Derivatization increases mosquito larvicidal activity of the sesquiterpene lactone parthenin isolated from the invasive weed Parthenium hysterophorus

Mosha M, Wampande E, Philemon R, N. Lwanga I, Seeley J, K. Sewankambo N. Public engagement by early career researchers during the COVID-19 pandemic: case studies from East Africa

Background

Community engagement and involvement (CEI) in research usually depends on face-to-face interactions. However, the COVID-19 pandemic prevented such interactions because of national lockdowns and social distancing. This paper highlights the ways in which early career researchers from East Africa tackled CEI activities during the pandemic.

Methods

We provide four case examples that illustrate how early-career researchers based in Kenya, Uganda and Tanzania, deployed different approaches and initiatives to community-engaged research during the pandemic to encourage participation and uptake of research findings.

Results

All the three early-career researchers attempted to use virtual/digital means to implement the CEI. However, in each country, this attempt was unsuccessful because of poor connectivity, as well as many poorer students lacking access to telephones and computers. Nevertheless, the researchers effectively engaged the students using different activities (making up songs, drawing comics, and taking part in quizzes) once the schools reopened.

Conclusion

These results highlight the complexity of implementing community engagement and involvement in health research when face-to-face interaction is not possible. The findings are relevant to researchers who wish to incorporate community engagement in their research and initiatives.

Neem-based products as potential eco-friendly mosquito control agents over conventional eco-toxic chemical pesticides-A review

Mosquitoes cause serious health hazards for millions of people across the globe by acting as vectors of deadly communicable diseases like malaria, filariasis, dengue and yellow fever. Use of conventional chemical insecticides to control mosquito vectors has led to the development of biological resistance in them along with adverse environmental consequences. In this light, the recent years have witnessed enormous efforts of researchers to develop eco-friendly and cost-effective alternatives with special emphasis on plant-derived mosquitocidal compounds. Neem oil, derived from neem seeds (Azadirachta indica A. Juss, Meliaceae), has been proved to be an excellent candidate against a wide range of vectors of medical and veterinary importance including mosquitoes. It is environment-friendly, and target-specific at the same time. The active ingredients of neem oil include limonoids like azadirachtin A, nimbin, salannin and numerous other substances that are still waiting to be discovered. Of these, azadirachtin has been shown to be very effective and is mainly responsible for its toxic effects. The quality of the neem oil depends on its azadirachtin content which, in turn, depends on its manufacturing process. Neem oil can be used directly or as nanoemulsions or nanoparticles or even in the form of effervescent tablets. When added to natural breeding habitat waters they exert their mosquitocidal effects by acting as ovicides, larvicides, pupicides and/or oviposition repellents. The effects are generated by impairing the physiological pathways of the immature stages of mosquitoes or directly by causing physical deformities that impede their development. Neem oil when used directly has certain disadvantages mainly related to its disintegration under atmospheric conditions rendering it ineffective. However, many of its formulations have been reported to remain stable under environmental conditions retaining its efficiency for a long time. Similarly, neem seed cake has also been found to be effective against the mosquito vectors. The greatest advantage is that the target species do not develop resistance against neem-based products mainly because of the innumerable number of chemicals present in neem and their combinations. This makes neem-based products highly potential yet unexplored candidates of mosquito control agents. The current review helps to elucidate the roles of neem oil and its various derivatives on mosquito vectors of public health concern.

Densovirus Oil Suspension Significantly Improves the Efficacy and Duration of Larvicidal Activity against Aedes albopictus

Aedes albopictus is the sole vector for various mosquito-borne viruses, including dengue, chikungunya, and Zika. Ecofriendly biological agents are required to reduce the spread of these mosquito-borne infections. Mosquito densoviruses (MDVs) are entomopathogenic mosquito-specific viruses, which can reduce the capacity of isolated vectors and decrease mosquito-borne viral disease transmission. However, their variable pathogenicity restricts their commercial use. In the present study, we developed a series of novel larvicide oil suspensions (denoted Bacillus thuringiensis (Bti) oil, Ae. albopictus densovirus (AalDV-5) oil, and a mixture of AalDV-5+Bti oil), which were tested against Ae. albopictus larvae under experimental semi-field and open-field conditions. The effect of AalDV-5 on non-target species was also evaluated. The combined effect of AalDV-5+Bti was greater than that of individual toxins and was longer lasting and more persistent compared with the laboratory AalDV-5 virus strain. The virus was quantified on a weekly basis by quantitative polymerase chain reaction (qPCR) and was persistently detected in rearing water as well as in dead larvae. Wildtype densovirus is not pathogenic to non-target organisms. The present findings confirm the improved effect of a mixed microbial suspension (AalDV-5+Bti oil) larvicide against Ae. albopictus. The development and testing of these products will enable better control of the vector mosquitoes.

