The importance of the domestic pig reservoir for Hepatitis E virus (HEV) was assessed by estimating the seroprevalence and prevalence of HEV contaminated livers in French slaughter-aged pigs. 6565 sera and 3715 livers were randomly sampled from 186 pig farms throughout the country. Taking the sampling design into account, the farm-level seroprevalence was 65% (95% CI 57-74) and 31% (95% CI 24-38) of the slaughter-aged pigs had antibodies against HEV. The individual prevalence of HEV RNA positive livers was 4% (95% CI 2-6) and 24% (95% CI 17-31) of the farms had at least 1 positive liver. Most isolates were of genotype 3f (76.7%) with smaller amounts of 3c (18.6%) and 3e (4.6%). The high prevalence of HEV in pigs and the similarities between HEV subtypes from pigs and humans corroborates the possible zoonotic origin of some HEV autochthonous infections.
Concomitant infections by different influenza A virus subtypes within pig farms increase the risk of new reassortant virus emergence. The aims of this study were to characterize the epidemiology of recurrent swine influenza virus infections and identify their main determinants. A follow-up study was carried out in 3 selected farms known to be affected by repeated influenza infections. Three batches of pigs were followed within each farm from birth to slaughter through a representative sample of 40 piglets per batch. Piglets were monitored individually on a monthly basis for serology and clinical parameters. When a flu outbreak occurred, daily virological and clinical investigations were carried out for two weeks. Influenza outbreaks, confirmed by influenza A virus detection, were reported at least once in each batch. These outbreaks occurred at a constant age within farms and were correlated with an increased frequency of sneezing and coughing fits. H1N1 and H1N2 viruses from European enzootic subtypes and reassortants between viruses from these lineages were consecutively and sometimes simultaneously identified depending on the batch, suggesting virus co-circulations at the farm, batch and sometimes individual levels. The estimated reproduction ratio R of influenza outbreaks ranged between 2.5 [1.9-2.9] and 6.9 [4.1-10.5] according to the age at infection-time and serological status of infected piglets. Duration of shedding was influenced by the age at infection time, the serological status of the dam and mingling practices. An impaired humoral response was identified in piglets infected at a time when they still presented maternally-derived antibodies.
Hepatitis E virus (HEV) can cause enterically-transmitted hepatitis in humans. The zoonotic nature of Hepatitis E infections has been established in industrialized areas and domestic pigs are considered as the main reservoir. The dynamics of transmission in pig herds therefore needs to be understood to reduce the prevalence of viremic pigs at slaughter and prevent contaminated pig products from entering the food chain. An experimental trial was carried out to study the main characteristics of HEV transmission between orally inoculated pigs and naïve animals. A mathematical model was used to investigate three transmission routes, namely direct contact between pigs and two environmental components to represent within-and between-group oro-fecal transmission. A large inter-individual variability was observed in response to infection with an average latent period lasting 6.9 days (5.8; 7.9) in inoculated animals and an average infectious period of 9.7 days (8.2; 11.2). Our results show that direct transmission alone, with a partial reproduction number of 1.41 (0.21; 3.02), can be considered as a factor of persistence of infection within a population. However, the quantity of virus present in the environment was found to play an essential role in the transmission process strongly influencing the probability of infection with a within pen transmission rate estimated to 2 ⋅ 10− 6g ge− 1d− 1(1 ⋅ 10− 7; 7 ⋅ 10− 6). Between-pen environmental transmission occurred to a lesser extent (transmission rate: 7 ⋅ 10− 8g ge− 1d− 1(5 ⋅ 10− 9; 3 ⋅ 10− 7) but could further generate a within-group process. The combination of these transmission routes could explain the persistence and high prevalence of HEV in pig populations.
The frequency of sporadic cases of hepatitis E in humans in developed countries has increased in recent years. The consumption of raw or undercooked pig liver-based products has been identified as an important source of human infection. The question of possible massive human exposure to this zoonotic agent has been raised by the high prevalence of hepatitis E virus (HEV) in swine herds. However, little is known about the epidemiology of HEV on pig farms. A retrospective study, based on a previous prevalence study of 185 farms, was conducted on 90 farms located in Western France, randomly selected from this database, to identify factors associated with the presence of HEV in pig livers and HEV seroprevalence in slaughter-age pigs. At least one HEV RNA-positive liver was found in 30% of the sampled farms while seroprevalence in slaughter-age pigs at the farm level reached almost 75%. Different factors were associated with the two conditions. The risk of having HEV-positive livers was increased by early slaughter, genetic background, lack of hygiene measures and surface origin of drinking water. High HEV seroprevalence was associated with mingling practices at the nursery stage and hygiene conditions. These results can be used to determine on-farm measures to reduce within-farm HEV spread and infection of slaughter-age pigs.
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