Attractant and repellent properties of Senna didymobotrya plant extracts to Amblyomma variegatum and Rhipicephalus appendiculatus.

The growing challenge of acaricide resistance and geographical range expansion of invasive tick species demands other interventions, like plant-based alternatives, for sustainable tick control. Leaves, flowers, seedpods, and twig branch extracts of Senna didymobotrya were analyzed using coupled gas chromatography mass spectrometry (GC-MS). Response of adult Amblyomma variegatum and Rhipicephalus appendiculatus to extracts was evaluated. The most attractive plant extract was fractionated and ticks' responses to its fractions assessed. Potential tick attractants in the attractive plant part extract and its fractions were identified by GC-MS analysis. Non- significant qualitative and quantitative differences were observed in the plant parts' extract composition (R = 0.6178). Flower extracts attracted both species, with a 0.1-fold higher attraction in A. variegatum compared to the standard attraction aggregation attachment pheromone (AAAP). Leaf and seedpod extracts repelled ticks at various concentrations. Bioassays after fractionating flower extracts identified hexane and ethyl acetate fractions as most attractive to A. variegatum (P < 0.001) and R. appendiculatus (P < 0.001), respectively. Chemical analysis of the most attractive extracts and fractions identified compounds, including documented acarine attractants, squalene and linoleic acid. A squalene and linoleic acid blend (1:1) at 1 mg/mL significantly attracted adult A. variegatum (P < 0.01) and R. appendiculatus (P < 0.001). The results of this study broaden comprehension of how ticks respond to plants in nature, and showcase the promising potential for integrating these insights into effective tick management programs.

Isoliensinine from Cissampelos pariera rhizomes exhibits potential gametocytocidal and anti-malarial activities against Plasmodium falciparum clinical isolates.

BACKGROUND: The unmet demand for effective malaria transmission-blocking agents targeting the transmissible stages of Plasmodium necessitates intensive discovery efforts. In this study, a bioactive bisbenzylisoquinoline (BBIQ), isoliensinine, from Cissampelos pariera (Menispermaceae) rhizomes was identified and characterized for its anti-malarial activity. METHODS: Malaria SYBR Green I fluorescence assay was performed to evaluate the in vitro antimalarial activity against D6, Dd2, and F32-ART5 clones, and immediate ex vivo (IEV) susceptibility for 10 freshly collected P. falciparum isolates. To determine the speed- and stage-of-action of isoliensinine, an IC50 speed assay and morphological analyses were performed using synchronized Dd2 asexuals. Gametocytocidal activity against two culture-adapted gametocyte-producing clinical isolates was determined using microscopy readouts, with possible molecular targets and their binding affinities deduced in silico. RESULTS: Isoliensinine displayed a potent in vitro gametocytocidal activity at mean IC50gam values ranging between 0.41 and 0.69 µM for Plasmodium falciparum clinical isolates. The BBIQ compound also inhibited asexual replication at mean IC50Asexual of 2.17 µM, 2.22 µM, and 2.39 µM for D6, Dd2 and F32-ART5 respectively, targeting the late-trophozoite to schizont transition. Further characterization demonstrated a considerable immediate ex vivo potency against human clinical isolates at a geometric mean IC50IEV = 1.433 µM (95% CI 0.917-2.242). In silico analyses postulated a probable anti-malarial mechanism of action by high binding affinities for four mitotic division protein kinases; Pfnek1, Pfmap2, Pfclk1, and Pfclk4. Additionally, isoliensinine was predicted to possess an optimal pharmacokinetics profile and drug-likeness properties. CONCLUSION: These findings highlight considerable grounds for further exploration of isoliensinine as an amenable scaffold for malaria transmission-blocking chemistry and target validation.

Contemporary exploitation of natural products for arthropod-borne pathogen transmission-blocking interventions.

An integrated approach to innovatively counter the transmission of various arthropod-borne diseases to humans would benefit from strategies that sustainably limit onward passage of infective life cycle stages of pathogens and parasites to the insect vectors and vice versa. Aiming to accelerate the impetus towards a disease-free world amid the challenges posed by climate change, discovery, mindful exploitation and integration of active natural products in design of pathogen transmission-blocking interventions is of high priority. Herein, we provide a review of natural compounds endowed with blockade potential against transmissible forms of human pathogens reported in the last 2 decades from 2000 to 2021. Finally, we propose various translational strategies that can exploit these pathogen transmission-blocking natural products into design of novel and sustainable disease control interventions. In summary, tapping these compounds will potentially aid in integrated combat mission to reduce disease transmission trends.

