- Split View
-
Views
-
CiteCitation
Hans L. Tillmann, Mark Thursz; Hepatitis C Virus Infection—Its Role in Pathogenesis, The Journal of Infectious Diseases, Volume 195, Issue 2, 15 January 2007, Pages 168–170, https://doi.org/10.1086/510250
Download citation file:
© 2018 Oxford University Press
Close -
Share
In this issue of the Journal of Infectious Diseases, Hansen et al. extend their earlier observations [1] reporting a 2.4‐fold increased overall mortality in relation to anti-hepatitis C virus (HCV) positivity in HIV‐positive patients. They hypothesized that HIV/HCV coinfection is a marker for a familial risk factor promoting premature death that is independent of the pathogenicity of HCV. To explore this hypothesis, they identified 437 siblings of HIV/HCV‐coinfected patients, whom they compared with 1856 siblings of HIV‐monoinfected patients and 285,509 siblings of matched uninfected control subjects. Importantly, they found a significantly higher mortality among siblings of HIV/HCV‐coinfected patients than among siblings of HIV‐monoinfected patients or of control subjects, and they concluded that HCV infection might merely be a marker for disadvantageous familial factors independent of the pathogenicity of HCV [2].
HCV was discovered in a search for an unknown hepatitis virus [3]. Subsequent studies proved that most patients with non‐A, non‐B hepatitis were infected with HCV. This was true for both transfusion‐acquired and sporadic non‐A, non‐B hepatitis [4, 5]. This led some researchers to perhaps overestimate the importance of HCV, as was suggested by the cited world prevalence of HCV infection. Although some researchers have estimated the prevalence of HCV infection to be as high as 170 million people, the World Health Organization now estimates the number at 130 million [6].
What is the main cause of death in patients who die with HCV infection? If one assumes that the main cause of death is liver disease, one might be wrong. Most patients with HCV infection die with their infection, not from it [7, 8]. Without doubt, there is a significant increase in liver‐related deaths in patients with HCV infection, but the impact of infection may be overestimated.
The ideal study to estimate the general impact of HCV infection would require an evaluation of cohorts recruited at the date of their infection. Retrospective data from tertiary referral centers have shown that HCV infection leads to liver cirrhosis in 15%–30% of infected patients within 10–20 years [9, 10]. However, this approach might be similar to estimating the risk of driving a car by only using a database derived from accident and emergency department data. Furthermore, many of these retrospective studies have been small. By contrast, several retrospective and prospective studies before 2000 uniformly showed a much more benign course for HCV infection, with cirrhosis ranging from as low as <1% to a maximum of 8% after 20–23 years of infection [11]. However, HCV has become a leading cause of liver transplantation in many countries, with a reported increase of 6.5%–38.4% of transplant procedures performed between 1990 and 1995 in the United States [12]. The difference between the epidemiological studies and the experience of transplant centers has not been adequately explained.
If the progression rate of HCV infection is overestimated, then we may be offering treatment to some HCV RNA-positive patients who do not need it, because a substantial number of patients identified with HCV infection in the absence of significant liver disease are not likely to progress [13]. Unlike HIV infection [14], there is little epidemiologic evidence that patients with HCV infection have poorer survival than those not infected. HCV infection may be rather benign; for example, only 1 of 17 patients died from liver cirrhosis in one 45‐year follow‐up study [15]. Furthermore, another study that prospectively monitored 222 posttransfusion patients with hepatitis from the date of their infection did not show a difference in survival, compared with 377 control subjects, after 25 years. Overall mortality was not significantly different (67% vs. 65%), despite marginally higher liver‐related mortality (4.1% vs. 1.3%; P=.05) [8]. These studies suggest that, although HCV can be associated with significant liver disease and even death, this does not occur in the majority of infected individuals. However, the only study with >30 years of follow‐up, as noted above, was limited to 17 patients. Because HCV‐induced liver disease progresses slowly, the true estimate of HCV‐attributable mortality will need more long‐term cohort studies. Even when cirrhosis develops in HCV disease, it may still progress slowly [16].
