Abstract
BackgroundHepatitis E virus (HEV) infection is a zoonosis for which pigs play a role as a reservoir. In Japan, the infection has been enzootic in swine. Clarifying the detailed mechanisms of transmission within farms is required in order to facilitate an understanding of the age-specific patterns of infection, especially just prior to slaughter.ResultsHere 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.ConclusionAlthough 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.
Highlights
Hepatitis E virus (HEV) infection is a zoonosis for which pigs play a role as a reservoir
Time required for seroconversion A simple logit model was applied to the cumulative distribution of the time required for seroconversion of antiHEV antibody based on inoculation experiments using swine HEV [9]
Expected values of λ ranging from 2.68–3.45 ×10-2 day-1 indicate that the average time of infection ranged from 29.0–37.3 days after the age of 30 days when individuals were first exposed to the risk of infection
Summary
Hepatitis E virus (HEV) infection is a zoonosis for which pigs play a role as a reservoir. 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 an important public health problem [3]. HEV infection is a zoonosis mainly seen in humans and pigs [4,5,6,7,8]. In addition to the maintenance of the virus in swine as a reservoir [9], the infection is seen in other primates [10,11,12]. Whereas humans are enterically infected mainly through contaminated foods, a waterborne outbreak can be caused if drinking water is contaminated with feces containing the virus [15]
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