Future effort should focus on host factors to explain variation in disease course in Chlamydia trachomatis infection, say researchers studying the infection in a mouse model. Host factors, not virulence factors, probably determine whether human infection with the commonest strain is symptomatic or not, they say.

The researchers used isolates of C trachomatis serovar E from infections in women to infect female mice of a strain used as a standard model of human female genital tract infection. Two isolates were from symptomatic infections in the women and their partners and two were from asymptomatic infections. The researchers recorded progress of infection over 56 days by looking for C trachomatis by culture and PCR in vaginal swabs taken at intervals and dissected tissues from the genitourinary tract at 14 and 56 days. They measured inflammation by leucocyte esterase activity. Incidence and length of infection were similar among all isolates and between the isolate pairs. So were inflammation of the lower genital tract and progress of infection in the upper genital tract. Thus virulence factors within this, the commonest C trachomatis serovar, do not influence the course of infection.

The results tie in with a recent epidemiological study of C trachomatis infection in over 1100 women that concluded that asymptomatic or asymptomatic infection is not governed by serovar.

Earlier epidemiological evidence had been inconclusive, and the researchers felt that it would be sensible to corroborate findings with an experimental model that can reliably distinguish different human isolates.