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.

Dengue 1 outbreak in Rosso, northern Senegal, October 2021: entomologic investigations.

Senegal has experienced periodic epidemics of dengue in urban areas with increased incidence in recent years. However, few data are available on the local ecology of the epidemic vectors. In October 2021, a dengue outbreak was reported in northern Senegal to the Institute Pasteur de Dakar. Entomologic investigations then were undertaken to identify the areas at risk of transmission and to identify the vector(s). Adult mosquitoes were collected indoors and outdoors at selected households, while containers with water were inspected for mosquito larvae. All the Aedes aegypti (L.) collected were tested for dengue virus NS1 protein using a rapid diagnostic test (RDT), and positive samples were confirmed by real-time RT-PCR. The qRT-PCR positive samples were subjected to whole genome sequencing using Nanopore technology. The majority of the larvae-positive containers (83.1%) were used for water storage. The Breteau and Container indices exceeded the WHO-recommended thresholds for the risk of dengue virus transmission except at 2 localities. Ae. aegypti, the only reputed dengue vector, was collected resting indoors as well as outdoors and biting during the day and night. The NS1 protein was detected in 22 mosquito pools, including one pool of females emerging from field-collected larvae. All NS1-positive results were confirmed by RT-PCR. Virus serotyping showed that the outbreak was caused by DENV-1. This study demonstrates the need for continuous control of adult and aquatic stages of Ae. aegypti to prevent future dengue epidemics in Senegal. RDTs appear to be a promising tool for dengue diagnostics and surveillance.

Resting Behavior of Blood-Fed Females and Host Feeding Preferences of Aedes aegypti (Diptera: Culicidae) Morphological Forms in Senegal.

Aedes aegypti (Linnaeus) is the main vector of most arboviruses in tropical and subtropical urban areas. In West Africa, particularly in Senegal, domestic and wild populations have been described. Both Ae. aegypti aegypti (Aaa) and Ae. aegypti formosus (Aaf) were found in progenies of Ae. aegypti families from several localities of Senegal. However, nothing is known about their resting and trophic behavior, which are key data for vector control. To fill this gap, blood-fed mosquitoes were collected monthly indoors and outdoors with BackPack aspirators and BG-Sentinel 2 traps between July and November 2019 from four urban sites. The enzyme-linked immunosorbent assay technique was used to analyze blood-fed Aaa and Aaf specimens. Both forms were found resting in all investigated places with the highest proportions found in scrap metals (51.7% for Aaa and 44.1% for Aaf) and used tires (19.2% for Aaa and 26.1% for Aaf). Blood-fed Aaf females showed lower occupation of the indoors environment compared to Aaa. Overall, the percentages of single bloodmeals from human were 80.5% (916/1138) for Aaa and 71.1% (263/370) for Aaf. A low frequency of other domestic hosts, including bovine, ovine, and cat were detected for both forms. This study provides the first data on resting and trophic behavior of Aaa and Aaf in Senegal. Both forms showed differences in their resting behavior but fed primarily on human and highlight the risk of arboviruses transmission in urban areas.

Real-Time RT-PCR Assays for Detection and Genotyping of West Nile Virus Lineages Circulating in Africa.

West Nile virus (WNV) is an emerging arbovirus, circulating worldwide between birds and mosquitoes, which impacts human and animal health. Since the mid-1990s, WNV outbreaks have emerged in Europe and America and represent currently the primary cause of encephalitis in the United States. WNV exhibits a great genetic diversity with at least eight different lineages circulating in the world, and four (1, 2, Koutango, and putative new) are present in Africa. These different WNV lineages are not readily differentiated by serology, and thus, rapid molecular tools are required for diagnostic. We developed here real-time RT-PCR assays for detection and genotyping of African WNV lineages. The specificity of the assays was tested using other flaviviruses circulating in Africa. The sensitivity was determined by testing serial 10-fold dilutions of viruses and RNA standards. The assays provided good specificity and sensitivity and the analytical detection limit was 10 copies/reaction. The RT-PCR assays allowed the detection and genotyping of all WNV isolates in culture medium, human serum, and vertebrate tissues, as well as in field and experimental mosquito samples. Comparing the ratios of genome copy number/infectious virion (plaque-forming units), our study finally revealed new insight on the replication of these different WNV lineages in mosquito cells. Our RT-PCR assays are the first ones allowing the genotyping of all WNV African variants, and this may have important applications in surveillance and epidemiology in Africa and also for monitoring of their emergence in Europe and other continents.

Experience on the management of the first imported Ebola virus disease case in Senegal.

The Ebola virus disease, as a first epidemic in West Africa, stands as the most deadly one throughout history. Guinea, the source of the epidemic, Sierra Leone and Liberia remain the most strongly affected. That epidemic thoroughly destabilized the health system of those countries. Following Nigeria, Senegal received its first imported case from the neighboring Republic of Guinea. In that sub regional psychotic context, such a situation has been handled and managed starting from the potential of a health system that is already suitably structured. The organization of the response, the management of the communication system and the rigorous monitoring of contacts have been decisive in the control of the epidemic. Our countries have to be prepared in order to face health threats, and that is the reason why the need to empower our health systems is important.