Ongoing transmission of onchocerciasis in the Pru District of Ghana after two decades of mass drug administration with ivermectin and comparative identification of members of the Simulium damnosum complex using cytological and morphological techniques.

BACKGROUND: Human onchocerciasis remains a public health problem in Ghana. Mass drug administration (MDA) with ivermectin (IVM) has reduced disease morbidity and prevalence, but the transmission of onchocerciasis remains ongoing in several endemic foci. We investigated parasite transmission in some endemic communities in Ghana that had received > 18 rounds of annual MDA with IVM and determined the species composition of black fly (Simulium damnosum) vectors in these areas. METHODS: Adult female black flies were collected using human landing catches and identified as either forest or savanna species using morpho-taxonomic keys. The adult flies underwent dissection to determine their parity and detect any O. volvulus larvae, followed by the calculation of entomological indices. Simulium damnosum s.l. larvae were collected and preserved in freshly prepared Carnoy's fixative and were later used for cytotaxonomic studies. RESULTS: A total of 9,983 adult flies were caught: 6,569 and 3,414 in the rainy and dry seasons respectively. Black fly biting activities over the study period showed bimodal or trimodal patterns. The highest monthly biting rate (MBR) of 10,578.75 bites/person/month was recorded in July in Beposo, while the highest monthly transmission potential of 100.69 infective bites/person/month was recorded in Asubende in August. Morphological analysis of 2,032 flies showed that 99.8% (2,028) of the flies were savanna species, with only 4 (0.2%) adult flies being of the forest species. Cytogenetic studies on 114 black fly larvae revealed three cytospecies (Simulium damnosum s.s., S. sirbanum and S. sanctipauli) in the study area. CONCLUSIONS: The present studies confirmed an ongoing transmission of onchocerciasis in the study communities except Abua-1. It also provides further information on biting behaviors and onchocerciasis transmission indices in the study communities. Further, our data confirmed the savanna species (S. damnosum s.s. and S. sirbanum) of the S. damnosum s.l. to be the major vectors of onchocerciasis in the study areas, with only an occasional influx of forest cytotypes.

Synthesizing environmental, epidemiological and vector and parasite genetic data to assist decision making for disease elimination.

We present a framework for identifying when conditions are favourable for transmission of vector-borne diseases between communities by incorporating predicted disease prevalence mapping with landscape analysis of sociological, environmental and host/parasite genetic data. We explored the relationship between environmental features and gene flow of a filarial parasite of humans, Onchocerca volvulus, and its vector, blackflies in the genus Simulium. We generated a baseline microfilarial prevalence map from point estimates from 47 locations in the ecological transition separating the savannah and forest in Ghana, where transmission of O. volvulus persists despite onchocerciasis control efforts. We generated movement suitability maps based on environmental correlates with mitochondrial population structure of 164 parasites from 15 communities and 93 vectors from only four sampling sites, and compared these to the baseline prevalence map. Parasite genetic distance between sampling locations was significantly associated with elevation (r = .793, p = .005) and soil moisture (r = .507, p = .002), while vector genetic distance was associated with soil moisture (r = .788, p = .0417) and precipitation (r = .835, p = .0417). The correlation between baseline prevalence and parasite resistance surface maps was stronger than that between prevalence and vector resistance surface maps. The centre of the study area had high prevalence and suitability for parasite and vector gene flow, potentially contributing to persistent transmission and suggesting the importance of re-evaluating transmission zone boundaries. With suitably dense sampling, this framework can help delineate transmission zones for onchocerciasis and would be translatable to other vector-borne diseases.

Human immune response against salivary antigens of Simulium damnosum s.l.: A new epidemiological marker for exposure to blackfly bites in onchocerciasis endemic areas.

