Using phylodynamic and phylogeographic methods, Angelos Hatzakis and colleagues find that the global spread of Hepatitis C virus coincided with widespread use of transfused blood and with the expansion of intravenous drug use.
Hepatitis C virus (HCV) is estimated to affect 130–180 million people worldwide. Although its origin is unknown, patterns of viral diversity suggest that HCV genotype 1 probably originated from West Africa. Previous attempts to estimate the spatiotemporal parameters of the virus, both globally and regionally, have suggested that epidemic HCV transmission began in 1900 and grew steadily until the late 1980s. However, epidemiological data suggest that the expansion of HCV may have occurred after the Second World War. The aim of our study was to elucidate the timescale and route of the global spread of HCV.
Methods and Findings
We show that the rarely sequenced HCV region (E2P7NS2) is more informative for molecular epidemiology studies than the more commonly used NS5B region. We applied phylodynamic methods to a substantial set of new E2P7NS2 and NS5B sequences, together with all available global HCV sequences with information in both of these genomic regions, in order to estimate the timescale and nature of the global expansion of the most prevalent HCV subtypes, 1a and 1b. We showed that transmission of subtypes 1a and 1b “exploded” between 1940 and 1980, with the spread of 1b preceding that of 1a by at least 16 y (95% confidence interval 15–17). Phylogeographic analysis of all available NS5B sequences suggests that HCV subtypes 1a and 1b disseminated from the developed world to the developing countries.
The evolutionary rate of HCV appears faster than previously suggested. The global spread of HCV coincided with the widespread use of transfused blood and blood products and with the expansion of intravenous drug use but slowed prior to the wide implementation of anti-HCV screening. Differences in the transmission routes associated with subtypes 1a and 1b provide an explanation of the relatively earlier expansion of 1b. Our data show that the most plausible route of the HCV dispersal was from developed countries to the developing world.
Please see later in the article for the Editors' Summary
About 150 million people (3% of the world's population) harbor long-term (chronic) infections with the hepatitis C virus (HCV) and about 3–4 million people become infected with this virus every year. HCV—a leading cause of chronic hepatitis (inflammation of the liver)—is spread through contact with infected blood. Transmission routes include medical procedures (for example, transfusions with unscreened blood) and needle-sharing among intravenous drug users. This second transmission route is the most common one in developed countries where blood is now routinely screened before being used in transfusions. HCV infection can cause a short-lived illness characterized by tiredness and jaundice (yellow skin and eyes), but most newly infected people progress to a symptom-free, chronic infection that can eventually cause liver cirrhosis (scarring) and liver cancer. HCV infections can be treated with a combination of two expensive drugs called interferon and ribavirin, but these drugs are ineffective in many patients.
Why Was This Study Done?
Noone knows for sure where HCV originated although there is some evidence that it appeared first in West Africa or Southeast Asia. It is also unclear when the current HCV epidemic began. In this study, the researchers try to elucidate both the timescale and route of the global spread of the HCV epidemic by analyzing the genome sequence of HCV samples collected at different times and places. HCV is a ribonucleic acid (RNA) virus. That is, it stores the information it needs to replicate itself—its genome—as a series of “ribonucleotides.” Like other RNA viruses, the HCV genome continually accumulates small changes (mutations) and, over time, HCV has evolved into several different “genotypes,” each of which has several distinct subtypes. Furthermore, the viruses within a single subtype have subtly different genomes. By analyzing this viral diversity using complex “phylodynamic” and “phylogeographic” methods, scientists can build up a picture of how HCV has evolved in populations and how it has spread to reach its current geographical distribution.
What Did the Researchers Do and Find?
By examining the genomes of HCV samples collected between 1994 and 2006 at the Athens University Medical School (Greece), the researchers first defined a variable region of HCV called E2P7NS2 that is more informative for phylodynamic studies than the NS5B region that has been used in previous studies. They then retrieved the sequences of both regions for subtype 1a and 1b samples collected over the past 20–30 years in the Los Alamos HCV sequence database; HCV subtypes 1a and 1b cause 60% of global HCV infections. The researchers' phylodynamic analyses of these globally representative sequences (collected in the USA, Germany, Switzerland, and Greece) indicate that the transmission of HCV subtype 1a occurred at a low rate from 1906 until the 1960s, at which time there was an explosive increase in its transmission rate. Similarly, subtype 1b transmission occurred at a low rate from 1922 until the late 1940s but then increased exponentially. From 1980 onwards, the prevalence of both subtypes stabilized at a high level. The researchers' phylogeographic analyses (which considered 1a and1b NS5B sequences collected in 21 and 29 countries, respectively) suggest that HCV subtypes 1a and 1b may have spread from the developed to the developing world.
What Do These Findings Mean?
These findings indicate that the epidemic of HCV subtype 1b began in the 1940s when the use of transfused blood and blood products became widespread whereas the start of the subtype 1a epidemic coincided with the expansion of injected drug use that occurred in the 1960s. The findings also suggest that the transmission rates of both subtypes may have slowed before the widespread implementation of HCV screening in the early 1990s, possibly because the medical community was aware by then of the general risks associated with blood contamination. Finally, these findings provide new insights into how the HCV epidemic spread around the world and suggest that HCV may be evolving faster than previously thought. However, because this study relied on a small number of samples collected over a short time period, its findings need to be confirmed in larger studies.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1000198.
The World Health Organization provides detailed information about hepatitis C and HCV
The US Centers for Disease Control and Prevention provides information on hepatitis C for the public and for health professionals (information is also available in Spanish)
The US National Institute of Diabetes and Digestive and Kidney Diseases provides basic information on hepatitis C (in English and Spanish)
MedlinePlus provides links to further resources on hepatitis C
The Los Alamos HCV database is available
The US National Center for Biotechnology Information provides a science primer on how scientists reconstruct evolutionary pathways from sequence information