Abstract
Dear Editor,
Yasri and Wiwanitkit (14) have raised concerns regarding our article, “A Nationwide Survey of the Seroprevalence of Hepatitis E Virus Infections Among Blood Donors in Thailand” in Viral Immunology (4). We would like to address their concerns as follows:
Question: First, it is questionable whether the data from this report represent a nationwide data. Thailand has 5 regions with >70 provinces, but Jupattanasin et al. selected to study <20 provinces from only 4 regions. In addition, blood donors might be an immigrant from one province to another province. The good example is the healthy worker who migrates to work in a workplace away from hometown.
Answer: Samples size of specimens in this study were precalculated based on the previous studies in the Thai population. Subsequently, total blood samples were randomly obtained from 16 provinces with 40 samples in each province distribution. The samples were collected from only four regions (central, northern, northeastern, and southern) based on the national and regional blood donation centers in this country. All the donors were healthy individuals who stayed in their hometown, rather than individuals who had migrated from other provinces. This project was approved by the university's ethical committee and funding scholarship. Therefore, we believe that our data represent a nationwide survey.
Question: The conclusion on the relationship with local pork consumption behavior might not be correct. Indeed, Jupattanasin et al. mentioned that the low hepatitis E virus (HEV) infection in southern region of Thailand was related to Islamic background. In fact, there are only some provinces in southern region of Thailand that have Muslim majority (only 4 from 14 provinces). The specific area of the southern region of Thailand that is populated by the Muslim is the southernmost part. The effect of background pork consumption on seroprevalence of hepatitis B was previously confirmed in this specific part, not all parts, of southern region of Thailand. In fact, in a recent report from Bangladesh, there is also a very high rate of infection among Muslim population. Despite pork is not consumed by the Muslims in Bangladesh, the high rate of infection can be observed. The conclusion from the present report should be there is a wide range of seroprevalence rates observed in different provinces in Thailand and the association with the social geographical background should be further in-depth investigated.
Answer: According to HEV epidemiology, fecal contamination of drinking water is associated with large HEV outbreaks of genotypes 1 and 2 in endemic areas. Sporadic transmission of HEV genotypes 3 and 4 in high-income countries has been associated with exposure to blood and animal contact (5). Based on our previous study and others in Thailand, all HEV isolated in this country have been clustered into HEV genotype 3, which are genetically close to swine HEV strains (11,12). In addition, it was previously reported that the pig is an HEV reservoir and transmits the virus to humans (13). Even though we only examined three provinces in the southern part of Thailand in this study, we could demonstrate low prevalence of HEV and low anti-HEV level (GMT) related to Muslim populations in the area where there was low pork consumption.
In Bangladesh, the occurrence of an outbreak of HEV infection was reported and HEV virus genotype 1 was associated with the sporadic hepatitis E in that country (3,10). Although the population of Muslims in Bangladesh does not consume pork, a high prevalence of HEV infection was found. From the study of anti-HEV IgG among Muslims in Bangladesh, ∼30% among 18–30 years were positive for HEV Ab (6,8). We believe that fecal contamination of drinking water or blood exposure might be associated with large HEV outbreaks and genotypes 1 in Bangladesh.
In addition, the seroprevalence of anti-HEV antibodies has been known to vary, depending on the sensitivity and specificity of the assays (1,7). No method is available to confirm the actual result of anti-HEV IgG. Only the history of exposure to HEV or the presence of HEV genome/anti-HEV IgM markers in blood would be extra evidence of HEV infection. In our study, our data were evaluated and the method validated by using at least three different assay kits. Herein, the prevalence of anti-HEV IgG was determined by the EUROIMMUN test kit, based on recombinant Ag derived from HEV genotypes 1 and 3, with a limit of detection of 0.1 IU/mL. This prevalence outcome was similar to that previously reported in earlier studies conducted between 2007 and 2014 in Thailand (2,11), whereas the other two test kits gave unreliable results in the same specimen with high prevalence of HEV IgG up to 60%.