Assessing the value of PCR assays in oral fluid samples for detecting African swine fever, classical swine fever, and foot-and-mouth disease in U.S. swine

Abstract

Introduction Oral fluid sampling and testing offers a convenient, unobtrusive mechanism for evaluating the health status of swine, especially grower and finisher swine. This assessment evaluates the potential testing of oral fluid samples with real-time reverse-transcriptase polymerase chain reaction (rRT-PCR) to detect African swine fever, classical swine fever, or foot-and-mouth disease for surveillance during a disease outbreak and early detection in a disease-free setting. Methods We used a series of logical arguments, informed assumptions, and a range of parameter values from literature and industry practices to examine the cost and value of information provided by oral fluid sampling and rRT-PCR testing for the swine foreign animal disease surveillance objectives outlined above. Results Based on the evaluation, oral fluid testing demonstrated value for both settings evaluated. The greatest value was in an outbreak scenario, where using oral fluids would minimize disruption of animal and farm activities, reduce sample sizes by 23%-40%, and decrease resource requirements relative to current individual animal sampling plans. For an early detection system, sampling every 3 days met the designed prevalence detection threshold with 0.95 probability, but was quite costly. Limitations Implementation of oral fluid testing for African swine fever, classical swine fever, or foot-and-mouth disease surveillance is not yet possible due to several limitations and information gaps. The gaps include validation of PCR diagnostic protocols and kits for African swine fever, classical swine fever, or foot-and-mouth disease on swine oral fluid samples; minimal information on test performance in a field setting; detection windows with low virulence strains of some foreign animal disease viruses; and the need for confirmatory testing protocol development.

Field Verification of an African Swine Fever Virus Loop-Mediated Isothermal Amplification (LAMP) Assay during an Outbreak in Timor-Leste

“…The successful detection of ASFV in oral/rectal fluids via the LAMP assay also suggests that this testing methodology could be paired with more sentinel/passive surveillance, which is an area needing further investigation in ASFV surveillance [ 45 ]. Surveillance using passive chew rope detection methods for ASFV and other diseases, may be facilitated with LAMP diagnostics, especially with some studies highlighting there is currently a lack of suitable diagnostic protocols that could perform this testing [ 57 , 58 ].…”

Evaluation of oral fluid as an aggregate sample for early detection of African swine fever virus using four independent pen‐based experimental studies

“…Therefore virus may be detected in pharyngeal swabs and oral fluid at early stages of infection (Zsak et al., 2005), suggesting oral fluid could be an ideal sample to detect the virus prior to onset of obvious clinical signs. In experimental studies utilising small groups of pigs, with the majority of animals inoculated with highly virulent ASFV Georgia 2007/1, ASFV genomic material was detected in oral fluid before the animals developed any noticeable clinical signs and pigs continued to chew on the ropes daily until they developed severe clinical signs (Beemer et al., 2019; Davies et al., 2017; Grau et al., 2015; Guinat et al., 2016b).…”

Point of care diagnostics and non-invasive sampling strategy: a review on major advances in veterinary diagnostics

“…Saliva comprises primarily of secretory IgA (sIgA), whereas OMT contains a mixture of sIgA, IgG and IgM, thus, provides a richer source of antibodies, including those directed against bacterial and viral pathogens (Corstjens et al 2012). Detection of antigens in oral fluids have been confirmed in several animal diseases following natural as well as experimental infections such as PRRS and PCV-2 infections (Prickett 2009), Johne's disease (Sorge et al 2013), FMD (Senthilkumaran et al 2017), bovine papular stomatitis (Eirai et al 2016), CSF (Beemer et al 2019), ASF (Beemer et al 2019) and PPR (Parida et al 2019). Bearing in mind the animal diseases with a diverse host range such as PPR, ASF, FMD, rabies, canine distemper and coronavirus infections, oral fluid-based surveillance of pathogens, as a non-invasive and safe source, would be an efficient approach in diagnosis of animal diseases in domestic as well as in wildlife.…”