Determinants of knowledge about aflatoxin and fumonisin contamination in sorghum and postharvest practices among caregivers of children aged 6-59 months in Kerio Valley, Kenya.

Stunting among children under five years old is still a problem in many developing countries including Kenya. However, there is little information linking stunting with mycotoxin contamination of complementary foods. The aim of this study was to assess knowledge about aflatoxin and fumonisin contamination in sorghum alongside postharvest handling and storage practices among caregivers of children under five years old in Kerio Valley, Kenya. A cross-sectional study was conducted to obtain data from 353 randomly selected caregivers of children aged 6-59 months. Qualitative data were obtained through Focus Group Discussions and Key Informant Interviews. Overall, majority of the caregivers of young children had poor knowledge (61.8%) about mycotoxin contamination of food, and poor postharvest handling and storage practices (74.5%). The caregiver's knowledge about mycotoxins was significantly associated with age [(AOR=4.629, (95% Cl: 2.530-8.472), p < .001], education level [(AOR=0.275, (95% Cl: 0.088-0.434), p = .001], marital status [(AOR=15.187, (95% Cl: 1.830-126.007), p = .012], and household monthly income [(AOR=2.623, (95% Cl: 1.550-4.439), p < 0,001]. Furthermore, the caregiver's age [(AOR=3.845, (95% Cl: 1.558-9.490), p = .003], education level [(AOR=0.196, (95% Cl: 0.088-0.434), p < .001], monthly income [(AOR=3.291, (95% Cl: 1.550-6.986), p = .002], and knowledge on mycotoxin contamination of sorghum [AOR, 5.428 (95% Cl: 2.855-10.319), p < .001] were significantly associated with postharvest handling and storage practices except for marital status [AOR, 3.579 (95% Cl: 0.403-31.775), p = .252]. In conclusion, caregivers of young children had poor knowledge about mycotoxin contamination of complementary foods and suboptimal postharvest handling and storage practices of sorghum. This increases the risk of mycotoxin exposure to young children and necessitates mitigation measures including sensitization campaigns and social behavior change communication.

Neurotoxic Zanthoxylum chalybeum root constituents invoke mosquito larval growth retardation through ecdysteroidogenic CYP450s transcriptional perturbations.

Intracellular effects exerted by phytochemicals eliciting insect growth-retarding responses during vector control intervention remain largely underexplored. We studied the effects of Zanthoxylum chalybeum Engl. (Rutaceae) (ZCE) root derivatives against malaria (Anopheles gambiae) and arbovirus vector (Aedes aegypti) larvae to decipher possible molecular targets. We report dose-dependent biphasic effects on larval response, with transient exposure to ZCE and its bioactive fraction (ZCFr.5) inhibiting acetylcholinesterase (AChE) activity, inducing larval lethality and growth retardation at sublethal doses. Half-maximal lethal concentrations (LC50) for ZCE against An. gambiae and Ae. aegypti larvae after 24-h exposure were 9.00 ppm and 12.26 ppm, respectively. The active fraction ZCFr.5 exerted LC50 of 1.58 ppm and 3.21 ppm for An. gambiae and Ae. aegypti larvae, respectively. Inhibition of AChE was potentially linked to larval toxicity afforded by 2-tridecanone, palmitic acid (hexadecanoic acid), linoleic acid ((Z,Z)-9,12-octadecadienoic acid), sesamin, ß-caryophyllene among other compounds identified in the bioactive fraction. In addition, the phenotypic larval retardation induced by ZCE root constituents was exerted through transcriptional modulation of ecdysteroidogenic CYP450 genes. Collectively, these findings provide an explorative avenue for developing potential mosquito control agents from Z. chalybeum root constituents.

Influence of task-based airborne lead exposures on blood lead levels: a case study of informal automobile repair artisans in Nakuru town, Kenya.

