Hepatitis C Virus PDF

The Hepatitis C Virus Although its means of transmission is fairly well documented, the hepatitis C virus itself largely remains a mystery. Hepatitis C is extremely small, even for a virus - it is only about 50 nanometers in diameter. A nanometer is one billionth of a meter - if you placed 200,000 h...

The Hepatitis C Virus Although its means of transmission is fairly well documented, the hepatitis C virus itself largely remains a mystery. Hepatitis C is extremely small, even for a virus - it is only about 50 nanometers in diameter. A nanometer is one billionth of a meter - if you placed 200,000 hepatitis C viruses end to end, they would be only a single centimeter long. (They are so small that they have no color - they are in fact smaller than the wavelength of visible light.) However, what is known about hepatitis C underscores the type of threat that it poses. Hepatitis C is an RNA virus - which means that it mutates frequently. Once an infection has begun, hepatitis C creates different genetic variations of itself within the body of the host. The mutated forms are frequently different enough from their ancestors that the immune system cannot recognize them. Thus, even if the immune system begins to succeed against one variation, the mutant strains quickly take over and become new, predominant strains. As a result, the development of antibodies against HCV does not produce an immunity against the disease like it does with most other viruses. More than 80% of the individuals infected with HCV will progress to a chronic form of the disease. As a result of this, hepatitis C is usually not self-limited as a disease. In more than 85% of all cases, whether they progress to chronic liver disease or not, the infected individual carries the virus for life. This means that they also remain contagious for a lifetime, able to transmit the virus to others. And because of the long progression of the illness, even patients who will eventually die as a result of hepatitis C carry the virus for decades before it takes their lives. 1 Hepatitis C viruses Most epidemics are self-limiting - they spread rapidly, but over a short period of time the affected population either dies or develops an immunity to the disease, and it stops spreading. Not so with hepatitis C. Much like HIV and AIDS, it lasts a lifetime, and kills slowly - giving the virus plenty of time to spread. There are six basic genotypes of HCV, with 15 recorded subtypes, which vary in prevalence in different regions of the world. Each of these major genotypes can differ significantly in their biological effects - in terms of replication, mutation rates, type and severity of liver damage, and detection and treatment options. However, these differences are not yet clearly understood. The 21 current variations in genotype, complicated by the constant mutation of the virus within infected individuals, represents a major challenge for the development of treatments and vaccines against HCV - and even for reliable detection of the virus. There is no guarantee that a treatment, test, or vaccine against one strain will be effective against all of them. Moreover, individuals cured of one strain will be prone to reinfection by any of the other strains. 2  Human immunodeficiency virus (HIV) is a lentivirus (a member of the retrovirus family) that causes acquired immunodeficiency syndrome (AIDS), a condition in humans in which the immune system begins to fail, leading to life-threatening opportunistic infections. Infection with HIV occurs by the transfer of blood, semen, vaginal fluid, pre-ejaculate, or breast milk. Within these bodily fluids, HIV is present as both free virus particles and virus within infected immune cells. The four major routes of transmission are unsafe sex, contaminated needles, breast milk, and transmission from an infected mother to her baby at birth (Vertical transmission). Screening of blood products for HIV has largely eliminated transmission through blood transfusions or infected blood products in the developed world. HIV infection in humans is considered pandemic by WHO. From 1981 to 2006, AIDS killed more than 25 million people. HIV infects about 0.6% of the world's population. In 2005 alone, AIDS claimed an estimated 2.4–3.3 million lives, of which more than 570,000 were children. A third of these deaths are occurring in sub-Saharan Africa, retarding economic growth and increasing poverty. According to current estimates, HIV is set to infect 90 million people in Africa, resulting in a minimum estimate of 18 million orphans.Antiretroviral treatment reduces both the mortality and the morbidity of HIV infection, but routine access to antiretroviral medication is not available in all countries. HIV primarily infects vital cells in the human immune system such as helper T cells (specifically CD4+ T cells), macrophages, and dendritic cells. HIV infection 3 leads to low levels of CD4+ T cells through three main mechanisms: firstly, direct viral killing of infected cells; secondly, increased rates of apoptosis in infected cells; and thirdly, killing of infected CD4 + T cells by CD8 cytotoxic lymphocytes that recognize infected cells. When CD4 + T cell numbers decline below a critical level, cell-mediated immunity is lost, and the body becomes progressively more susceptible to opportunistic infections. Eventually most HIV-infected individuals develop AIDS. These individuals mostly die from opportunistic infections or malignancies associated with the progressive failure of the immune system. Without treatment, about 9 out of every 10 persons with HIV will progress to AIDS after 10–15 years. Many progress much sooner. Treatment with anti-retrovirals increases the life expectancy of people infected with HIV. Even after HIV has progressed to diagnosable AIDS, the average survival time with antiretroviral therapy (as of 2005) is estimated to be more than 5 years. Without antiretroviral therapy, death normally occurs within a year. Classification HIV is a member of the genus Lentivirus, part of the family of Retroviridae. Lentiviruses have many common morphologies and biological properties. Many species are infected by lentiviruses, which are characteristically responsible for long-duration illnesses with a long incubation period. Lentiviruses are transmitted as enveloped RNA viruses. Upon entry of the target cell, the viral RNA genome is converted to double-stranded DNA by a virally encoded reverse transcriptase that is present in the virus particle. This viral DNA is then integrated into the cellular DNA by a virally encoded integrase, along with host cellular co-factors, so that the genome can be transcribed. After the virus has infected the cell, two pathways are possible: 4 either the virus becomes latent and the infected cell continues to function, or the virus becomes active and replicates, and a large number of virus particles are liberated that can then infect other cells. There are two strains of HIV known to exist: HIV-1 and HIV-2. HIV-1 is the virus that was initially discovered and termed LAV. It is more virulent, relatively easily transmitted, and is the cause of the majority of HIV infections globally. HIV-2 is less transmittable and is largely confined to West Africa. Comparison of HIV species Species Virulence Transmittability Prevalence Purported origin HIV-1 High High Global Common Chimpanzee HIV-2 Lower Low West Africa Sooty Mangabey Signs and symptoms A generalized graph of the relationship between HIV copies (viral load) and CD4 counts over the average course of untreated HIV infection; any particular 5 individual's disease course may vary considerably. CD4+ T cell count (cells per µL) HIV RNA copies per mL of plasma Infection with HIV-1 is associated with a progressive decrease of the CD4+ T cell count and an increase in viral load. The stage of infection can be determined by measuring the patient's CD4+ T cell count, and the level of HIV in the blood. HIV infection has basically four stages: Incubation period, acute infection, latency stage and AIDS. 1-The initial incubation period upon infection is asymptomaticand usually lasts between two and four weeks. 2-The second stage, acute infection, which lasts an average of 28 days and can include symptoms such as fever,lymphadenopathy (swollen lymph nodes), pharyngitis (sore throat), rash, myalgia (muscle pain), malaise, and mouth and esophageal sores. 3-The latency stage: which occurs third, shows few or no symptoms and can last anywhere from two weeks to twenty years and beyond. 4- AIDS: the fourth and final stage of HIV infection shows as symptoms of various opportunistic infections. A study of French hospital patients found that approximately 0.5% of HIV-1 infected individuals retain high levels of CD4 T-Cells and a low or clinically undetectable viral load without anti-retroviral treatment. These individuals are classified as HIV controllers or Long-term nonprogressors. – Acute HIV infection 6  Diagram of HIV 7