Molluscicidal Activity of Selected Plant Extracts against Adult and Juvenile Biomphalaria Pfeifferi

Human Schistosomiasis is a debilitating infection whose transmission depends solely on the presence of snail intermediate hosts. It is a major public health problem second only to malaria in terms of morbidity and mortality and predominant in tropical and subtropical countries. Globally, over 240 million people are infected and close to 600milion are at risk.Strategies for Control of Schistosomiasis include; Chemotherapy with praziquantel, mollusciciding with Niclosamide, health education, community participation, provision of clean water and improved sanitation. Chemotherapy and use of synthetic molluscicides faces serious drawbacks of being costly, poses negative impact on environment and development of resistant strains of intermediate host snails and parasites. Plant extracts that are effective against host snails and non-toxic to non-target organisms could provide an alternative molluscicide to the current Niclosamide.This study evaluated molluscicidal activity of aqueous and methanol extracts against juvenile and adult Biomphalaria pfeifferi in vitro.Assesment of snail susceptibility to extracts was done by immersion method in accordance to WHO protocal.10 adult and juvenile snails were exposed separately to serial dilutions of 10, 20, 50, 100 and 150ppm (mg/l) of both aqueous and methanol extracts for 48 hours. Mean mortality of snails was subjected to probit analysis to determine the lethal dose (LD50) that killed 50% of the snails. The most active extracts on both juvenile and adults were Phytolacca dodecandra (LD50 8.78 and 12.58ppm) and Solannum linaeanum (LD50 16.81 and 23.25ppm) respectively.This was followed by Solanum americanum (LD50 36.17 and 38.00ppm) and Annona squamosa (LD50 51.96 and 59.00ppm) respectively. The least active extracts were Piper nigrum (LD50 74.13 and 89.95ppm) and Rhizophora mucranata LD50 94.56 and 109.82 ppm) respectively. Average mortality of Phytolacca dodecandra and solanum linaeanum was significantly similar (p ˃ 0.05) to that of niclosamide the currently used molluscicde.Since a good molluscicide should kill snails at a concentration of 100ppm or lower, this study demonstrated potency of four plant species from Kenya with molluscicidal activity against the intermediate hosts of Schistosoma mansoni. Keywords: Schistosomiasis, Biomphalaria pfeifferi, Schistosoma mansoni, Molluscicide, Phytolacca dodecandra, Solanum linaeanum, Solanum americanum, Annona squamosa

Evaluation of Cercaricidal and Miracicidal Activity of Selected Plant Extracts Against Larval Stages of Schistosoma Mansoni

Schistosomiasis is a parasitic disease caused by blood-flukes of the genus Schistosoma. It is one of the most widespread of all human parasitic diseases, ranking second only to malaria in terms of its socioeconomic and public health importance in tropical and subtropical areas.More than 207 million people, 85% of whom live in Africa, are infected with schistosomiasis,and an estimated700 million people are at risk of infection in 76 countries.Control of schistosomiasis faces serious drawbacks of emergence of drug resistant parasites and molluscicide resistant snail hosts.Due to improper waste disposal,infected faecal matter enter water bodies such as canals rivers and springs where miracidia that hatch from parasite eggs  develop into cercariae inside snail intermediate hosts and are infective to humans upon release in to the water.This study sought to evaluate the miracicidal and cercaricidal activity of selected plant extracts on larval stages of Schistosoma mansoni.Ten cercariae and miracidia were exposed to extract concentrations ranging from 10-150ppm.The most active extracts were Phytolacca dodecandra (LT50 10.84 and16.91minutes) and Solanum linaeanum (LT50 of 22.86 and 26.96 minutes) respectively that killed 50% of miracidia and cercariae in less than 30minutes.This was followed closely by Solanum americanum (LT50 31.02 and 31.89) and Anonna squamosa LT50 35.29 and 40.46minutes respectively.Piper nigrum was the least active recording LT50 46.84 and 56.75 of miracidia and cercaria respectively.Miracidia were more susceptible to extracts than cercariae.The higher susceptibility of miracidia to extracts has also been reported in other studies and it is advantageous since killing one miracidium prevents the formation of thousands of cercariae which are infective to humans.All the extracts killed larvae within one hour at concentration less than 100ppm and could be categorized as potent cercaricide and miracicides. Keywords: Miracidal, Cercaricidal,Schistosomiasis,Phytolacca dodecandra,Solanum linaeanum,Solanum americanum,Anonna squamosa and Piper nigru

Repellency and composition of essential oils of selected ethnobotanical plants used in Western Kenya against bites of Anopheles gambiae Sensu Stricto

The essential oils of Ocimum gratissimum Linn, Hyptis suaveolens (L) Poit and Vitex keniensis, which are used traditionally in Western Kenya for personal and space protection against mosquito bites, were screened for repellence against Anopheles gambiae Sensu Stricto. Essential oils were extracted from their leaves by hydrodistillation, characterised by gas chromatography linked with mass spectrophotometer and electroantennogram detectors. The repellency of the oils and their selected blends was studied by the reduction in probing and feeding on the human arm. The oils showed promising repellency for Anopheles gambiae, O. gratissimum (RD50 = 2.77 × 10-5 mg cm-2, 95% CI), Vitex keniensis (RD = 5.68 × 10-5 mg cm-2) and Hyptis suaveolens (6.27× 10-5 mg cm-2) as compared to that of DEET (control) RD = 1.25×10-5 mg cm-2). The bioactive constituents of each oil were identified by Gas chromatography-linked with Mass spectrometry and Electroantennography. Some compounds were confirmed by co-injections of the oil with available authentic standards. The results provide a scientific rationale for the traditional use of these plants in repelling disease vectors and other biting insects, and lay down some useful groundwork for downstream development of more effective products for personal and space protection