Lead poisoning is an emerging worldwide public health concern, especially in the developing countries. Occupational tasks such as spray painting and welding in informal automobile repair enterprises present risks of exposures to lead generally through inhalation and ingestion. The artisans therefore risk high blood lead (BPb) levels, which is critical to chronic adverse health effects of lead. The study aimed at assessing the influence of occupational tasks on personal airborne lead exposures and to evaluate the association between these exposures with blood lead (BPb) levels among the artisans. A cross-sectional study was conducted in ten informal automobile repair workshops. Task-specific personal inhalable air samples and blood samples were collected concurrently for 20 participants performing five distinct occupational tasks. Lead levels were analysed using inductively coupled plasma atomic emission spectroscopy and data analysed by analysis of variance, simple and multiple linear regressions. The results indicated significant differences in airborne lead (PbA) exposure levels in different occupational tasks (p = 0.000). Lead-acid battery repairs recorded mean PbA exposure level of [76.11 ± (10.81 SE) µg/m3] exceeding the WHO 50 µg/m3 airborne lead permissible exposure limit. The average (PbA) exposure level was 22.55 ± (5.05 SE) µg/m3, while the mean (BPb) level was 25.08 ± (3.48 SE) µg/dl. A significant positive correlation between task-based airborne lead with blood lead levels was observed (r = 0.68, p = 0.001). In conclusion, the occupational tasks influenced personal airborne lead exposure levels, which in turn was an important predictor of blood lead levels. The study recommends lead exposure assessments, medical screening and intervention measures to minimize the risk and consequences of occupational exposures to lead among the study population.

Maize Chlorotic Mottle Virus Induces Changes in Host Plant Volatiles that Attract Vector Thrips Species.

Maize lethal necrosis is one of the most devastating diseases of maize causing yield losses reaching up to 90% in sub-Saharan Africa. The disease is caused by a combination of maize chlorotic mottle virus (MCMV) and any one of cereal viruses in the Potyviridae group such as sugarcane mosaic virus. MCMV has been reported to be transmitted mainly by maize thrips (Frankliniella williamsi) and onion thrips (Thrips tabaci). To better understand the role of thrips vectors in the epidemiology of the disease, we investigated behavioral responses of F. williamsi and T. tabaci, to volatiles collected from maize seedlings infected with MCMV in a four-arm olfactometer bioassay. Volatile profiles from MCMV-infected and healthy maize plants were compared by gas chromatography (GC) and GC coupled mass spectrometry analyses. In the bioassays, both sexes of F. williamsi and male T. tabaci were significantly attracted to volatiles from maize plants infected with MCMV compared to healthy plants and solvent controls. Moreover, volatile analysis revealed strong induction of (E)-4,8-dimethyl-1,3,7-nonatriene, methyl salicylate and (E,E)-4,8,12-trimethyltrideca-1,3,7,11-tetraene in MCMV-infected maize seedlings. Our findings demonstrate MCMV induces changes in volatile profiles of host plants to elicit attraction of thrips vectors. The increased vector contact rates with MCMV-infected host plants could enhance virus transmission if thrips feed on the infected plants and acquire the pathogen prior to dispersal. Uncovering the mechanisms mediating interactions between vectors, host plants and pathogens provides useful insights for understanding the vector ecology and disease epidemiology, which in turn may contribute in designing integrated vector management strategies.

Perennial and seasonal contamination of maize by aflatoxins in eastern Kenya.

BACKGROUND: Aflatoxin contamination of grain is a major constraint to sustained quality cereal production. The causative fungi, Aspergillus species infect crops in the field and continue to do so post-harvest where they produce toxins in store. The current study aimed at establishing seasonal variation in levels and types of aflatoxins in maize from the Eastern region of Kenya- the hot-spot for aflatoxicosis. Maize kernels were collected from farmers' households in May and December 2013 -2 months after long rain and short rain season respectively. The total aflatoxins were quantified using Enzyme-Linked Immunosorbent Assay (ELISA), while the toxin composition was determined using Thin-Layer Chromatography (TLC) and confirmed using High-Performance Liquid Chromatography (HPLC). RESULTS: Generally, grain harvested after the long rains (May) had significantly (p = 0.019) lower aflatoxin levels and variation (5.68 ± 6.31 ppb, 100% Aflatoxin B1) than that of short rains (10.77 ± 10.14 ppb, 72% AFB1). Additionally, from the long and short rain seasons, the samples exceeding regulatory allowed limit (10 ppb) were 16 and 44% respectively. CONCLUSION: In Eastern Kenya, consumption of maize harvested in the long rain season presents a recurrent risk of exposure to low levels of AFB1; while consumption of maize harvested after the short rain season presents a risk of seasonal exposure to high levels and mixed type of toxins However, this long term risk of exposure to aflatoxins is poorly documented hence these findings necessitate mitigation measures because AFB1- is a potent class 1 mutagenic toxin likely to cause liver cancer.

