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OBJECTIVE To determine the minimum infectious dose of porcine epidemic diarrhea virus (PEDV) in virus-inoculated feed. ANIMALS 30 crossbred 10-day-old pigs. PROCEDURES Tissue culture PEDV was diluted to form 8 serial 10-fold dilutions. An aliquot of stock virus (5.6 × 10(5) TCID50/mL) and each serial PEDV dilution were mixed into 4.5-kg batches of feed to create 9 PEDV-inoculated feed doses; 1 virus-negative dose of culture medium in feed was also created. Pigs were challenge exposed via oral administration of PEDV-inoculated feed, and fecal swab specimens were collected. All pigs were euthanized 7 days after challenge exposure; fresh tissues were collected and used for PCR assay, histologic examination, and immunohistochemical analysis. RESULTS The PCR cycle threshold (Ct) decreased by approximately 10 when PEDV was added to feed, compared with results for equivalent PEDV diluted in tissue culture medium. Pigs became infected with PEDV when challenge exposed with the 4 highest concentrations (lowest concentration to cause infection, 5.6 × 10(1) TCID50/g; Ct = 27 in tissue culture medium and 37 in feed). CONCLUSIONS AND CLINICAL RELEVANCE In this study, PEDV in feed with detectable Ct values of 27 to 37 was infective. The Ct was 37 for the lowest infective PEDV dose in feed, which may be above the limit of detection established for PEDV PCR assays used by some diagnostic laboratories. Overall, results indicated 5.6 × 10(1) TCID50/g was the minimum PEDV dose in feed that can lead to infection in 10-day-old pigs under the conditions of this study.

Objective: To determine the survival of porcine reproductive and respiratory syndrome virus (PRRSV) on nonliving substances (fomites) at 25 to 27 C., Design: Prospective controlled study., Sample Population: 3 solid, 6 porous, and 7 liquid fomites., Procedure: The fomites were contaminated with known concentrations of PRRSV. Samples for virus isolation were obtained on day 0 through day 11, assayed in cell cultures, and stained with fluorescent antibody conjugate., Results: The virus was recovered only on day-0 samples of alfalfa, wood shavings, straw, plastic, boot rubber, and stainless steel. Virus was isolated from city water through day 11, from well water through day 9, and from 2 buffer solutions for 4 and 6 days. The virus was isolated only on day 0 from swine saliva, urine, and fecal slurry., Clinical Implications: Results indicated that PRRSV is a fairly labile virus, but because of its duration of viability in water, contamination of drinking water and lagoons by PRRSV-shedding swine would serve as sources of virus to infect susceptible swine.