis, hemoglobinuria, and high mortality.
Question 5: A dog recently returned from the southwestern US presents with fever, weight loss, and hilar lymphadenopathy. BAL cytology shows large spherules with endospores. What is the diagnosis?
- Histoplasmosis due to Histoplasma capsulatum
- Coccidioidomycosis due to Coccidioides immitis (Correct answer)
- Cryptococcosis due to Cryptococcus gattii
- Aspergillosis due to Aspergillus fumigatus
Correct answer: Coccidioidomycosis due to Coccidioides immitis
Coccidioides immitis is a dimorphic fungus endemic to arid southwestern US soil that forms pathognomonic spherules (20-200 µm) filled with endospores in tissue.
Question 6: Which mechanism allows Staphylococcus aureus to resist beta-lactam antibiotics such as methicillin (MRSA) in veterinary patients?
- Production of extended-spectrum beta-lactamase (ESBL) that hydrolyzes the beta-lactam ring
- Acquisition of mecA gene encoding a modified penicillin-binding protein (PBP2a) with low antibiotic affinity (Correct answer)
- Efflux pumps that expel beta-lactam antibiotics from the bacterial cell
- Reduced outer membrane permeability preventing antibiotic entry
Correct answer: Acquisition of mecA gene encoding a modified penicillin-binding protein (PBP2a) with low antibiotic affinity
The mecA gene encodes PBP2a, an altered penicillin-binding protein with very low affinity for all beta-lactam antibiotics, conferring broad resistance in MRSA strains.
Question 7: Borna disease virus causes encephalitis primarily in horses in central Europe. To which order does this neurotropic negative-sense RNA virus belong?
- Mononegavirales (Correct answer)
- Nidovirales
- Picornavirales
- Herpesvirales
Correct answer: Mononegavirales
Borna disease virus belongs to the family Bornaviridae within the order Mononegavirales, which includes other non-segmented negative-sense RNA viruses like rhabdoviruses and paramyxoviruses.
BCSE BCSE - Basic and Clinical Sciences Examination Veterinary Microbiology and Infectious Diseases Questions and Answers 5
Which of the following best describes the pathogenesis of Type D enterotoxemia (pulpy kidney disease) in sheep caused by Clostridium perfringens?