What Is A Genotype?
Like all living things, viruses are believed to have a common ancestor. Hepatitis C comes from a family of viruses, of which more than half are mosquito and tick-borne. (A person cannot get HCV from mosquitoes or ticks.) A genotype is a permanent mutation of the original virus. Although there is no longer an original form of the virus in existence, scientists have a good idea about original genetics, and when genotypes first appeared. They know HCV began splitting into genotypes somewhere between 500-2,000 years ago. That’s quite a distance of time, to be sure, but currently, it’s as close as science can get. HCV probably originated in Central Africa, from which untold numbers of viruses have come, including HIV and Ebola. Experts mark this location because of the wide range of genetic diversity of HCV-G4 within the population there; the longer a virus lives in any given location, the more genetically diverse it becomes.
Hepatitis C was first discovered in 1989, in a joint project between the NIH, CDC and Chiron, a corporation known for manufacturing vaccines. Scientists obtained HCV by a method called molecular cloning. A blood sample was taken from a chimpanzee infected with what was then known as hepatitis non-A–non-b. The resulting viral strand, called HCV-1, was the basis for all ensuing research. As increasing numbers of people tested positive for HCV-1, now named hepatitis C, researchers discovered significant genetic variations in the infected population. These variations became the genotypes of hepatitis C. They were discovered gradually, as the virus slowly gave up its secrets.
Despite these genetic differences, all genotypes have major clinical similarities: they all can lead to catastrophic liver damage, cirrhosis, and hepatocellular carcinoma – liver cancer. One of the main differences in genotypes is response to known and forthcoming therapies. Will each genotype require a different medication? Will one medication eventually cure all? Researchers are working on these questions now, and the future of geno-spefic drugs looks most promising.
Everyone infected with hepatitis C has a specific genotype. There are now 9 recognized genotypes in the world today. However, genotypes 7, 8, 9 exist only in the Vietnamese population, which leaves us with genotypes 1-6 occurring most commonly in humans. These genotypes are classified further into subtypes and predominant geographical location. While all genotypes are present all over the world, each geographical region usually harbors one prevailing genotype.
Hepatitis C: Genotypes And Geography, In Order Of Prevalence
- Genotype 1: (46%) North & South America, Northern Europe, North Coastal Africa, East Asia, Japan, Indonesia, Australia
- Genotype 3: (30%) India, Pakistan, Afghanistan, Bangladesh, Malaysia, Singapore
- Genotype 2: (9%) West Africa, parts of Scandinavia
- Genotype 4: (8%) Central Africa, Middle East(8%, 5%) South Africa
- Genotype 5, 6: (5%, less than 1%)
Statistics: Hepatology, JAN 2015, 77-87
Sovaldi alone now cures about 84% of all genotype-1 cases, so other drugs are needed to achieve cure rates over 90+%. Recent trials for other genotypes include PEG/RBN and small-molecule Direct Acting Antivirals. Hopefully, we’re leaving the age of interferon.
Although most Americans with hepatitis C have genotype-1, there is a growing incidence of genotype-2 among injection drug users.
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