It has been reported that the outcome of viral diseases in humans can be influenced by concurrent infection with other viruses. Scientists at the National Institute of Oncology in Budapest, Hungary, have reported the successful use of a therapy for hepatitis B and C, based on the use of a nonpathogenic, genetically engineered Newcastle Disease virus (MTH-68/B).Newcastle Disease virus is a large RNA avian paramyxovirus which causes avian pneumoencephalitis (Newcastle disease). The virus can be transmitted to humans through contact with infected birds but it is considered minimally pathogenic in humans.The MTH-68/B strain shortened the duration of the first icteric phase in patients with acute hepatitis B and C virus. Phase II trials with MTH-68/B have been carried out at Budapest's Szent Laszlo Hospital. Larger scale clinical trials are to be conducted in the future. In addition to these clinical studies, case reports of 3 patients with chronic B and C viral hepatitis who had received MTH-68/B as a therapy indicated that 2 patients were essentially cured within a few months whereas the third moribund patient exhibited significantly improved clinical symptoms. A full 6-month course of treatment with MTH-68/B has been estimated to cost $US400 to 800.The mechanism by which MTH-68 exerts its therapeutic action is not well understood but it appears to involve selective killing of infected cells, either by direct lysis or by stimulation of cytokine release. Although the researchers involved refer to MTH-68 as being a vaccine, the antibodies induced against the virus are not involved in its therapeutic action and may actually inhibit the efficacy of treatment.