Transmission dynamics of hepatitis E among swine: potential impact upon human infection

Here we reanalyze a large-scale seroprevalence survey dataset from Japanese pig farms to estimate the force of infection. The forces of infection of swine HEV were estimated to be 3.45 (95% confidence interval: 3.17, 3.75), 2.68 (2.28, 3.14) and 3.11 (2.76, 3.50) [×10-2 per day] in Hokkaido, Honshu and Kyushu, respectively. The estimates with our model assumptions indicated that the average ages at infection ranged from 59.0–67.3 days and that the basic reproduction number, R0, was in the order of 4.02–5.17. Sensitivity analyses of age-specific incidence at different forces of infection revealed that a decline in the force of infection would elevate the age at infection and could increase the number of virus-excreting pigs at the age of 180 days.Although our estimates imply that more than 95% of pigs are infected before the age of 150 days, the model shows that a decline in the force of infection could increase the risk of pig-to-human transmission. If the force of infection started to decline, it might be necessary to implement radical countermeasures (e.g. separation of uninfected pigs from infected herds beginning from the end of the suckling stage) to minimize the number of virus-positive pigs at the finishing stage.Hepatitis E virus (HEV) is a positive-strand RNA virus without an envelope, which is classified as a member of the genus Hepevirus in the family Hepeviridae [1,2]. The virus is distributed worldwide, especially in the tropical and subtropical regions of Asia, Africa and Latin America, causing acute hepatitis in humans and is thus an important public health problem [3]. HEV infection is a zoonosis mainly seen in humans and pigs [4-8]. In addition to the maintenance of the virus in swine as a reservoir [9], the infection is also seen in other primates [10-12]. The virus is mainly transmitted via fecal-oral routes among swine [13,14]. Whereas humans are also enterically infected mainly through contaminated foods, a water-borne outbreak can be caused if