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A Study on the Malaria Vector (Anopheles Spp) in a Sudano-Sahelian Savannah Area of Borno State North Eastern Nigeria and the Insect Growth Regulator Pyriproxyfen (S-31183)

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A Study on the Malaria Vector (Anopheles Spp) in a Sudano-Sahelian Savannah Area of Borno State North Eastern Nigeria and the Insect Growth Regulator Pyriproxyfen (S-31183)

Abstract

Malaria is a major problem in the Sudano-sahel Northeastern Nigeria with the highest prevalence of malaria in pregnancy of 64.5 percent. Little is known about the major malaria vector and its role in malaria transmission. Longitudinal entomological and parasitological surveys were conducted to better understand the relationship of the key components in malaria transmission dynamics .

Anopheles mosquitoes were sampled using pyrethroid spray collection and identified morphologically and by molecular methods of Polymerase chain reaction (PCR). Enzyme linked immunosorbent Assay (ELISA) was used for the blood-meal analysis and mosquito infectivity by circumsporozoite detection.

Malariometric indices were determined following the World Health Organization procedures. A total of 1030 female Anopheles mosquitoes were caught consisting of five species, namely, 1026 (99.6%) of Anopheles gambiae complex further identification using PCR showed the predominant sibling species were An. arabiensis Patton 95%(n=221) and An. gambiae s.s. 5%(n=12).

Other Anopheles mosquitoes collected were morphologically identified as An. pharoensis, An. squamosus and An. rhodesiense. Results showed that the population of Anopheles arabiensis was significantly higher than that of Anopheles gambiae s.s (P<0.05). Mosquito infection was determined by ELISA method for the detection of Plasmodium falciparum sporozoites 7(2.4%) were positive for P.falciparum circumsporozoite antigen.

All seven were An.arabiensis. Indoor collection was significantly higher than the outdoor collection (P<0.01). Mosquito blood feeding source determined by direct ELISA showed human bloodmeal was (98%, 94/96) for indoor collections and (2%, 2/96) for outdoors (P<0.01). The Human Blood Index (HBI) was 0.98. The results implicate

An.arabiensis as the main malaria vector in the area. Of a total of 692 children consecutively screened over a period of one year, significant difference (p<0.05) in infection rates was observed between the males and the females. The levels of parasitaemia asexual parasite were significantly related to age (p<0.05).

The majority of infected children (68.0%) were aged between 12-60 months and their asexual parasite density was between 1000-5000 of whole blood. The month of September recorded the highest geometric mean parasite density (GMPD) of 13,655 while the lowest parasite densities were observed during the dry season months of March, April, and May while gametocytaemia was not significantly affected by the age of the patients nor the season (p>0.05).

Overall average Inhibition of Emergence (IE) rates were 86% for the first week (0-7days) then peaked to 100% during the second week (8-14days) and declined to 73% (15- 21days) on the third week and finally to 36% on the fourth week (22-28day). Percentage Inhibition of Emergence between 0.1 and 0.5mg (a.i)/l treatments were not different (P> 0.05).

In planning effective site specific malaria vector control programmes under the Integrated Vector Management (IVM) program of the Federal Government of Nigeria, results of this study has highlighted the need to give special consideration to the predominance of a single malaria vector An. arabiensis in the Sudanosahel and the strong seasonality of malaria in contrast to other regions of Nigeria.

Findings also demonstrated the potentials of pyriproxyfen as an effective mosquitoes larvicide for consideration under the Integrated Vector Management (IVM) program for use in Sudanosahel Northeastern Nigeria.

 

TABLE OF CONTENTS

TITLE PAGE
CERTIFICATION – – – – – – – ii
DECLARATION – – – – – – – iii
ACKNOWLEDGEMENT – – – – – – – iv
DEDICATION – – – – – – – vi
TABLE OF CONTENTS – – – – – – – vii
LIST OF TABLES – – – – – – – xi
LIST OF FIGURES – – – – – – – xii
LIST OF PLATES – – – – – – – xiii
APPENDICES – – – – – – – xiv
ABSTRACT – – – – – – – xv

CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND OF THE STUDY – – – – – 1
1.2 STATEMENT OF THE PROBLEM – – – – – 3
1.3 JUSTIFICATION – – – – – – – 4
1.4 LIMITATION OF THE STUDY – – – – – 6
1.5 AIM AND OBJECTIVES OF THE STUDY – – – – 6
1.6 HYPOTHESIS – – – – – – – 7

