A Study on Mosquito as a Primary Malaria Vector

A Study on Mosquito as a Primary Malaria Vector

Chapter One

AIMS AND OBJECTIVES

The aims and objectives of this study are:

To identify the breeding sites of mosquitoes.
To know the species of mosquitoes that are highly prevalent in Uyo urban.
To determine the physico-chemical parameters of the breeding sites.
To know their various control measures.

CHAPTER TWO:

LITERATURE REVIEW

Malaria burden

Malaria is a disease caused by Plasmodium parasites which are transmitted to humans by female anopheles mosquitoes. Five Plasmodium species are known to cause malaria; Plasmodium falciparum, P. ovale, P. vivax, P. malariae, and P. knowlesi. P. falciparum is the most pathogenic and common in Africa where it causes severe forms of malaria (Hay et al. 2011).

Malaria accounts for about (300 to 660) million clinical attacks, worldwide where about 2.2 billion individuals are exposed to infections with P. falciparum malaria (Hay et al. 2011). According to WHO 3.3 billion individuals were at risk of malaria infection in 2014 (World Health Organisation 2014). In 2013, there were approximately 198 million malaria cases resulting in 584,000 deaths globally, majority (90%) of which were in Africa (World Health Organisation 2014). About 78% of these deaths were in children under 5 years (World Health Organisation 2014). However, there has been a considerable success in malaria control, malaria cases and deaths have decreased by 670 million and 4.3 million respectively between 2000 and 2013 globally which was attributed to heightened prevention and control interventions (World Health Organisation 2011).

Malaria in Nigeria

Nigeria is classified as a malaria endemic country by WHO (Henninger 2013). The country has four malaria ecologic zones based on microclimate, altitude and level of transmission. Nineteen

(19) out of 30 districts are epidemic prone and 11 districts are endemic. Malaria transmission in Nigeria occurs with two peaks throughout the year in rainy season; May to June and November to December. In addition to the favorable climate, other factors such as proximity to marshlands, irrigation schemes and cross border movement of people influence the transmission especially in parts which include Enugu and the eastern parts of the country (President’s Malaria Initiative 2014a).

Current situation of Malaria in Nigeria

Use of malaria control interventions such as use of long lasting insecticide-treated mosquito nets, indoor residual house spraying with insecticides and effective treatments resulted in significant decline of malaria transmission between 2006 and 2008 in the country (Bizimana et al. 2015). Also malaria related mortality rate in children under-five years old decreased by 61 percent between 2000 and 2010, where prevalence of malaria in this age group was 1.4% in 2010 from 2.6% in 2007 (President’s Malaria Initiative 2014b). However, according to WHO report in 2014, the situation changed with, admissions and confirmed malaria cases increasing twofold between 2012 and 2013 from 5,306 to 9,508 and 483,000 to 962,000 respectively (World Health Organisation 2014). In 2014 the situation worsened and malaria cases in Nigeria increased to 1,597,143. The morbidity rate in the country was 5.8% in 2012 but increased to 10% in 2013 and 14.8% in 2014. This increase is blamed on climatic change, insecticide resistance and ineffective mosquito nets (Nigeria Ministry of Health 2014).

Malaria Vectors Biology

Mosquitoes of the genus Anopheles are the most studied and best understood due to their vectorial capacity for malaria and lymphatic filariasis. About 537 Anopheles species are known and most (87%) have been named. Among these, about 20 taxa are species complexes, which contain about 115 sibling species in total. The sibling species of the complex are morphologically similar which makes it hard to identify them morphologically and can only be identified using molecular techniques such as PCR (Manguin 2013). However, they differ genotypically and in their biological characteristics such as resting and feeding behavior and susceptibility to insecticides (Manguin 2013).

The greatest burden of malaria (90%) is in Africa (MARA/ARMA collaboration (Mapping Malaria Risk in Africa) 2002). This is due to the presence of the most efficient vector species. These vectors can be grouped into two sibling species complexes; An. funestus and An. gambiae. The latter is the most efficient and has 8 sibling species namely; An. gambiae s.s, An .bwambae, An. arabiensis, An. quadriannulatus, An. melas, An. amharicus, An. merus and An. coluzzii (Sinka, Rubio-palis, et al. 2010).