A new cytotoxic sesquiterpene lactone from Euphorbia microsphaera Boiss against human breast cancer (MCF-7) and human fibrosarcoma (HT1080) cells

A new guaianolide sesquiterpene lactone with cytotoxic properties was isolated from Euphorbia microsphaera Boiss. To determine the highest active fraction and isolate bioactive compounds, a bioassay guided fractionation approach was used. The general toxicity properties of the plant's extracts and fractions (fr_1-10) were assessed against Artemia salina, Oryzeaphilus mercator, and Tribolium castaneum. Cytotoxic activities were investigated against normal human foreskin fibroblasts and two malignant cell lines, including human breast cancer (MCF-7) and human fibrosarcoma cells (HT1080) using the MTT assay at different time points of 24, 48, and 72 h. Single crystal X-ray diffraction (SC-XRD) and mass spectrometry data were used to determine the structure of the active guaianolide sesquiterpene lactone (3aR,4S,4aS,5R,7aS,9aS)-5-hydroxy-5,8-dimethyl-3-methylene-2-oxo-2,3,3a,4,4a,5,6,7,7a, 9a decahydroazuleno [6,5-b] furan-4-yl acetate (named aryanin). Chloroformic fraction 7 (fr₇, LC₅₀ = 93.50 μg/mL for general toxicity) had the highest toxicity result, with a mortality rate of more than 50% for both insect species after 12 h at 15 mg/mL. The highest cytotoxicity of aryanin was observed on 24 h treated MCF-7 with an IC₅₀ of 13.81 μg/mL. After 24 h, the inhibition of MCF-7 cell proliferation was 92%-94% at concentrations of 25-50 μg/mL, respectively. On MCF-7, the IC₅₀ was found to be 49.35 μg/mL after 72 h. This compound had a considerable cytotoxicity (IC₅₀ ≤ 12.5 μg/mL, 24 h) on human foreskin fibroblasts. In contrast to the MCF-7 cell line, the proliferation of human foreskin fibroblasts was increased after 72 h.

Parthenin-A Sesquiterpene Lactone with Multifaceted Biological Activities: Insights and Prospects

Parthenin, a sesquiterpene lactone of pseudoguaianolide type, is the representative secondary metabolite of the tropical weed Parthenium hysterophorus (Asteraceae). It accounts for a multitude of biological activities, including toxicity, allergenicity, allelopathy, and pharmacological aspects of the plant. Thus far, parthenin and its derivatives have been tested for chemotherapeutic abilities, medicinal properties, and herbicidal/pesticidal activities. However, due to the lack of toxicity-bioactivity relationship studies, the versatile properties of parthenin are relatively less utilised. The possibility of exploiting parthenin in different scientific fields (e.g., chemistry, medicine, and agriculture) makes it a subject of analytical discussion. The present review highlights the multifaceted uses of parthenin, on-going research, constraints in the practical applicability, and the possible workarounds for its successful utilisation. The main aim of this comprehensive discussion is to bring parthenin to the attention of researchers, pharmacologists, natural product chemists, and chemical biologists and to open the door for its multidimensional applications.

Naturally Occurring Compounds With Larvicidal Activity Against Malaria Mosquitoes

Female Anopheles mosquitoes transmit Plasmodium parasites that cause human malaria. Currently, vector control is the most widely deployed approach to reduce mosquito population and hence disease transmission. This relies on use of insecticide-based interventions including Long-lasting Insecticide-treated Nets (LLINs) and Indoor Residual Spraying (IRS) where scale-up has contributed to a dramatic decline in malaria deaths and morbidity over the past decade. Challenges to their effective use include the emergence and spread of insecticide resistance by malaria vector populations coupled with the inability to curb outdoor transmission. Under these situations, use of larvicides through larval source management (LSM) can complement these existing measures. The need to minimize environmental impact and effect on non-target organisms has spurred interest in the development of eco-friendly larvicides of natural origin. Here, we review literature published in the last five years to highlight compounds of natural origin found to exhibit larvicidal activity against malaria mosquitoes. Specifically, the larvicidal activity of different classes of compounds is discussed including their effect on non-target organisms. Additionally, we provide suggestions for future research into mosquito larvicides including the use of chemical synthesis to improve the bioactivity of known natural compounds.

Root exudate chemical cues of an invasive plant modulate oviposition behavior and survivorship of a malaria mosquito vector

Gravid female Anopheles gambiae mosquitoes identify suitable oviposition sites through a repertoire of cues, but the influence of allelochemicals, especially root phytochemicals in modulating this behavior and impacting subsequent progeny bionomics remains unexplored. We addressed these questions in the malaria vector Anopheles gambiae and its invasive host plant Parthenium hysterophorus. Using chemical analysis combined with laboratory behavioral assays, we demonstrate that a blend of terpenes, namely α-pinene, α-phellandrene, β-phellandrene, 3-carene and (E)-caryophyllene emitted from P. hysterophorus root exudate treated-water attracted gravid females. However, fewer eggs (55%) hatched in this treatment than in control water (66%). The sesquiterpene lactone parthenin, identified in both the natural aquatic habitat harboring P. hysterophorus and root exudate-treated water was found to be responsible for the ovicidal effect. Moreover, larvae exposed to parthenin developed 2 to 3 days earlier but survived 4 to 5 days longer as adults (median larval survival time = 9 days (all replicates);11 to 12 days as adults) than the non-exposed control (median larval survival time = 11 days (reps 1 & 2), 12 days (rep 3); 6 to 7 days as adults). These results improve our understanding of the risk and benefits of oviposition site selection by gravid An. gambiae females and the role root exudate allelochemicals could play on anopheline bionomics, with potential implications in malaria transmission.