Globally, over 250 million people are chronically infected with HBV. 15-20 million (6-8%) of these patients are estimated to be infected with HDV. Since HDV is dependent on HBV for infection, its mode of transmission and geographical distribution is similar to HBV. HDV is endemic in Mediterranean countries, the Middle East, Mongolia, Pakistan, Central Africa, East Pacific Islands (Kiribati and Nauru), and the northern parts of South America.
In developed countries, HBV vaccination campaigns have made significant gains in the past 20 years and this has led to a concurrent decrease in HBV and HDV infections. In these countries, HDV is now mainly found in HBsAg-positive (HBV infected) intravenous drug users and in growing immigrant populations. Overall, the prevalence seems to have stabilised in many European nations where approximately 8-10% of patients are infected with HDV.
Despite the overlap with HBV, HDV prevalence does show some unique patterns depending on host susceptibility, virulence, and local social behaviors. For example, HDV prevalence remains low in Mainland China and the Far East despite the established prevalence of HBV.
The various genotypes of the HDV virus have distinct geographical distributions. HDV 1 has a global prevalence while HDV 2 and 4 are found in Siberia; South and East Asia. HDV 3 is present in the Amazon basin and HDV 5-8 are present in sub-Saharan Africa.
Author: Minaam Abbas