Introduction

Hepatitis E Virus (HEV) is a small (27–34 nm), non-enveloped, icosahedral, single-stranded RNA virus of approximately 7.2 kb in length. Analysis of its RNA helicase and RNA-dependent RNA polymerase region shows that the virus forms a phylogenetically distinct group that was recently placed into a separate genus, Hepevirus in the Hepeviridae family [1, 2]. The family contains mammalian HEV and a more distant avian HEV [3]. Phylogenetic analysis of the mammalian isolates showed that there are at least seven genotypes and four major human genotypes (genotypes 1–4) [4, 5]. The human genotypes can be subdivided in 24 subtypes [6]. Each HEV genotype appears to have a specific geographic distribution: Genotypes HEV-1 and HEV-2 are restricted to humans and are mainly responsible for large water-borne epidemics in Asia and Africa [6], while genotypes HEV-3 and HEV-4 are found in human and animal reservoirs (swine, wild boar, deer, mongooses) and are mainly responsible for sporadic cases of HEV in developed countries [7]. HEV-1, HEV-2 and HEV-4 have a higher pathogenicity and virulence than HEV-3, hence the clinical burden of HEV-3 cannot be compared with that of the other HEV genotypes [8]. The incidental discovery of a novel swine virus closely related to human HEV in 1997 [9, 10] was extremely important for studying the epidemiology of HEV. In recent years, autochthonous (locally acquired) zoonotic hepatitis E has been found in many developed countries in Europe, New Zealand, North America (all HEV-3) [11–13] and Japan (HEV-3 and HEV-4) [14]. It is now believed that HEV in developed countries is zoonotic and food borne, mainly associated with eating uncooked or undercooked meat or viscera of deer, boars and pigs or by exposure to infected animals [15, 16]. This route of transmission in the MENA is unlikely since pig farming is prohibited in the Islamic culture, as is the case in most countries of the region. Furthermore, boars and deer hunting is not commonly practiced in MENA. HEV is currently the focus of greater attention worldwide and the number of HEV-related articles has more than doubled in the last 10 years.

Seroprevalence of HEV

Rates of IgG positivity in a certain area are believed to be a reflection of the frequency of HEV infection in that area. However, estimating the burden of HEV infection in a population is not an easy task. The true figure in many developing countries could be much higher than that reported since earlier studies used assays with poor sensitivity [17]. Higher results are expected when more sensitive assays are used [18]. Sera tested in recent IgG immunoassays based on a variety of HEV antigens gave broadly concordant results suggesting that antibodies detected are truly directed against HEV [19].

In endemic areas, such as India and Southeast Asia, studies on HEV seroprevalence have shown high frequencies in the general population, ranging from 27 to 80 % in the general population. In contrast, in non-endemic regions, seroprevalence varies from 2 to 8 % in Europe, Japan and South America to 18.0 to 21.0 % in the USA, Russia, UK, Southern France, Hong Kong, Korea, and China [20]. In developing countries, water-borne epidemics of HEV mainly affect young adults, the clinical attack rate being highest among 15–35 year olds [21] and men are clinically infected 2–5 times more than women in most outbreaks [22]. Asymptomatic infections have been estimated to exceed the number of symptomatic cases by 2–4 times in water-borne outbreaks [23]. Although routine surveillance and reporting of HEV infection is far from universal and sensitive anti-HEV assays are still lacking, it is clear that the majority of disease burden due to HEV is in the low and medium income countries of Asia and Africa [24].

Mode(s) of transmission and endemicity

One of the earliest documented massive outbreaks of infectious hepatitis took place in New Delhi, India in late 1955 where at least 30,000 clinical cases of jaundice were reported with elevated morbidity and mortality in pregnant women [25]. Outbreaks with similar characteristics to the New Delhi outbreak were also documented in Kashmir Valley in 1978 [26] and in Afghanistan in 1983 [27]. All three outbreaks were associated with fecal contamination of drinking water or flooding. In 1990–1991, the etiological agent of such outbreaks was isolated, partially cloned and was labeled hepatitis E virus [28]. HEV is now considered the leading cause of enterically transmitted non-A hepatitis in low socio-economic communities [29] and is considered endemic in developing countries. In these outbreaks, the severe infection during pregnancy maybe linked to the greater virulence of HEV-1 genotype and the genetic repertoire of Asian populations [8].

