Authored by Berinyuy B Eustace*
Abstract
Hepatitis B virus is among the common viral infectious agents of public health concern. An estimated two billion people are infected worldwide with approximately 350 million others suffering the chronic form of the disease. Nigeria, a tropical country, has been documented as highly endemic for HBV infection and about 75% of its population is likely to have been exposed to the virus at one time or the other in their lives. Currently about 18 million Nigerians are infected. A prevalence rate of 4.3 % to 23.3% have been reported from different part of the country This paper presented up-date prevalence of hepatitis B virus from different part of Nigeria. The structure, mode of transmission, replication, pathogenesis, diagnosis, prevention and possible treatment of the disease were also mentioned.
Keywords: Hepatitis B; Prevalence; Nigeria; Infections; Blood
Introduction
Hepatitis B virus is among the common viral infectious agents of public health importance globally. An estimated two billion people are infected worldwide with approximately 350 million others suffering the chronic form of the disease [1,2] In Africa, more than 50 million people are chronically infected, with mortality risk of about 25%. The carrier rates of the virus in Sub-Sahara Africa range from 9% - 20% [3]. Hepatitis B virus (HBV) infection is a serious health problem worldwide. Once chronic infection is established, HBV may persist in the liver for lifetime [4], which not only causes severe HBV-related sequalae such as cirrhosis and hepatocellular carcinoma but also constitutes the reservoir of the virus [5].
The spectrum of the symptoms of HBV disease varies from subclinical hepatitis to icteric, hyperacute, acute and subacute hepatitis during the primo-infection phase and from an asymptomatic carrier state to chronic hepatic cirrhosis and hepatocellular carcinoma during the chronic phase. In the acute phase, the incubation period is 1-6 months [6]. Anicteric hepatitis is a predominant form of expression for this disease, at this phase most of the patients are asymptomatic. Patients with anicteric hepatitis have a greater tendency to develop chronic hepatitis. Icteric Hepatitis B is associated with a prodromal period, during which a serum sickness-like syndrome can occur [7].
The predominant routes of transmission is commonly through blood transfusion, blood products, body fluids (urine, semen, sweat, saliva, and tears), use of contaminated needles, vertical transmission (mother to child through infected birth canal), and sexual contact [8]. Neonates born of chronically infected mothers have a 70–90% risk of the infection progressing to a chronic phase [9]. The demand for safe blood or blood products in life-saving interventions is critical to avoiding non curable infectious diseases [3]. Blood transfusions carry the risk of transfusion-transmitted infections such as hepatitis B. In order to measure their severity, the World Health Organization has recommended a pre-transfusion blood test. The residual risk of infection from HBV is higher than that of hepatitis C virus (HCV) in non-endemic countries [10].
Nigeria, a tropical country, has been documented as highly endemic for HBV infection and about 75% of its population is likely to have been exposed to the virus at one time or the other in their lives [11]. Currently about 18 million Nigerians are infected [12]. A prevalence rate of 4.3 % was reported from Port Harcourt [13], 5.7% from Ilorin [14], 11.6% from Maiduguri [15] and 8.3% from Zaria [16] A seroprevalence of 23.3% was reported among patients attending all clinics at the Aminu Kano Teaching Hospital (AKTH) [17].
Historical Background of HBV
The hepatitis B virus was discovered in 1965 when Blumberg and co-workers found the hepatitis B surface antigen which was originally called the Australia antigen because it was found in serum from an Australian patient [18]. Dr Baruch Samuel Blumberg was awarded the 1976 Noble Prize in Physiology or Medicine for this discovery. The virus was fully described in the 1970s [19]. In recent times, the rapid and continuous discoveries of the viral disease around the whole world have improved our understanding of the complexity of this unusual virus. Although there has not been any substantial decrease in the overall prevalence of HBV, there is the hope that the next generation will see a decline in both the worldwide carrier rate and the incidence of new HBV infections if current HBV vaccinations are intensified [20].
