Hepatitis B virus transmission in West Africa: a role for tropical ulcer?

Transmission of hepatitis B virus infection in Gambian families revealed by phylogenetic analysis

BACKGROUND/AIMS

Transmission of hepatitis B virus (HBV) in Africa occurs horizontally, with most people becoming infected between the ages of 1 and 5 years. The index cases in such events have been assumed to come from within the family unit or from sources outside the immediate family, such as other families or inhabitants of the same compound or village. Here, we define these routes of transmission by phylogenetic tree analysis of sequences from the entire pre-core/core region of the virus, in Gambian chronic carriers.

METHODS

Amplification by polymerase chain reaction of serum extracted HBV-DNA was followed by direct sequencing of the target region. Following editing and alignment of these sequences, phylogenetic tree analysis was performed using the neighbour-joining and maximum-likelihood methods.

RESULTS

Despite the overall conserved nature of the sequences of the pre-core/core region from 142 chronic carriers, distinct clusters were easily defined at the family and village level, but not on a wider geographical separation.

CONCLUSIONS

Phylogenetic tree analysis of sequences obtained from family members provided strong evidence of intrafamilial transmission of HBV in at least two-thirds of the families studied from Gambia.

How AIDS forces reappraisal of hepatitis B virus control in sub-Saharan Africa

For developing countries the cost-benefit of vaccination in the control of hepatitis B virus (HBV) infection is great since the acute infection is generally subclinical and the benefit is the prevention of small numbers of cases of cirrhosis and hepatocellular carcinoma. Since the pattern of HBV infection in Africa is such that, compared with south-east Asia, infection occurs later in childhood and spread is horizontal rather than vertical, investigation of the method of spread of HBV may result in a means of control other than by vaccination. In the meantime, because of the overlap in the means by which HBV and human immunodeficiency virus (HIV) are spread, it could be worthwhile taking advantage of existing AIDS prevention programmes to educate people about how to avoid both HBV and HIV infections.

Risk factors for transmission of hepatitis B virus to Gambian children

Risk factors for hepatitis B virus transmission were examined in 973 Gambian children aged 6 months to 5 years. 33% had evidence of infection with hepatitis B virus and a third of these were carriers. A significant association was found between infection and tropical ulcer scars, and between e antigenaemia and the presence of bedbugs in each child's bed. There was no association between infection and traditional scarring, circumcision, or injections. Skin disease and arthropods are the two most likely modes of transmission of hepatitis B virus between children in West Africa.

The hazard of infection from the shared communion cup

Interest and concern that the shared communion cup may act as a vehicle for indirectly transmitting infectious disease was reawakened when the human immunodeficiency virus (HIV) was detected in the saliva of infected persons. Bacteriological experiments have shown that the occasional transmission of micro-organisms is unaffected by the alcoholic content of the wine, the constituent material of the cup or the practice of partially rotating it, but is appreciably reduced when a cloth is used to wipe the lip of the cup between communicants. Nevertheless, transmission does not necessarily imply inoculation or infection. Consideration of the epidemiology of micro-organisms that may be transmitted via saliva, particularly the herpes group of viruses, suggests that indirect transmission of infection is rare and in most instances a much greater opportunity exists for direct transmission by other means. There is substantial evidence that neither infection with hepatitis B virus nor HIV can be transmitted directly via saliva so that indirect transmission via inanimate objects is even less likely. No episode of disease attributable to the shared communion cup has ever been reported. Currently available data do not provide any support for suggesting that the practice of sharing a common communion cup should be abandoned because it might spread infection.

Hepatitis B infection in households of acute cases

Seroepidemiological studies conducted in 369 household contacts of 80 acute cases of hepatitis B in Singapore showed that asymptomatic chronic carriers of hepatitis B surface antigen (HBs Ag) are the main source of acute hepatitis B infection. The HBs Ag prevalence rate in asymptomatic household members was 20% compared with a 6% prevalence for the general population. The majority of the household carriers (60%) were highly infectious with positive hepatitis e antigen (HBe Ag). The overall prevalence of HBV infection (with at least one HBV marker) of the household contacts was 40.7%. Spouses and parents of acute cases had a significantly higher prevalence of HBV infection than other members of the families. HBV prevalence rate showed no association with the household size. Factors associated with the risk of transmission of HBV infection included sharing of various personal and household articles, such as toothbrush, towel, handkerchief, clothing, razor, comb, bed and bedding. Sleeping in the same bedroom, eating together at meals, and sharing of eating and drinking utensils were not associated with an increased risk of transmission of infection. Follow-up studies six months later showed that 30% of the acute cases became chronic HBs Ag carriers (with 46% HBe Ag positive), thus providing an additional source of infection in the families, while 8% of the susceptible household members acquired asymptomatic HBV infection. Health education on the prevention of HBV transmission in the homes of acute cases should be based on sound epidemiological information. Household contacts of acute cases of hepatitis B should be routinely screened and the susceptible vaccinated against the disease as soon as possible.