Serology of HBV and its clinical implications among Nigerian subjects

Hepatitis has diverse causes and among those of viral origin, hepatitis B virus (HBV) infection continues to be a significant cause of high morbidity and mortality globally, particularly in the tropics. The infection has protean clinical presentation and is associated with diverse serological markers of varying significance and consequence.[1,2,3] Both acute and chronic forms of the infection may be symptomatic or asymptomatic and may be discovered incidentally only through laboratory assay of the viral markers. These markers can present singly or in different combinations depending on the natural history of the infection.2 Similarly, there is varied or incomplete expression of the serological markers depending on the types of HBV genotype prevalent in any community as well as the type of the variants / mutants of the virus.[4,5,6]

Early in the course of HBV infection, hepatitis B surface antigen (HBsAg) is present in the serum and disappears with the production of antibodies to HBsAg (anti-HBs) and recovery from the disease. In the interregnum of these two markers, others such as hepatitis Be antigen (HBeAg), antibodies to HBeAg (anti-HBe) and hepatitis B core antigen (anti-HBc) may also be detected in the sera of sufferers.[7]

Each serological marker of HBV infection has its clinical importance (Table 1), thus determination of these markers will unveil the serological pattern (Table 2) prevalent in the infected subjects.[5,7,8,9,10,11,12,13] This may assist in clinico-serological diagnosis of the infection as well in the determination of its line and course of management.[7,14]

Methods

The study was conducted after ethical clearance was obtained from the UI-UCH Ethical Review Board.

The study involved seventy four healthy Nigerian adults consisting of 60 non-immunised (NIM) and 14 immunedised (IM) subjects against HBV infection from their relevant biodata.. The sera of their blood specimens were assayed for hepatitis B surface antigen (HBsAg), hepatitis Be antigen (HBeAg), antibodies to HBeAg (anti-HBe), hepatitis B core antigen (anti- HBc), HBsAg (anti-HBs) and hepatitis C virus (anti-HCV) using 3^rd generation ELISA kits at the Department of Virology, University College Hospital, Ibadan.

The data were analysed statistically and a p- value of < 0.05 was considered significant.

Results

The subjects were 21-70 years old with male:female ratio of 26:11. The mean + standard deviation of the ages of the IM were 45+7 and 33+8 years for the male and female subjects, respectively while those for the respective genders for the NIM were 33.6+4.5 and 32+4years. There were no differences in the ages of the respective genders for IM and NIM.

The detection rates of each serological marker for HBV and HCV were as shown in Table 3. There was no difference between the detection rates of HBsAg and the duo of HBsAg and anti-HBc in the subjects. However, the detection rate of HBeAg was greater than that of anti-HBe, p< 0.005 but the detection rates of both HBsAg and anti-HBs were similar.

Among the subjects seropositive for HBsAg, 40% and 8% also had HBeAg and anti-Hbe, respectively. The serodetection rates of HBsAg, HBeAg, anti-HBe and anti-HBc were higher among the NIM (p<0.05 each) compared to the IM while the rates of detection of anti-HBs were similar in both groups. Only serodetection rates of anti-HBe and anti-HBc were significantly greater among the male subjects compared to the female subjects.

Serum anti-HCV was detected in only 10.8%, a value less than that of HBV (39.2%, measured by HBsAg or HBsAg +anti- HBc) among the subjects, p<0.05 and is also unrelated to either the gender status or the HBV immuned standing of the subjects.

(Table 4) The subjects had serological diagnoses suggestive of early non-infective phase (HBsAg+), infectivity (HBeAg+ + anti-HBe+), carrier state (HBsAg+ and anti-HBc+) and no exposure to HBV infection in 23%, 13.5%, 2.7% and 60.8%, respectively while 35.1% of all subjects had possible exposure to two HBV serotypes ( HBsAg and anti-HBs seropositive) out of which 23% were anti-HBc seronegative. In addition, 13.5% of all subjects were infectious for HBV with 10.8% and 2.7% accounting for high (HBeAg seropositive) and intermediate (both HBeAg and anti-HBe seropositive) infectivity, respectively. Only 14.3% of the IM had evidence of HBV infection compared to 45% of the NIM group, p<0.05.

Discussion

Hepatitis B virus infection has varied clinical presentation and serological marker expression . The detection of some of its markers in varied proportions in our subjects is a pointer to the inscrutable nature of the infection among Nigerians.

