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Review
. 2021 Feb 5;7(1):16.
doi: 10.1186/s40813-021-00189-z.

Infection dynamics and persistence of hepatitis E virus on pig farms - a review

M Meester  1 , T J Tobias  2 , M Bouwknegt  3 , N E Kusters  4 , J A Stegeman  2 , W H M van der Poel  4
Affiliations
Review

Infection dynamics and persistence of hepatitis E virus on pig farms - a review

M Meester et al. Porcine Health Manag. .

Abstract

Background: Hepatitis E virus (HEV) genotype 3 and 4 is a zoonosis that causes hepatitis in humans. Humans can become infected by consumption of pork or contact with pigs. Pigs are the main reservoir of the virus worldwide and the virus is present on most pig farms.

Main body: Though HEV is present on most farms, the proportion of infected pigs at slaughter and thus the level of exposure to consumers differs between farms and countries. Understanding the cause of that difference is necessary to install effective measures to lower HEV in pigs at slaughter. Here, HEV studies are reviewed that include infection dynamics of HEV in pigs and on farms, risk factors for HEV farm prevalence, and that describe mechanisms and sources that could generate persistence on farms. Most pigs become infected after maternal immunity has waned, at the end of the nursing or beginning of the fattening phase. Risk factors increasing the likelihood of a high farm prevalence or proportion of actively infected slaughter pigs comprise of factors such as farm demographics, internal and external biosecurity and immunomodulating coinfections. On-farm persistence of HEV is plausible, because of a high transmission rate and a constant influx of susceptible pigs. Environmental sources of HEV that enhance persistence are contaminated manure storages, water and fomites.

Conclusion: As HEV is persistently present on most pig farms, current risk mitigation should focus on lowering transmission within farms, especially between farm compartments. Yet, one should be aware of the paradox of increasing the proportion of actively infected pigs at slaughter by reducing transmission insufficiently. Vaccination of pigs may aid HEV control in the future.

Keywords: Compartmental model; Environmental contamination; HEV; On-farm persistence; Risk factors; Risk mitigation; Transmission; Veterinary public health; Zoonosis.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Course of HEV infection as observed in experimentally infected pigs
Fig. 2
Fig. 2
HEV compartmental infection model
Fig. 3
Fig. 3
Flowchart of the significant risk factors for a high farm level HEV prevalence or seroprevalence. The black and grey shapes contain names that categorize the risk factors. The different colors of blue and purple represent farm compartments. The given risk factors represent a high HEV prevalence or seroprevalence
Fig. 4
Fig. 4
Potential mechanisms for HEV persistence on pig farms. Solid arrows represent mechanisms of persistence confirmed by literature, dashed arrows may be sources of persistence, yet more research is needed to conclude on these sources and dotted arrows are unlikely sources of persistence
See this image and copyright information in PMC

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