HEV is estimated to cause approximately 20 million new infections annually, leading to around 3.3 million symptomatic cases and 70,000 deaths. However, these figures may be underestimated due to limited surveillance capacity and suboptimal access to laboratory diagnostics, which often leave many infections, especially pauci-symptomatic and subclinical cases, undetected and under-reported. Nepal, considered endemic for hepatitis E virus, has experienced repeated outbreaks of HEV with sporadic cases of acute hepatitis between such outbreaks. Most previous seroprevalence studies in Nepal are conducted using convenience samples (healthy blood donors or individuals seeking care in a hospital setting), and it is unknown how well these estimates represent the general population.
Therefore, team at Center for Infectious Disease Research and Surveillance at Dhulikhel Hospital Kathmandu University Hospital, Nepal, led by Dr. Dipesh Tamrakar and Nishan Katuwal, in collaboration with Dr. Kristen Aiemjoy from UC Davis, USA, performed a longitudinal HEV serosurvey among a geographically random population-based sample of children and young adults (aged 0 to 25 years) residing in Kathmandu and Kavre districts of Nepal. The aim was to gain a better understanding of the geographic distribution of HEV, characterize the incidence, and investigate risk factors related to exposure.
In this study, now published in PLoS NTD, the team collected dried-blood-spots (DBS) from participants of urban and peri-urban areas, every 6 months and tested the samples to detect past and new infections of HEV. The sample were analysed for anti-HEV IgG using endpoint ELISA. Their study, involving 923 individuals, showed seroprevalence of 4.8% and seroincidence rate of 10.9 seroconversions per 1000 person-years. These findings were consistent with the growing body of evidence suggesting that HEV is endemic in many parts of Nepal. Further, each year, about 11 in 1000 people were found to be newly exposed to the virus. The seroprevalence was found to be increasing with age (11.1% for age group 15-25). The team identified water source as a potential risk factor for HEV seroincidence, where individuals consuming surface water had more than four times the seroincidence rate of HEV compared to those relying on other water sources.
The authors acknowledge some limitations in this study. The cohort was specifically designed to assess burden of enteric fever and excluded individuals over the age of 25. This limitation constrains their ability to comment on HEV burden in older age groups. Nonetheless, previous research suggests that highest HEV burden is among young adults. The authors recommend that future studies should focus on characterizing HEV seroincidence in older populations within the Kathmandu Valley. Furthermore, the use of DBS, while being logistically advantageous, due to its reduced sensitivity could have underestimated the burden (by upto 20%). Despite this, studies have demonstrated that DBS can be equivalent to plasma when properly stored.
This study demonstrates that HEV is endemic in Nepal and that the infection risk increases with age. Further, water may be a potential source of exposure. Thus, these insights emphasize the need for targeted public health strategies such as improved water and sanitation infrastructure and potential vaccination implementation in areas with high seroprevalence.
Read the full article (PLoS Negl Trop Dis. 2024 Aug 5;18(8):e0012375): DOI: 10.1371/journal.pntd.0012375
