Possibilities of developing an anti-dengue vaccine are discussed based on our experimental findings with a dengue virus type 1 (DEN-1) Mochizuki strain. The Mochizuki strain virus was attenuated for human beings in the course of several passages through mouse brains since its isolation from the blood of a dengue patient in the 1943 epidemic in Nagasaki, Japan. This attenuated virus in the living state induced no abnormal symptoms after injection into human volunteers or monkeys, yet it stimulated production of specific anti-DEN-1 NT and HI antibodies and induced a prophylactic effect on the human beings against virulent dengue viruses (in the form of patient's serum) given experimentally. The immunogenic effects of the virus was maintained after passages in primary monkey kidney tissue cultures. Using the tissue culture virus, together with the 17D yellow fever (YF) vaccine, a combined immunization of human beings against DEN and YF was possible; production of the antibodies of significant titers against both viruses was unequivocally demonstrated. The partially purified virus was similarly effective in stimulating production of the anti-DEN antibodies, and the same statements could be made as to the viral components obtained by sucrose density gradient centrifugation. The virus was shown to multiply in the WI-38 cell line cultures, and this suggests application of this cell line to produce a live tissue culture vaccine.
Conclusions of this review are : (1) the Mochizuki virus is completely attenuated; (2) yet it stimulates production of specific anti-DEN antibodies and induces protection against DEN-1 infection by virulent human virus; and (3) that possibility of developing a live tissue culture vaccine is suggested; this also makes possible a combined DEN-YF vaccination on the experimental basis. It is stated in the connection that the purified virus or its components can be used for the above purposes.
Problems regarding the implication of “hypersensitivity hypothesis” of dengue and dengue hemorrhagic fever-shock syndrome in anti-DEN vaccination are in addition discussed.