The origin of hepatitis C (HCV) is unknown. The
current theory is that it may have originated in horses, but while the
virus found in horses is similar to the hepatitis C virus the
scientific evidence linking it to hepatitis C is far from clear.
Where the virus originated is on more solid ground—it is believed to
have originated in West Africa. Hepatitis C is spread by direct
blood-to-blood contact. So how did it develop into such a huge problem
with an estimated 130-150 million people infected worldwide? How did
genotype 1 become the most common genotype worldwide? The answer to
both questions is well-known—blood transfusions and unsafe injections.
In the study “The Global Spread
of Hepatitis C Virus 1a and 1b: A Phylodynamic and Phylogeographic
Analysis,” by G Magiokinis et al., the authors used a complicated
system of analysis with various models (molecular clock & the
Bayesian skyline demographic). The model tracked how genotype 1a and
1b spread throughout the world. First it was found that genotype 1a had
a steady rate of expansion from about 1906 through the 1960’s.
Moreover, it was found that from the 1960’s through the 1980’s it
dramatically expanded. This corresponds to the increase in injection
drug use from the 1960’s through the present day.
Genotype 1b on the other hand
expanded at a steady rate from 1922 to the late 1940s. Then from the
1950’s until the 1980s it showed the greatest expansion. Thus, the
highest rate of expansion of genotype 1b was ~16 years before genotype
1a. An interesting observation was that early on in the hepatitis C
epidemic it was thought that genotype 1b led to more cases of liver
cancer. A possible explanation of this is that people with genotype 1b
were infected longer and were more likely to have had more disease
progression. As the authors pointed out, the connection between
genotype 1b, liver cancer and the earlier spread of genotype 1b needs
to be validated in future studies.
To validate their findings of the earlier expansion of genotype 1b, however, the authors pointed to other evidence:
Back to why genotype 1 is the
most common genotype. The most likely reason is that genotype 1 was
introduced into developed western countries and spread by the
introduction of blood transfusions, plasma pooling and unsafe
injections (reuse or improper needle sterilization) of medicines to
treat many diseases. In the late 1920s through the present day the
epidemic of injection drug use and sharing needles and drug preparation
tools is another reason for the spread of HCV genotype 1.
One has to wonder how different
it would be if genotype 2 had been ‘the genotype’ that had been the
one that had greatly expanded instead of genotype 1. Treatment of
genotype 2 produced very high cure rate early on in the history of
treatment. Still with current treatments we have the potential to
eradicate hepatitis C in a lifetime. If only we could increase
treatment access for everyone with hepatitis C.
Facts about genotype 1:
Genotype 1 is the most common genotype worldwide at 83.4 million (46.2%) people.
Genotype 1 is the most common genotype in the United States at 70% of the population with HCV.
Genotype 1a and 1b are the most common subtypes; subtypes 1c, d, e, f, g, h, i, k and l have been identified but are uncommon.
The current standard of care
for the treatment of hepatitis C can cure 90 to 100% of people who take
the medications (HARVONI and VIEKIRA PAK). Treatment durations are
usually 12 weeks but vary from 8 to 24 weeks.
Labels: Epidemiology, Genotype 1, genotype dispersion, genotype history