CHAPTER ONE
1.0 INTRODUCTION
1.1 Backgroundto
the study
Plants have always served as food and medicine to man since
the beginning of life. Their nutritional and medicinal potentials have been
attributed to the phytochemicals and other chemical constituents contained in
them. Despite their importance, it has been reported that out of the 250,000 to
500,000 species of existing plants on earth, only about 300 species are
utilized in the food, pharmaceutical, cosmetics and perfume industries.
Traditionally used medicinal plants produce a variety of compounds of known
therapeutic properties (Umedum et al., 2014).
Medicinal plants are used in traditional treatments to cure
variety of diseases. In the last few decades there has been an exponential
growth in the field of herbal medicine. Natural products have been a source of
drugs for centuries (Dinet al., 2011). Traditional medicines (plants
source) has been used for thousands of years for the treatment of malaria and
are the source of two main groups (artemisinin and quinine derivatives) of
modern antimalarial drugs (Kazembe et al., 2012).
Repellents are substances applied to the skin, which prevent
insects from biting such surface (Traoré-Coulibalyet al., 2013).An
insect repellent is a substance that causes an organism to move away from the
odour source, insects perceive thevolatile repellents by smell (Luts etal.,
2014).
Essential oils are volatile natural complex
secondarymetabolites characterized by a strong odour and have agenerally lower
density than that of water (Arun et al., 2009). They are natural volatile
mixtures of hydrocarbons with a diversity of functional groups, and their
1
repellent activity has been linked to the presence of
monoterpenes and sesquiterpenes (Moreiraet al., 2010;Chaubey 2012;
Traoré-Coulibalyet al., 2013). Essential oils are plant products
obtained by hydro-distillation or other methods (Luts et al., 2014).
This complex of compounds are produced by plants, giving them their
characteristic smell and taste, and are usually composed of 20–80 or more
substances. Their main components are monoterpenes (C10) and sesquiterpenes
(C15) derived from isoprene (Luts et al., 2014).Several monoterpenes
have been reported as insect repellents (Luts et al., 2014).There are
17,500 aromaticplant species among higher plants andapproximately 3,000
essential oils are known out of which300 are commercially important for
pharmaceuticals,cosmetics and perfume industries. Apart from insecticidal
potential they are lipophilic in nature and interfere with basic metabolic,
biochemical, physiological and behavioural functions of insects. They are also
used as flavour in food products, odorants in flagrances, pharmaceuticals
(antimicrobial) and as insecticides(Moreiraet al., 2010).
Hyptis suaveolens (L.Poit) is one of
the important traditional medicinal plants belonging tofamily lamiaceae
(Umedum et al., 2014). It is commonly called Bush mint, Bush tea,
Pignut, or Chan. It is known generally as Vilayati Tulsi in Hindi, Konda
Thulasi in Telugu, Bhustrena in Sanskrit, Daddoya-ta-daji ( family name) and
specifically Sarakuwan sauro in Hausa, Efiri (family name) in Yoruba, Nchuanwu
(family name) in Ibo, and Tanmotswangi-eba in Nupe (Umedum et al., 2014;
Ghafari et al., 2014).
Leaves of Hyptis suaveolens have been traditionally
used as a stimulant, antisplasmoidic, against colds and diarrhoea (Shaikat et
al., 2012). It has been and still in use traditionally to repel mosquitoes
by burning the leaves (Singh et al., 2011; Vongsombothet al.,
2012).
The repellent activity of the whole Hyptis suaveolens
essential oil and single major constituents against adults of S. granarius
has been evaluated (Benelli et al., 2012). Amongst
2
the several methods available
to evaluate the repellence of natural products, the filter paper tests in Petri
dish is one of the most commonly used bioassays (Benelli et al., 2012).
Several authors reported a large variability in the composition of this family
due to genetic, geographical and seasonal factors. Since the biological
activities of essential oils are composition-dependent, it is apparent that it
is very important to fully characterize these mixtures from the chemical point
of view (Benelli et al., 2012).
Malaria is a major public
health problem with an estimated two million children worldwide dying of it
yearly. Regardless of the fact that it is one of the oldest recorded diseases,
malaria remains one of the world‘s most deadly infectious diseases. It is
arguably, the greatest menace to modern society in terms of morbidity and
mortality. Though preventable, treatable and curable, there is no known vaccine
against the disease. This makes it an efficient and unrepentant killer. Several
centuries after its discovery, malaria still remains a devastating human
infection, resulting in 300-500 million clinical cases and three million deaths
every year. Malaria is endemic throughout Nigeria (Olurishe et al.,
2007; Nigeria Malaria Indicator Survey 2010; Okafor and Oko-Ose 2012; Etusim et
al., 2013; Odey et al., 2013).
The management of severe malaria remains challenging, mainly
due to the fact that it does not only depend on the use of effective
anti-malaria drugs but also the use of effective parenteral anti-malaria drugs.
