Doxycycline in the prevention of experimental plague induced by plague microbe variants]

A comparative study was performed on the efficacy of doxycycline in experimental plague infection induced in albino mice by strain 231 of the plague microbe and its variant 231 Fra- deprived of the ability to produce the fraction I antigen. It was shown that the LD50 for strain 231 during animal treatment with doxycycline was significantly higher than that for variant 231 Fra-. Prophylaxis of the plague infection caused by the Fra- forms of the plague microbe required significantly higher doses of doxycycline (ED50) than that of the infection caused by the Fra+ forms. The use of the daily maximum permissible doses of doxycycline (50 to 100 mg/kg a day) for 10 days in treatment of albino mice infected with the strain Fra- did not provide animal survival at the level higher than 60 to 70 per cent while the survival rate in the animals infected with the strain Fra+ of the plague microbe and treated according to the same scheme amounted to 90-100 per cent. The lower therapeutic efficacy of doxycycline in the treatment of the infection caused by the fractionless variant of the plague microbe should be considered in development of rational schemes for prophylaxis and treatment of plague.