Measuring human infection rates is the current method for epidemiologic studies of schistosomiasis.28
To estimate the level of schistosomiasis transmission in Morocco, serologic detection was preferred for three reasons: current available serologic methods are exquisitely sensitive and specific; large numbers of samples can be obtained and tested quickly and inexpensively; and, the direct examination of urine for S. haematobium
eggs is specific, but its sensitivity is highly limited by the sporadic fecundity of the adult worms and the low rate of recovery of parasitic ova from samples. Thus, patients with low egg counts can be misdiagnosed and can continue to transmit the disease.29
Urine examination is also slow, labor-intensive, and esthetically unpleasant.30
Moreover, a serologic test with a sensitivity of 95% and a specificity of 96–100% is a better predictor of prevalence than a single direct examination using 10 mL of urine. These arguments support the use of serologic detection to monitor the epidemiologic status of schistosomiasis in our study areas.27,31
There are two primary methods used for the serologic surveillance of schistosomiasis, the ELISA and the EITB. Typically, ELISAs use a crude antigen mixture, binding antibodies to any component, whether specific or non-specific, to produce a reaction. In contrast, the EITB uses components of the antigen mixture that are separated from each other by sodium dodecyl sulfate–polyacrylamide gel electrophoresis, and reactions to specific and non-specific antigen bands can be distinguished from each other. In some studies, screening using Falcon assay screening test–ELISA (FAST-ELISA) followed by MAMA-EITB has been used.7,32
In our study, EITB alone was selected for three reasons. The first reason is its high sensitivity of 99% and specificity of 99%. Because the FAST-ELISA uses S. mansoni
MAMA antigens, it is only 90% sensitive for detection of S. haematobium
, compared with its 99% sensitivity for detection of S. mansoni
No advantage in sensitivity or specificity was observed by using the FAST-ELISA in this setting. The second reason is that the EITB alone conserved HAMA antigen; the EITB required 5 ng of antigen per strip, and one strip was used to test up to four samples. In contrast, the FAST-ELISA would have used 200 ng of antigen/well, and only one sample could have been be tested per well. Finally, because the HAMA-EITB was used alone, only one test was performed. If the FAST-ELISA had been used as a screening assay followed by immunoblot confirmation, two tests would have to be performed. Thus, time saving was also realized.
In the Tata, Chtouka Ait Baha, Errachidia, El Kelaa des Sraghna, and Beni Mellal provinces, specific antibodies against S. haematobium
were not detected in any cases in the study population. This study is our second in a series of studies to examine the current status of human Haematobium
schistosomiasis in Morocco. The first study was carried out in 2001 in collaboration with the CDC in Atlanta, the diagnostics reference center at Cairo University, and our study team. Serum samples from approximately 1,500 persons of different ages were collected from three disease-endemic areas with low incidence: Targa Ntouchka, Oudaya, and Akka from Ait Baha, Marrakech, and Tata provinces, respectively. Samples were screened by using the FAST- ELISA and confirmed by using the S. haematobium
EITB. In this previous study, a seroprevalence rate of 10% was found only in the Tata province where cases were limited to children less than 14 years of age.13
The present study showed the reduction to zero of the prevalence of schistosomiasis in all defined geographic areas that represents the last foci of the disease in Morocco.
The data presented are evidence that transmission of schistosomiasis has been interrupted in Morocco. These findings are the result of the effective and deliberate efforts of NPSC during which annual control activities were regularly performed during 1983–2007, and interventions were initiated in cases of reactivation of infection. These efforts included active detection in schools and localities; mass drug administration in disease-endemic localities in 1987, in Akka in 2004, and in Chtouka Ait Baha, Tata, and Larache in 2005 and 20066
; annual surveillance of breeding sites and physical and chemical control of snails by using molluscocides; implementation of environmental controls with irrigation systems; intersectoral collaboration between the Ministries of Agriculture and the Interior; and education to prevent fecal contamination of affected and potential transmission sites.6
Another factor that impacted the schistosomiasis incidence rate was the rainfall deficit (> 20%), which occurred during 1990–2000 in Morocco and resulted in the natural drying of irrigation canals and a decrease in snail habitats. Furthermore, infrastructure developments, such as safe water supplies as a means of excreta disposal and an advanced primary health care system in rural zones, played crucial roles in schistosomiasis elimination.34,35
All of these factors contributed to reducing the prevalence and intensity of infection to a level of zero.
In conclusion, among 74 countries with schistosomiasis, only Japan, Puerto Rico, Tunisia, Sulawesi, and parts of China have eliminated schistosomiasis.36
During the past decade, the NPSC of Morocco made the deliberate decision to shift programmatic efforts from controlling the morbidity of infection to the ultimate interruption of transmission. The results of this study suggest that those efforts have been successful and that the transmission of S. haematobium
from snails to human hosts has been interrupted.