CHAPTER TWO
LITERATURE REVIEW
2.1 THE DISEASE MALARIA – – – – – – 8
2.1.1 Malaria Epidemiology and Distribution – – – – 11
2.1.2 Human Plasmodia – – – – – – – 13
2.1.3 The Malaria Parasite and its Life Cycle – – – – 15
2.2 MALARIA TRANSMISSION – – – – – – 18
2.2.1 Anopheles-Plasmodium-Relationships and Impact on Malaria
Transmission – – – – – – – 18
2.2.2 Malaria transmission in Nigeria – – – – – 20
2.2.3 Malaria Transmission in Unstable (Epidemic Prone) Areas – 23
2.2.4 The Epidemiology of Malaria in Borno State, North-eastern Nigeria 26
2.3 THE IMPACT OF CLIMATIC FACTORS ON MALARIA
TRANSMISSION IN THE ARID SAHEL – – – – 28
2.3.1 Temperature – – – – – – – – 30
2.3.2 Rainfall – – – – – – – – 33
2.3.3 Relative Humidity – – – – – – – 34
2.4 DIAGNOSIS – – – – – – – – 35
2.5 MALARIA TREATMENT – – – – – – 36
2.6 VECTOR CONTROL UNDER THE GLOBAL MALARIA CONTROL
STRATEGY – – – – – – – – 37
2.7 VECTOR CONTROL METHODS – – – – – 40
2.7.1 Measures against Adult Mosquitoes – – – – 40
2.7.2 Measures against the Mosquito Larvae – – – – 44
2.8 MOSQUITOES – – – – – – – 45
2.8.1 Biology of Malaria Vector Species – – – – – 46
2.8.2 Malaria Vector Sibling Species Identification – – – 52
2.8.3 Methods of vector species identification – – – – 55
2.9 MOSQUITO BIONOMICS – – – – – – 63
2.9.1 Immature Stages of the Mosquito – – – – 64
2.9.2 Activities of Adult Mosquitoe – – – – – 65
2.9.3 Mating Behaviour – – – – – – – 66
2.9.4 Dispersal and Flight Range – – – – – 66
2.9.5 Life Cycle of the Mosquito – – – – – 68
2.10 MALARIA PREVALENCE IN NIGERIA – – – – 70
2.10.1 Clinical Features and Pathology of Malaria – – – 72
2.10.2 Mechanism of Immunity in Malaria – – – – 73
2.10.3 Acquired Immunity – – – – – – – 74
2.11 INSECT GROWTH REGULATORS – – – – – 77
2.11.1 Juvenile hormone analogues – – – – – 80
2.11.2 Chitin synthesis inhibitors – – – – – – 80
2.11.3 Pyriproxyfen – – – – – – – – 80

CHAPTER THREE
MATERIALS AND METHODS
3.1 STUDY SITE – – – – – – – – 87
3.1.1 Maiduguri Study site – – – – – – 87
3.1.2 Damboa Study Site – – – – – – – 88
3.1.3 Climate and Vegetation – – – – – – 90
3.1.4 Demography – – – – – – – – 91
3.2 ENTOMOLOGICAL INVESTIGATION – – – – 92
3.2.1 Mosquito Collection, Preservation and Processing – – 92
3.2.2 Morphological identification of Mosquito Samples – – 93
3.2.3 Dissection of Mosquitoes – – – – – – 101
3.2.4 PCR identification of the members of the Anopheles gambiae
Sibling Species – – – – – – – 101
3.2.5 ELISA Detection of Plasmodium falciparum Circumsporozoite
Protein Analysis – – – – – – 107
3.2.6 Identification of Bloodmeal Origin – – – – – 109
3.2.7 Determination of Human Blood Index (HBI) – – – 110
3.3 HUMAN PARASITOLOGICAL EXAMINATION – – – 111
3.3.1 Detection/ Examination for Parasitaemia – – – 111
3.3.2 Blood Examination for Gametocytes – – – – 112
3.3.3 Examination of Past Hospital Malaria Parasitology
Laboratory Reports – – – – – – 112
3.3.4 Statistical Analysis of Data – – – – – – 113
3.4 LABORATORY EVALUATION OF PYRIPROXYFEN – –
3.4.1 Source of Mosquito larvae – – – – – – 113
3.4.2 Test Chemical – – – – – – – 113
3.4.3 Manufacturers Note – – – – – – – 113
3.4.4. Experimental Design – – – – – – 113
3.4.5 Data Analysis – – – – – – – 114

