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Enrichment of wild-type virus during chronic infection. The ratios of wild-type virus to 2619A virus in the serum of ducks 11, 30, 40, and 41 on days 6 through 47 were determined and used to calculate the enrichment, E, over the earliest time point (day 6 for birds 11 and 40 and day 7 for birds 30 and 41). The linear regression was calculated for the combined data for all four birds.
