EVALUATION OF BIOACTIVE METABOLITE CONTENTS, MOSQUITO LARVICIDAL AND ANTI-PLASMODIAL ACTIVITIES OF EXTRACTS OF THE SPIDER Neoscona adianta

ABSTRACT

In spite of the extensive control efforts, over the years, mosquito still transmit serious human diseases, cause millions of deaths every year and the development of resistance to chemical insecticides resulting in rebounding vectorial capacity. This situation is aggravated with the re-emergence of drug resistance of mosquito borne diseases especially malaria. The current study was therefore designed to assess the mosquito larvicidal potency and antiplasmodial efficacy of the crude and fractions of the extract of the spider (Neoscona adianta). The zoochemical components of the crude and fractions of the spider extracts were assessed following standard procedures. The larvicidal potency of the crude and fractions of the spider was carried out according to World Health Organization (WHO) standard protocol with slight modifications. Graded concentrations (ranging from 0.2 to 2.0 mg/k) of the crude and fractions of the spider extracts were tested against 25 batches of healthy 4th instar larvae of Culex mosquito species, and larval mortality was recorded after 24 hours exposure period. Acute oral toxicity of the crude extract was carried out to establish the oral safe dose. The antiplasmodial activates of the crude extract and fractions were bio-assayed against established infection in chloroquine-sensitive Plasmodium berghei infected mice. The results indicated the presence of zoochemicals including flavonoid, tannins, saponnins, alkaloids steroids total phenol and terpeniods in the crude extract and fractions of the spider. The results of the larvicidal bio-assay revealed that both crude and fractions showed a dose and concentration-dependent larvicidal potency. Larvicidal activities was significantly higher (P<0.05) in the ethylacetate and n-henane fractions than in the crude methanol extract. Similarly, only the ethylacetate and n-hexane recorded 100% mortality for the highest concentration tested (2.0 mg/h). The best larvicidal activity was found in the n- hexane  fraction  with  an  LC50  of  0.46mh/L,  followed  by  ethylacetate  with  LC50  of 0.94mg/L. The results of the acute oral toxicity revealed that the spider extract is safe for oral administration with an LC50 greater than 5000mg/kg body weight. The crude and fractions of the spider extract showed a dose dependent antiplasmodial activities with peak activity recorded of the group of mice treated with 600mg/kg b.wt crude extract. The crude and fractions did not  ameliorate fall in PCV but promoted body weight  change and elongated the survival time. The results support the medicinal use of spider extracts in folkloric medicine and suggest that this spider contained bio-active compounds that could be developed as potent antimalarial drug as well as potent bio-pesticide agent against mosquito vector.

CHAPTER ONE

1.0       INTRODUCTION

1.1       Background to the Study

Malaria is a mosquito-borne infectious disease of humans and other animals caused by eukaryotic protists of the genus Plasmodium. In humans, the disease is transmitted by the female mosquito of the genus Anopheles. The Plasmodium species that cause malaria in human include P. falciparum, P. vivax, P. malariae, P. ovale and the zoonotic is P. knowlesi (mainly monkey parasite, similar to P. malariae and confirmed by PCR) (WHO, 2018).

Malaria is a potentially deadly disease characterized by cyclical bouts of fever with muscle stiffness, shaking and sweating (WHO, 2015; Macleod (1998) also stated that malaria is a parasitic infection transmitted to humans through the bites of an infected female Anopheles mosquito. The name “malaria” is derived from the Italian words Mal (bad) and aria (air). It arose originally because the citizens of Rome thought that the disease was contracted by breathing the bad air of the Pontine Marshes (Greenwood and Mutabingwa, 2002). (Hornby, 2007) defined malaria (ague, marsh fever, periodic fever, paludism) as an infectious disease due to the presence of parasitic Protozoa of the genus Plasmodium (P. falciparum, P. malariae, P. ovale or P. vivax) within the red blood cells. The disease is confined to tropical and subtropical areas.