CHAPTER FOUR
RESULTS
4.1 ENTOMOLOGICAL INVESTIGATION – – – – 116
4.1.1 Relative Abundance and Species Composition – – – 116
4.1.2 Species Composition – – – – – – 116
4.1.3 Seasonal Population Dynamics of Female Anopheles Mosquitoes 116
4.1.4 Resting Preference of Anopheline Mosquitoes – – – 117
4.1.5 Examination of Abdominal State of Anophelines – – 117
4.1.6 Feeding Preference of Anopheline Mosquitoes – – – 117
4.1.7 PCR Identification of Two Sibling Species – – – 118
4.1.8 ELISA Test for Plasmodium falciparum CSP – – – 118
x
4.1.9 Determination of Bloodmeal Source (HBI) – – – 118
4.2 HUMAN PARASITOLOGICAL EXAMINATION – – – 132
4.2.1. Blood Examination for Asexual Parasites – – – – 132
4.2.2 Blood Examination for Gametocytes – – – – 132
4.2.3 Seasonal variation of Gametocyte density – – – 133
4.2.4 Past Hospital Malaria Parasitology Laboratory Reports – – 142
4.3 LABORATORY EVALUATION OF PYRIPROXYFEN – – 148
4.3.1 Mean Inhibition of Emergence – – – – – 148
4.3.2 Evaluation of residual effect on Emergence Inhibition (EI) – 148

CHAPTER FIVE
DISCUSSION
5.1 PCR ANALYSIS OF ANOPHELES GAMBIAE SIBLING SPECIES – 153
5.2. ELISA RESULTS OF CIRCUMSPOROZOITE PROTEIN ANALYSIS 154
5.3 HUMAN BLOOD INDEX – – – – – – 156
5.4. LONGITUDINAL PARASITOLOGICAL STUDY – – – 158
5.4.1 Asexual Parasite – – – – – – – 158
5.4.2 Sexual Parasites (Gametocytes) – – – – – 160
5.4.3 Review of Past Hospital malaria Laboratory Reports – – 163
5.5 EVALUATION OF S-31183 PYRIPROXYFEN – – – 164
5.6. CONCLUSION – – – – – – – 166
5.7 RECOMMENDATIONS – – – – – – 169
5.8 SUGGESTION OF AREAS FOR FUTURE RESEARCH 170
5.9 SUMMARY OF RESULTS – – – – – – 171
5.10 CONTRIBUTION TO KNOWLEDGE – – – – 175
REFERENCES – – – – – – – 178
APPENDICES – – – – – – – 224

LIST OF TABLES
TABLE PAGE
1 Malaria Vectors of bioclimatic Zones of Nigeria – – – 51
2 Polymerase Chain Reaction Protocol – – – – 102
3 Relative Abundance/Numbers of Anophilines – – – 119
4 Species Composition of Anopheles Species – – – 120
5 Resting Preference of Anopheline Mosquitoes – – – 122
6 Abdominal State of Anopheles Species – – – – 123
7 Direct ELISA Identification of Feeding Preference – – 127
8 ELISA Test for Plasmodium Falciparum CSP – – – 128
9 ELISA Test for Plasmodium Falciparum CSP – – – 129
10 ELISA Determination of Blood Feeding Source – – – 130
11 ELISA Determination of Human Blood Index – – – 131
12 P. falciparum (Asexual Parasite) in relation to sex in children 134
13 Relationship between Asexual Malaria Parasite Density and Age
in Children – – – – – – – – 135
14 Parasitological Data on Asexual Stages of Malaria Parasites
(June-Sept 2003) – – – – – – – 136
15 Parasitological Data on Asexual Stages of Malaria Parasites
(October-January 2004) – – – – – – 137
16 Parasitological Data on Asexual Stages of Malaria Parasites
(February-June, 2004) – – – – – – 137
17 Distribution of Gametocytaemia in Children in Relation to Sex 138
18 Age Related Distribution of Gametocytaemia in Children – 139
19 Relationship between Gametocytaemia and Season. – – 140

