Using heterogeneity in the population structure of U.S. swine farms to compare transmission models for porcine epidemic diarrhoea

Eamon B. O’Dea; Harry Snelson; Shweta Bansal

We first provide a brief background on the natural history PED outbreaks to make clear the features that our models replicate and those that they do not. The time from the introduction of infected animals to the appearance of clinical symptoms in PEDV-naive herds is typically less than 7 days. 9, 24 PED may spread rapidly within farms following the first appearance of clinical signs . 9, 16, [25] [26] [27] The spread may also be actively promoted as a part of recommended feedback procedures to establish herd immunity. 24 The duration of an outbreak can vary substantially. The lower bound would be roughly a week, as virus shedding from individuals has been observed in experimental settings to subside within 9 days of infection, 28 and an infected animal's diarrhoea has been observed in the field to typically last for 5 days. 25 However, it can take affected farms several weeks to return to baseline production levels. 9, 25 In summary, within a farm spread is often rapid and complete enough that assuming all animals on the farm to have the same status is justified when observation occurs at weekly intervals.