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HBV infection among the Nicobarese

 
     
 

Studies were carried out to understand the epidemiology of HBV infection and to identify important modes of transmission of the infection among the Nicobarese tribe of Car Nicobar Island. All the permanent residents (65.9% of the total population of the village) aged 45 years or less residing in 27 tuhets of one of the villages of Car Nicobar island were included in the study. Tuhet is a joint family of Nicobarese and is the unit of all social life among them. Venous/capillary blood samples were collected from these subjects and tested for different markers of HBV infection. Information on possible risk factors were also collected from these subjects.

 
 

Fig 1. Prevalence of various markers of hepatitis B infection among Nicobarese

 

 

Fig 2. Age-specific prevalence of various markers of hepatitis B infection among Nicobarese

  
     
 

The serological analysis of the samples showed a high prevalence of chronic carrier state (Fig. 1). A comparable proportion of the population was anti-HBs positive and almost half of the HBsAg and anti-HBs negative individuals were anti-HBc positive. The age-wise prevalence of these markers is shown in Fig. 2.  Age, past history of hospital admission, intramuscular injections and number of carriers in the tuhet were found to be significantly associated with exposure to Hepatitis B virus (table 1). Horizontal transmission through close contact with carriers appears to be more important mode of transmission of HBV than vertical route in this community. Besides, use of unsafe injections represented an independent risk factor for acquiring HBV infection in this population

  
 
Variable B SE OR (95% CI) P
Age (years)
0-5 1.00 (ref. category)
6-14 1.45 0.38 4.28 (2.02-9.03) 0.0000
15-24 2.94 0.41 18.91 (8.54-41.89) 0.0000
25-34 3.39 0.43 29.63 (12.71-69.05) 0.0000
35-45 3.24 0.45 25.63 (10.69-61.42) 0.0000
Sex (Male) 0.16 0.24 1.18 (0.73-1.90) 0.506
No. of carriers in tuhet
1-2 1.00 (ref. category)
3-5 1.44 0.34 4.22 (2.17-8.20) 0.000
6-10 1.61 0.33 5.01(2.62-9.60) 0.000
>10 1.87 0.39 6.50 (3.04-13.91) 0.000
History of hospitalization 0.71 0.25 2.04 (1.26-3.30) 0.004
History of IM injections 0.56 0.24 1.75 (1.09-2.80) 0.021
History of IV medication 0.19 0.29 1.21(0.68-2.14) 0.514
History of blood transfusion -0.39 0.51 0.68 (0.25-1.84) 0.449
History of jaundice in family 0.23 0.56 1.26 (0.42-3.74) 0.681
History of ear/nose piercing -0.27 0.27 0.76 (0.45-1.29) 0.309
 

Table 1. Results of multiple logistic regression with hepatitis B exposure as dependant variable and various personal, social and behavioural factors as independent variables

  

HBV infection among the Jarawas

Jarawas, one of the four Negrito tribes of Andaman islands were living in isolation since several centuries. Since last 4-5 years, they have started mixing with non-Jarawa people, shedding their hostility. Several outbreaks of various infectious diseases have been reported since their coming in contact with outsiders.

A Jarawa tribesman fishing at beach

Blood samples collected from 64 Jarawas during one such outbreak were screened for different serological markers of HBV infection. 65.6% of the samples were positive for HBsAg, whereas 68.8% of the samples had antibodies against hepatitis B core antigen. 40.1% of the HBsAg positive individuals were also positive for HBeAg. Overall, 75% of the Jarawas  screened had exposure to HBV. The HBV exposure is very high in children with 86.4% of them positive for HBsAg and/or anti-HBc.

These findings indicate a very high endemicity of HBV infection among the Jarawas. It is least likely that Jarawas have acquired this infection after coming in contact with outside world, as they were not exposed to any known modes of transmission like parenteral treatment etc. during this period.

 Such a high carrier rate in this tribe is a matter of concern and warrants immediate control measures. Vaccinating the susceptible individuals with hepatitis-B vaccine appears to be the only solution for preventing further spread of the virus in the community. Treating the chronic carriers with anti-viral therapy also seems worth considering in this population.

Hepatitis B infection among the Karen

Besides the six tribes, these islands are also home to Karen, a group of Indo-Chinese tribe living principally in Burma, were brought to these islands as laborers by the British Government in 1926. Karens are presently rehabilitated in six villages in Mayabunder tehsil, North Andaman and have a population of about 2000. The Centre carried out a sero-survey to assess the problem of hepatitis-B among them.

Karen tribe of Mayabunder, Andaman

The findings of the serological analysis showed that 11.6% of the Karen were positive for HBsAg whereas 34.2% of the individuals had antibodies against HBsAg. Antibodies against hepatitis B core antigen were detected in  4.9% of the individuals. The prevalence of HBsAg, anti-HBs and overall exposure to HBV were found increase linearly with age.