Recent studies have focused attention on the direct contribution of HCV to mortality. A retrospective/prospective study from Australia of patients with acute HCV infection identified an excess mortality that was not related to liver disease [7]. This was the first hint that excess mortality in anti‐HCV-positive patients might be unrelated to direct effects of HCV infection on the liver. This notion is further supported by the Hansen et al. article in this issue of the Journal [2].
The link between HCV infection and excess sibling mortality is intriguing. The increased risk for siblings suggests either a shared environmental factor or a genetic link. If we focus on the genetic link, 2 possible explanations emerge: genetic susceptibility to infectious diseases and genetic influence on impulsive behavior. It is well established that susceptibility to any major infectious disease in one sibling substantially increases the risk of any infectious disease in another [17]. Therefore, susceptibility to HCV in the index case would increase the likelihood that a sibling would acquire a lethal infection caused by another pathogen. However, the acquisition of HCV infection frequently involves high‐risk or impulsive behavior, such as intravenous drug use and needle sharing. It is clear that the genetic background contributes to this form of behavior, and a number of candidate genes have recently been identified [18]. These gene pathways are particularly important because they may influence addictive behavior, impulsiveness, and the risk of suicide. One might therefore speculate that the excess mortality in patients with HCV infection and their siblings might be due to high‐risk behavior and/or suicide. Further studies to determine causes of death in this population are both feasible and justified. However, feasibility is greatly benefited by the existence of a general database structure similar to that used by Hansen et al. in Denmark—the Danish Civil Registration System, for which every person gets a personalized code at birth, which enables the retrieval of data at death—as well as by sufficient funding for tracing people and their relatives.
If HCV infection per se is not particularly detrimental, as some people believe, in either HIV‐infected or HIV‐uninfected individuals, then how do we select patients for treatment? This is a particularly important question, because current interferon and ribavirin-based therapy itself poses a not‐insignificant risk to the patient. Although HCV‐specific antiviral agents may be available in the near future, these agents will likely initially be added to current therapy.
Our ability to identify patients with HCV infection who are likely to progress to end‐stage liver disease is clearly limited. In a number of cross‐sectional studies and short‐term cohort studies that examined rates of fibrosis progression in HCV‐infected patients who acquired infection at an older age, male sex and excess alcohol consumption were consistently associated with a poor prognosis. However, statistical analysis demonstrated that these factors contribute only ∼30% of variability in the rate of progression [18, 19]. It has been suggested that genetic factors may also contribute to the rate of disease progression, but, to date, only a limited number of gene variants have been consistently associated with fibrosis progression [20, 21]. Although genetic markers may form the basis of prognostic tests in the future, the overall contribution of the markers presently available is limited and of no immediate clinical value [22]. The issue of the pathogenicity of HCV in coinfected patients is likely different from that in HCV‐monoinfected patients. It has been observed that HCV has an accelerated course in patients with an immune deficiency, such as hypogammaglobulinemia [23]. In HIV infection, we and others have observed impaired survival in relation to HCV only after AIDS has developed [24, 25], whereas increased mortality in relation to hepatitis B virus was observed, irrespective of immune status, in HIV‐positive patients before the administration of highly active antiretroviral therapy (HAART) [24]. Interestingly, during the pre‐HAART era, there was no difference in overall survival between anti‐HCV-positive patients with HCV RNA and those without HCV RNA in their serum [24].
When HAART became available to treat HIV infection, several reports showed poorer survival for anti‐HCV-positive patients [26, 27]. Liver‐related mortality was higher in anti‐HCV-positive patients (incidence rate ratio [IRR], 11.7–12.3) [28], which was higher than that in patients positive for hepatitis B surface antigen (HBsAg) (IRR, 3.3–3.5) [29]. Overall mortality was reported to be increased to a relative risk of 1.4–1.8 and 1.5 for anti‐HCV [28] and HBsAg [29] positivity, respectively. Still, the absolute numbers of deaths presumably due to HCV seem to be reduced by HAART [30]. Further prospective study of the outcomes of liver disease will be required to clarify this issue.
Although a number of key questions remain unanswered in the natural history of HCV infection, an individualized approach to management seems to be warranted that balances the risks of disease progression, the likely response to treatment, and the dangers associated with treatment. In addition, we may now have to think about other mortality risks in HCV‐infected patients that are not related to their liver disease.
