DVM Preventive Medicine and Zoonoses 4 — Questions and Answers
Question 1: Bovine tuberculosis (Mycobacterium bovis) is primarily controlled in US cattle herds through which regulatory program?
- Mandatory annual vaccination with BCG
- Federal-state cooperative test-and-slaughter program (Correct answer)
- Prophylactic antibiotic treatment in all reactor animals
- Voluntary herd monitoring with no mandatory action
Correct answer: Federal-state cooperative test-and-slaughter program
The US bovine TB eradication program relies on the caudal fold tuberculin test (CFT) with slaughter of reactor animals and traceback investigations under federal-state cooperative authority.
Question 2: Which of the following zoonotic diseases is correctly matched with its primary animal reservoir in the United States?
- Plague (Yersinia pestis) — white-tailed deer
- Hantavirus pulmonary syndrome — deer mice (Peromyscus maniculatus) (Correct answer)
- West Nile virus — domestic dogs
- Trichinellosis — cattle
Correct answer: Hantavirus pulmonary syndrome — deer mice (Peromyscus maniculatus)
Deer mice (Peromyscus maniculatus) are the primary reservoir for Sin Nombre virus, the agent of hantavirus pulmonary syndrome in the US.
Question 3: A sensitivity analysis on a diagnostic test reveals that at 85% sensitivity and 95% specificity, the positive predictive value (PPV) drops below 50% when disease prevalence falls below approximately:
- 25%
- 15%
- 8% (Correct answer)
- 30%
Correct answer: 8%
With 85% sensitivity and 95% specificity, PPV falls below 50% when prevalence drops below approximately 8%, illustrating how low prevalence dramatically reduces PPV.
Question 4: Marek's disease in poultry is best prevented through which approach?
- Antibiotic supplementation in feed
- Vaccination of day-old chicks in the hatchery combined with management practices (Correct answer)
- Depopulation of all flocks showing any neurological signs
- Treatment with antiviral medications at first clinical signs
Correct answer: Vaccination of day-old chicks in the hatchery combined with management practices
Vaccination of day-old chicks at the hatchery with herpesvirus of turkeys (HVT) or bivalent vaccines is the cornerstone of Marek's disease prevention, as the vaccine prevents tumor formation but not infection.
Question 5: Which of the following is the recommended approach for managing a confirmed Porcine Epidemic Diarrhea Virus (PEDV) outbreak on a naïve sow farm?
- Immediate slaughter of all sows with diarrhea
- Controlled feedback of virus-containing material to non-pregnant gilts and sows to accelerate herd immunity (Correct answer)
- Administration of broad-spectrum antibiotics to all animals
- Strict individual isolation of every affected pig
Correct answer: Controlled feedback of virus-containing material to non-pregnant gilts and sows to accelerate herd immunity
Controlled exposure (feedback) of non-pregnant animals to virus-containing material accelerates development of lactogenic immunity in sows before farrowing, protecting piglets through colostrum.
Question 6: Psittacosis in humans is caused by Chlamydia psittaci. Which group of workers is at highest occupational risk?
- Dairy farmers and cattle ranchers
- Pet bird owners, aviary workers, and poultry processing plant employees (Correct answer)
- Swine confinement facility workers
- Aquaculture workers handling fish
Correct answer: Pet bird owners, aviary workers, and poultry processing plant employees
Pet bird owners, aviary workers, and poultry processing employees have the highest exposure to C. psittaci through contact with infected birds or inhalation of dried fecal dust.
Question 7: The 'Swiss cheese model' of accident causation, as applied to veterinary biosecurity, describes:
- A single perfect barrier that prevents all disease entry
- Multiple imperfect layers of protection where aligned holes allow pathogen penetration (Correct answer)
- A system where animals must pass through sequential chemical disinfection baths
- The Swiss federal system for regulating veterinary biologics
Correct answer: Multiple imperfect layers of protection where aligned holes allow pathogen penetration
The Swiss cheese model illustrates that multiple imperfect biosecurity layers are needed because any single layer has gaps (holes), and disease only penetrates when holes in all layers align simultaneously.
DVM Preventive Medicine and Zoonoses 4
Bovine tuberculosis (Mycobacterium bovis) is primarily controlled in US cattle herds through which regulatory program?