Abstract

Background: Malaria has been a great challenge to humanity since time immemorial. An estimated 300-500 million people are affected by malaria throughout the world annually. Source from the World Health Organization (WHO) indicates that 95% of malaria-related deaths occur in sub-Saharan Africa, with children younger than  five years and pregnant women being the most severely affected.

Anopheles gambiae (Culicidae) is the main vector for malaria which is endemic in Cameroon and Africa at large. Mosquitoes have become resistant to synthetic materials used for their control. The introduction of plant metabolites which are relatively biodegradable may be more potent and safer for human health in the control programme of this vector.

Plants of the Simaroubaceae family are very rich in bioactive secondary metabolites and have displayed insecticidal properties in various studies. Hence, as part of this global effort, this present study aimed at evaluating  the larvicidal activity of the crude methanol extracts, of  Brucea antidysenterica and Brucea guineensis against the IV instar larvae of the malaria vector An. gambiae mosquitoes.

Methods: The leaves of B. antidysenterica and B. guineensis were collected, dried, ground to powder and extracted in cold methanol. The extracts were screened qualitatively for the presence of secondary metabolites. Larvicidal activity was  investigated on the larvae of Anopheles gambiae by direct contact method. Twenty instar larvae of  An. gambiae  were put in disposable cups containing  99 mL of water and 1ml of the extracts at various concentrations  (2000, 1000, 500, 250, 125 and 62.5 mg/mL solution of the extract),  and were evaluated . After 24 and 48hours respectively the number of dead larvae in each cup were counted, percentage mortality was calculated and LD50 was determined using a non-linear regression analysis software.

Results: Qualitative phytochemical screening revealed the presence of moderate amounts of tannins, saponins and sterols and trace amounts of phenols. The crude methanolic extracts of both plants showed toxicity against the larva.  B. guineensis displaying 100% mortality at 2000 mg/mL after 48hr exposure with an LD50 of 141.67mg/ml and 58.33 mg/ml after 24 hr and 48 hr respectively.  Brucea antidysenterica after 48 hours and displayed 33.3% mortality at 2000mg/ml.

Conclusion

Both plants possess intrinsic larvicidal effects against the Anopheles gambiae and hence can be developed as an ecologically sustainable vector control agent. Brucea guineensis was more active and could be further studies to isolate the compounds responsible for.

CHAPTER ONE

INTRODUCTION 

1.1 INTRODUCTION

Malaria is the most important mosquito-borne disease and is caused by the Plasmodium parasites through an infective bite of female Anopheles mosquitoes. It affects millions of people mainly in the tropics. In spite of many efforts undertaken for its control, through chemotherapy treatment and vector control, an increase in malaria incidence has occurred in the last 30 years, primarily caused by socio-economic factors, underdevelopment and drug and insecticidal resistance. [1].

The female Anopheles mosquito is the vector for human malaria and over sixty species of Anopheles have been identified as vectors of Plasmodium. Globally, malaria caused an estimated 219 (range 154-289) million cases and 660,000 (range 490,000-836,000) deaths in 2010. Approximately 80% of the cases and 90% of the deaths occur in Africa [2].

Malaria remains a serious and growing health problem in many developing countries, particularly in the Afro-tropical region (sub-Saharan Africa) (WHO, 2000). One of the programs designed to reduce the transmission of important vector-borne diseases, such as malaria, is the use of chemicals in reducing the risk of human-vector contact  [3].

Mosquitoes act as a vector for most of the life threatening diseases like malaria, yellow fever, dengue fever, chikungunya ferver, filariasis, encephalitis, West Nile Virus infection, etc. Under the Integrated Mosquito Management (IMM), emphasis was given on the application of alternative strategies in mosquito control.[4].  The continuous application of synthetic insecticides causes development of resistance in vector species, biological magnification of toxic substances through the food chain and adverse effects on environmental quality and non-target organisms including human health [4].

Furthermore, the use of synthetic insecticides against mosquitoes may lead to resistance development and potential health hazards in humans and the environment. Consequently, a paradigm needs to shift towards the use of botanical insecticides that could strengthen an insecticide resistance management programme[5].

Application of active toxic agents from plant extracts as an alternative mosquito control strategy was available from ancient times. These are non-toxic, easily available at affordable prices, biodegradable and show broad-spectrum target-specific activities against different species of vector mosquitoes[4].

In this research, the current state of knowledge on phytochemical of two plants of the Simaroubaceae family, their larvicidal activity against the Anopheles gambiae mosquitoes, and their effects after prolonged exposure to the larvae have been investigated.

1.2. Problem Statement

The burden of Malaria is increasing, with an estimated 619000 malaria deaths globally in 2021 compared to 625000 in the first year of the pandemic. The overuse and misuse of synthetic insecticides have led to the emergence of resistance and they are highly hazardous to humans and the environment, and leave residues.

1.3   Research Question

1. What are the secondary metabolites present in Brucea antidysenterica and Brucea guineensis ?
2. Are Brucea antidysenterica and Brucea guineensis toxic to An. gambiae larvae?
3. Is there a significant difference in the toxicity of the plants after 24 hours and 48 hours exposure to the larvae?

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