Samuel Dadzie

Malaria transmission dynamics at a site in northern Ghana proposed for testing malaria vaccines.

We studied the malaria transmission dynamics in Kassena Nankana district (KND), a site in northern Ghana proposed for testing malaria vaccines. Intensive mosquito sampling for 1 year using human landing catches in three micro‐ecological sites (irrigated, lowland and rocky highland) yielded 18 228 mosquitoes. Anopheles gambiae s.l. and Anopheles funestus constituted 94.3% of the total collection with 76.8% captured from the irrigated communities. Other species collected but in relatively few numbers were Anopheles pharoensis (5.4%) and Anopheles rufipes (0.3%). Molecular analysis of 728 An. gambiae.s.l. identified Anopheles gambiae s.s. as the most dominant sibling species (97.7%) of the An. gambiae complex from the three ecological sites. Biting rates of the vectors (36.7 bites per man per night) were significantly higher (P < 0.05) in the irrigated area than in the non‐irrigated lowland (5.2) and rocky highlands (5.9). Plasmodium falciparum sporozoite rates of 7.2% (295/4075) and 7.1% (269/3773) were estimated for An. gambiae s.s. and An. funestus, respectively. Transmission was highly seasonal, and the heaviest transmission occurred from June to October. The intensity of transmission was higher for people in the irrigated communities than the non‐irrigated ones. An overall annual entomological inoculation rate (EIR) of 418 infective bites was estimated in KND. There were micro‐ecological variations in the EIRs, with values of 228 infective bites in the rocky highlands, 360 in the lowlands and 630 in the irrigated area. Approximately 60% of malaria transmission in KND occurred indoors during the second half of the night, peaking at daybreak between 04.00 and 06.00 hours. Vaccine trials could be conducted in this district, with timing dependent on the seasonal patterns and intensity of transmission taking into consideration the micro‐geographical differences and vaccine trial objectives.

Lymphatic filariasis in Ghana: entomological investigation of transmission dynamics and intensity in communities served by irrigation systems in the Upper East Region of Ghana

We conducted an entomological study to document the effect of irrigation on the vectors and transmission dynamics of lymphatic filariasis in the Upper East Region of Ghana. Mosquitoes were collected by indoor spraying of houses in a cluster of communities located around irrigation projects (Tono and Vea) and others without reservoirs (Azoka). Anopheles gambiae s.s. was the dominant species and major vector, followed by An. funestus. Anopheles arabiensis constituted 9–14% of the An. gambiae complex but none were infective. Culex quinquefasciatus was also not infective in these communities. Chromosomal examinations showed that >60% (n=280–386) of the An. gambiae s.s. in irrigated communities were Mopti forms whilst 73% (n=224) in the non‐irrigated area were Savannah forms. Infectivity rates (2.3–2.8 vs. 0.25), worm load (1.62–2.04 vs. 1.0), annual bites per person (6.50–8.83 vs. 0.47) and annual transmission potential (13.26–14.30 vs. 0.47) were significantly higher in irrigated communities.

Lymphatic filariasis in Ghana: establishing the potential for an urban cycle of transmission

Lymphatic filariasis is a significant public health and economic problem in many tropical and sub‐tropical regions. Unplanned urbanization leading to a lack of proper sanitary conditions has resulted in an increase in the urban‐based transmission of a number of vector‐borne diseases, including lymphatic filariasis. It has been well established that lymphatic filariasis is endemic in rural areas of Ghana. The goal of this study was to determine if there is a potential of establishing urban transmission cycles in Ghanas major cities. We clinically and immunologically assessed 625 individuals from the three major urban areas (Bawku, Bolgatanga and Secondi/Takoradi), finding that the prevalence of infection with Wuchereria bancrofti ranged from 0 to 12.5%. The results of a polymerase chain reaction based analysis of mosquitoes collected from these areas suggested that there is a low but detectable prevalence of mosquitoes infected with W. bancrofti. We conclude that there may be a potential for an established urban transmission of lymphatic filariasis in Ghana.

A Community-Wide Study of Malaria Reduction: Evaluating Efficacy and User-Acceptance of a Low-Cost Repellent in Northern Ghana

NO MAS (NM) mosquito repellent was evaluated in two farming villages (4 km apart) in the Kassena Nankana district of northern Ghana. We determined its efficacy against local malaria vectors, degree of user acceptance, and its effect on malaria prevalence in households using insecticide-treated bed nets. The average protective efficacy of NM against Anopheles mosquitoes over 9 hours was 89.6%. Controls averaged 86 bites/person/night versus 9 bites/person/night with the use of NM. Use of repellent was associated with a decrease of absolute malaria prevalence by 19.2% in the repellent village and by 6.5% in the control village (45.5 to 26.3, and 29.5 to 23.0, respectively). The user-acceptance rate of NM repellent was 96.1%. Ten percent (10%) of repellent users reported irritation as the main adverse effect during the period. Eighty-five percent (85%) of the users found the odor of NM appealing and 87% reported no inconvenience in applying the repellent daily.

