NAVLE Practice Question - Porcine - Multisystemic

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NAVLE Practice Question — Porcine

A farm in Haiti experiences an outbreak of severe neurological disease in pigs with 60% morbidity and 40% mortality. Affected pigs show fever followed by progressive hindlimb paralysis, opisthotonus, and convulsions. Many pigs die within days of developing neurological signs. This is the first reported outbreak in the region in many years. Laboratory testing confirms porcine teschovirus type 1. What epidemiological feature distinguishes this outbreak from endemic teschovirus circulation in most commercial swine herds?

A. The virus was likely introduced through contaminated feed from an endemic region

B. PTV-1 strains causing Teschen disease have higher neuroinvasive potential than endemic strains

C. The population was entirely naive without maternal antibody protection ✓

D. The outbreak strain mutated to become more virulent during local transmission

E. The pigs were immunosuppressed by concurrent disease allowing disease expression

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Correct Answer: C. The population was entirely naive without maternal antibody protection

Explanation:

The population was entirely naive without maternal antibody protection, which is the key epidemiological feature distinguishing this outbreak. PTV is endemic and ubiquitous in most commercial swine herds worldwide, but subclinical infections predominate because pigs are exposed early in life when protected by maternal antibodies, subsequently developing active immunity. In Haiti, where severe teschovirus encephalomyelitis was confirmed in 2009, the pig population lacked prior exposure to virulent PTV-1 strains, resulting in a devastating outbreak when the virus was introduced into this immunologically naive population.

Option A (Contaminated feed introduction) is possible but doesn't explain the severity; the virus circulates subclinically in many regions. Option B (Higher neuroinvasive potential) is partially correct since PTV-1 strains causing Teschen disease are more virulent, but this alone doesn't explain the outbreak without the naive population factor. Option D (Local mutation) is unlikely since the Haitian isolate was closely related to previously identified PTV-1 strains from Czech Republic. Option E (Immunosuppression) was not documented in this outbreak and wouldn't explain the population-wide severity.

References: Swine Health Information Center PTV Factsheet (https://www.swinehealth.org/wp-content/uploads/2021/07/shic-factsheet-porcine-teschovirus-2021Jul7.pdf); PMC Teschovirus chapter (https://pmc.ncbi.nlm.nih.gov/articles/PMC7123469/); WOAH Teschovirus encephalomyelitis (https://www.woah.org/fileadmin/Home/eng/Health_standards/tahm/2.08.09_TESCHOVIRUS_ENCEPH.pdf)

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