Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry traces the geographical source of Biomphalaria pfeifferi and Bulinus forskalii, involved in schistosomiasis transmission.

BACKGROUND: Freshwater snails of the genera Bulinus spp., Biomphalaria spp., and Oncomelania spp. are the main intermediate hosts of human and animal schistosomiasis. Identification of these snails has long been based on morphological and/or genomic criteria, which have their limitations. These limitations include a lack of precision for the morphological tool and cost and time for the DNA-based approach. Recently, Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight (MALDI-TOF) mass spectrometry, a new tool used which is routinely in clinical microbiology, has emerged in the field of malacology for the identification of freshwater snails. This study aimed to evaluate the ability of MALDI-TOF MS to identify Biomphalaria pfeifferi and Bulinus forskalii snail populations according to their geographical origin. METHODS: This study was conducted on 101 Bi. pfeifferi and 81 Bu. forskalii snails collected in three distinct geographical areas of Senegal (the North-East, South-East and central part of the country), and supplemented with wild and laboratory strains. Specimens which had previously been morphologically described were identified by MALDI-TOF MS [identification log score values (LSV) ≥ 1.7], after an initial blind test using the pre-existing database. After DNA-based identification, new reference spectra of Bi. pfeifferi (n = 10) and Bu. forskalii (n = 5) from the geographical areas were added to the MALDI-TOF spectral database. The final blind test against this updated database was performed to assess identification at the geographic source level. RESULTS: MALDI-TOF MS correctly identified 92.1% of 101 Bi. pfeifferi snails and 98.8% of 81 Bu. forskalii snails. At the final blind test, 88% of 166 specimens were correctly identified according to both their species and sampling site, with LSVs ranging from 1.74 to 2.70. The geographical source was adequately identified in 90.1% of 91 Bi. pfeifferi and 85.3% of 75 Bu. forskalii samples. CONCLUSIONS: Our findings demonstrate that MALDI-TOF MS can identify and differentiate snail populations according to geographical origin. It outperforms the current DNA-based approaches in discriminating laboratory from wild strains. This inexpensive high-throughput approach is likely to further revolutionise epidemiological studies in areas which are endemic for schistosomiasis.

Profile: the Niakhar Health and Demographic Surveillance System.

The Health and Demographic Surveillance System (HDSS) in Niakhar, a rural area of Senegal, is located 135 km east of Dakar. The HDSS was established in 1962 by the Institut de Recherche pour le Développement (IRD) of Senegal to face the shortcomings of the civil registration system and provide demographic indicators. Some 65 villages in the Niakhar area were followed annually by the HDSS from 1962-1969. The study zone was reduced to 8 villages from 1969-1983, and from then on the HDSS was extended to include 22 other villages, covering a total of 30 villages for a population estimated at 43 000 in January 2012. Thus, 8 villages in the Niakhar area have been under demographic surveillance for almost 50 years and 30 villages for 30 years. Vital events, migrations, marital changes, pregnancies, and immunizations are routinely recorded every 4 months. The HDSS data base also includes epidemiological, economic, and environmental information obtained from specific surveys. Data were collected through annual rounds from 1962 to 1987. The rounds became weekly from 1987-1997, followed by routine visits conducted every 3 months between 1997 and 2007 and every 4 months since then. The data collected in the HDSS are not open to access, but can be fairly shared under conditions of collaboration and endowment.