The present study compared qualitative and quantitative urine microscopy findings after a single MDA of praziquantel for urogenital schistosomiasis between Al Jabalain and El Salam in the White Nile State, Sudan. The baseline prevalence of S. haematobium infection was 5.5% in Al Jabalain and 27.5% in El Salam. All SAC in Al Jabalain received 2 MDAs within the recent 4 years, while those in El Salam had not. At 8 months after the MDA, the prevalence rates in both Al Jabalain and El Salam were significantly reduced compared to baseline rates (80.3% and 84.4%, respectively). The two reduction rates of prevalence were similar regardless of the baseline prevalence rate. Also, the reduction rates of prevalence were almost similar between boys and girls, or among age groups. The 2013 baseline prevalence rate of 27.5% in El Salam locality was at the level of the past prevalence of S. haematobium infection in the White Nile State (21.4%) in 1996 [11] and the baseline prevalence in Al Jabalain before MDA in 2009 (28.5%) [9]. Although the two localities had different MDA histories, the chemotherapeutic effect of a single praziquantel MDA was good and stable based on the observed reduction rate of prevalence. Reduction of prevalence rate after MDA represents the proportion of cure among the infected population, and the present similar findings were observed between gender and age groups as well as between the two localities. Our reduction rate of prevalence after a single dose of praziquantel was similar to previous reports in SAC of Sudan and Burkina Faso [21–22].
The infection intensity–which is quantified using egg counts (GMI of EP10 in the present study)–is an important index of schistosomiasis epidemiology. The egg counts can estimate the burden of infecting worms and represent the degree of morbidity by eggs in the bladder [23]. In the present study, the baseline GMI of Al Jabalain was 14.5 EP10, which was significantly lower than 18.5 EP10 in El Salam. The GMI of EP10 was significantly reduced by MDA in both localities, and the reduction rate was lower in El Salam (39.5%) than in Al Jabalain (51.0%). By gender, the GMI reduction was significantly higher in girls than in boys. While the prevalence reduction was similar, the findings suggest less reduction of infection intensity in populations with heavier infection burdens.
El Salam demonstrated a higher prevalence rate of urogenital schistosomiasis and higher EP10 counts than Al Jabalain. A single MDA produced a similar reduction efficacy of prevalence rate (i.e. cure rate) in El Salam, but a lower efficacy of worm reduction in the human body; this suggested that most of the light burden children were cured by MDA and the proportion was similar in both localities, but heavy burden cases remained uncured with lowered EP10 counts after MDA. A complete cure is important for individual care; therefore, it is recommended to use 20 mg/kg praziquantel × 2 for diagnosis-based medication of individuals [24] while MDA reduces the general prevalence and morbidity in a community. The present findings support the idea that a single MDA with a 40 mg/kg dose is less effective to cure heavy burden schistosomiasis, and recommends repeated MDAs for community control programs.
The above-mentioned results were analyzed on the basis of each locality. When we breakdown the prevalence rates and egg counts by subdistricts in the localities, there were wide variations in both localities. Even in Al Jabalain, there were subdistricts with a low reduction rate of prevalence, such as Joda and Al Naeem units. In Al Naeem unit, the GMI increased after MDA, because many absent children with high GMI of S. haematobium infection were involved at follow-up survey however they did not participate the baseline survey and praziquantel treatment. Ongoing refugee immigration from South Sudan also influences the villages of both localities and necessitates extra care of this population during refugee migration and settlement.
When interpreting the MDA effects between the 2 localities, we have to consider reinfection. We examined the urine microscopy at 8 months after MDA, which was a long enough period to be influenced by reinfection after MDA. A single 40 mg/kg dose of praziquantel is known to produce a 73.6% cure rate and a 94.7% egg reduction rate for S. haematobium infections [25]. The present prevalence reduction rate was over 80%, which was similar to the known cure rate. However, the intensity reduction rate (39.5% in El Salam and 51.0% in Al Jabalain) was much lower than the known 90% egg reduction rate, although the estimation method was different. The egg passers after MDA included failed treatments and reinfected cases together without clear identification. In heavy endemic areas, children are more rapidly and heavily reinfected after chemotherapy because they are more exposed. The reinfection force is determined by the egg seeding amount within the local area. Other risk factors, such as drug coverage rates and seasonality of the follow-up survey, may have affected the reduction rates of infection intensity in this study. The praziquantel coverage rate in El Salam was lower than in Al Jabalain, thus it may be possible that the proportion of infected SAC at the follow-up survey was higher in El Salam. The follow-up survey was done 8 months after MDA, after passing the hot and humid rainy season and long summer vacation; thus, SAC may contact water (such as during swimming) more frequently. The present study confirmed that the intensity reduction was much less in Sudan than expected. Therefore, repeated MDA may diminish the reinfection force by reducing the egg seeding population and the total amount of egg production in a community. Once repeated MDA starts to effectively keep the egg seeding amount under the reinfection threshold, schistosomiasis may finally be eliminated.
The present study had some limitations. The follow-up data at 8 months after the MDA included both treatment failure and reinfection after medication, but it was impossible to differentiate their impacts. The other limitation was the influence of immigrants from South Sudan who were included in the study population.