Since 2013, porcine epidemic diarrhea virus (PEDv) has threatened the North American swine industry, and despite the industry’s best efforts, not much is known about its survivability and infectivity within open lagoons over time.
In an attempt to find some answers in regard to survivability and infectivity, researchers Hein M. Tun of the University of Manitoba; John P. Carney of the Manitoba Livestock Manure Management Initiative; Mark Fynn of the Manitoba Pork Council; Lorne Grieger of the Prairie Agricultural Machinery Institute, and Ehsan of the University of Manitoba, turned to two PEDv positive farms in Manitoba. The first was infected 20 weeks before the study, and the second was identified during the initial farm study.
Lagoon samples were collected over a seven week period during fall 2014 where active viral shedding was (lagoon 2) or was not present (lagoon 1). Lagoon sampling was conducted using a grid layout of 12 sites at three depths in lagoon 1, and 16 sites at two depths in lagoon 2.
For lagoon 2, spring sampling was conducted in mid-May. Survivability of PEDv was tested using duplex qRT-PCR for virulent PEDv (subgroup 2a) and the 2014 variant. 99.5% of lagoon samples collected in the fall were positive for virulent PEDv, whereas all samples tested negative for the 2014 variant.
The PEDv survival in the lagoons exceeded 27 weeks within lagoon 1, and viral load significantly increased over time (P < 0.01), the researchers reported in an abstract prepared for presentation during the late breaking research session at the Joint Annual Meeting for the American Society of Animal Scientists and American Dairy Science Assn. in Orlando, Fla., July 12.
The researchers reported that the viral load was high in the initial weeks within the top and middle layers, but the reverse trend was observed in subsequent weeks with the highest levels detected within the bottom layer (P = 0.076). The viral load within lagoon 2 was significantly higher due to active shedding during week 1 of sampling but decreased in subsequent weeks (P < 0.01), they said. The virus infectivity was based on viral replication in Vero cells, showing 15% of samples were infective.
In both lagoons, the virus was infective at the last week of fall sampling with higher infectivity in the middle layer of lagoon 1 (P = 0.015), and in the bottom layer of lagoon 2 (P = 0.285). In total, 87.5% of lagoon 2 samples were still positive for PEDv in the spring, 9 months after the outbreak, but only 28% were infective. The data show the presence and infectivity of PED virus exceeding 9 months in infected lagoons, they reported.