Recent reports showed higher HEV seroprevalence in specific groups as paid blood donors and in repeatedly transmitted hemodialysis patients [30, 31]. Furthermore, the recent reporting of transmission of HEV through blood transfusion from Saudi Arabia [32], Japan [33] and the UK [34] has led to the suggestion that the parenteral route could be an important route in the transmission of HEV. As early as 1996 we speculated on the possible transmission of HEV by blood transfusion in Saudi Arabia [35]. Blood safety came into the light recently when Hewitt and her colleagues in England [36] showed that blood components (platelets preparations, red cells granulocyte pool and fresh frozen plasma) were associated with HEV-3 transmission while in Japan, the most prevalent genotypes were HEV-3 and HEV-4 [8]. Since HEV is endemic in developing countries, including countries of the MENA region, the awareness of an infectious threat to blood safety is legitimate. The purpose of this manuscript, therefore, is to review the status of HEV in the MENA region countries and to see whether the transfusion–transmission route has been critically evaluated.

Methods

Related articles were collected, by searching through the countries of the MENA region. Over the past 14 years (from January 2000 to August 2014), literature was reviewed using countries of the MENA region Pubmed and Medline. The search was conducted using predefined combination of keywords: “Hepatitis E Virus”, “Hepatitis E”, “Hepatitis E Infection”, “blood donors” in combination with all the names of the countries of the MENA region. The MENA region includes 25 countries (Algeria, Bahrain, Cyprus, Djibouti, Egypt, Iran, Iraq, Israel, Jordan, Kuwait, Lebanon, Libya, Mauritania, Morocco, Oman, Palestine, Qatar, Saudi Arabia, Somalia, Sudan, Syria, Tunisia, Turkey, UAE and Yemen) and covers a population of over 380 million people. One hundred articles were reviewed, of which 25 articles were excluded; the excluded papers were written in non-English Language or had uninterpretable data (did not have seroprevalence data).

Results

Hepatitis E virus seroprevalence (anti-HEV IgG and IgM) and HEV-RNA across age groups and in different categories of populations in various countries of the MENA region during the past 14 years are shown in Table 1.

Table 1 Hepatitis E virus (HEV) markers in different categories of populations in the Middle East and North Africa (MENA) countries
Full size table

There were eight articles published on HEV in blood donors (Table 2) of which only two studies performed HEV-RNA testing to see whether or not the donor was viremic at the time of donation. Only one study from Saudi Arabia was a prospective study [32].

Table 2 Hepatitis E virus (HEV) markers among blood donors in the Middle East and North Africa (MENA) countries
Full size table

Anti-HEV in Egypt exceeds 12.5 % in children and can reach 84.0 % in adults. In Iran, anti-HEV varies from region to another (2–14 %), but it does not exceed 14 %. Similarly anti-HEV among Saudis varied from 4.0 to 8.0 % in the general population and in one study a seroprevalence of 19 % was reported among blood donors [107]. Regional variation in anti-HEV seroprevalence was also reported in the Turkish population (2––13 %) and anti-HEV was as high as 35 % among agriculture workers. Anti-HEV variation (18–22 %) was reported among Iraqis and a seroprevalence of 11 % was reported in Yemen. Molecular studies were not attempted in most of the studies reported. High HEV-RNA positivity was reported in pediatric patients with acute hepatitis in Egypt (23 %), in hepatitis outbreaks in Sudan (20–27 %) in patients with chronic hepatitis C in Turkey (55 %) and in pregnant women in UAE (30 %). Table 2 summarizes the seroprevalence of HEV markers among blood donors in the MENA countries.

Discussion

In recent years, studies from developed countries have shown asymptomatic viremia (HEV-RNA) in blood donors which is suggestive of ongoing subclinical infection [36, 109–112]. The presence of HEV-RNA is in the serum of healthy donors indicates that there is a potential risk of transmission of HEV through blood and indeed transmission of HEV by transfusion has been reported on several occasions from Europe and Japan [34, 113–116]. The first molecularly confirmed case of transfusion-transmitted HEV-4 was reported in 2004 from Japan [114]. Other cases have been confirmed in Sweden, Germany and the United States [109, 110], in the United Kingdom [34] and in France [113]; to mention a few. Recent articles have already reviewed the risk of HEV infection by blood donation from developed countries. The incidence of HEV in the blood donor population in developed countries, however, is unclear and is likely underestimated and this could be possibly due to several factors including: (1) the lack of well-validated assays; (2) the asymptomatic nature of HEV infection among most of the adults; (3) the lack of testing; and (4) finally, the underreporting of HEV disease in all countries.

