Experimental quantification of the transmission of Sarcoptes scabiei var, suis among finishing pigs

In this study, the rate of S. scabiei var, suis transmission among finishin g pigs was quantified in a contact transmission experiment. Forty piglets o riginating from a mange free farrow-to-finish herd were randomly allocated to three groups and one S. scabiei var. suis infested finishing pig was sub sequently added to each of these groups. After 35 days, the three seeder pi gs were removed from the groups and the remaining 40 pigs were re-allocated to five pens. Ear scrapings, to be examined for mites, were collected from each pig on days 1, 14, 28, 42, 56, and 84 of the experiment. Blood sample s, to be tested for antibodies against S. scabiei, were collected from each pig on days 0, 14, 28, 42, 56, 70, 84 and 112 after the introduction of th e seeder pigs. From the results of the ear scrapings and the blood samples the number of s usceptible (not infested) and infested pigs was derived at the time of each sample collection and the number of new infestations in-the intervals betw een the sample collections. From these data the infestation rate parameter beta (average number of new infestations per infested pig per day) was esti mated by use of a Generalised Linear Model (GLM) and accordingly, beta was estimated at 0.056 (95% CI: 0.037-0.085) infestations per infested pig per day. Next, by use of beta, the transmission of S. scabiei was simulated in a pop ulation of 100 finishing pigs for 100 days after the introduction of a sing le infested pig. For this purpose, 500 simulations were done. The 90% confi dence interval of the number of infested pigs at day 100 ranged from 12 to 88 (median: 63).It was concluded that transmission of S. scabiei among fini shing pigs is slow. Due to the presumed lower contact rate between sows as compared to finishing pigs, it is anticipated that transmission of S. scabi ei among sows will even be slower than among finishers These findings are o f particular interest for the development of surveillance programmes for S. scabiei free herds. (C) 2000 Elsevier Science B.V. All rights reserved.