Transmission
The HBI can be transmitted by the same modes as with the human immunodeficiency virus (HIV), even though the HBV is hardier and 50-100 times more infectious than the HIV (WHO, 2008). Unlike HIV, the virus can survive outside the body for at least 7 days. During that time, the virus can still cause infection if it enters into the body of a person who is not infected. Transmission of hepatitis B virus results from exposure to infectious blood or body fluids. Possible modes of transmission include but are not limited to unprotected sexual blood transfusions, re-use of contaminated needles and syringes, and vertical transmission from mother to child during childbirth. Without intervention, a mother who is positive for HBsAg confers a 20% risk of passing the infection to her offspring at the time of birth (WHO, 2008).
This risk is as high as 90% if the mother is also positive for HBeAg. The HBV infection can be transmitted between family members within households, possibly by contact of non-intact skin or mucous membrane with secretions or saliva containing HBV (Petersen et al., 1976). However, at least 30% of reported hepatitis B among adults cannot be associated with an identifiable risk factor (Shapiro, 1993). In many developed countries (e.g. those in Western Europe and North America), patterns of transmission are different from those mentioned above. Today, most infections in these countries are transmitted during young adulthood by sexual activity and injecting drug use. HBV is a major infectious occupational hazard of health workers (WHO, 2008). HBV is not spread by contaminated food or water and cannot be spread casually in the workplace. The virus incubation period is 90 days on average but can vary from about 30 to 180 days (AASLD, 2007). HBV may be detected 30 to 60 days after infection and persist for widely variable periods of time.
Stages of HBV Infection
Remarkable progress has been made in the understanding of the three (3) main natural stages of the HBV infection in hosts: acute infection, chronic asymptomatic and chronic symptomatic stages (AASLD, 2007). However, not all HBV-infected patients go through all the three stages. The risk to develop liver–related complications, such as cirrhosis and hepatocellular carcinomas increases as patient progresses from acute to chronic stage of the infection. Indeed, most HBV infections end up at the acute stage (~ 90%) with a few progressing on to the chronic stage.
Acute HBV infection
This is the initial stage of the infection and every HBV- infected patient goes through this, even though not all patients transit beyond this stage. Early phases of this stage of the infection are characterized serologically by the presence of HBsAg, high serum HBV DNA, HBeAg, and normal level of serum aminotransferase level (ALT), and minimal or insignificant inflammation on liver biopsy [21]. A later phase, also called immunity phase, is marked by increased serum titres of anti-HBsAg IgG (HBsAb), anti-HBcAg IgG, lowered or disappearance of HBsAg and HBV DNA, normal liver histology. This is true for those who recover fully from the infection after attaining full and permanent immunity through exposure. The duration of either phase differs among patients but generally lasts between 5-8 months (AASLD, 2007). However, those patients who fail to mobilize adequate immune response factors to combat the infection end up with the fate of living with the disease their entire lifetime. In this case, it is said the disease has become chronic. The physical signs and symptoms, such as jaundice, fever, dark-urine formation, nausea, among others, would occur, even though they will last shortly after which they get resolved following recovery. Generally, transition from the acute stage to the chronic stage depends on several factors including age, gender, viral genotype, and host immune competence.
Chronic HBV infection
This occurs as a progression of the early phase of the acute HBV infection due to the host‘s failure to mount the necessary immune stimulus to ensure total viral clearance and consequent resolution of the disease. It is serologically marked by relative rise in serum anti- HBcAg IgG, disappearance or lower titres of anti-HBsAg IgG, and either normal or significant liver damage as shown by ultrasonography (WHO, 2008). Also, this stage of the disease may be characterized by normal or elevated serum aminotransferase levels (aspartate amino transferase (AST) and alanine amino transferase (ALT)) and other markers of hepatic integrity (AASL, 2007).
The serological presence of HBeAg is real in all stages of the disease. The presence of this antigen together with elevated viral load (HBV DNA > 10 3 copies/ml) and higher ALT (> 60 IU/l) is a strong indication of viral activity, replication, and infectivity (WHO, 2008). Patients with such manifestations are put on retroviral. A key event in the natural history of HBeAg – positive CHB patients is HBeAg seroconversion (Sharma et al., 2005). It is believed that seroconversion of HBeAg to HBeAb is accompanied with cessation of HBV replication and remission of liver disease. Several studies have shown that seroconversion with a marked reduction in HBV replication is associated with biochemical and histological remission of inflammatory activity in the majority of patients [22].
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