NAVLE Veterinary Public Health 5

Question 1

A state veterinarian receives a report of a cluster of human cases of hemolytic uremic syndrome (HUS) in a rural county. Epidemiological investigation links the cases to a small farm that sells raw milk and allows petting zoo visits. Which of the following zoonotic transmission pathways is MOST likely responsible, and what is the primary regulatory authority responsible for interstate commerce of the implicated product?

Accepted Answer

Fecal-oral transmission of Escherichia coli O157:H7 via raw milk; FDA under the Grade A Pasteurized Milk Ordinance (PMO)

Answer

E. coli O157:H7 is the classic cause of HUS, particularly in children, and raw milk is a well-documented vehicle. The FDA regulates interstate raw milk commerce under the PMO (21 CFR Part 1240.61 prohibits interstate sale of raw milk for direct human consumption). The fecal-oral route from cattle reservoirs through unpasteurized milk is the primary pathway in this scenario. Campylobacter causes gastroenteritis but rarely HUS. Cryptosporidium is waterborne and causes diarrhea, not typically HUS. USDA-FSIS covers meat/poultry, not dairy.

Question 2

During a foot-and-mouth disease (FMD) outbreak response, a foreign animal disease diagnostician (FADD) must apply a stamping-out policy. Which of the following best describes the correct depopulation zone hierarchy under the USDA-APHIS FAD PReP guidelines, and what is the primary reason wildlife surveillance is included in the response plan?

Accepted Answer

Infected Premises → Dangerous Contact Premises → Suspect Premises → Monitored Premises; wildlife surveillance detects spillover into feral swine or white-tailed deer that could sustain transmission after livestock depopulation

Answer

USDA FAD PReP protocols define concentric zone classifications: Infected Premises (confirmed positive), Dangerous Contact Premises (high-risk exposure), Suspect Premises (clinical signs, awaiting confirmation), and Monitored Premises (under surveillance). Wildlife surveillance — particularly of feral swine and white-tailed deer — is critical because these species are susceptible to FMD and could serve as maintenance hosts after livestock depopulation, undermining eradication. Migratory birds are not significant FMD hosts. OIE notification is a consequence, not the primary driver of wildlife surveillance.

Question 3

A public health veterinarian is investigating a Q fever outbreak among abattoir workers processing pregnant ewes. Serology confirms acute Coxiella burnetii infection in 14 of 22 workers. Which of the following control measures has the STRONGEST evidence base for reducing occupational exposure in this specific setting, and which worker subpopulation requires the most rigorous exclusion from the work area?

Accepted Answer

Negative-pressure isolation of lambing/kidding and parturition areas combined with high-efficiency particulate air (HEPA) filtration; pregnant women and immunocompromised workers require exclusion due to risk of chronic Q fever and adverse pregnancy outcomes

Answer

C. burnetii is shed in massive quantities in placental tissues, birth fluids, and feces of parturient ruminants. Engineering controls (negative pressure, HEPA filtration) combined with PPE provide the strongest occupational protection. Pregnant women face risk of placentitis, spontaneous abortion, and premature birth; immunocompromised individuals risk chronic Q fever (endocarditis, hepatitis). While Australian Q-VAX exists, pre-exposure skin testing is mandatory due to severe hypersensitivity in previously sensitized individuals — making 'universal vaccination without testing' incorrect. Doxycycline prophylaxis is not standard practice for all exposed workers. Workers with valvular disease are high-risk for chronic infection but are not the primary exclusion group in the parturition work context.

Question 4

A veterinary public health officer is reviewing a HACCP plan for a federally inspected poultry slaughter establishment. The establishment proposes a single critical control point (CCP) — post-chill chlorinated water immersion at 50 ppm — for Salmonella control. Which of the following is the most accurate assessment of this plan's adequacy under current USDA-FSIS regulations?

Accepted Answer

The plan is inadequate; FSIS requires pathogen reduction performance standards for Salmonella that must be validated with microbial testing data, and a single post-chill intervention without upstream interventions (ante-mortem, scalding, defeathering CCPs) is unlikely to meet the Salmonella performance standard for broilers

Answer

FSIS mandates Salmonella performance standards (9 CFR Part 381) requiring establishments to demonstrate through microbial sampling that their process consistently produces product meeting the standard. A HACCP plan must be validated — meaning the establishment must show the CCP actually achieves the food safety objective. A single post-chill CCP is generally insufficient because a multi-hurdle approach (scalding temperature, inside-outside bird washer, antimicrobial rinses at multiple points) is needed to achieve meaningful log reductions. FSIS allows chlorine up to 20 ppm in water that contacts carcasses for human consumption without rinsing, but chiller water at higher concentrations with rinsing is managed under different tolerances — the regulatory limit issue is real but secondary to the validation inadequacy. NARMS participation is voluntary.

Question 5

In a One Health investigation of a novel influenza A virus detected in a Great Lakes commercial mink farm, whole-genome sequencing reveals a reassortant virus with PB2 from a North American H5N1 clade 2.3.4.4b wild bird isolate, PA and PB1 from a human seasonal H3N2 virus, and HA/NA from swine IAV-S. Which of the following statements BEST characterizes the public health threat assessment for farm workers?

Accepted Answer

The PB2 gene segment origin from a highly pathogenic avian influenza (HPAI) strain warrants heightened concern because avian-origin PB2 (particularly the E627K or D701N mutation) is a key mammalian adaptation marker, and the presence of human seasonal gene segments suggests prior human-to-animal transmission that could facilitate further human adaptation

Answer

The PB2 gene segment is critical in influenza A host adaptation. Avian-origin PB2 with mutations at position 627 (E627K) or 701 (D701N) dramatically increases replication efficiency at mammalian lower respiratory tract temperatures (33°C vs. 41°C in birds). Detection of human seasonal H3N2 internal gene segments in a mink-farm virus indicates prior reverse zoonosis (human→mink), meaning the virus has already had exposure to a mammalian host capable of selecting for human-adaptive mutations. Mink are also relevant historically — a 2021 Danish mink SARS-CoV-2 cluster demonstrated efficient mink-human transmission. Reassortant viruses are not inherently less fit; pandemic influenza strains (2009 H1N1) were reassortants. The HA receptor binding site is important, but internal gene constellations profoundly affect mammalian pathogenicity independent of HA binding.

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE Veterinary Public Health 5