BACKGROUND: Simulium damnosum sensu lato (s.l.) blackflies transmit Onchocerca volvulus, a filarial nematode that causes human onchocerciasis. Human landing catches (HLCs) is currently the sole method used to estimate blackfly biting rates but is labour-intensive and questionable on ethical grounds. A potential alternative is to measure host antibodies to vector saliva deposited during bloodfeeding. In this study, immunoassays to quantify human antibody responses to S. damnosum s.l. saliva were developed, and the salivary proteome of S. damnosum s.l. was investigated. METHODOLOGY/PRINCIPAL FINDINGS: Blood samples from people living in onchocerciasis-endemic areas in Ghana were collected during the wet season; samples from people living in Accra, a blackfly-free area, were considered negative controls and compared to samples from blackfly-free locations in Sudan. Blackflies were collected by HLCs and dissected to extract their salivary glands. An ELISA measuring anti-S. damnosum s.l. salivary IgG and IgM was optimized and used to quantify the humoral immune response of 958 individuals. Both immunoassays differentiated negative controls from endemic participants. Salivary proteins were separated by gel-electrophoresis, and antigenic proteins visualized by immunoblot. Liquid chromatography mass spectrometry (LC-MS/MS) was performed to characterize the proteome of S. damnosum s.l. salivary glands. Several antigenic proteins were recognized, with the major ones located around 15 and 40 kDa. LC-MS/MS identified the presence of antigen 5-related protein, apyrase/nucleotidase, and hyaluronidase. CONCLUSIONS/SIGNIFICANCE: This study validated for the first time human immunoassays that quantify humoral immune responses as potential markers of exposure to blackfly bites. These assays have the potential to facilitate understanding patterns of exposure as well as evaluating the impact of vector control on biting rates. Future studies need to investigate seasonal fluctuations of these antibody responses, potential cross-reactions with other bloodsucking arthropods, and thoroughly identify the most immunogenic proteins.

Field evaluation of DNA detection of human filarial and malaria parasites using mosquito excreta/feces.

We recently developed a superhydrophobic cone-based method for the collection of mosquito excreta/feces (E/F) for the molecular xenomonitoring of vector-borne parasites showing higher throughput compared to the traditional approach. To test its field applicability, we used this platform to detect the presence of filarial and malaria parasites in two villages of Ghana and compared results to those for detection in mosquito carcasses and human blood. We compared the molecular detection of three parasites (Wuchereria bancrofti, Plasmodium falciparum and Mansonella perstans) in mosquito E/F, mosquito carcasses and human blood collected from the same households in two villages in the Savannah Region of the country. We successfully detected the parasite DNA in mosquito E/F from indoor resting mosquitoes, including W. bancrofti which had a very low community prevalence (2.5-3.8%). Detection in the E/F samples was concordant with detection in insect whole carcasses and human blood, and a parasite not vectored by mosquitoes was detected as well.Our approach to collect and test mosquito E/F successfully detected a variety of parasites at varying prevalence in the human population under field conditions, including a pathogen (M. perstans) which is not transmitted by mosquitoes. The method shows promise for further development and applicability for the early detection and surveillance of a variety of pathogens carried in human blood.

Biting Behavior and Molecular Identification of Aedes aegypti (Diptera: Culicidae) Subspecies in Some Selected Recent Yellow Fever Outbreak Communities in Northern Ghana.

Aedes aegypti (L.) (Diptera: Culicidae) is a diurnal feeder that lives in close association with human populations. It is the principal vector of yellow fever, dengue fever and the Zika Virus. Issues of arboviral diseases have been on the ascendency in most countries including Ghana where Aedes mosquito is the main vector of yellow fever. A comparative study of the biting behavior of Ae. aegypti and the identification of subspecies were undertaken using molecular technique. Standard human landing technique was used to collect both indoor and outdoor biting mosquitoes at three zones located in the Upper East (Bolgatanga), Upper West (Nadowli), and Northern (Damongo) Regions of Ghana during the dry and rainy seasons between 0600 and 1800 Greenwich Mean Time (GMT). All collected mosquitoes were identified morphologically using taxonomic keys. random amplified polymorphic DNA polymerase chain reaction was used to categorize Ae. aegypti into subspecies. Adult female Aedes mosquitoes identified formed 62% (n = 1,206) of all female mosquitoes collected. Aedes aegypti 98% and Aedes vittatus 2% were the only Aedes species identified. Bolgatanga recorded the largest number of Ae. aegypti 42%, whereas Nadowli 22% recorded the least. Aedes vittatus was observed in Nadowli. Aedes aegypti exhibited a bimodal biting behavior peaking at 0600-0800 GMT and 1500-1600 h GMT. Molecular findings revealed 69% Ae. aegypti aegypti and 31% Ae. aegypti formosus as the two subspecies (n = 110). This information is important for implementing effective vector control programs in the three regions of the northern Ghana.