title: How hepatitis D virus can hinder the control of hepatitis B virus.
abstract: BACKGROUND
  Hepatitis D (or hepatitis delta) virus is a defective virus that relies on hepatitis B virus (HBV) for transmission; infection with hepatitis D can occur only as coinfection with HBV or superinfection of an existing HBV infection. Because of the bond between the two viruses, control measures for HBV may have also affected the spread of hepatitis D, as evidenced by the decline of hepatitis D in recent years. Since the presence of hepatitis D is associated with suppressed HBV replication and possibly infectivity, it is reasonable to speculate that hepatitis D may facilitate the control of HBV.
  
  
  RESULTS
  We introduced a mathematical model for the transmission of HBV and hepatitis D, where individuals with dual HBV and hepatitis D infection transmit both viruses. We calculated the reproduction numbers of single HBV infections and dual HBV and hepatitis D infections and examined the endemic prevalences of the two viruses. The results show that hepatitis D virus modulates not only the severity of the HBV epidemic, but also the impact of interventions for HBV. Surprisingly we find that the presence of hepatitis D virus may hamper the eradication of HBV. Interventions that aim to reduce the basic reproduction number of HBV below one may not be sufficient to eradicate the virus, as control of HBV depends also on the reproduction numbers of dual infections.
  
  
  CONCLUSIONS
  For populations where hepatitis D is endemic, plans for control programs ignoring the presence of hepatitis D may underestimate the HBV epidemic and produce overoptimistic results. The current HBV surveillance should be augmented with monitoring of hepatitis D, in order to improve accuracy of the monitoring and the efficacy of control measures.
authors.affiliation: Centre for Infectious Diseases Control, National Institute of Public Health and the Environment, Bilthoven, The Netherlands. maria.xiridou@rivm.nl
authors.forename: Maria
authors.initials: M
authors.lastname: Xiridou
authors.forename: Barbara
authors.initials: B
authors.lastname: Borkent-Raven
authors.forename: Joost
authors.initials: J
authors.lastname: Hulshof
authors.forename: Jacco
authors.initials: J
authors.lastname: Wallinga
mesh_terms: D006509:Hepatitis B / Q000635:transmission; D006515:Hepatitis B virus / Q000502:physiology*; D003699:Hepatitis D / Q000635:transmission; D003698:Hepatitis Delta Virus / Q000502:physiology*; D008962:Models, Theoretical