Hepatitis C Virus in mainland China with an emphasis on genotype and subtype distribution

The literature search on HCV GT detection among clinical cases in mainland China was conducted using China National Knowledge Infrastructure (CNKI), PubMed and Wanfang Data (a Chinese professional academic database developed by Wanfang data limited-liability Company) with the key words “HCV” or “Hepatitis C virus”; “genotype” or “subtype”, “sequencing” or sequence analysis”; “transfusion transmitted disease” and “China” or “Mainland China”. No language restrictions were applied.

The inclusion criteria included: 1) The study was conducted only in mainland China (Hong Kong, Taiwan and Macao were excluded); 2) Studies involving the HCV genotype and (or) subtype distribution; 3) The study object were hospitalized patients; 4) Studies with clear sample size.

The exclusion criteria were as follows: 1) studies without exact sample size, publication year and methods; 2) Overlapping or paradoxical studies: data from literature were repeat or inconsistent between the context; 3) The study objects were blood donors or intravenous drug user; 4) HCV GTs prevalence rate in patients with HIV/HCV co-infection; 5) Comments, reviews or conference abstracts. When investigating the trends of HCV GT spatio-temporal distributions, literatures without exact study year were not included.

HCV GT distribution usually varied in different populations such as in blood donors, IDUs, hemodialysis patients (HDs) and hepatitis patients. The distribution pattern changes with the change of transmission modes [227]. Generally, transfusion transmitted HCV were strongly associated with subtypes 1b and 2a [89, 180, 181]. Encouragingly, the paid blood donation is not common in China with the implementation of the Blood Donation Law in 1998. In voluntary blood donors, GTs 1b and 2a account for the highest proportion [228], and HCV GT distribution exhibits significant geographical difference: The most common GTs in Shanxi, Henan, Jiangsu, Anhui, Shanghai, Shaanxi, Hebei and Xinjiang are 1b and 2a; the prevalent GTs in Guangdong and Fujian Province are 1b and 6a; the dominant GTs in Chongqing and Yunnan are 3a and 2a/3b; GTs 1b, 1a and 1b, 3b are most common in Guangxi and Qinghai, respectively. In addition, the proportion of subtypes 1b and 2a in volunteers decreased in recent years, and yet subtypes 3 and 6 increased [179, 229]. Some reasons may explain this GT shift: 1) Increasing of drug abuser and commercial sex activity resulted in transmission from high risk population to general population; 2) Upgrade of genotyping methods accompanied by new HCV GTs and subtypes. Among IDUs, HCV-1a, 1b, 2a, 3a, 3b, 6a, 6n and 6u have been found, of which HCV-6a and 3b/3a/1b were the most popular GTs. In HD patients, the prevalence of genotype 1 is the highest, and HCV GTs among HDs are very complex with the co-infection accounting for a big proportion [224, 230, 231], which may be ascribed to long-term dialysis, repeatedly blood transfusion and iatrogenic factors. In addition, some cases of subtype 2a are found in individuals with high risk sexual behaviors, while 1b was more popular in clinical cases [194, 232, 233].

According to statistic results, discrepancy results displayed the association between HCV GTs and gender, age in infected patients. Most studies showed no statistical difference between HCV GT and gender [7, 20, 31, 136, 137, 234], while the rest displayed significant difference, of which the proportion of subtype 1b was higher in male than in female. And on the contrary, subtype 2a showed the opposite distribution [13, 32, 40, 83, 156]. The reasonable explanation for this significant difference may be that different genders exhibit different immune response against HCV infections with different GTs. For the relationship between HCV GT and age, most studies reported no statistical difference. However, there were a few studies showed that GT 1 and 2 were more common in the older group while GT 3 and 6 in the younger group [78, 137, 235]. The reason may be ascribed to be that the transmission routs are more inclined to blood transfusion in the elder group and the main GTs were HCV-1 and 2. While in the younger group, the patients were mainly infected by HCV-3 and 6 via intravenous drug abuse and high risk sexual behaviors. However, one study in 2012 showed that subtype 1 was found more often in younger patients (<40) [125], and another report showed no statistical difference between HCV-2a and age [78]. In view of the above discrepancy results, a large-scale multiple-center study involved a wider area is needed to clarify the association between HCV GT and age or gender in China.

Many present studies were designed to determine the association between HCV GTs and viral loads in chronic hepatitis patients. It has been well known that HCV genotype/subtype together with viral load variations during treatment are very important to guide the therapeutic strategies and relapse rates [236]. However, many discrepant results were reported. Generally speaking, the higher HCV RNA loads would cause more severe liver damage with more obvious clinical manifestations [78]. The viral load in patients chronically infected with HCV is associated with GTs that the level of HCV RNA in HCV-1 patients is higher than that in GT non-1, and HCV-1 and 6 is higher than HCV-2 and 3 [52, 77, 78, 96, 152, 237], which might be due to more efficient viral replication of GTs 1 and 6 [238‐240]. Some foreign studies also reported the similar results [241]. However, another study reported that among patients with high viral load in China, HCV 2a was more common than other GTs [113], while some foreign studies reported that genotype 3 or 4 were found to be significantly higher viral load as compared to other genotypes [242, 243]. In addition, higher levels of viral load were also seen in HCV co-infection [156]. Interestingly, some other studies found no significant correlation between HCV GTs and viral loads [31, 52, 78, 92, 101, 135, 153].