Antimicrobial and cytotoxicity properties of the organic solvent fractions of Clerodendrum myricoides (Hochst.) R. Br. ex Vatke: Kenyan traditional medicinal plant.

BACKGROUND/AIM: Clerodendrum myricoides is a Kenyan herbal plant used in the management of respiratory diseases. In the current study, we investigated in vitro antimicrobial activity, cytotoxicity, and phytochemical screening of C. myricoides. MATERIALS AND METHODS: Antimicrobial activities of C. myricoides organic fractions against array of microorganisms including: (i) Mycobacterium tuberculosis (MTB) H37Rv, (ii) Staphylococcus aureus, (iii) Klebsiella pneumoniae, (iv) Escherichia coli, (v) Candida albicans, (vi) Pseudomonas aeruginosa, (vii) Cryptococcus neoformans, (viii) Salmonella typhi, (ix) Shigella sonnei, and (x) Methicillin-resistant S. aureus (MRSA) were investigated by disc diffusion and microdilution techniques. Antituberculous activity was investigated using BACTEC MGIT 960 system while cytotoxicity was analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay on HEp-2 cells. Finally, phytochemicals were screened using standard procedures. RESULTS: Methanolic fractions exhibited a broad spectrum activity inhibiting 75% of test pathogens. It had the highest activity with minimal inhibition concentration (MIC) values of ≤62.5 µg/ml recorded against 62.5% tested microbes. It yielded the highest zone of inhibition of 20.3 mm (S. aureus), lowest MIC of <12.5 µg/ml (MTB), and the lowest minimal bactericidal concentration of 62.5 µg/ml (C. albicans), within the acceptable toxicity limit (CC50 >90 µg/ml). The phytochemicals largely believed to be responsible for the observed activity included: Alkaloid, phenols, anthraquinones, terpenoids, and flavonoids. CONCLUSION: Methanolic fraction had remarkable activity against MRSA, S. aureus, E. coli, S. sonnei, C. albicans, and MTB, which are of public health concerns due to drug resistance and as sources of community and nosocomial infections. To the best of our knowledge, this is the first report exploring the antituberculous activity of C. myricoides and thence a major output in search of novel, safe drug leads to mitigate the global tuberculosis threat.

Antimicrobial and cytotoxicity properties of the crude extracts and fractions of Premna resinosa (Hochst.) Schauer (Compositae): Kenyan traditional medicinal plant.

BACKGROUND: Premna resinosa (Hochst.) Schauer also called "mukarakara" in Mbeere community of Kenya is used in the management of respiratory illness. In this study we investigated antituberculous, antifungal, antibacterial activities including cytotoxicity and phytochemical constituents of this plant. METHODS: Antibacterial and antifungal activities were investigated by disc diffusion and micro dilution techniques. Antituberculous activity was investigated using BACTEC MGIT 960 system while cytotoxicity was analyzed by MTT assay on Vero cells (Methanolic crude extract) and HEp-2 cells (fractions). Finally, phytochemicals were profiled using standard procedures. RESULTS: P. resinosa had high antituberculous activity with a MIC of <6.25 µg/ml in ethyl acetate fraction. The antibacterial activity was high and broad spectrum, inhibiting both Gram positive and Gram negative bacteria. Dichloromethane fraction had the best antibacterial MIC of 31.25 µg/ml against Methicillin-resistant S. aureus while Ethyl acetate fraction had the highest zone of inhibition of 22.3±0.3 against S. aureus. Its effects on tested fungi were moderate with petro ether fraction giving an inhibition of 10.3±0.3 on C. albicans. The crude extract and two fractions (petro ether and methanol) were not within the acceptable toxicity limits, however dichloromethane and ethyl acetate fractions that exhibited higher activity were within the acceptable toxicity limit (CC50<90). The activity can to some extent be associated to alkaloids, flavonoids, terpenoids, anthraquinones and phenols detected in this plant extracts. CONCLUSION: Our findings demonstrate that P. resinosa has high selective potential as a source of novel lead for antituberculous, antibacterial and antifungal drugs. Of particular relevance is high activity against MRSA, S. aureus, C. albicans and MTB which are great public health challenge due to drug resistance development and as major sources of community and hospital based infections.

