Hepatitis B: A Concise Overview of Its Characteristics and Pathogenesis, Specifically Its Etiology

Abstract 

Hepatitis B is a viral infection that adversely impacts the liver – the body’s largest internal organ –  by causing inflammation and hence, subsequent damage to the hepatocytes (liver cells). The primary method of transmission is through infected blood and bodily fluids such as saliva. A vaccine for hepatitis B is the most effective way to prevent infection. This article aims to provide an explanation of the etiology and transmission routes; this includes pathogen transmission through sexual contact, needle sharing by intravenous drug-users, blood transfusions and from a mother to her child. Furthermore, it intends to offer an overview on its general characteristics.

Introduction 

Affecting millions internationally and having claimed many lives as a result of developing into acute infections and causing chronic sequelae, the five main hepatitis viruses have solidified themselves as a substantial global health concern [1]. They belong to several different families - the major ones being: Picornaviridae which Hepatitis A virus (HAV) belongs to, Hepadnaviridae which Hepatitis B virus (HBV) belongs to, Flaviviridae being the family of the Hepatitis C virus (HCV),  and the Hepatitis E virus (HEV) emerging from the Hepeviridae family. Hepatitis D virus (HDV), however, is a subviral satellite of HBV and is currently unassigned to a family[2].

Characteristics 

The hepadnavirus group includes double-stranded DNA viruses which replicate remarkably by reverse transcription;  a member of this category of pathogenic microorganisms is HBV. It is endemic in the human population overall with 350-400 million patients suffering from chronic hepatitis B, and is hyperendemic in various parts of the world, especially the East[1]. Hyperendemic refers to a disease that is continually prevalent at a greater level of occurrence in a particular geographical area or population[4]. These regions are concentrated in Asia and include the Indian subcontinent, sub-Saharan Africa and central Asia. The populations consist of the Asian Pacific Islanders, Alaskan Eskimos and Australian aborigines [3,5]. 

Patients infected with HBV are generally asymptomatic, some even traversing the entire infection stage without any clinical manifestation. In these instances, meticulous history taken by doctors and medical professionals is crucial to reach the correct diagnosis. However, some patients do exhibit symptoms which encompass but are not limited to fatigue, abdominal pain, nausea and anorexia. Notably, patients with acute HBV infection have  syndrome much like serum sickness during which they have a fever, skin rashes, arthritis and arthralgia [3]. 

Pathogenesis 

Pathogenesis encompasses the study of how a pathogen enters a host, establishes an infection and causes the development of a disease. In other words, it is the process by which a condition arises and consequently proceeds, from the interaction of the host with the pathogen to the biological and molecular processes carried out as the infectious agent engages with the body cells . Pathogenesis also encompasses how the infection progresses and whether it ultimately leads to recovery, death or chronic illness[6]. This article aims to summarize its etiology

Etiology and Transmission 

Etiology refers to the cause or origin of disease or infection [8]. HBV has multiple routes of transmission, one being via transfusions of unscreened blood. HBV is bloodborne. If blood which is contaminated with the pathogenic microorganism, and has not been effectively screened to ensure that the absence of the virus is administered to a healthy individual, transmission occurs, and HBV begins to replicate in the body.

 Furthermore, another etiological factor is sexual contact. HBV infection as a sexually transmitted infection (STI) is extensively explained. An STI is defined as an infection resulting from the transmission of pathogens by sexual contact which comprises any genital or anal contact with another person’s mouth, anus or genitals[7,9]. It is common among heterosexual individuals who have multiple sex partners or contact with sex workers in the industry. Infection is also frequent amongst men who have sex with men (MSM) as anal sex is more injurious than vaginal intercourse which leads to a higher risk of exposure to blood carrying HBV[7]. 

It can also be transmitted from a mother to her child. Even if the mother’s body performs successful immunoprophylaxis by administering the HBV antibodies to the child, breakthrough infection is still possible. Mother to infant transmission of HBV commonly occurs in the perinatal period. However, it is important to note that postnatal maternal transmission and intrauterine infection can also occur. It is observed that mothers that are positive for the e antigen (HBeAg), and with a high viral load, meaning that the virus is present and replicating to make more copies of itself in the bodies of the aforementioned, are more likely to transmit the pathogen[10].

Moreover, HBV can spread through sharing and use of contaminated needles by intravenous drug users as well as in other environments. As mentioned before, HBV is a bloodborne pathogen; the virus is present in the blood and bodily fluids of the infected. If a needle contaminated with these fluids is able to pierce through the skin and into the flesh of an uninfected individual, the virus thus enters into their body and causes infection. This has routinely occured over the years when needles are shared between drug users. Additionally, accidental needlestick injuries occurring with healthcare workers dealing with HBV patients is a common route of transmission as well. Besides those two instances, transmission through contaminated needles is common in tattooing, piercing and acupuncture facilities if the appropriate sterilization procedures are not carried out[11]. 

Conclusion

Hepatitis B is a critical viral infection impacting the liver where repeated inflammation can lead to the development of chronic disease, cirrhosis, liver cancer and even death. Presently, there is no definitive cure for chronic hepatitis B, but administration of antiviral medication and regular surveillance for any sign of liver cancer can lessen the morbidity and mortality.

Resources

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8. https://www.cancer.gov/publications/dictionaries/cancer-terms/def/etiology 

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