Genital Schistosomiasis - Treatment

Treatment

For clearance of urinary ova excretion and reduction of morbidity, a single oral dose of praziquantel 40 mg/kg (or 60 mg/kg in 2 divided doses) is recommended with food and drink in order to minimise gastrointestinal side effects. Based on a number of reports, WHO has decided to also recommend praziquantel to pregnant and lactating women. Treatment for urinary schistosomiasis has been found equally effective in HIV-positive and -negative patients. Praziquantel does not seem to influence plasma HIV viral load in S. mansoni-infected individuals.

As of 2011, one study has directly explored the treatment of genital schistosomiasis. Although urinary ova excretion decreased following treatment (OR, 10.3 95% CI 3.8-27.8, p<0.001), praziquantel was not associated with a significant reduction in genital lesions or contact bleeding (p=0.31-0.94). Sandy patches remained strongly associated with contact bleeding and vessel abnormalities, even after treatment, and findings were independent of HIV status. Such lesions (common, and apparently refractory to treatment for at least 12 months) may be an important risk factor for both the acquisition and transmission of the human immunodeficiency virus in sexually-active women.

In the urinary tract, the effect of praziquantel has largely been determined by resolution of lesions detectable by ultrasound scan and decreased ova excretion in the urine. Sandy patches in the bladder have been found post-mortem, in surgical specimens or as seen by cystoscopy; however, there have been no large-scale cystoscopic studies on the natural course of sandy patches or the effect of praziquantel on the clinical morphology of bladder lesions. The outcome of treatment in the urinary tract may be variable, depending on four factors:

• Age of the patient
• Pre-treatment intensity of infection
• Degree of fibrosis or calcification
• Site of the lesion

Urinary-tract lesions in younger patients are more responsive to treatment, and this may be so in the genital tract as well. However (as mentioned previously), given the same age group and exposure rates, lesions in the bladder decrease faster than lesions in the upper ureteres after treatment. Hence, the effects of treatment in the urinary tract cannot automatically be extrapolated to the genital tract.

Praziquantel (which kills the mature worm) is the standard treatment for all types of schistosomiasis, and there will be a decrease in S. haematobium ova excretion in the urine 4–26 weeks after treatment. Occasionally, repeated courses are be necessary to cure S. haematobium in the urinary tract—even in children, and sometimes in returned travellers long after the worm should have matured. Case reports indicate that praziquantel may have an immunomodulatory effect on lesions, so the lesions resolve. However, although praziquantel kills the egg-laying worms, lesions not yet visible may develop around ova already deposited in tissues. Once ova deposition has occurred in the cervix, ova excretion and lesion development are independent processes; praziquantel affects the former almost immediately, but possibly not the latter.

Egg excretion in the urine of lesions in genital mucosa are not directly comparable, and little is known about the effect of treatment in the genital tract. Prior to the Zimbabwean study there had been no longitudinal study, and only a few case reports on the effects of treating genital schistosomiasis. The case reports describe regression of sandy patches in lower-genital-tract schistosomiasis after treatment with praziquantel for a course of 1 week to 6 months. After less than two years, treatment has been described to resolve schistosomal infertility (with pregnancy) in up to 6 of 13 infertile women.

It has been hypothesised (and debated) that the release of worm fragments upon death enhances immunological protection against reinfection, and possibly also removes the immunosuppressive effect of the adult worm. Moreover, there is a second effect on transmission. By interfering with the cycle, there will be decreased infection of the snails and decreased excretion of cercaria and infection of humans, especially if mass chemotherapy is carried out in the low-transmission season. Other forms of treatment— such as arthemeter (recently tested), metrifonate (for S. haematobium, recently withdrawn from the market), niridazole, oxamniquine, hycanthone, amoscanate and antimony (no longer in use for schistosomiasis)—will not be discussed here.

WHO has recommended mass treatment for women and children in schistosomiasis-endemic areas, to prevent long-term morbidity. This is often done through schools, most often with the active participation of the teaching staff. Mass treatment has been recommended at six-month to three-year intervals, depending whether there is a continuous high or seasonal low transmission (more often with the former). Studies have found that the prevalence of schistosomiasis is higher in non-enrolled children. Moreover, girls are often underrepresented in schools; in an Egyptian study, it was estimated that 59% of infected boys but only 18% of infected girls were reached through school programmes.