LIST OF FIGURES
FIGURE PAGE
1 Global Distribution of Malaria – – – – – 12
2 Generalized Life Cycle of the Malaria Parasite – – – 17
3 Sketch Map of Borno State, showing Study Location – – 89
4 An. gambiae Wings, Palps and Leg for Morphological Identification 95
5 An. funestus Wings, Palps and Leg for Morphological Identification 97
6 Heads of Male and Female Anophiline and Culicine Mosquitoes 98
7 Wings of Prominent Anopheline Mosquitoes for Morphological
Identification – – – – – – – – 99
9 Monthly Relative Abundance of Mosquitoes – – – – 121
12 Seasonal Variation of Gametocyte Density – – – 141
13 Outpatient’ Attendance, Admission and Deaths – – 143
14 Outpatient Cases and Proportion of Malaria 2001-2004 – 144
15 Admissions and Proportions of Malaria 2001-2004 – – 145
16 Mortality and Proportion due to Malaria – – – – 146
17 Trend of Monthly Cases and Deaths 2001-2004 – – 147
18 Average Emergence Inibition of Pyriproxyfen against 4th inster
larvae of An. gambiae week 1 – – – – – – 149
19 Average Emergence Inhibition of pyriproxyfen against 4th instar
larvae of An. gambiae week 2 – – – – – – 150
20 Average Emergence Inhibition of pyriproxyfen against 4th instar
larvae of An. gambiae week 3 – – – – – – 151
21 Average Emergence Inhibition of pyriproxyfen against 4th instar
larvae of An. gambiae week 4 – – – – – – 152

LIST OF PLATES
PLATE PAGE
1 Anopheles mosquito abdominal pigment – – – 96
2 Anopheles mosquito – – – – – – 100
3 Anopheles mosquito wing – – – – – – 104
4 Anopheles mosquito leg – – – – – – 105
5 Anopheles mosquito head for CSP- – – – – 106
6 Bloodfed Anopheles specimen for Bloodmeal analysis – – 108
7 PCR Identification of An. gambiae – – – – – 124
8 PCR Identification of An. gambiae – – – – – 125
9 PCR Identification of An. gambiae – – – – – 126

 

INTRODUCTION

Malaria is by far the most important insect transmitted disease (Gilles and Warrell, 1993). Latest World Health Organisation estimates are that there are 300-

500 million cases of clinical malaria per year, with 1.4-2.6 million deaths, many among African children. Malaria is therefore a major cause of infant mortality and is the only insect borne parasite disease comparable in impact to the Worlds major killer transmissible diseases: diarrhea, acute respiratory infections, tuberculosis and AIDS (Curtis, 2006).

In Nigeria, up to 60% of outpatient attendance in health facilities is due to malaria and 30% of all hospital admissions.It is estimated that malaria is responsible for nearly 110 million clinical cases and an estimated 300,000 deaths per year, The disease is responsible for 25% infant mortality, 30% childhood mortality and is associated with 11% maternal deaths.

The economic burden of this disease in Nigeria is estimated to be N132 billion lost annually in terms of treatment costs,prevention,loss of man hours etc (FMOH, 2005b; 2009d).

Most malaria deaths occur at home hence are not reported (Rugemalila, 2006). The disease can be attributed almost entirely to the mosquitoes Anopheles gambiae, An. arabiensis and An.funestus, three of the most efficient malaria vectors in the world.

All live almost exclusively in close association with humans and feed on blood, primarily from humans (Collins and Besansky 1994). The power of An. gambiae as a malaria vector for instance, is well illustrated by its accidental introduction into Brazil, where in 1938 after a series of small but intense local outbreaks, it caused the worst epidemic of malaria ever recorded there, with over 14,000 deaths in less than 8 months

(Collins and Besansky, 1994). In Africa alone, the economic burden is about US$12billlion annually. Malaria is estimated to slow economic growth in African countries by about 1.3% per year. Malaria constitutes a major economic burden on endemic communities in Africa including Nigeria.

The disease thus constitutes a great burden on the already depressed Nigerian economy. Malaria causes great misery to sufferers, and adversely affects the social and psychological wellbeing of individuals, families and the nation at large (FMOH, 2004).

Forty percent (40%) of the worlds population are at risk of malaria, of this number 500million are in Sub Saharan Africa.240 -400 million cases are recorded yearly with children experiencing between 1-9 attacks per child per year and adults experiencing between 1-4 attacks.

Deaths due to malaria are between 1-2 million; at least 90% of this figure is in Africa. Malaria is directly responsible for 10% of deaths in children under the five years and indirectly responsible for 25% of all childhood deaths (Molta, 2000b).

Despite the fact that strong attempts to eradicate malaria have been made, the disease burden is still on the rise and some estimate that the number of cases could double in the next twenty years without the development of new methods of control (Sachs and Malaney, 2002). Aside from the human tragedy this predicts, an economic disaster is likely for the stricken countries (Cahill, 2004).

The malaria parasite also interacts with other afflictions, such as HIV and under-nutrition, in ways that are still not well understood. These estimates render malaria the prominent tropical parasitic disease and one of the top three killers among communicable diseases (Rugemalila et al., 2006).

