Hepatitis E virus chronic infection of swine co-infected with Porcine Reproductive and Respiratory Syndrome Virus

Abstract

In developed countries, most of hepatitis E human cases are of zoonotic origin. Swine is a major hepatitis E virus (HEV) reservoir and foodborne transmissions after pork product consumption have been described. The risk for HEV-containing pig livers at slaughter time is related to the age at infection and to the virus shedding duration. Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) is a virus that impairs the immune response; it is highly prevalent in pig production areas and suspected to influence HEV infection dynamics. The impact of PRRSV on the features of HEV infections was studied through an experimental HEV/PRRSV co-infection of specific-pathogen-free (SPF) pigs. The follow-up of the co-infected animals showed that HEV shedding was delayed by a factor of 1.9 in co-infected pigs compared to HEV-only infected pigs and specific immune response was delayed by a factor of 1.6. HEV shedding was significantly increased with co-infection and dramatically extended (48.6 versus 9.7 days for HEV only). The long-term HEV shedding was significantly correlated with the delayed humoral response in co-infected pigs. Direct transmission rate was estimated to be 4.7 times higher in case of co-infection than in HEV only infected pigs (0.70 and 0.15 per day respectively). HEV infection susceptibility was increased by a factor of 3.3, showing the major impact of PRRSV infection on HEV dynamics. Finally, HEV/PRRSV co-infection - frequently observed in pig herds - may lead to chronic HEV infection which may dramatically increase the risk of pig livers containing HEV at slaughter time.

Figure 1

Experimental design of the co-infection experiment. Inoculated and susceptible contact animals are represented by black triangles and white diamonds, respectively. Rooms 2 and 3 contained three pens housing three HEV/PRRSV co-inoculated (black triangles) and three susceptible contact pigs (white diamonds). One negative control group was housed in Room 1.

Figure 2

HEV RNA quantification in fecal and liver samples from HEV/PRRSV co-infected animals and contact pigs. Quantitative HEV RT-PCR results on individual fecal samples (HEV copies/g of feces) at each sampling time and from liver samples at necropsy. Shaded zones correspond to periods in which infected individuals were considered infectious, corresponding to the time between the first and last HEV positive fecal samples for each animal. dpi: day post infection; *tested in duplicate; abs: missing.

Figure 3

HEV serology results on individual sera samples from HEV/PRRSV co-infected animals and contact pigs. Optical density (450 nm) values of ELISA test HEV 0.4v per animal at different days post infection. For each group, inoculated animals are indicated in black (n = 3), contact pigs in light grey (n = 3) and negative control in dark grey (n = 2). The cut off value is indicated by a dashed grey line.

Figure 4

PRRSV RT-PCR results on individual blood samples. Shaded zones correspond to periods in which individuals were considered viremic. The results are expressed in terms of Ct. dpi: day post infection; nt: not tested; N/A: not amplified; Ct: cycle threshold.

Figure 5

Survival curves of time-to end of HEV shedding according to early or late HEV seroconversion. The black and red survival curves correspond to the duration of the infectious period in pigs having an early seroconversion (less than 25 dpi) or a late or absent seroconversion (more than 25 dpi) respectively.

Figure 6

Distribution of the number of HEV genome equivalent (log ge/g feces) shed by individual pigs with time in inoculated animals with or without PRRSV co-infection. Co-infected animals are indicated in green (n = 9), only-HEV infected animals [25] are in black (n = 18).

Figure 7

Estimation of HEV environmental accumulation with PRRSV/HEV co-infection. Evolution of the estimated HEV genome load (ge/g) in the environment of each pig group of the PRRSV/HEV co-infection experiment.