Detection of malaria sporozoites by standard ELISA and VecTestTM dipstick assay in field‐collected anopheline mosquitoes from a malaria endemic site in Ghana

We compared the VecTestTM dipstick assay for detection of Plasmodium sporozoites in Anopheles vectors of malaria with standard circumsporozoite (CS) microplate ELISA for detection of Plasmodium falciparum circumsporozoite protein (PfCSP) in Anopheles mosquitoes. Mosquitoes were collected from a malaria endemic site (Kassena Nankana district) in northern Ghana. Of 2620 randomly sampled mosquitoes tested, the standard CS‐ELISA gave a sporozoite rate of 10.8% compared with 11.2% by VecTestTM, which was not statistically different (P = 0.66). Visual reading of the CS‐ELISA results gave a sporozoite rate of 13.4%, which was higher than the other tests (P > 0.05). To allow a more objective evaluation of the sensitivity of the dipstick, an additional 136 known CS‐ELISA‐positive specimens were analysed. The prevalence of the test (including the additional samples) was 14.6% and 14.7% for CS‐ELISA and dipstick, respectively (P > 0.05). The estimated prevalence by visual assessment of the CS‐ELISA results was 17.5%. The relative specificity and sensitivity of the VecTestTM dipstick and visually read ELISA were estimated based on the CS‐ELISA as a gold standard. The specificities of the dipstick and visual ELISA were high, 98.0% and 96.6%, respectively. However, the sensitivities of the two assays were 88.8% for VecTest and 100% for visual ELISA (P < 0.01). Concordance between VecTest and CS‐ELISA was good (κ = 0.86). Similarly, there was a good concordance between the dipstick and the visually read ELISA (κ =  0.88). Extrapolating from PfCSP controls (titrated quantities of P. falciparum sporozoites), mean sporozoite loads of CS‐ELISA‐positive An. gambiae (286 ± 28.05) and An. funestus (236 ± 19.32) were determined (P = 0.146). The visual dipstick grades showed high correlation with sporozoite load. The more intense the dipstick colour, the higher the mean sporozoite load (+ = 108, ++  = 207, +++ = 290, r = 0.99, r2 = 1). The VecTest dipstick offers practical advantages for field workers needing rapid and accurate means of detection of sporozoites in mosquitoes.

Discovery of Point Mutations in the Voltage-Gated Sodium Channel from African Aedes aegypti Populations: Potential Phylogenetic Reasons for Gene Introgression

Background Yellow fever is endemic in some countries in Africa, and Aedes aegpyti is one of the most important vectors implicated in the outbreak. The mapping of the nation-wide distribution and the detection of insecticide resistance of vector mosquitoes will provide the beneficial information for forecasting of dengue and yellow fever outbreaks and effective control measures. Methodology/Principal Findings High resistance to DDT was observed in all mosquito colonies collected in Ghana. The resistance and the possible existence of resistance or tolerance to permethrin were suspected in some colonies. High frequencies of point mutations at the voltage-gated sodium channel (F1534C) and one heterozygote of the other mutation (V1016I) were detected, and this is the first detection on the African continent. The frequency of F1534C allele and the ratio of F1534C homozygotes in Ae. aegypti aegypti (Aaa) were significantly higher than those in Ae. aegypti formosus (Aaf). We could detect the two types of introns between exon 20 and 21, and the F1534C mutations were strongly linked with one type of intron, which was commonly found in South East Asian and South and Central American countries, suggesting the possibility that this mutation was introduced from other continents or convergently selected after the introgression of Aaa genes from the above area. Conclusions/Significance The worldwide eradication programs in 1940s and 1950s might have caused high selection pressure on the mosquito populations and expanded the distribution of insecticide-resistant Ae. aegypti populations. Selection of the F1534C point mutation could be hypothesized to have taken place during this period. The selection of the resistant population of Ae. aegypti with the point mutation of F1534C, and the worldwide transportation of vector mosquitoes in accordance with human activity such as trading of used tires, might result in the widespread distribution of F1534C point mutation in tropical countries.