Malaria has a worldwide distribution, affecting people of all ages, with an enormous burden amounting to 300-500 million clinical cases per year (Lucas and Gills, 2003; Williams et al., 2016). Globally ten new cases of malaria occur every second, which is a major public health problem in the tropics where about 40% of the world population lives. It is responsible for more than a million deaths each year, of which 90% occur in sub-Saharan Africa (WHO, 2009). Malaria is caused by four different protozoa in the plasmodium genus: either Plasmodium vivax, which is more prevalent in low endemic areas, P. ovale, P. malaria, and P. falciparum, the most dangerous of the four. The P. falciparum has a life cycle in the mosquito vector and also in the human host. The Anopheles gambiae mosquito is the vector responsible for the transmission of malaria.

The prevalence of malaria is dependent on the abundance of the female anopheles species, the propensity of the mosquito to bite, the rate at which it bites, its longevity and the rate of development of the plasmodium parasite inside the mosquito. When the female mosquito bites and sucks the blood of a person infected with malaria parasites she becomes infected; she then transmits the parasites to the next human host she bites. Malaria incubates in the human host for about eight to ten days. (WHO, 2020).The spread of malaria needs conditions favorable to the survival of the mosquito and the plasmodium parasite. Temperatures of approximately 70 – 90 degrees Fahrenheit and a relative humidity of at least 60 percent are most conducive for the mosquito (WHO, 2009).

Nigeria is at an alarming pace of malaria diseases, been the most populous country in Africa. The success of its malaria control programs will have a significant impact on the overall control of malaria in the region. Because a large proportion of the population in Nigeria’s rural areas lives in poverty, a control plan focused on those areas will be effective. Also, there are factors that are responsible for the increase in the resurgence of malaria that must be addressed in malaria transmission and control. These factors include the large scale resettlement of people usually associated with ecological changes and conflicts, increasing urbanization disproportionate to the infrastructure, drug resistant malaria, insecticide resistant mosquitoes, inadequate vector control operations and public health practices (Onah et al., 2017). .

The year 2000 went down in history as the year in which the most influential alliance (till date) in efforts to eradicate malaria converged in Abuja, Nigeria. That was the Roll Back Malaria (RBM) Partnership, and the targets set have come to be known as the ”Abuja Targets”. One of the goals set by the RBM Partnership was that by 2010, 80% of patients with malaria would be diagnosed and treated with effective antimalarial medicines (RBM,

2005). Over 1 decade later, malaria remains a public health concern in the world’s poorest countries, Nigeria chief among them. As at 2010, deaths from malaria in Nigeria were the highest recorded worldwide (Onah et al., 2017). In 2005, artemisinin-based combination therapies (ACTs) were adopted as the first-line treatment for uncomplicated malaria in Nigeria (FMOH, 2005).

This is a strange phenomenon since so much effort has been geared towards eradicating this dreaded disease in Nigeria. Hence the need to critically investigate the reasons or challenges confronting eradication efforts of Malaria in Nigeria. Conventional antimalarial drugs have been the mainstay of clinical management, both for prophylaxis and treatment. Artemisin based combination drugs are the frontline for treatment currently with artemisinin- lumefantrine being the first line and artemisininpiperaquine being second line oral treatment. Parenteral artesunate is initially instituted with intravenous quinine being the last line of defence for severe malaria. Previously used drugs such as sulphadoxine- pyrimethamine (SP), mefloquine, chloroquine, primaquine, amodiaquine have been limited due to development of resistance. Emergence of multidrug resistant strains which has accompanied each new class of antimalarial drugs may be viewed as one of the most significant threats to the health of tropical populations. While it is widely agreed that a new approach to prevention and treatment is needed, solutions have targeted more of development of new drug classes’. With renewed interest and funding, there are over 15 new antimalarials in various development stages. The main concern is that they act at known targets and therefore may be subject to common resistance mechanisms. New drugs for new plasmodia targets are needed.

