Simplifying sampling for African swine fever surveillance: Assessment of antibody and pathogen detection from blood swabs

Abstract

SummaryAfrican swine fever (ASF) is a notifiable disease with serious socio-economic consequences that has been present in wild boar in the Baltic States and Poland since2014. An introduction of ASF is usually accompanied by increased mortality, making fallen wild boar and hunted animals with signs of disease the main target for early warning and passive surveillance. It is difficult, however, to encourage hunters and foresters to report and take samples from these cases. A pragmatic and easy sampling approach with quick-drying swabs could facilitate this. In this study, we further evaluated the use of dry blood swabs for the detection of ASFV antibody and genome with samples from animal trials and diagnostic submissions (blood, bone and organs) from Estonia. Compared to serum samples, dried blood swabs yielded 93.1% (95% confidence interval: [83.3, 98.1]) sensitivity and 100% [95.9, 100.0] specificity in a commercial ASFV antibody ELISA. Similarly, the swabs gave a sensitivity of 98.9% [93.4, 100.0] and a specificity of 98.1% [90.1, 100.0] for genome detection by a standard ASFV p72 qPCR when compared to EDTA blood. The same swabs were tested in a VP72-antibody lateral flow device, with a sensitivity of 94.7% [85.4, 98.9] and specificity of 96. 1% [89.0, 99.2] compared to the serum ELISA.When GenoTube samples tested in ELISA and LFD were compared, the sensitivity was 96.3% [87.3, 99.5] and the specificity was 93.8% [86.0, 97.9]. This study demonstrates reliable detection of ASFV antibody and genome from swabs. A field test of the swabs with decomposed wild boar carcasses in an endemic area in Estonia also gave promising results. Thus, this technique is a practical approach for surveillance of ASF in both free and endemic areas. Quick-drying swabs decrease the growth of opportunistic organisms and preserve sample DNA or RNA without refrigeration (Costa et al., 2014). In previous studies, sample material in GenoTubes remained usable for genome and antibody detection for more than a week (unpublished results show stability over several month) and gave good results with accredited qPCR and ELISA methods (Blome et al., 2014;Petrov et al., 2014).The objectives of the present study were to demonstrate the suitability of the swab sampling method for routine ASFV genome and antibody detection. To this means, blood and other routine sample matrices were compared to swabs dipped into EDTA blood. In the majority of cases, paired samples of the same animal were tested to ensure comparability. In addition to the blood and serum that had been previously tested (Blome et al., 2014), organ and bone marrow samples were included in this comparative study to broaden the scope. Furthermore, the analyses were extended to a lateral flow device (LFD) for antibody detection, which could provide a useful and easy tool for point-of-care tests. | MATERIALS AND METHODS | Swine studies and sample originPaired EDTA and serum samples from experimentally infected animals at the Friedrich-Loeffler-Institut (FLI) were used for the study (see ...

African Swine Fever Laboratory Diagnosis—Lessons Learned from Recent Animal Trials

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