Role of Species Composition in Malaria Transmission by the Anopheles funestus Group (Diptera: Culicidae) in Ghana

ABSTRACT: Malaria remains a public health problem in Ghana, with Anopheles gambiae and Anopheles funestus as the predominant vectors. While much information exists on the species composition of An. gambiae, very little exists for An. funestus. This study was carried out to determine the species composition of An. funestus Giles populations from three ecological areas in Ghana and investigate their role in malaria transmission. Mosquitoes were collected using human landing and pyrethrum spray methods. A total of 10,254 Anopheles individuals were collected, out of which An. funestus constituted 53.6% (5,496). An. funestus sensu stricto (s.s.) and Anopheles lessoni were identified as the only members of the An. funestus group in all three ecological areas. All 62 sporozoite positive specimens that were identified as An. funestus s.s. were highly anthropophilic with a human blood index in the range of 80–96%, whereas more than 83% of the An. leesoni had fed on either bovine, goat, or sheep. Malaria transmission was higher in the Sahel savannah area than the rest of the ecological zones, with An. funestus s.s. being implicated as a vector of malaria in all ecological zones. Anopheles leesoni occurred in all the ecological areas but played no role in malaria transmission. The study established the importance of An. funestus s.s. in malaria transmission in Ghana.

Strategies towards attainment of universal coverage of long lasting insecticide treated nets (LLINs) distribution: experiences and lessons from Ghana

Long lasting Insecticidal nets continue to provide effective protection against disease vectors including mosquitoes that transmit malaria. In many countries, promotion of LLIN usage and ownership has focused on the attainment of universal coverage. However modalities for achieving these objectives remain a challenge in many countries. This paper shares Ghana’s experience and strategies adopted to attain universal LLINs coverage.

Studies on the feeding behaviour of larvae of the predaceous mosquito Culex (Lutzia) tigripes Grandpre and Chamoy (Diptera: Culicidae)

Experiments were carried out to determine the factors that influence the feeding behaviour of Culex tigripes, a mosquito whose larvae are predators of other mosquito larvae. The results indicated that the efficiency of predatory activities of Cx tigripes larvae increased as they developed from 1st to 4th instar with regard to the number of mosquito prey larvae they consumed in a given period of time. Fourth instars of Cx tigripes are the most voracious of all the stages and are better adapted for catching and consuming all stages of mosquito larvae. The mean number of mosquito larvae consumed in 24 hours increased with increasing prey density. When offered a mixture of different prey species and larval stages, Cx tigripes larvae consistently selected 4th instars of mosquitoes over pupae and preferred Aedes aegypti larvae to the larvae of Cx quinquefasciatus and Anopheles gambiae. Prey size, density and mobility were also found to influence prey selection by Cx tigripes.RésuméDes expériences ont été effectuées pour déterminer les facteurs qui influencent le comportement d’alimentation des Culex tigripes, un moustique dont les larves sont des prédateurs d’autres larves de moustique. Les résultats ont montré que l’efficacité des activités prédatrices des larves de Cx tigripes augmentait pendant qu’elles évoluaient du 1er au 4ème stade larvaire quand on considère le nombre de larves de moustique qu’elles ont consommées dans une période donnée. Les larves du 4ème stade de Cx tigripes sont les plus voraces de tous les stades larvaires et les mieux adaptées à la capture et à la consommation des larves autres moustiques. Le nombre moyen de larves consommées en 24 heures a augmenté avec l’acroissement de la densité des proies. Mises dans un millieu contenant un mélange de différentes espèces de proies, les larves de Cx tigripes ont montré une préférence pour les larves d’Aedes aegypti au détriment de celles de Cx quinquefasciatus et d’Anopheles gambiae. De même dans leur choix des différents stades larvaires à consommer, elles ont toujours préféré les larves du 4ème stade aux nymphes. Cette étude montre que les principaux facteurs qui influencent la sélection des proies par les larves de Cx tigripes sont la taille, l’abondance et la mobilité des proies.

Detection of a novel putative phlebovirus and first isolation of Dugbe virus from ticks in Accra, Ghana

Ticks are ectoparasites that transmit various types of human and animal pathogens. In particular, emerging and re-emerging diseases caused by tick-borne viruses are public health concerns around the world. However, in many countries of the sub-Saharan African region, epidemiological information on tick-borne viral infections is limited, and their prevalence and distribution remain largely unknown. In this study, we conducted surveillance on ticks to detect medically important tick-borne bunyaviruses in three study sites in and near to Accra, the capital city of Ghana, in 2015. Domestic dogs and cattle were surveyed and were found to be infested with various tick species belonging to the genera Rhipicephalus, Amblyomma and Haemaphysalis. Importantly, we detected a novel putative phlebovirus in Rhipicephalus ticks, and successfully isolated a new strain of Dugbe virus from Am. variegatum ticks. To our knowledge, this is the first report of tick-associated viruses in Ghana other than Crimean-Congo hemorrhagic fever virus.