The high detection rate of HBsAg among our subjects confirms previous reports among Nigerians especially among subjects in hospital settings.[16]

Furthermore, the absence of any difference between the rates of HbsAg and the duo of HBsAg and anti-HBc in our subjects does not obviate the isolated occurrence of either HBsAg or anti-HBc, rather it confirms it with many of the subjects (27%, having HBsAg without anti-HBc), being at the early phase of the infection. This shows the natural course of HBV infection among our subjects with anti-HBc appearing after HBsAg.[7]

However, the higher rate of HBeAg compared to that of anti-HBe among the subjects studied and the high rate of HBeAg among HBsAg seropositive subjects showed the high infectivity of HBV infection among Nigerians, a characteristic of endemic areas such as Nigeria.[17]

The presence of similar high rates of anti-HBs and HBsAg among the subjects presents a major problem about HBV infection in Nigeria. This is because it indicates that the former offers no protection against new HBV infection or that the subjects are being exposed to more than one type of HBV serotype and/or genotype, prevalent in Nigeria or in the neighboring countries of the West African Community.[5,10] This calls for efforts at local development of vaccine against the different HBV serotypes and genotypes prevalent in the region.

In contrast, subjects immunised against HBV infection had lower rates of HBsAg and were without HBeAg, anti-HBe and anti-HBc compared to the non-immunised subjects. These show the protective value of immunisation against HBV infection.[7] Furthermore, the similarity in the rates of anti-HBs among both IM and NIM may be secondary to the presence of natural immunity among NIM (12.2%) and waning of the protective level of anti-HBs among IM. This shows the importance of routine screening for anti-HBs in order to determine its protective level in each IM subject with subsequent administration of booster doses of vaccine to those having un-protective values.[7]

The higher rates of anti-HBe and anti-HBc among our male subjects, confirmed the earlier report of the higher occurrence of HBV infection as well as greater infectivity in the male population and this might be a consequence of better handling of the infection by the female gender.[18]

Concerning the different patterns of HBVserology observed among the subjects, the study showed that a very high proportion of Nigeria is still unexposed to the virus despite the presence of various phases of the infection among Nigerians. This calls for urgent vaccination of all Nigerians against the virus. It is unremarkable that the subjects exposed to HBV infection are asymptomatic because a majority of them (58.6%) are in the early non-infective phase, 34.5% are infective while only 6.9% are carriers of the infection. Our results are the first of its kind among Nigerians. This unveils how rife the infection is, in the community and portends a silent devastating disease, ravaging the population indiscernibly as shown by the level of infectivity of the virus in the community[10]. Hence, there is need for the provision of proper serodiagnosis of the infection including molecular characterisation of the HBV genotype.[19] This is pivotal to proper management of subjects with the infection especially in monitoring them through the pre-, intra- and post-drug treatment phases. Hence, it would help to determine when there is eradication of the organism and curtail its protracting and unfathomable sequelae.

The presence of subjects having a combination of anti- HBs and HBsAg especially among those with early phase of the course of HBV infection is not uncommon and it is likely secondary to the occurrence of anti-HBs escape HBV mutants among Nigerians as reported among population in France[12] with the anti-HBs in the subjects directed to HBsAg subtypes other than the coexisting one.[13]

The carrier rate of HBV infection among our subjects is lower than in other endemic areas of Africa, this may be because the present study is a point prevalence study rather than a follow up study of infected subjects.[7]

The observation of a lower rate of HCV compared with that of HBV infection follows a previous report[15] while the lack of its relationship with any pattern of HBV’s serology may be related to different characteristic behaviour of each virus. The presence of HCV co-infection with HBV is significant as the former may impair humoral reponse to the latter.[20]

In conclusion, various proportions of the different serological markers of HBV occur among healthy Nigerian subjects especially in the male population. Although, Nigerian subjects immunised against HBV infection are protected against the virus, there is need for booster vaccination to sustain the protective level of immunity. About 60% of Nigerians are unexposed to HBV infection while amongst the exposed subjects, about 60% of them are in the early non-infective stage of the course of the infection, another third actively spreading the infection in the community and only about 7% are carriers of the infection. Multiple HBV serotypes and/or genotypes seem to be prevalent among Nigerians. Although, HCV infection is uncommon compared to HBV infection, it has no predisposition to any pattern of HBV serology. A study involving a larger population size will be needed to corroborate the above findings.

Acknowledgement

We are very grateful to GlaxoSmithKline Pharmaceuticals West Africa for the provision of the assay kits.

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