8 Hepatitis Viruses What is hepatitis? • Hepatitis = Greek, hepar (liver) + itis (inflammation) – may be temporary (acute) or long term (chronic) depending on whether it lasts for less than or more than six months. – Acute hepatitis can sometimes resolve on its own, progress to chronic hepatitis, or rarely result in acute liver failure (fulminant hepatitis). – The chronic form may progress to fibrosis, cirrhosis, or liver cancer. – Some people have no symptoms whereas others develop yellow discoloration of the skin and whites of the eyes, poor appetite, vomiting, tiredness, abdominal pain, or diarrhea Causative agents of Hepatitis • Hepatitis can have many causes – Viral infections; the most common cause worldwide – Heavy alcohol use – Certain medications (Drugs) – Toxins – Other infections (parasites, bacteria) – Autoimmune diseases – Non-alcoholic steatohepatitis (NASH) – . – . Hepatitis viruses • A group of unrelated pathogens termed “hepatitis viruses” cause the vast majority of virally induced hepatitis cases. • Each starts with a letter with the exception of the newly identified transfusion transmission virus (TTV) and SEN viruses. – Hepatitis A (infectious hepatitis) – Hepatitis B (serum hepatitis) – Non-A, non-B hepatitis • Hepatitis C, D, E, G Viral hepatitis Viral hepatitis • Both HAV & HEV are transmitted by the fecal–oral route, more common in developing countries, and cause self-limiting illnesses that do not lead to chronic hepatitis. • HBV, HCV, and HDV are transmitted when blood or mucous membranes are exposed to infected blood and body fluids, such as semen and vaginal secretions. Viral particles have also been found in saliva and breast milk. However, kissing, sharing utensils, and breast feeding do not lead to transmission unless these fluids are introduced into open sores or cuts. • In adults, HBV infection is most commonly self-limiting, with less than 5% progressing to chronic state. However, infection in infants and children frequently leads to chronic infection. Most cases of HCV lead to chronic infection. • Hepatitis D is a defective virus that requires HBV as a helper virus to replicate and is only found with HBV co-infection. Mechanism of viral hepatitis • Hepatitis viruses do not directly cause apoptosis (cell death). • Rather, infection of liver cells activates the innate and adaptive immune systems leading to an inflammatory response which causes cellular damage and death. • Depending on the strength of the immune response, the types of immune cells involved and the ability of the virus to evade the body's defense, infection can either lead to clearance (acute disease) or persistence (chronic disease) of the virus. • Natural killer cells are the primary drivers of the initial innate response and create a cytokine environment that results in the recruitment of CD4 T-helper and CD8 cytotoxic T-cells. • Individuals with an impaired immune response are at greater risk of developing chronic infection Acute viral hepatitis Acute viral hepatitis involves three distinct phases: 1. Initial prodromal phase (preceding symptoms); 1-2 weeks • Non-specific and flu-like symptoms common to many acute viral infections. • Fatigue, nausea, vomiting, poor appetite, joint pain, and headaches. • Fever is common in cases of hepatitis A and E. • Late in this phase, choluria (dark urine) and clay-colored stools. 2. Jaundice phase; can last for up to 4 weeks • The non-specific symptoms typically disappear • Yellowing of the skin and whites of the eyes • Develop an enlarged liver and right upper abdominal pain or discomfort. 3. The recovery phase • Resolution of the clinical symptoms of hepatitis • Hepatitis A and E fully resolve after 1–2 months. Most hepatitis B cases resolve in 3–4 months. Few cases of hepatitis C resolve completely. Fulminant hepatitis • Fulminant hepatitis, or massive hepatic cell death; a rare and life-threatening complication of acute hepatitis that can occur in cases of hepatitis B, D, and E • More frequent in instances of hepatitis B and D co-infection at a rate of 2–20% and in pregnant women with hepatitis E at a rate of 15–20% • In addition to the signs of acute hepatitis, signs of coagulopathy (abnormal coagulation studies with easy bruising and bleeding) and encephalopathy (confusion, disorientation, and sleepiness). • Mortality is typically the result of various complications including cerebral edema, gastrointestinal bleeding, sepsis, respiratory failure, or kidney failure. Chronic hepatitis • Chronic hepatitis continues for more than six months • Initially often asymptomatic but, as the inflammation progresses, constitutional symptoms similar to acute hepatitis follow • Chronic hepatitis interferes with hormonal functions of the liver which can result in acne, hirsutism (abnormal hair growth), and amenorrhea (lack of menstrual period) in women. • Extensive damage and scarring of the liver over time defines cirrhosis, resulting in jaundice, weight loss, coagulopathy, ascites (abdominal fluid collection), and peripheral edema (leg swelling). • Cirrhosis can lead to other life-threatening complications such as hepatic encephalopathy, esophageal varices, hepatorenal syndrome, and liver cancer Laboratory Diagnosis of Viral Hepatitis Infections • Diagnosis based on: – Symptoms (e.g. jaundice) – Blood tests for liver enzymes (e.g. ALT, AST, ALP, GGT) – Viral antibodies (e.g. IgM) – Viral genetic material (e.g. RT-PCR or PCR) • Screening the Blood Supply for Viral Hepatitis Agents – 1971 Hepatitis B surface antigen – 1987 anti-HBcAg – 1986-2003 screening for elevated ALT levels – 1990 anti-HCV – 1999 nucleic acid test for HCV genomes – Blood is not screened for other hepatitis viruses Hepatitis A virus • A member of the Hepatovirus genus of the Picornaviridae family • A positive single-stranded, nonenveloped RNA virus of 7.5 kb in length • At least six genotypes; three of them (I to III) are of human origin • Stable at low pH but inactivated by high temp, formalin, chlorine HAV mRNA Translation • The +ssRNA viral genome acts directly as a mRNA for the synthesis of a large polyprotein (genome = mRNA). • The polyprotein is processed by a viral 3C protease into structural and nonstructural proteins of the virus. HAV life cycle Hepatitis A pathogenesis Diagnosis • Acute infection: detection of HAV-IgM in serum by ELISA • Past infection (immunity); detection of HAV-IgG by ELISA • Cell culture-difficult and takes up to 4 weeks, not routinely performed • Direct detection by EM or RT-PCR in feces. Can detect illness earlier than serology but rarely performed Prevention • Hepatitis A vaccines - Inactivated whole virus; HAVRIX (GSK), VAQTA (MERK) - Pediatric and adult formulations - Licensed for persons ≥ 2 years • Typically given in two doses; booster shot after six months. • 95% seropositive after one dose; 100% seropositive after two doses • The following individuals must receive the vaccine: - Laboratory workers who may come in contact with hepatitis A, - High risk groups; travelers, homosexual men, injecting drug users - People who receive treatment of clotting factor concentrates, - Individuals with chronic liver diseases (hepatitis B or C) • No specific treatment; supportive care Hepatitis B Virus • Initial characterization of hepatitis B infections – Baruch Blumberg, 1963: antibodies in the serum of a New York hemophiliac reacted with an antigen present in the blood of an Australian aborigine infected with hepatitis – Australia antigen was the hepatitis B surface antigen (HBsAg) – Further experiments by David Dane led to the discovery of the Dane particle (complete infectious hepatitis B virus) 3 Types of Hepatitis B Particles • Most abundant HBV particle in carriers a spherical 17-25 nm particle. • Less numerous are noninfectious filamentous particles that are up to 200 nm in length • Dane particles (infectious) 42 nm in diameter, enveloped. HBV Genome • Circular partially dsDNA - Full length strand (- strand), 3.2 kb - Shorter strand (+ strand), 1.7 kb • 4 ORFs; S, C, P, X HBV Life cycle HBV Management and Prevention • 3 drugs commonly used to treat HBV – Interferon -2b – Lamivudine – Adefovir • Immune globulin used as an adjunct to HBV vaccine in preventing HBV transmission from an infected mother to fetus HBV Vaccines • Early vaccines prepared by harvesting 17-25 nm particles from plasma of chronically infected individuals – Particles purified and inactivated by heat, formaldehyde, urea or pepsin. • Subsequently, vaccine manufacturers used genetic engineering to express HBsAg in yeast – Purified HBsAg self assembles into spherical particles resembling 17-25 nm particles found in the serum of people with chronic hepatitis HCV Transmission • Spread almost exclusively through blood contact. • Individuals who received blood products before 1992 are at risk for contracting HCV Hepatitis C Virus (HCV) • Icosahedron-shaped, enveloped virus • +ssRNA flavivirus; the only flavivirus that is not transmitted by arthropods • Similar to picornaviruses (except HCV particles are enveloped) • Viral nucleic acid cloned in 1989 The HCV life cycle and points of intervention A Breakthrough for Hepatitis C Virus Research - Growing Hepatitis C Viruses in Cell Culture - • 1989 HCV discovered • 2005 , 3 different research laboratories made it possible to grow HCV in cell culture • Huh-7.5 cells HCV Treatment No vaccine available Treatment for hepatitis C can help make sure the body clears the virus Treatment may include: • Getting a lot of rest • Eating well and drinking enough water • Avoiding alcohol and other