Malaria caused by Plasmodium species, notably Plasmodium  falciparum is  a major cause  of  morbidity  and  mortality  in  children  and  adults  in  Borno  State.  It  is responsible for 70 percent attendance in hospitals, 91 percent of eleven notifiable diseases, 83 percent of diagnosable infection and at least 32 percent of deaths.

In this state, transmission of the disease occurs all-year-round with peaks were observed during the middle to late rainy season( August –October/November) and transmission declining during the dry season (December-April/May) thereby demonstrating strong seasonality (Pull and Grammicia, 1976; Sibina 1984; Molta et al.,1991; Molta et al.,1995;Oguche et. al., 2001).

Plasmodium infection ranged from 35.2% in Maiduguri to 70.2% in Damboa both located in Borno State. The overall rate of infection was 50% (Molta et al., 1993, 2004) The possible malaria vectors in the sahel include An. gambiae s.l., An. funestus, An. pharoensis, An. squamosis, An. coustani and An. ziemanni (Gadzama, 1983; Bariki, 1988; Sara,1990 and Kalu, 1992).

The national malaria control strategic plan aims to reduce by 50% malaria related morbidity and mortality in Nigeria by 2010 and sustain the level to 2013 to minimize the socioeconomic impact of the disease; and to achieve the relevant millennium Development Goal i.e to have halted by 2015 and begun to reverse the incidence of malaria and other major diseases (FMOH, 2009c).

REFERENCES

Abbott, W.S. (1925). A method of computing the effectiveness of an insecticide. Journal of Mosquito Control Association. 18:265-267.

Ali, A., Nayar, J.K. and Xue, R.D. (1995). Comparative toxicity of selected larvicides and Insect growth regulators to a Florida Laboratory population of Aedes albopictus, Journal of American Mosquito Control Association 11: 72-76.

Amajoh, C.N. (1997). A review of Malaria Vector behaviour in Nigeria. Abstracts of two days National symposium on malaria in Nigeria held at Nigerian Institute of Medical Research Yaba, Lagos. 4th to 5th November 1997.

Anderson, D. (1932). Notes on mosquitoes-borne diseases in Southern Nigeria III.Differences in the periodicity of various mosquitoes. Journal of Tropical Medicine and Hygiene 35:305-308.

Ansari, M.A., Sharman, V.P., Mittal, P.K., Razdan, R.K. (1991). Evaluation of juvenile hormone analogue JHM /5-383 against immature stage of mosquitoes in natural habitats. Indian Journal of Malariology 28: 9-43.

Anyanwu, G. I. and Iwuala, M.O.E. (1999). Mosquito breeding sites: Distribution and relative abundance. Journal of Medical Entomology and Zoology 50 (3): 234-249.

A M ZKHCuticular hydrocarbon discrimination between Anopheles gambiae ss and An. arabiensis larval karyotypes. Annals of Tropical Medicine and Parasitology 95(8): 843-852

Anyanwu, G. I., Omoregie, U., Opara, H.C., Yarlings, V.V., Idoko, J.S. and Yanaga, E.T. (2002). Plasmodium and filarial infections in mosquitoes on the Jos Plateau State. Nigerian Journal of Experimental and Applied Biology 3(2): 171-178.

Anyanwu, G. I. and Alli, S.O. (2001). Species abundance of malaria and other mosquito vectors breeding in the vicinity of the Jos metropolis. Journal of Pest, Disease and Vector Management 3:212-219.

Awolola, T.S. (2007). Integrated Vector Management in Africa: Contributions of molecular entomology,biochemistry and social sciences to malaria control. Tropical Disease Research News 79:34-35.

Awolola, T.S., Oduola, O.A., Obansa, J.B., Chukwurah, N.J. and Unyimadu, J.P. (2007). Anopheles gambiae s.s. breeding in polluted water bodies in urban Lagos, Southwestern Nigeria. Journal of Vector Borne Diseases 44:241-244. Awolola, T.S., Okwa, Hunt, R.H., Ogunrinade, A.F. and Coetzee, M. (2002). Dynamics  of  the  malaria-vector  populations                     in coastal Lagos, South eastern Nigeria., Annals of Tropical Medicine and Parasitology 96(1): 75- 82.

Awolola, T.S., Ibrahim. K., Okorie, T., Koekemoer, L.L., Hunt, R.H. and Coetzee. (2003). Species composition and biting activities of anthropophilic Anopheles mosquitoes and their role in malaria transmission in a holoendemic area of Southwestern Nigeria. African Entomology 11(2): 227- 232.

 

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