Selective Population Chemotherapy Research Articles

Long-term suppression of adult bladder morbidity and severe hydronephrosis following selective population chemotherapy for Schistosoma haematobium.

Repeated selective population chemotherapy of school age children reduces infection and morbidity associated with Schistosoma haematobium infection. To examine the long-term effect of this treatment on susceptibility to re-infection and late disease, a cohort of Kenyans (n = 194) were re-examined for infection and urinary tract morbidity 7-13 years after they underwent annual ultrasonography and treatment for an average of 5 years beginning in 1984 as children. Controls were previously untreated age-matched individuals residing in the same or adjacent villages. The overall prevalence and intensity of infection were equivalent between the 2 groups. In contrast, the prevalence of bladder wall pathology was 11-fold lower in previously treated (1.5%) versus untreated subjects (17%). Severe hydronephrosis was completely reversed. These data demonstrate that treatment significantly reduced urinary tract morbidity despite re-infection, and suggest that the important risk factors for urinary tract morbidity in adulthood are cumulative intensity and duration of infection during early adolescence.

The relationship between prevalence of Schistosoma haematobium infection and different morbidity indicators during the course of a control programme on Pemba Island

A long-term schistosomiasis control programme was initiated on Pemba Island,Tanzania in 1986 with the aim of eliminating morbidity due to Schistosoma haematobium infection. The programme used haematuria as a community indicator of morbidity for surveillance and for identifying individuals for selective population chemotherapy. Analysis of the first 3 evaluation studies showed that the prevalence of microhaematuria was linearly related to the prevalence of infection, and that visually detectable haematuria was a marker of the intensity of infection and risk of morbidity in a community. These relationships remained consistent during repeated community-based chemotherapy, suggesting that measures of haematuria may be useful tools for surveillance.

Control of Morbidity Due to Schistosoma haematobium on Pemba Island: Egg Excretion and Hematuria as Indicators of Infection

The variability of Schistosoma haematobium egg excretion using a quantitative syringe filtration technique and the variability of hematuria detected visually and by reagent strips were studied in a population of 520 subjects from the village of Pujini (Pemba Island, Zanzibar, Tanzania) for 6 consecutive days. A high degree of day-to-day variability of egg excretion within subjects was found both in the whole population and in the 5-19 year age group. Subjects with 1 urinary egg count of greater than or equal to 50 eggs/10 ml urine were not similarly classified in 36-61% of the other 5 examinations and 4-16% of their other examinations were negative. Gross hematuria had a specificity of almost 100%, when related to a positive filtration on any day, and was closely related to egg counts of greater than or equal to 50 eggs/10 ml urine. The finding of a strongly positive reaction for hematuria on a given single day was closely associated with the subject having a high egg count (greater than or equal to 50 eggs/10 ml urine) on at least one of the 6 days of the study. At the primary health care level, single highly positive semiquantitative values for hematuria were a more useful diagnostic indicator than a single egg count to select patients with heavy infections for selective population chemotherapy.

Control of morbidity due to Schistosoma haematobium on Pemba island; selective population chemotherapy of schoolchildren with haematuria to identify high-risk localities

In Pemba, Tanzania, 2 sequential surveys were made of the prevalence of haematuria in children (aged 5–19 years) in 52 schools, using direct observation of gross haematuria (bloody urine) and chemical reagent strips as indicators of Schistosoma haematobium infection. 24 462 children were examined in the first survey and 25 575 in the second, 6 months later. The prevalence of gross haematuria was initially 15·8% (3876 cases); 6 months later, after a single dose of praziquantel (40 mg/kg), it was only 2·4% (613 cases), a reduction of 84·9%. The total number of cases of haematuria (gross or otherwise) dropped similarly, from 13 920 (54%) to 6638 (26%), a 52·2% reduction. In towns the degree of reduction was positively correlated with the standard of water supply and sanitation available, and the initial prevalence of gross and total haematuria in schools was positively correlated with the prevalence 6 months later. The cost per person reduced from US$ 0·83 in the first survey to US$ 0·48 in the second (excluding field staff wages paid in local currency), the reduction being due to the reduced number of positive persons. This study has demonstrated the feasibility of using indirect techniques on a large scale for the diagnosis of S. haematobium infection to identify schoolchildren requiring treatment, and to monitor its impact on clinical morbidity in a highly endemic area.

A review of achievements of the national schistosomiasis control program in middle and upper Egypt areas.

In Egypt the "national schistosomiasis control program" was formulated to control transmission by reduction of prevalence and intensity of current infections, and thereby achieve an acceptable level of schistosomiasis disease control. The program was implemented foremost in Middle Egypt (1977) and Upper Egypt (1980), collectively extending 800 km alongside of the River Nile and accommodate about 10.5 million people. Schistosoma haematobium has been essentially the prevailing species infection in both areas. The strategy of control entailed both area-wide mollusciciding with niclosamide, and selective population chemotherapy with metrifonate. Evaluation in 1986 showed that prevalence dropped from pre-control 29.4% in Middle Egypt and 26.3% in Upper Egypt to 6% and 7.8% respectively, together with a remarkable drop of infections among children. Also mean intensity attained low levels consistent of low grade infections. It is evident therefore that in these areas where an enhancement of schistosomiasis infections had been anticipated the employment of the twofold strategy effected a state of low-prevalence/low-intensity signifying a lowered reservoir of infection and a substantial interference with the potentials of transmission.

