Detecting and Monitoring Porcine Hemagglutinating Encephalomyelitis Virus, an Underresearched Betacoronavirus

Abstract

Members of family Coronaviridae cause a variety of diseases in birds and mammals. Porcine hemagglutinating encephalomyelitis virus (PHEV), a lesser-researched coronavirus, can infect naive pigs of any age, but clinical disease is observed in pigs ≤4 weeks of age. No commercial PHEV vaccines are available, and neonatal protection from PHEV-associated disease is presumably dependent on lactogenic immunity. Although subclinical PHEV infections are thought to be common, PHEV ecology in commercial swine herds is unknown. To begin to address this gap in knowledge, a serum IgG antibody enzyme-linked immunosorbent assay (ELISA) based on the S1 protein was developed and evaluated on known-status samples and then used to estimate PHEV seroprevalence in U.S. sow herds. Assessment of the diagnostic performance of the PHEV S1 ELISA using serum samples (n = 924) collected from 7-week-old pigs (n = 84; 12 pigs per group) inoculated with PHEV, porcine epidemic diarrhea virus, transmissible gastroenteritis virus, porcine respiratory coronavirus, or porcine deltacoronavirus showed that a sample-to-positive cutoff value of ≥0.6 was both sensitive and specific, i.e., all PHEV-inoculated pigs were seropositive from days postinoculation 10 to 42, and no cross-reactivity was observed in samples from other groups. The PHEV S1 ELISA was then used to estimate PHEV seroprevalence in U.S. sow herds (19 states) using 2,756 serum samples from breeding females (>28 weeks old) on commercial farms (n = 104) with no history of PHEV-associated disease. The overall seroprevalence was 53.35% (confidence interval [CI], ±1.86%) and herd seroprevalence was 96.15% (CI, ±3.70%).IMPORTANCE There is a paucity of information concerning the ecology of porcine hemagglutinating encephalomyelitis virus (PHEV) in commercial swine herds. This study provided evidence that PHEV infection is endemic and highly prevalent in U.S. swine herds. These results raised questions for future studies regarding the impact of endemic PHEV on swine health and the mechanisms by which this virus circulates in endemically infected populations. Regardless, the availability of the validated PHEV S1 enzyme-linked immunosorbent assay (ELISA) provides the means for swine producers to detect and monitor PHEV infections, confirm prior exposure to the virus, and to evaluate the immune status of breeding herds.

Keywords: ELISA; coronavirus; encephalomyelitis; porcine encephalomyelitis virus; porcine hemagglutinating encephalomyelitis virus; seroprevalence; vomiting and wasting disease.

FIG 1

PHEV S1 ELISA sample-to-positive (S/P) ratios of serum IgG responses. Each line represents the dynamic of PHEV antibodies in PHEV- and control-inoculated groups. Each time point is represented by the S/P mean and standard errors. Colored bars represent the percentages of positive samples over time in pigs experimentally inoculated with PHEV (Mengeling strain; n = 12) or mock inoculated with culture medium (control group; n = 12). Samples with an S/P ratio of >0.6 (dashed line) were considered seropositive to PHEV.

FIG 2

Distribution of cumulative PHEV S1 IgG ELISA sample-to-positive (S/P) ratios from experimental serum samples collected at −7, 0, 3, 10, 14, 17, 21, 28, 35, and 42 dpi from pigs inoculated with PHEV (Mengeling strain; n = 12) to evaluate the diagnostic sensitivity (DxSe), mock inoculated with culture medium (n = 12) to evaluate the diagnostic specificity (DxSp), and inoculated with PEDV (USA/IN/2013/19338E; n = 12), TGEV Miller (ATCC VR-1740; n = 12), TGEV Purdue (ATCC VR-763; n = 12), PRCV (ATCC VR-2384; n = 12), or PDCoV (USA/IL/2014; n = 12) to evaluate the analytical specificity (AnaSp). Samples above the S/P 0.6 cutoff (dashed line) were considered positive.

FIG 3

Within-herd seroprevalence distribution in the United States. Bars represent the frequency of farms (n = 104) with different levels of within-herd seroprevalence. Only the results of herds with at least two positive sows were displayed.

FIG 4

Geographic distribution of PHEV seropositive farms (herd prevalence by state) in the United States. The map indicates the percentages of PHEV-seropositive herds by U.S. state. The table indicates the total numbers evaluted and percentages of positive farms by state and 95% confidence intervals (CIs).

FIG 5

Geographic distribution of PHEV seropositive sows (overal invididual prevalence by state) in the United States. The map indicates the percentages of PHEV-seropositive sows detected by state. The table indicates the total numbers evaluated and percentages of positive sows by state with the 95% confidence intervals (CIs).