In recent years, the applicability of oral fluid samples for diagnostics of infectious
disease like porcine reproductive and respiratory syndrome (PRRS), caused by the PRRS
virus (PRRSV) has seen increased discussion in scientific literature. Several methods
of detecting PRRSV RNA and PRRSV antibodies (Ab), using both different molecular diagnostic
methods and serological techniques, were developed 1]-3]. Sampling techniques were evaluated 4] and the effect of the stabilization of the oral fluid 5] and sample processing 6] was determined with the intention to improve the results. Different ropes for the
oral fluid collection were tested 6],7]. Some ELISAs, specifically developed for PRRSV Ab detection in oral fluid, show results
comparable to serum ELISAs 2],8]. The usage of cotton ropes as chewing material for oral fluid collection was found
to be the method of choice 6],7]. This system is highly suitable for pen-wise oral fluid collection in weaning pigs
and fatteners. For individual oral fluid collection, however, especially from sows
and boars, the animals have to be trained to chew on the cotton rope 4],7]. This is a time consuming measure and is not widely accepted among European pig producers.
On the other hand, the continuous testing of individual animals via oral fluid sampling
would be a substantial improvement in the monitoring in PRRSV negative herds like
boar studs. This presupposes an easy, rapid, animal friendly and efficient sampling
method as well as the uncomplicated storage and transport of the samples. Self-drying
foam swabs like GenoTubes Livestock (Prionics, Schlieren, Switzerland) that were developed
for the detection of minimal DNA amounts in forensic medicine have a small sample
volume and can be stored at room temperature for several weeks 9].
For the collected oral fluid samples, test systems with a high specificity and sensitivity
are needed, as they are continuously developed and improved for serum samples 10],11]. A recently developed ELISA detecting IgG Ab against PRRSV in individual oral fluid
collected with cotton ropes has according to Kittawornrat et al. 8] a specificity of 100% (95% confidence interval at 99%, 100%) and a sensitivity of
94.7% (92.4%, 96.5%). According to the manufacturer of the cited IDEXX PRRS OF ELISA
(IDEXX, Ludwigsburg, Germany), the specificity is quoted at 98.7% (92.2%, 100%) in
77 tested individual oral fluid samples whereas the sensitivity is 100% (94.2%, 100%)
in 78 tested samples. For the IDEXX PRRS X3 Ab test (IDEXX), which is generally considered
to be the de facto gold standard ELISA in the detection of PRRSV Ab in serum, the
manufacturer quotes a sensitivity of 98.8% and a specificity of 99.9%.
The objective of the study was to test the efficacy and practicability of oral fluid
collection from individual pigs via cotton gauze swabs and a dry foam swab (GenoTube)
as well as the re-collection of oral fluid from these materials. Furthermore, the
specificity of the IDEXX PRRSV OF ELISA for the detection of PRRSV Ab in oral fluid
collected with these methods was evaluated in comparison to the IDEXX PRRS X3 in serum
samples. To ensure the sensitivity of the oral fluid ELISA, a number of PRRSV positive
pigs were tested as well.