Comparative Detection of Foot-and-Mouth Disease Virus by the two Commonly used Assays of NSP ELISA and RT-PCR In Uganda with Quantitative Real Time RT-PCR on Field Samples
Foot-and-mouth disease (FMD) is a viral disease of Ungulates; both Artiodactyla and Perissodactyla. The mortality rates are low in adult animals but it affects milk yield and international trade. In endemic countries, diagnosis can be based on clinical signs. But these are shared by other vesicular diseases, so a laboratory is needed to confirm the disease. In Uganda the commonly used assays for the laboratory diagnosis of FMD are NSP ELISA and RT-PCR. Serology using ELISA techniques may fail to distinguish between vaccinated and new infection so compromising its sensitivity. The gel passed PCR is involves a lot of advance sample treatment increasing errors due to carry over which also compromises its sensitivity. This work reports comparative the detection of foot-and-mouth virus by NSP ELISA and RT-PCR with real time PCR which was taken as the gold standard. The assays were compared in terms of sensitivity, specificity and disease prevalence and likelihood ratios. A total of 176 cattle were used from which samples that included epithelial tissues (17.05%) and oral swabs (84.09%) were collected from outbreak cases in Eastern Districts of Mbale and Budaka. These were used for molecular assays of real time PCR and Conventional PCR using primers and probes targeting the 3D pol gene. The corresponding sera from all the 176 cattle (100%) were used for NSP ELISA using the Prio CHECK®FMDV NSELISA kit. The sensitivities and specificities of conventional PCR and NSP ELISA were compared with real-time PCR taken as the gold standard. The RT PCR and NSP ELISA had sensitivities of 100.00% (95% CI=86.77% – 100.00%) and 37.50% (95% CI=29.92% – 49.04%) respectively. However, NSP ELISA was more specific than with a RT PCR with sensitivities of 95.83% (95% CI= 89.67% – 98.85%) and 94.67% (95%CI=89.76% – 97.67%) respectively. The kappa value for diagnostic agreement between real time PCR and RT PCR was 0.84 (95% CI = 0.733 – 0.947) at a standard error (SE) of 0.055 showing a very