Infection and re-infection rates of opisthorchiasis in the water resource development area of Nam Pong project, Khon Kaen Province, northeast Thailand.

A one-year investigation on re-infection rates of opisthorchiasis was carried out in three villages in the Nam Pong Water Resource Development Project, Thailand. In the two villages where selective population chemotherapy was combined with improvements in sanitation and health education aimed at changing food habits, the mean monthly re-infection rate was 2.0% and the annual cumulative rate was 21.5%. In the third village, where only selective population chemotherapy was carried out, the monthly re-infection rate was 5.0% and the annual cumulative rate was 55.5%. Studies on new infections in initially negative individuals were also carried out in the three villages, with inconclusive results.

Routine focal mollusciciding after chemotherapy to control Schistosoma mansoni in Cul de Sac valley, Saint Lucia

Concluding results of a 10-year schistosomiasis control programme in Cul de Sac valley, Saint Lucia, are described. After an area-wide mollusciciding campaign (1970–1975), and a surveillance/treatment programme supplemented with selective population chemotherapy in 1975 and 1976, prevalence rates of Schistosoma mansoni were reduced to low levels. To prevent a resurgence of transmission a cost effective routine focal mollusciciding programme, suitable for public health implementation was evaluated from 1977 to 1981. Streams and main collector drains in banana fields, considered to be potential S. mansoni transmission sites, were treated every four weeks with Bayluscide 6076 emulsifiable concentrate (Clonitralide). Snail populations were effectively controlled in the treated areas but large numbers were present where no treatment was given. Only 0·06% of sentinel snails became infected. Prevalence of infection in the human population remained low (over-all 5%) and intensity of infection at a level not normally associated with schistosomal disease. Since control started 10 years earlier the level of potential contamination has fallen by 92% in high transmission areas. The four-year programme cost US$12,909, of which 54% was for molluscicide, 27% for labour and 19% for transport, equipment and sundries. The average annual cost per head of population was US$0·46.

Schistosoma mansoni control in Cul de Sac valley, Saint Lucia. II. Chemotherapy as a supplement to a focal mollusciciding programme

After an intensive area-wide mollusciciding campaign, over four and a half years, transmission of Schistosoma mansoni was reduced. A cheaper scheme suitable for the follow-up or consolidation stage of control was evaluated and two selective population chemotherapy campaigns using hycanthone (2 mg/kg b.w.) and oxamniquine (15 mg/kg b.w.) were mounted. Prevalence dropped to 6% and 3% in areas with previously high and low levels of transmission respectively. Calculations suggested that these figures were falsely low and that perhaps 20% of the population were still excreting S. mansoni ova in small numbers. The unco-operative groups in the population are probably more important in maintaining a reservoir of infection in the community than persons with light infections undetected by the sedimentation concentration stool examination technique used. The benefit of more sensitive but more costly examination techniques is not clear since the importance of very light infections in transmission is uncertain. Case detection absorbs an increasing proportion of the total cost of chemotherapy programmes with fewer cases being found amongst the same number screened. Using hycanthone (649 treated) the cost per person protected was $0·74 and using oxamniquine (264 treated) $0·94. The need to develop low cost consolidation or follow-up procedures for preventing a resurgence of transmission after successful control, when the infection is no longer of public health importance, is stressed.

Quantification of infection with Schistosoma haematobium in relation to epidemiology and selective population chemotherapy. II. Mass treatment with a single oral dose of metrifonate.

Determination of the efficacy of mass treatment of schistosomiasis is usually based on the rate of cure. However, schistosomes do not multiply in the human host, disease tends to cluster in the small proportion of individuals with heavy infections, and reinfection continually occurs in endemic areas. Thus drastic reduction in worm burdens can be a reasonable goal for mass treatment campaigns. The standard dose and regimen of metrifonate for the treatment of schistosomiasis haematobia is 7.5 mg/kg administered in three doses two weeks apart. This treatment results in a cure rate of approximately 50% and a reduction in egg output of 94.5%. In the present study, 72 infected children with egg counts before treatment that averaged from 0.1 to 2,334/10 ml of urine were treated with a single oral dose of 10 mg of metrifonate/kg: the cure rate was 22%, and the reduction in egg output was 96.5%. No side effects were recorded.

Quantification of infection with Schistosoma haematobium in relation to epidemiology and selective population chemotherapy. I. Minimal number of daily egg counts in urine necessary to establish intensity of infection.

The intensity of infection with Schistosoma haematobium (worm burden) can be approximated by quantifying the number of parasite eggs excreted in the urine. A new method of egg counting has been developed in which urine samples are passed through transparent Nuclepore filters (Nuclepore Corp., Pleasanton, Calif.). The method requires no staining, is rapid, and can be performed in the field. It has previously been reported, however, that there is a significant daily fluctuation in output of eggs in the urine of patients with schistosomiasis haematobia. In the present study, daily urine samples were obtained on each of the 10 school days during a 12-day period from 121 schoolchildren in Coast Province, Kenya (total, 10 samples per child). In terms of detecting infection, it was of interest that egg counts of 0 were very rarely recorded for subjects whose mean egg counts were greater than 20/10 ml of urine. When the patients were classified into one of four groups, according to egg count (less than 1, 1--100, 101--400, greater than 400), the proportion correctly classified based on a single urine specimen was 75%; this proportion rose to 78% when the classification was based on two specimens and to 83% with three specimens. Most of the urine specimens that were misclassified belonged in an adjacent group.