Larvicidal activity of selected aloe species against Aedes aegypti (Diptera: Culiciade).

Management of mosquito vectors by current classes of mosquitocides is relatively ineffective and necessitates prospecting for novel insecticides with different modes of action. Larvicidal activities of 15 crude extracts from three geographically isolated Aloe ngongensis (Christian), Aloe turkanensis (Christian), and Aloe fibrosa (Lavranos & L.E.Newton) (Xanthorrhoeaceae) species (five each) were evaluated against Aedes aegypti (Linnaeus in Hasselquist) (Diptera: Culiciade L.) yellow fever mosquito. Freshly collected leaves were separately shade-dried to constant weight at room temperature (25 ± 2°C) and powdered. Each powder was macerated in solvents of increasing polarity (hexane, chloroform, ethyl acetate, acetone, and methanol) for 72 h and subsequently filtered. Third-instar larvae (n = 25) of the mosquito were exposed to the extracts at different concentrations for 24 h to establish dose response relationships. All the fractions of A. ngongensis were active below 1 mg/ml except A. fibrosa and A. turkanensis. The highest activity (LC50) mg/ml was obtained with extracts of A. fibrosa hexane (0.05 [0.04-0.06]), followed by A. ngongensis hexane (0.11 [0.08-0.15]) and A. turkanensis ethyl acetate (0.11 [0.09-0.12]). The activities are apparently Aloe species specific and extraction solvent dependent. These findings suggest that extracts from selected Aloe species have mosquitocidal principles that can be exploited in development of new insecticides.

Evolution and Structural Analyses of Glossina morsitans (Diptera; Glossinidae) Tetraspanins.

Tetraspanins are important conserved integral membrane proteins expressed in many organisms. Although there is limited knowledge about the full repertoire, evolution and structural characteristics of individual members in various organisms, data obtained so far show that tetraspanins play major roles in membrane biology, visual processing, memory, olfactory signal processing, and mechanosensory antennal inputs. Thus, these proteins are potential targets for control of insect pests. Here, we report that the genome of the tsetse fly, Glossina morsitans (Diptera: Glossinidae) encodes at least seventeen tetraspanins (GmTsps), all containing the signature features found in the tetraspanin superfamily members. Whereas six of the GmTsps have been previously reported, eleven could be classified as novel because their amino acid sequences do not map to characterized tetraspanins in the available protein data bases. We present a model of the GmTsps by using GmTsp42Ed, whose presence and expression has been recently detected by transcriptomics and proteomics analyses of G. morsitans. Phylogenetically, the identified GmTsps segregate into three major clusters. Structurally, the GmTsps are largely similar to vertebrate tetraspanins. In view of the exploitation of tetraspanins by organisms for survival, these proteins could be targeted using specific antibodies, recombinant large extracellular loop (LEL) domains, small-molecule mimetics and siRNAs as potential novel and efficacious putative targets to combat African trypanosomiasis by killing the tsetse fly vector.

Genetic diversity in Napier grass (Pennisetum purpureum) cultivars: implications for breeding and conservation.

Napier grass is an important forage crop for dairy production in the tropics; as such, its existing genetic diversity needs to be assessed for conservation. The current study assessed the genetic variation of Napier grass collections from selected regions in Eastern Africa and the International Livestock Research Institute Forage Germplasm-Ethiopia. The diversity of 281 cultivars was investigated using five selective amplified fragment length polymorphism (AFLP) markers and classical population genetic parameters analysed using various software. The number of bands generated was 216 with fragments per primer set ranging from 50 to 115. Mean percentage polymorphic loci was 63.40. Genetic diversity coefficients based on Nei's genetic diversity ranged from 0.0783 to 0.2142 and Shannon's information index ranged from 0.1293 to 0.3445. The Fst value obtained was moderately significant (Fst = 0.1688). Neighbour-joining analysis gave two distinct clusters which did not reflect geographical locations. Analysis of molecular variance showed all variance components to be highly significant (P < 0.001), indicating more variation within (91 %) than between populations (9 %). Results suggested moderate genetic differentiation among Napier grass populations sampled, which could imply a high germplasm exchange within the region. The AFLP markers used in this study efficiently discriminate among cultivars and could be useful in identification and germplasm conservation.