An. arabiensis and An. gambiae s.s. have a wide geographic distribution. An. gambiae s.s. mainly occurs in humid savannah zones and forests while An. arabiensis is more successful in arid environments. The breeding sites of both sibling species are usually small, shallow, sunlit fresh water bodies without vegetation. Larvae of both species often cohabit in the same habitats. Adult An. gambiae s.s. is mainly anthropophagic whereas An. arabiensis is more zoophagic. However, studies show that host preference and biting behavior of the species highly vary across Africa (Tirados 2006). For instance, studies have shown that in western Africa An. arabiensis populations are more anthropophagic, endophilic and endophagic whereas those in the east are more zoophagic and exophilic. An. gambiae s.s. is mainly endophagic and endophilic with few exceptions, whereas An. arabiensis displays high variation in these behaviors (Tirados 2006; Coetzee et al. 2013).

Two sibling species An. merus and An. melas are found in brackish water. These species occupy areas with mangrove belts such as estuaries, lagoons and swamps. An. merus is found in the coast of east Africa whereas An. melas is found in the West African coast. An. bwambae occur in geothermal springs in western Uganda. The sibling species An. quadriannulatus is known to be mainly zoophagic hence has little impact on human malaria (Gillies M. T. 1987).

The An. funestus species complex has nine siblings’ species. Of these, only An. funestus s.s. is the known vector of malaria in Africa. The others An. rivulorum (West-East Africa), An. confuses (East Africa), An. aruni (Zanzibar), An. fuscivenosus (Zimbabwe), An. vaneedeni (North of South Africa), An. brucei (Nigeria), An. parensis (East Africa), and An. leesoni (West-East Africa) are not malaria vectors, they are mainly zoophagic (Sinka, Bangs, et al. 2010).

A part from the main malaria vectors, An. gambiae Giles and An. funestus Giles, a number of others are suspected to play a role in local transmission of malaria especially following the introduction of indoor residual house spraying intervention. These include: An. tenebrosus, An. coustani, An. ziemanni, An. pharoensis, An. squamosus, An. marshalli, An. rivulorum, An. paludis and An. maculipalpis (Gillies 1964).

Current Malaria control strategy

Since the introduction of insecticides with long residual effects in 1950’s, the control of vectors has relied on application of these chemicals using different innovative technologies. Initially, residual indoor spraying targeting indoor resting vectors was considered the most successful technology globally and the global community considered this as the feasible option for malaria eradication. In the 1980’s the introduction of insecticide treated nets was invented and has since improved further by manufacturing long lasting insecticide treated nets (LLINs), which do not require regular re-treatment. Currently, the two technological innovations LLINS and Indoor residual house spraying, are considered as the primary methods of malaria vector control (World Health Organisation 1993).

Mosquito nets have been shown to reduce malaria transmission. A study conducted by Lengler, in 2009 showed that child mortality rate, clinical malaria and severe malaria cases in populations using mosquito nets reduced by 20%, 50% and 45% respectively (Lengeler 2009). Use of mosquito nets reduced malaria parasite incidence, incidence of severe malaria anemia and the prevalence of low birth weight by 38% ,47% and 28% respectively (Kuile et al. 2003).

In Nigeria, LLIN and IRS have been widely used. According to PMI report of 2014, the overall ITN coverage for 2013 was 83% and 74% for children under five years (President’s Malaria Initiative 2014b). IRS is mainly focused in areas with high malaria burden e.g. Gisagara, Nyagatare and Bugesera. In 2013, IRS coverage rate in these three endemic areas was 99.6% which protected a total of 522,315 people of which 8,935 and 81,433 were pregnant women and children under five years, respectively (President’s Malaria Initiative 2013).

CHAPTER THREE:

METHODOLOGY

Study Design

This was a community based cross-sectional descriptive study.

Study Population

The study was conducted on malaria vector mosquitoes and children under 5 years in each selected household of Uyo general hospital. All apparently healthy children less than five years old in Uyo general hospital were included in the study. Children on treatment against malaria were excluded.