Considering these conflicting and complex results above, we extracted the qualified literature [17, 18, 32, 33, 44, 83, 133, 135, 152, 202, 234, 244] from the screened hospitalized patients to summary the related cases in mainland China among different GTs based on HCV RNA quantitative level (<10⁶ copies/ml indicates low viral load; ≥10⁶ copies/ml indicates high viral load), and performed the statistical analysis of between them. The overall result showed significant statistical difference (P < 0.05), which indicate HCV GT is associated with HCV viral load. No significant difference between subtypes 2a and 3a was found, and the significant difference was found in the other subtypes (Table 4) that HCV RNA level with subtypes 1b and 6a was higher than 2a, 3a and 3b. Various factors may be taken into account: 1) Different viral replication ability among various subtypes; 2) Regional GT distribution difference; 2) HCV infection time was not restricted exactly and identified in the same or similar stage. Since high viral load is difficult to treat than low viral load, we suggest precise mechanism study should be performed to ascertain the correlation between HCV genotypes and viral load and to further design the therapeutic strategies.

The varied HCV GTs, subtypes and strains showed different degree of liver damage [83, 245, 246]. Subtype 1b, which has more efficient viral replication ability and poor prognosis and possesses major proportion of severe liver disease (LD), is associated with HCV-related LC and HCC [83, 88, 117, 158, 247] than non-1b subtypes. The viral genome rapid replication is higher in patients with GT 1 than that in other GTs. As a result, the consequent liver histological grading and hepatitis progress speed are considerably higher than those of GT 2 infected patients, which would lead GT 1 more incline to progress into HCC consistently with previous report [87]. A study found that 5 patients with LC among 94 cases were all GT 1b [50], while 1a, 2a, 2b, 3a were more common in chronic hepatitis patients without LC and liver cancer [117, 248]. Patients infected with subtype 4 were also reported to be associated with the decompensated liver complications [249], and this strong cytotoxic effect may be associated with specific proteins encoded by subtype-specific mutant genes [250, 251]. However, other research showed that no significant differences were found between HCV GTs and outcome of HCV infections [31, 96, 128, 252]. Even so, consistent results reported presently in and out of the county were found that 1b account for a larger proportion in moderate and severe chronic hepatitis and LC than in acute, mild chronic hepatitis [253, 254], which may give us some suggestion that a proactive clinical management should be important for patients infected by HCV 1b. In addition, researches launched outside China also showed that HCV-GT 3 was associated with severe LD [255, 256].

Considering these conflicting and complex results above, we extracted the qualified literature [8, 41, 59, 65, 83, 85, 87, 96, 97, 126, 128, 140] from the screened hospitalized patients to summary the related cases in mainland China among different GTs based on severity of hepatitis (chronic hepatitis; cirrhosis; hepatocellular carcinoma), and performed the statistical analysis. The overall result showed significant difference (P < 0.05), which may indicate HCV GT is associated with severity of hepatitis. Significant difference was found between subtypes 1b and 2a, 3b, and the significant difference was not found in the other subtypes (Table 5). The possible reason for subtype 1b being more inclined to cause severe LD than subtypes 2a and 3b may be that subtype 1b has stronger pathogenicity and replication ability. In addition, the host factor should also be considered. Based on the above results, this may provide useful and instructional information for clinical treatment, and further mechanism study may be badly needed to clarify the association between HCV GTs and severity of hepatitis.

In China, the current standard-of-care (SOC) for the treatment of patients chronically infected with HCV is the combination therapy of PEGylated interferon alpha and ribavirin (PEG-IFN and RBV, PR); however, HCV GT is an important viral factor to predict therapeutic response and duration of treatment [257, 258]. Various genotypes of HCV have showed different treatment effects. Patients with GT 2 and 3 can achieve relative high SVR of 70–80%, yet patients with GT 1 and 4 showed bad effect with the low SVR of 40–50% [259‐262]. This may be ascribed to the different pathogenicity and replication ability of HCV with different GTs and the host cell factor [263, 264]. However, the mechanism still need to be clarified in the future, and some previous studies have reported that this may be associated with increased amount or mutation of E2 protein and the binding of NS5A protein to the protein kinase (PKR) [265, 266], a kind of antiviral protein normally induced by IFN during treatment.

With the development of new potent DAA and its combinations, the cure rate of HCV infection reaches >90% in almost all HCV GTs and stages of LD [267, 268]. Especially, Epclusa, the first oral fixed-dose combination, shows high SVR for all six major HCV genotypes, and even in patients with decompensated cirrhosis, the SVR12 can achieve 94% [269]. Actually, China has completed the clinical trials of some DAA drugs that sofosbuvir - daclatasvir or Harvoni, daclatasvir + asunaprevir, Ledipasvir/sofosbuvir and sofosbuvir + PEG/RBV are all safe and effective in Chinese patients with chronic hepatitis C [270]. Unfortunately, this DAA combination therapy is not cost-effective and for the moment, PR remains a good alternative to treat Chinese patients chronically infected with HCV with above 80% SVR which is higher than that in Europe and America [271].