Until now, the identification of serological markers in HEV infections using accurate diagnostic serology assays remain a challenge in the epidemiological and clinical settings. There is plethora of issues regarding the performance of HEV serological assays that require urgent attention. In the present paper, we conducted a study on sporadic cases of acute non-A-C hepatitis in Qatar by comparing the performance of four dominant, commercially available Wantai HEV-IgM, Wantai HEV-IgG, Wantai HEV-Ag assays, and MP HEV-Total Ab test to RT-PCR to investigate the current status of their performance.
Acute HEV infections were identified in 23.1% of the non-A-C hepatitis patients. In this study, this prevalence of HEV-RNA could be underestimated. That is, the HEV-RNA can be detected in serum only during the viremia stage and last for a very short period during the early convalescence stage [3, 21, 9]. For instance, three samples showed positive HEV-IgM, HEV-IgG, HEV-Total Ab and high ALT value, but negative RT-PCR results. These 3 patients could be in an early convalescence stage, where RNA disappeared or could be due to the low level of HEV-RNA [27]. As the HEV-RNA detected for a longer period in the stool than the blood during the acute stage [28], any future study should include stool samples from these patients for better estimation of the HEV prevalence.
In the 24 RNA positive specimens that were tested by all assays, HEV antibodies were identified in 66.7 % (16/24) of the patients, at least, by two serological assays as shown in table 2. Thus, in agreement with the dynamic of acute infection, 66.6% of patients were in the early post-seroconversion stage (all three markers positive) [29]. Only four patients (No. 55, 66, 67, 68) were in the window period of the acute phase where antibodies were not yet detectable, and viremia and ALT values were the only markers of infection (4, 11). Another reason could be that these patients might not have elicited enough antibody response is that the samples were collected too early to be positive during the acute phase. These results suggest that ALT could also be used as a good acute hepatitis E marker.
Zhang et al. has indicated that HEV-Ag in macaques became detectable in the serum at almost the same time as HEV-RNA in feces [23]. They and others suggested that HEV-Ag detection should be a valuable tool for the diagnosis of acute hepatitis E, particularly in the window period before seroconversion to anti-HEV [23, 30]. To our knowledge, Wantai Ag-ELISA is the only commercial assay that is currently present in the market for the diagnosis of HEV Ag. Our study is one of the very few studies that evaluated the performance of HEV Ag for the diagnosis of acute hepatitis E [11, 31, 32]. However, our results showed that the sensitivity Wantai Ag-ELISA was the lowest (36.36%) compared to the other serological assays, as shown in Table 4, suggesting that the Wantai HEV-Ag might not be very useful to be used as a single screening assay. In addition, the Wantai HEV-IgM and MP HEV-Total Ab conventional assays showed better sensitivity of 71.43% and 77.27%, respectively, suggesting that Wantai HEV-IgM and MP HEV-Total Ab assays for diagnosis of acute HEV are superior to HEV-Ag assay. Our study confirms the findings of a recent study conducted by Vollmer et al., where they evaluated the performance of Wantai HEV-Ag and HEV-IgM assays for the detection of HEV-Ag and HEV-IgM in positive blood donors in comparison to the RT-PCR assay [11, 32]. In Vollmer’s study, Wantai HEV-Ag was able to detect HEV-Ag only in 40% (4/10) of the positive HEV-RNA donors. In addition, HEV-IgM was detected in 70% (7/10) of the same donors, which are in agreement with our results. In contrast, two other studies had demonstrated that Wantai HEV-Ag assay could be used as an alternative early detection marker for the diagnosis of acute HEV [31-33] and HEV-Ag demonstrated a good concordance with HEV-RNA, while the presence of HEV-IgM did not demonstrate any concordance with HEV-RNA [31]. However, our findings, along with Vollmer et al. results, showed a significant diagnostic gap between the presence of HEV-RNA and HEV-Ag (kappa 0.44) by ELISA and to a lesser degree, with HEV-IgM by ELISA tests (kappa 0.71).
The seroprevalence of Wantai HEV-IgG was the highest among non-A-C hepatitis patients (27.41%) followed by MP HEV-Total Ab (IgG, IgM and IgA) (20.5%) and Wantai HEV-IgM (7.72%) as shown in Table 4. Our results are almost similar to the recent study, where they reported that the seroprevalence for HEV-IgG was 18.0 % among blood donors in Qatar. However, as expected, HEV-IgM was much higher in acute non-A-C hepatitis patients (7.72%) compared to blood donors (only 0.2 %).
Even though the Wantai HEV-IgG resulted in a significantly higher seroprevalence (Table 3), it showed the weakest performance compared to the rest of the assays (sensitivity=63.64 %, specificity= 72.15, and kappa =0.29). The reason behind this might be because all the samples were collected in the acute phase of the infection, where HEV-IgG immunoglobulins are yet below the detectable limits. In other words, HEV IgG appears shortly after the IgM response, which appears one week to two months after the onset of illness. Similar to our results, in a series of 44 children with acute HEV (confirmed with HEV viremia in serum and stool by cell culture and RT-PCR), only 35 percent of patients tested positive for HEV-IgM in serum and only 3 percent were positive for HEV-IgG [34]. In another study, HEV-RNA was detected in 23 % of patients followed by the detection of specific HEV-IgM in 17% and HEV-IgG in 13% of patients. This might explain the high discordance between assays of HEV-IgG antibody (depending on the time of sample collection) as compared with assays for HEV-IgM antibody [35]. Another reason, IgG positivity could be due to a previous infection, especially those that are HEV-RNA and HEV-IgM negative samples.
HEV genotype 1 is the principal cause of hepatitis in most countries of Asia, the Middle East, and Africa, whereas genotype 2 is associated with outbreaks in Mexico and central Africa [9]. Genotypes 1 and 2 may be more virulent than genotypes 3 and 4 and exclusively infect humans. A similar study to ours was conducted in Italy, which aimed to diagnose HEV infection by RT-PCR and serology among acute non-A-C hepatitis cases collected sporadically from new Italian immigrants and local Italians. The majority of these immigrants were originally from India, Bangladesh, and Pakistan [29]. Interestingly, the incidence of HEV-RNA in these individuals was 44.2%. As expected, Asian genotype 1 was the most frequently detected genotype, suggesting that HEV was imported from outside Italy, as genotype 3 is the most prevalent genotype in Europe [7]. In our study, we believe that most of the HEV cases in Qatar were also imported from outside through a high influx of migrant workers to Qatar or by traveling of locals to the HEV highly endemic areas. As shown Table 2, 19 samples out of the 24 HEV positive samples (79%) were from immigrant workers coming from South Asia (Bangladesh, India, Nepal, Pakistan and Sri Lanka). Recently a new genotype 7 was isolated in UAE (close to Qatar) from both camels and humans, yet it is now known if this genotype would also be found in Qatar [36, 37]. Thus, in the future, it would be also interesting to determine the most prevalent genotype in Qatar.
Overall, our data suggest that HEV-IgM positivity represents the main biological marker of HEV acute infection in the clinical setting of developed countries as it showed the best overall performance and best concordance with RT-PCR with a kappa value of 0.71, which denotes substantial agreement. Although Wantai HEV-Ag is the only commercial assay that is currently present in the market for the diagnosis of acute HEV-Ag, the employment of this assay with such a low sensitivity (36.36%) could erroneously fail to confirm HEV-IgM results and which could cause an underestimation of acute HEV infection cases [38].