A beef cow herd experiences a cluster of late-term abortions (7–9 months gestation) over 3 weeks. Fetuses show autolysis with placentitis. Serologic titers for Neospora caninum are elevated in affected cows but not in non-aborted herdmates. Which epidemiologic pattern best supports transient epidemic neosporosis rather than endemic neosporosis in this herd?

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