Sample size determination

The sample size for malaria prevalence determination was calculated using prevalence of malaria in under 5 years children of 5.5% obtained in the study done by Gahutu (Gahutu et al. 2011).

The formula of Cochran (Cochran 1953) was used to calculate sample size: n = Z²P Q

Where n = sample size being calculated,

Z = z statistic at 95% confidence interval, 1.96

P = Estimated prevalence from the most recent previous study, 5.5% Q = 1-P,

L = Allowable margin of error = 3 %

n = 1.96² 0.055(1–0.055) = 221.85 ≈ 222

0.03 2

Therefore, minimum sample size was 222 children.

CHAPTER FOUR:

RESULTS

Introduction

This chapter presents the findings of the study. The findings are presented and interpreted based on the objectives of the study. A total of 222 parents/guardians with children less than five years gave consent for participation in the study at Uyo general hospital, Nigeria. The respondents were drawn from 13 villages. Moreover, 567 mosquitoes were collected from 39 households and 22 breeding sites for mosquitoes were also included in the study. The results are presented in sections that cover: Socio-demographic characteristics of parents/guardians and children; prevalence of malaria and its associated factors; malaria vector species; sporozoite rate in malaria vectors, source of blood meal for malaria vectors and breeding habitats of malaria vectors.

CHAPTER FIVE:

CONCLUSION AND RECOMMENDATIONS

CONCLUSIONS

This study shows that the prevalence of P. falciparum infection is high (12.2%) among children less than five years of age in the study area. Gender and sleeping under treated bed nets are independently associated with malaria infection. The primary potential malaria vector in the study area is An. gambiae s.l. However secondary vectors like An. ziemanni, An. squamosus and An. maculipalpis might also play an important role in the local malaria transmission. The indoors resting density is high ranging from 0 to 10 anopheles per house per day and the overall indoor resting density was 5 anopheles per house per day. Vectors in the study area are more anthropophagic although they can feed on other available hosts. Irrigation and other agricultural practices have significant influence on mosquito breeding habitat and some abiotic factors are associated with anopheles larval density as well. These factors should be considered when implementing larval control strategies which should be based on habitat productivity and water management.

RECOMMENDATIONS

Based on the study findings, the following recommendations were made

The high number of indoor collection suggest that the vector is more endophilic and endophagic therefore indoor residual spray should be done in the area to reduce the vector density.
Larval control strategies should be applied to reduce vector
Identification of malaria vectors present in the study area at sibling level is
Larger studies are needed for establishing the role of secondary vectors in localmalaria transmission.
Baseline study determination of the susceptibility of malaria vectors in the study area to pyrethroids used in insecticide treated nets widely distributed by the Nigeria Ministryof Health should be
Chemical parameters like dissolved oxygen, nitrate, phosphate of anopheline mosquito larval habitats in Uyo general hospital is
Studies on proper usage of ITNs should be carried out in the

REFERENCES

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Bizimana, J., Twarabamenye, E. & Kienberger, S., 2015. Assessing the social vulnerability to malaria in Nigeria. Malaria Journal, 14(1), pp.1–21.
Cheesbrough, M., 1998. District Laboratory Practice in Tropical Countries,
Christen M., Laura C., V.F. et. al, 2011. Unexpected Anthropophily in the Potential Secondary. Vector -Borne and Zoonotic Diseases, 11(8).
Cochran, W.G., 1953. Sampling Techniques. Second Edition. John Wiley & Sons, Inc. New York. 1953-1963. Library of Congress Catalog Card Number : 63-7553.
Coetzee, M., Hunt, R.H. & Wilkerson, R. et al., 2013. Anopheles coluzzii and Anopheles amharicus, new members of the Anopheles gambiae complex. Zootaxa, 3619(3), pp.246–Available at: www.mapress.com/zootaxa/.
Division of Malaria Control, 2010. Division of Malaria Control (Ministry of Public Health and Sanitation), Kenya National Bureau of Statistics, and ICF Macro.2011. 2010 Kenya Malaria Indicator Survey. Nairobi, Kenya:DOMC,KNBS and ICF Macro,

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