Animal venoms are valuable sources of novel pharmacological tools whose specific actions are useful for characterizing their receptors. Hundreds of toxins from snakes, scorpions, spiders and marine invertebrates with a range of pharmacological activities have all been characterized (Lucas et al, 2003; Park, 2002; Hill et al., 2006).

Spider venoms contain a wide spectrum of biologically active substances, which selectively target a variety of vital physiological functions in both insects and mammals (FMoH, 2005). The spider toxins are “short” polypeptides with molecular mass of 3-8 kDa and a structure that is held together by several disulfide bonds. There are two main groups of these peptides, the neurotoxins that target neurone receptors, neurone ions channels or presynaptic proteins involved in neurotransmitter release, and the non-neurotoxic peptides, such as necrotic peptides and antimicrobial peptides (for a review, see (WHO,2005)). Recent studies have characterized the venoms of the genuses Brachypelma, Pterinochilus and Theraphosa (Bawah and Binka, 2005 ;). Several peptides that inhibit atrial fibrillation (United Nations Country team, 2004), block the Kv2 and Kv4 subfamilies of voltage-dependent potassium channels (Lawn et al., 2005), or multiple sodium channels (Adam et al., 2005), and proton- gated sodium channels (Steketee et al., 2001) have been recently isolated. Although spider toxins bind to their receptors with high affinity, specificity, and selectivity, little is known about them and little work has been done to develop these toxins for therapeutic use.

Spider venoms are mixtures of biologically active peptides, proteins, glycoproteins, and small organic molecules which interact with cellular and molecular targets to trigger severe, sometimes fatal effects. However, the spider venom could be particularly interesting for the treatment of general diseases as a scaffold for toxin-based drug research. Several venom- based drugs or venom-derived molecules have found extensive use as tools for therapies. For instance, “Captopril”, a competitive inhibitor of angiotensin-converting enzyme, is broadly used and well-established antihypertensive drug developed from a polypeptide toxin isolated from the venom of Bothrops jararaca; “Conotoxin” from the sea cone snail Conus magus used as an analgesic for severe chronic pain and “exendins”; and, recently,   proteins   obtained   from   the   saliva   of   the   Gila   monster   Heloderma suspectum benefited the treatment of type II diabetes (Lucas, 2003; Park, 2002; Hill et al., 2006).

1.2       Statement of the Research Problem

Malaria remains one of the most serious world health problems and the major cause of cause of morbidity and mortality in the endemic areas (WHO, 2018). Despite all effort to curb the prevalence of malaria, the disease continues to spread even across some areas where it had been previously eradicated (WHO, 2018). Plasmodium falciparum, the most lethal etiological agent for human malaria, is becoming increasingly resistant to standard antimalarial drugs in almost all parts of endemic areas especially Africa (WHO, 2020).

1.3       Justification of the Study

Malaria is one of the most important parasitic diseases in the world. It remains a major public health problem in Africa responsible

1.4       Aim and Objectives of the Study

The aim of the study is to evaluate the antimalarial and mosquito larvicidal activities of the extracts of spider

The objectives of the study are to determine the:

i. entomochemical constituents of the extract of spider.

ii acute oral toxicity (LD50) of the crude extract of spider.

iii. antiplasmodial potency of the crude and solvent fractions of spider in Plasmodium berghei-infected mice.

iv. effect of the spider crude and fractionated extracts on body weight change and haematological parameters of Plasmodium berghei-infected mice.

v.  larvicidal activities of the crude and fractionated extracts of spider. vi. LD50 and LD90 of the crude and fractionated extracts of spider. vii. structure of the bioactive compound in the extract or fraction with best for the annual death of over one million children below the age of five years (White, 2010). Plasmodium falciparum is becoming increasingly resistant to standard antimalarial drugs which necessitate a continuous effort to search for new drugs, particularly with novel modes of action.

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