An assessment of participatory integrated vector management for malaria control in Kenya

BACKGROUND : The World Health Organization (WHO) recommends integrated vector management (IVM) as a strategy to improve and sustain malaria vector control. However, this approach has not been widely adopted. OBJECTIVES : We comprehensively assessed experiences and findings on IVM in Kenya with a view to sharing lessons that might promote its wider application. METHODS : The assessment used information from a qualitative external evaluation of two malaria IVM projects implemented between 2006 and 2011 and an analysis of their accumulated entomological and malaria case data. The project sites were Malindi and Nyabondo, located in coastal and western Kenya, respectively. The assessment focused on implementation of five key elements of IVM: integration of vector control methods, evidence-based decision making, intersectoral collaboration, advocacy and social mobilization, and capacity building. RESULTS : IVM was more successfully implemented in Malindi than in Nyabondo owing to greater community participation and multistakeholder engagement. There was a significant decline in the proportion of malaria cases among children admitted to Malindi Hospital, from 23.7% in 2006 to 10.47% in 2011 (p < 0.001). However, the projects’ operational research methodology did not allow statistical attribution of the decline in malaria and malaria vectors to specific IVM interventions or other factors. CONCLUSIONS : Sustaining IVM is likely to require strong participation and support from multiple actors, including community-based groups, non-governmental organizations, international and national research institutes, and various government ministries. A cluster-randomized controlled trial would be essential to quantify the effectiveness and impact of specific IVM interventions, alone or in combination.Grants from the Biovision Foundation (Switzerland) through the International Centre of Insect Physiology and Ecology (ICIPE).http://ehp.niehs.nih.govam2016School of Health Systems and Public Health (SHSPH

<b>2-Hydroxy-4-methoxybenzaldehyde: Larvicidal structure-activity studies</b>

2-Hydroxy-4-methoxybenzaldehyde (<b>1</b>), a compound isolated from <i>Mondia whytei</i> (Hook) Skeels (Asclepiaceae) roots exhibited larvicidal activity (LD₅₀ 22 &mu;g/mL). A total of 18 other derivatives and closely related congeners revealed varying levels of larvicidal activity. Several closely related congeners, like 2-benzyloxy-4-methoxybenzaldehyde (<b>2</b>), 2-hydroxybenzaldehyde (<b>12</b>), 2-benzyloxybenzaldehyde (<b>3</b>) and benzylphenyl ether (<b>4</b>), showed marked improvement in activity (LD₅₀ 10, 9, 4.8, 1.2 &mu;g/mL, respectively) against <i>Anopheles gambiae</i> larvae. 2-Benzoyloxy-4-methoxybenzaldehyde (<b>5</b>) exhibited similar activity level (LD₅₀ 28 &mu;g/mL) as <b>1</b>

Larvicidal activity of extracts from three Plumbago spp against Anopheles gambiae

Three Plumbago spp have been tested for mosquito larvicidal activity. The crude extracts exhibiting the highest larvicidal activity against Anopheles gambiae were hexane (LC50 = 6.4 μg/mL) and chloroform (LC50 = 6.7 μg/mL) extracts from Plumbago zeylanica Linn, chloroform (LC50 = 6.7 ug/mL) extract from Plumbago stenophylla Bull and ethyl acetate (LC50 = 4.1 μg/mL) extract from Plumbago dawei Rolfe. These LC50 values were within 95% confidence limits. 5-hydroxy-2-methyl-1,4-naphthoquinone (plumbagin) 1 (LC50 = 1.9 μg/mL) and β-sitosterol 2 were characterised from ethyl acetate extract of root bark of P. dawei, a native medicinal plant growing in Kenya, based on spectral analysis and comparisons with data in literature

Mosquitoes Larvicidal Activity of Ocimum kilimandscharicum Oil Formulation under Laboratory and Field-Simulated Conditions

Mosquitoes are vectors of many severe diseases, including malaria, yellow as well as dengue fever, and lymphatic filariasis. The use of synthetic chemical insecticides for mosquito control has been associated with resistance development and detrimental human, and ecological effects. For a safer alternative, the emulsified Ocimum kilimandscharicum oil formulation was evaluated for its larvicidal activity. The oil was analyzed by GC and GC/MS. The formulations were evaluated against third instar mosquito larvae in the laboratory and later compared with Bacillus thuringiensis subsp. israelensis against An. gambiae under field-simulated conditions. Thirty-nine compounds were identified in the oil, the main ones being D-camphor (36.6%) and limonene (18.6%). The formulation showed significant larval mortalities against An. gambiae and An. arabiensis larvae with LC50 of 0.07 and 0.31 ppm, respectively, at 24 h. Under the field-simulated trial, within 24 h, the formulation showed 98% mortality while Bti had achieved 54%. On day three, it caused 100% mortality while Bti achieved 76.5%. The high bioactivity and sublethal toxic effects to offspring of treated mosquito larvae, in terms of disruption of larval morphological aspects, suggest the high potential of the formulation as a botanical larvicide. The formulation, thus, may provide a valuable alternative for the effective and eco-friendly control of disease vectors.ISSN:2075-445