Other factors that make management of malaria challenging are; cost-intensive
supportive measures, unavailability of highly skilled personnel, insufficient
functional referral systems, lack of blood transfusion services, lack of good
infrastructure and inadequate organization of hospital services. Parenteral
quinine had been the first-line treatment for severe malaria in Nigeria until
June 2011 when the policy was revised to intravenous artesunate as a first-line
antimalarial drug (Odey et al., 2013).
3
Malaria caused byPlasmodium
falciparum is the most dangerous form of the disease resulting in life
threatening complications such as anaemia and cerebral malaria. The pattern of
exposure to malaria infection, the type of treatment and the degree of
compliance with the anti-malaria regimen, local drug resistance patterns,
individual‘s age and genetic makeup all tend to influence the severity of the
disease (Etusim et al., 2013).
A synthetic insecticide is a poisonous chemical or mixture
of chemicals that is intended to prevent, repel, or kill any insect or pest.
However, synthetic insecticides present hazardous impacts far beyond their
intended targets. Insecticides have
inherent toxicity because they are designed to kill living organisms that are
considered “pests”, that is any unwanted insect. Many insecticides
are known to pose significant, acknowledged health risks to people— including
birth defects, damage to the nervous system, disruption of hormones and
endocrine systems, respiratory disorders, skin and eye irritations and various
types of cancers (Agency for Toxic Substances and Diseases Registry, 1994).
The synthetic insecticide Dichloro diphenyl trichoroethane
(DDT) was widely used in urban aerial sprays to control urban mosquito and
other insects. DDT has caused chronic effects on the nervous system, liver,
kidneys, immune systems,tremors, increased blood levels of liver-produced
enzymes, changes in the cellular chemistry in the central nervous system, hind
leg paralysis, convulsions and subtle effects on neurological development and
decreased in thyroid function in experimental animals.Teratogenic, mutagenic,
carcinogenic effects and sterility were also observed in experimental
animals(Agency for Toxic Substances and Diseases Registry, 1994).
Chemical repellents are important in protecting people from
blood-feeding insects and may therefore also reduce transmission of arthropod
borne diseases. N,N-diethyl-3-methylbenzamide (DEET) is one of the most
well-known arthropod repellents. DEET is
4
generally safe for topical use if applied as recommended,
although adverse effects such as serious neurologic effects have been reported.
It does not readily degrade by hydrolysis at environmental pHs and has been
identified as aubiquitous pollutant in aquatic ecosystems (Abagli and Alavo
2011).
5
1.2 Statement of
the Problem
Ø Paré
Toéet al.,(2009) have shown that people‘s motivation to use mosquito
nets considerably decreased less than a year after the campaigns and people
prefer to
spend night without
insecticidal nets. Therefore, use of mosquito net is not sufficient to
effectively control malaria vectors, especially in the West African countries
where urbanization promotes the proliferation of mosquitoes.
Ø To
achieve successful vectors control and reduce substantially the prevalence of
malaria and other vector-borne diseases, an integrated management of these
vectors
must
be adopted.
Ø Insecticides
have inherent toxicity and are known to pose significant health risks to
people.
Ø Globally,
the malaria situation is serious and still deteriorating, hence the need to
search for solution.
Ø Malaria
predominantly affects the poor and underprivileged hence the need to search for
affordable means of eliminating the disease.
6
1.3 Justification
Ø Traditionally,Hyptis
suaveolens has been used and is still in use to repel mosquito but the
scientific basis behind this practice has not been validated.
Ø Mosquitoes
have become the most important single group of insects well-known for their
public health importance (Singhet al., 2011).
Ø Considering
the use of the plant to repel mosquitoes, it is worthwhile exploring the
repellency properties of the plant essential oil and larvicidal property for a
possible
mosquito
control strategy (Singh et al., 2011).
Ø On
the possible eradication of malaria, Arigbabuwo opined that prevention is
better than cure (Okafor and Oko-Ose 2012). Hence the search for possible
eradication of
mosquito
right at the larvae stage.
Ø To
the best of my knowledge, there are no sufficient data available on the
physicochemical properties of essential oil of Hyptis suaveolens leaves,
hence looking
at its physicochemical properties for possible use in making
soap, cream or perfume for use to repel the mosquito.
7
1.4 Aim and Objectives
1.4.1
Aim
The general aim of
this research work is to extract and characterise the insecticidal properties
of essential oil of Hyptis suaveolens leaves.
1.4.2
Specific objectives
The
specific objectives of this work are to;
i.
Extract essential oil of Hyptis suaveolens leaves
through hydro-distillation.
ii.
Determine the mosquitocidal capability of the essential oil.
iii.
Determine the mosquito
repellency properties of essential oilof Hyptis suaveolens leaves
iv.
Determine the larvicidal activities of the essential oil of Hyptis
suaveolens.
v.
Explore the physicochemical
properties of the essential oil so as to recommend its possible use as body
cream, perfume or toilet soap that can be use on the body to repel mosquitoes.
vi.
Characterise the oil by GC-MS and FTIR.