Detection and quantification by molecular techniques of early infection by Lawsonia intracellularis in suckling piglets.

Abstract

Background Lawsonia intracellularis is the causative agent of Porcine Proliferative Enteropathy (PPE), one of the most prevalent pig enteric diseases worldwide, but with sparse information about role of sows and suckling piglets as a source of infection. With that aim, this study evaluates the prevalence of L. intracellularis in 3-week-old piglets by analysing ileal digesta content and mucosal scrapings from 383 pigs from 16 batches (aprox., 25 pigs/batch) by real-time qPCR and droplet digital PCR (ddPCR). Results Forty-nine samples yielded a qPCR positive result. Eleven samples from eight batches were confirmed as positive with concentrations of L. intracellularis from 3.5 log₁₀ to 4.5 log₁₀ bacteria/g of sample. Another 16 samples, eight batches, were classified as low positive (2.07-2.38 log₁₀ bacteria/g) and 22 provided an uncertain result. Finally, 334 samples tested negative for L. intracellularis. At batch level, half of the batches included in the study had at least one positive sample and in 10 batches (62.5%) there was at least one low positive sample. The ddPCR was run in 50 of the 383 samples based on their PCR output (including low positive, uncertain and negative samples). Correlation analyses revealed a strong association between qPCR and the ddPCR results (ρ=0.75; p<0.001). The ddPCR allowed us to detect and confirm a positive result in the 19 samples classified as uncertain by the qPCR and detect L. intracellularis in 8 of 15 negatives negative by qPCR. Conclusions The results of the study demonstrate that a number of piglets already are infected with L. intracellularis during the lactation period underlining the potential role of sow-piglet transmission in the epidemiology of PPE. Study results also evidence the usefulness of a combination of qPCR and ddPCR to improve qPCR sensitivity but assuring high specificity.