Hepadnaviridiae
Hepadnaviridiae is a family of viruses primarily known for causing infections in liver cells, which can lead to severe health issues, including liver cancer. The most notable member of this family is the hepadnavirus responsible for hepatitis B (HBV), a major public health concern affecting millions worldwide. Hepadnaviruses possess small genomes consisting of partially double-stranded and single-stranded circular DNA, and they are characterized by their small, spherical, and enveloped virions. HBV is highly infectious, often transmitted through sexual contact, and can remain undiagnosed in many individuals.
In the United States alone, approximately 1.2 million people live with chronic hepatitis B, with significant mortality rates attributed to liver diseases related to this infection. The disease can manifest in acute or chronic stages, with symptoms such as fever, abdominal pain, jaundice, and joint pain varying in severity and duration. While some individuals can clear the virus, others may require long-term antiviral treatment to manage chronic infections and prevent severe complications, including liver failure and cirrhosis. Vaccination against hepatitis B is a critical preventive measure, especially recommended for high-risk groups. Overall, hepadnaviruses represent a significant challenge to global health, necessitating ongoing research and public health initiatives.
Hepadnaviridiae
- TRANSMISSION ROUTE: Direct contact
Definition
The hepadnaviruses are a family of viruses that causes infection of the hepatocytes, often resulting life-threatening conditions such as liver cancer in humans and animals. Hepadnavirus is specifically responsible for hepatitis B (hepatitis A, C, and D are caused by other viruses), which is a significant public health problem.
Natural Habitat and Features
The hepadnavirus is made up of two very small genomes of partially double-stranded and partially single-stranded circular DNA (deoxyribonucleic acid), one being positive-sense and the other negative-sense. The virions are small and spherical and enveloped, and they are 40 to 48 nanometers (nm) in diameter. Reverse transcriptase is used for virus replication in the host during infection.
Most strains of the virus replicate only in specific hosts, making in vitro laboratory experiments extremely difficult. However, the duck hepatitis virus, which shares several fundamental features with human hepatitis B, serves as an excellent in vitro and in vivo study model.
Pathogenicity and Clinical Significance
According to the US Department of Health and Human Services, between 880,000 and 1.89 million people have chronic hepatitis B in the United States, and many do not know they are infected. It is most commonly spread through sexual contact and is up to one hundred times more infectious than human immunodeficiency virus (HIV), according to the Hepatitis B Foundation. The Centers for Disease Control and Prevention (CDC) notes that infants with a hepatitis B infection have about a 90 percent chance of developing a chronic hepatitis B infection as adults. Each year, about 820,000 people die from hepatitis B-related liver disease.
After a person is first infected, he or she can develop what is known as acute stage hepatitis B, which can range from a severe infection to a mild illness with few or no symptoms. Acute hepatitis usually occurs the first six months after exposure to the virus. Many people are able to fight the infection, clear the virus from their body, and never show signs of hepatitis infection. However, if the infection remains in the body, the virus progresses to the chronic stage, in which it cannot be cleared from the body. This stage requires treatment and management to prevent the potential life-threatening complications of the disease, including liver failure, cirrhosis, and liver cancer.
Symptoms for both acute and chronic hepatitis are similar, although in some people, chronic hepatitis symptoms can take several years or even decades to appear. Acute hepatitis will usually appear forty days to six months after exposure, except in children, who are usually asymptomatic. Some of the most common symptoms are fever, arthritis, abdominal pain, thrombocytopenia, dark urine, joint pain, gray stools, and jaundice.
Drug Susceptibility
Several options are available for drug treatment for HBV; however, the drugs should be used in concert with the unique biochemistry of HBV. As the acute stage of the virus progresses into several stages, drugs are either very effective at reducing the viral load, completely ineffective, or harmful to the patient. A chronic patient may remain on antiviral therapy throughout his or her life.
Careful monitoring of both acute and chronic patients should occur during drug therapy. Patients without other medical comorbidities have the best treatment success, but even patients with common comorbidities such as HBV and HIV can keep both viruses under control and lead healthy lives with careful monitoring of antiviral therapy.
Most therapies involve a combination of interferon and several antivirals. Interferon is the preferred drug for younger patients. There are many antivirals in use; however, resistance is an ongoing issue. New drugs that stimulate B cell and T cell responses to achieve suppression of the viral replication have been studied as options to the conventionally used drugs.
Safe hepatitis B vaccines are available for persons of all ages and are recommended as part of an infant’s vaccine schedule. It is especially important also to immunize high-risk groups, including intravenous drug users, infants born to women with HBV, health care workers who come in contact with blood as part of the job, persons who engage in unprotected sex with multiple partners, persons from countries where HBV is endemic, persons on dialysis, and inmates in jails and prisons. Persons with kidney or liver disease also are at risk.
Bibliography
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"Hepatitis B." American Liver Foundation, 17 Apr. 2023, liverfoundation.org/liver-diseases/viral-hepatitis/hepatitis-b/. Accessed 3 Feb. 2025.
“Hepatitis B.” In Red Book: 2009 Report of the Committee on Infectious Diseases, edited by Larry K. Pickering et al. 28th ed. Elk Grove Village, Ill.: American Academy of Pediatrics, 2009.
"Hepatitis B Basic Information." US Department of Health and Human Services, 31 Mar. 2023, www.hhs.gov/hepatitis/learn-about-viral-hepatitis/hepatitis-b-basics/index.html. Accessed 3 Feb. 2025.
"Hepatitis B Facts and Figures." Hepatitis B Foundation, www.hepb.org/what-is-hepatitis-b/what-is-hepb/facts-and-figures/. Accessed 4 Feb. 2025.
Jafri, Syed-Mohammed R., and Anna Suk-Fong Lok. “Antiviral Therapy for Chronic Hepatitis B.” Clinical Liver Disease 14 (2010): 425-438.
Roggendorf, M., D. Yang, and M. Lu. “The Woodchuck: A Model for Therapeutic Vaccination Against Hepadnaviral Infection.” Pathologie Biologie 58 (2010): 308-314.