Experimental evaluation of possible new short-term drug regimens for treatment of multibacillary leprosy.

Groups of nude mice, with both hind footpads infected with 10(8) Mycobacterium leprae organisms, were treated with 4-week courses of different drug combinations. The effect treatment on each group was evaluated by subinoculating footpad homogenates from the treated mice into groups of normal and nude mice for subsequent regrowth, assessed 1 year later. A combination of rifampin (RMP) with clarithromycin (CLARI), minocycline (MINO), and ofloxacin (OFLO) resulted in the complete killing of M. leprae after 3 weeks of treatment. A combination of sparfloxacin (SPAR) and RMP also resulted in a similar bactericidal effect after 3 weeks of treatment. Other drug combinations showed variable effects. Very little or no effect was observed with any regimen if the treatment was given for less than 2 weeks. World Health Organization (WHO) multidrug therapy (MDT) given for 8 weeks was as effective as the two combinations described above. The results suggest that multidrug combinations consisting of RMP-OFLO (or SPAR)-CLARI (and/or MINO) are as effective as the WHO MDT for the treatment of experimental leprosy. Moreover, they imply that these combinations, which were found to be active in a 4-week experimental treatment protocol, could be administered as treatment to patients for a period of time shorter than the present 2-year regimen without a loss of effectiveness.

Activity of sparfloxacin against Mycobacterium leprae measured by the proportional bactericidal test.

The activity of 25 mg/kg and 50 mg/kg sparfloxacin was measured against Mycobacterium leprae in normal (immunocompetent) mouse foot pads by the proportional bactericidal test. This was compared with the action of 25, 50, and 150 mg/kg ofloxacin by the same method. Sparfloxacin, at both concentrations, was found to be strongly bactericidal by this method, comparable to 150 mg/kg ofloxacin.

An experimental study to evaluate the bactericidal activity of ofloxacin against an established Mycobacterium leprae infection.

The bactericidal effect of a new quinolone, ofloxacin (OFLO), was determined on an established Mycobacterium leprae infection in nude mice. Various drug regimens, including combinations of drugs, were examined for different treatment periods. OFLO and rifampin (RMP) individually failed to produce significant killing after treatment with a single large dose. However, when single large doses of OFLO and RMP were given in combination, a 100-fold reduction in viability was achieved. For a longer period of treatment both of these drugs, at lower doses, produced a moderate reduction in viability. The addition of dapsone to the lower dose of OFLO resulted in a significant reduction in viability, while lower doses of RMP and OFLO together produced a moderate reduction in viability.

Effect of simultaneous administration of interferon-gamma and chemotherapy against Mycobacterium leprae in experimental infection in nude mice.

The possibility of synergy between immunotherapy with recombinant interferon-gamma (IFN-gamma) and chemotherapy with rifampin (RMP) and dapsone (DDS) against Mycobacterium leprae was examined in nude mice. IFN-gamma alone failed to show any effect on the growth of M. leprae in the nude mouse foot pad. No synergy was demonstrable between DDS, either at 0.0001% or at 0.001%, and IFN-gamma. A subinhibitory level of RMP with IFN-gamma was also ineffective, but RMP at 0.006% with IFN-gamma produced a statistically significant enhancement of killing (26-fold) when compared with RMP at 0.006% only. It should be emphasized, however, that results obtained in the immunodeficient nude mouse model may not be comparable to those which might have been given by lepromatous leprosy patients.

Mode of transmission and histology of M. leprae infection in nude mice.

Athymic (nude) mice were experimentally infected with Mycobacterium leprae via the alimentary and respiratory tracts and through the skin. Animals were allowed to inhale aerosols of M. leprae or had bacilli instilled into the nostrils or directly into the lungs. Others were fed M. leprae by gastric tube or had bacilli placed on the tongue. Attempts were also made to transmit M. leprae from infected footpads by Aedes aegyptii mosquitoes. The most successful infections resulted from nasal instillations and from bacilli inoculated onto the tongue surface: in these cases heavy systemic infections occurred. M. leprae was also shown to survive passage through the alimentary tract and bacilli recovered from the faeces were capable of causing infection in recipient nude mice. The possible epidemiological significance of these findings for the transmission of leprosy in man is discussed.

Rifampicin-resistant strains of Mycobacterium leprae may have reduced virulence.

A strain of Mycobacterium leprae resistant to rifampicin (RMP) failed to infect normal mice when injected into the foot pads (FP) at a dose of 10 or 100 bacilli/FP, although it could be maintained by serial passage in mice by the use of inocula of 10(4) bacilli/FP; normal mice can be infected by RMP-sensitive M. leprae at a dose of 10 bacilli/FP. By contrast, nude (athymic) mice could be infected with an inoculum of 10 bacilli/FP of the RMP-resistant strain. It is suggested that the strain concerned possessed reduced virulence for normal mice, and the implications of this for the probability of occurrence of human disease caused by RMP-resistant strains of M. leprae are discussed.

Multiplication of Mycobacterium leprae in the nude mouse, and some applications of nude mice to experimental leprosy.

Two aspects of the immune deficiency of nude mice make these animals particularly useful tools for leprosy research. Nude mice are capable of supporting multiplication of M. leprae to levels approaching 10(10) per g in peripheral body tissues. In addition, nude mice may be inoculated with greater than 10(4) (in fact, with as many as 10(8) organisms per foot pad, without provoking an immune response that prevents multiplication of the organisms. Thus, the nude mouse should be particularly suitable for detecting persisting M. leprae in treated patients, and as a model of the patient for evaluating chemotherapeutic regimens.