On the other hand, in endemic countries including countries of the MENA region, the impact of HEV transmission through blood transfusion has rarely been evaluated. The possibility of transmission through blood transfusion was based mainly on retrospective evaluation in transfusion recipients [113, 117] and that multi-transfused had significantly higher prevalence of markers for acute HEV (anti-IgM and HEV-RNA) as compared to controls [31, 118, 119]. In the MENA region, out of the 75 published articles that showed interpretable data during the past 14 years, only 8 articles provided data on HEV in blood donors: seven of the articles reported on the seroprevalence of HEV in blood donors and only one study was prospective. Anti-HEV (IgG) in blood donors ranged from 5.4 % among Tunisians to over 50 % among Egyptians. In one study from Saudi Arabia, anti-HEV (IgG) in blood donors was as high as 19.0 % [107]. It is interesting to note that the blood donors in this Saudi study were from one location (Makkah) where the majority of the people drank well water [107]. Moreover, 4.3 % of the blood donors tested were anti-HEV (IgM) positive implicating HEV as a potential transfusion risk. In the prospective study from Saudi Arabia [32], HEV disease developed in 3 of 22 susceptible patients following blood transfusion. The infections were traced to infected donor samples (HEV-RNA positive) and occurred within the incubation period of HEV infection. Thus, asymptomatic viremia may occur in healthy adults in endemic areas and viremia and fecal shedding have been reported in symptom-free carriers. The available but scanty data, therefore, show that the disease burden of HEV infection in blood donors in countries with experience of outbreaks of HEV infection is grossly under-investigated. This fact, in addition to the high endemicity of HEV in developing countries, and the risk of transmission of HEV by transfusion documented in some developed countries lead to the emerging awareness of threat of HEV infection to blood safety in developing countries.

As for the seroprevalence of HEV in the MENA region, published data during the past 14 years confirm the endemicity of HEV in all 12 MENA countries studied, but data on the remaining 13 countries are still lacking. Except for Egypt where anti-HEV reaches 100 % in certain populations, the seroprevalence of HEV in the general population ranges from 2.3 to 37.5 % and is higher in males than in females. Prevalence increased with age, but exposure seems to be in early life in Egypt as high prevalence was detected in young children [120]. This increase in percentage of anti-HEV with age could be consistent with cumulative exposure to infection over time [121].

It must be emphasized, however, that our study suffers serious limitations. The major limitation is in the methodology of the reported studies where the selection of patients and the assays used were very different. Moreover, earlier assays used were less sensitive than the recent ones [122] which cast some doubt on the frequencies reported as underestimated and hence not representative. In addition, data on HEV on the remaining 13 countries of the MENA region are still missing. Furthermore, only three studies reported on HEV genotypes. In Egypt, HEV-1 (2 cases) [43] and HEV-3 (1 case) [41] were reported while in Sudan, HEV-1 (23 cases) was detected during an outbreak in Darfur [79]. Based on these few cases, it can be concluded that HEV-1 is the prevalent genotype in the MENA region which concurs with the global distribution of HEV genotypes [8]. However, more research is needed to identify the predominant genotype(s) in various countries and even in various populations of the MENA region.

It can be concluded that more extensive investigations are required to determine the risk of HEV transmission by blood donations in developing countries [112]. This will include exploring epidemiological, virological and cultural data in evaluating the risk of HEV exposure via blood transfusion in these countries. National surveillance screening of donors and recipients for markers of recent HEV infection is of utmost importance. The reliability of the data depends on the reliability of the tests employed. IgM antibodies to HEV are present for several weeks following acute HEV infection [123] indicating that perhaps screening for HEV IgM class antibodies could be a marker for detecting active HEV infection. No infectivity data, however, are available for anti-HEV IgM-positive donations in the MENA region. HEV-RNA on the other hand does not persist for long (1–2 months) and in some patients may persist for a longer period [8] where in immunocompromised patients the persistence extends to several years [124].

Although the risk of transmission for HEV at present is higher than other viruses such as HIV, screening for HEV in blood donors is still not a universal requirement [112]. However, selective screening is to be recommended in certain circumstances. Recent evidence shows that HEV infection can take a severe or even fatal course resulting in liver failure in immunocompromised, pregnant women or patients with chronic liver disease [123, 125–129]. Since these patients often require blood transfusion, it is prudent that screening for HEV-RNA or at least for anti-HEV IgM in donated blood for these patients should be implemented as soon as possible.