INFECTIOUS DISEASES

Hepatitis B virus

Hepatitis B is a worldwide healthcare problem in developing countries. An estimated one third of the global population has been infected with the hepatitis B virus (HBV). Approximately 350 million people are lifelong carriers, and only 2% are spontaneously seroconvert annually. HBV is transmitted hematogenously and sexually. The outcome of this infection is a complicated viral-host interaction that results in either an acute symptomatic disease or an asymptomatic disease. Patients may become immune to the hepatitis B virus (HBV), or they may develop a chronic carrier state. Later consequences are cirrhosis and the development of hepatocellular carcinoma. Antiviral treatment may be effective for approximately one third of the patients who receive it, and for selected candidates, liver transplantation currently seems to be the only viable treatment for the latest stages of hepatitis B.

The viral genome consists of a partially double-stranded circular DNA of 3.2 kilobase (kb) pairs that encodes 4 overlapping open reading frames as follows:

  • The best indication of active viral replication is the presence of hepatitis B virus (HBV) DNA in the serum. In Al-Jawahra Centre Molecular Diagnostic Unit, more sensitive polymerase chain reaction (PCR) techniques are used to detect the viral genome in the serum.
  • With the newest PCR techniques, identification of variants form of hepatitis B virus (HBV) genome (variant strains) is possible.
  • The pathogenesis and clinical manifestations of hepatitis B are due to the interaction of the virus and the host immune system. The latter attacks the hepatitis B virus (HBV) and causes liver injury. The final state of hepatitis B virus (HBV) disease is cirrhosis. Patients with cirrhosis and HBV infection are likely to develop hepatocellular carcinoma.

 

Hepatitis C Virus

The World Health Organization (WHO) estimates that 170 millions of individuals worldwide are infected with hepatitis C virus (HCV). However, the prevalence of HCV infection varies throughout the world. Medical care costs associated with the treatment of HCV infection are very high in the West. Most patients infected with HCV have chronic liver disease, which can progress to cirrhosis and hepatocellular carcinoma. Chronic infection with HCV is one of the most important causes of chronic liver disease. HCV is a spherical, enveloped, single-stranded RNA virus belonging to the Flaviviridae family and Flavivirus genus. HCV can produce at least 10 trillion new viral particles each day. RNA-dependent RNA polymerase, an enzyme critical in HCV replication, lacks proofreading capabilities and generates a large number of mutant viruses known as ‘quasispecies’.

6 major HCV genotypes and numerous subtypes have been identified. Molecular differences between genotypes are relatively large, and they have a difference of at least 30% at the nucleotide level. The major HCV genotype worldwide is genotype 1, which accounts for 40-80% of all isolates. Genotypes 1a and 1b are prevalent in the United States, whereas in other countries, genotype 1a is less frequent. Genotypes 2 and 3 are also found globally and account for a significant minority of infections. HCV genotype 1, particularly 1b, does not respond to therapy as well as genotypes 2 and 3. Genotype 1 also may be associated with more severe liver disease and a higher risk of HCC.

The other genotypes have a more specific geographic distribution. Genotype 3 is found in Australia, the Indian subcontinent, and Thailand. Genotype 4 is the most prevalent genotype in Egypt and in the Middle-East. Genotype 5 is found in South Africa, and genotype 6 is more common in Southeast Asia, particularly in Hong Kong, Macao, and Vietnam.

In Al-Jawhara Centre Molecular Diagnostic Unit, the full quantiation of the HCV virus and also genotyping of HCV is proposed with the most sophisticated molecular diagnostic technology.