Spatial Distribution of Malaria in Warri Metropolis

This study examined the spatial distribution of malaria in Warri metropolis. To achieve this, data were generated from medical archival records from hospitals in Warri metropolis. The medical records contain recorded cases by place of diagnosis in 2011. The data were analysed by using ANOVA to ascertain the spatial differences in the spread of malaria in the metropolis. The result revealed that malaria is at its peak in June and minimal in September owing to the heavy floods in June. It was observed that there is a variation in the prevalence of malaria in the metropolis which is significantly high in area of Okumagba prevalence of malaria in Warri is significantly different from the prevalence of malaria in Uvwie and Udu. It is anticipated that an increase in malaria is attributed to water bodies, thus, it is recommended that vulnerability mapping should be carried out to identify areas prone to malaria.


INTRODUCTION
Thousands of people are currently living in areas where the malaria vectors are present and circumstances are suitable for parasite development [1].Tropical zones like sub-Saharan Africa are amenable to high endemic stability, and strongly anthropophilic mosquitoes in many of these areas make malaria transmission very effective [2].Landscape epidemiology recognizies that disease does not occur sporadically across the landscape; rather there are physical characteristics of a place such as elevation, temperature, and vegetation that contribute to disease expression [3].
Malaria transmission, however, is a complex interac-tion of many factors, including not only vector and parasite densities and behaviour, but also land-use change [4], public health control measures [5][6][7], human migration [8,9], and drug resistance [10].The risk of transmission can vary from one geographical area to another and in the same geographical area from one village to another [11].Distance to breeding sites [12,13] and type of houses are local environmental factors frequently associated with high mosquito density.The location of people and houses within the metropolis with respect to breeding sites as well as randomness, affect the distribution of individual cases at the lowest scale.According to the [14], malaria kills over one million people each year, while 300 to 500 million people are suffering from chronic malaria around the world.This is one of the most common and serious diseases in our time.The difficulty in diagnosis is one of many reasons why the actual figures are expected to be much higher.The death toll is predicted to double in the next 20 years if no new control measures are developed [15].Adding to the scenario are the anthropogenic changes in our environment.Members of the Anopheles genus are adequate breeders and therefore require rainfall for the production of habitats with suitable level of surface water [16], the eggs are deposited in pools [17] shortly after rainfall [18] and resulting larvae develops in the aquatic environment [19] (see Figure 1).Mosquito-borne disease transmission is climate sensitive for several reasons; mosquitoes require standing water to breed, and a warm ambient temperature is critical to adult feeding behaviour and mortality, the rate of larval development, and speed of virus replication [20,21] (see Figure 1).If the climate is too cold, viral development is slow and mosquitoes are unlikely to survive long enough to become infectious.Although a suitable climate is necessary for disease transmission, other factors are needed for an epidemic to take place, including a source of infection, vector populations, and a susceptible human population.
In Warri metropolis, most of the natural drains have been closed and the constructed drains are blocked with litters of garbage, hence making areas like Okumagba Avenue, Airport road, Makiava areas etc. experience flood; which in turn results in breeding grounds for mosquitoes.The people are vulnerable to mosquito bite resulting in malaria because most of the houses are within the fringes of water bodies, farm gardens and tall grasses as well as within flight distance from their respective breeding habitats.At the same time, malaria transmission intensity varies at different spatial scales.
The location of people and houses within the metropolis with respect to breeding sites as well as randomness, affect the distribution of individual cases at the lowest scale.There have been several attempts to define the global and national distributions of malaria.Common to all previous attempts at mapping malaria risk is that they derive from a combination of expert opinion, limited data and the use of crude geographical and climate isolines.None has a clear and reproducible numerical definition: consequently, their comparative value becomes limited.Consequently, this paper examines the spatial distribution of malaria in Warri metropolis.This research is geared to proffer possible suggestion towards policies implementation to reduce the risk of malaria.

STUDY AREA
Warri metropolis is located between latitudes 5˚30 1 N and 5˚35˚N and Longitudes 5˚29 1 E and 5˚48 1 E. Warri metropolis is made up of Warri South, Udu and Uvwie Local Government areas.The area is characterized by hydromorphic soils, which is a mixture of course alluvial and colluvium deposits [22].The rocks are of sedimentary rock types with sand to a top layer (4 -6 m) which is followed by a thick (up to 17 m) layer of silt and becoming coarse and pebbly at depth below.The area is characterized by tropical equatorial climate with mean annual temperature of 27.4˚C and rainfall amount of 275.21 mm.
Rainfall period ranges from January-December, with the minimum value of 20.4 mm in January and over 499.1 mm in September [23].The temperature of 27.4˚C enhances the transmission of malaria which is caused plasmodium falciparum which requires a minimum temperature of 19˚C [24].Furthermore, its soil and low relief feature results in water stagnating on the ground surface which act as breeding ground for mosquitoes causing malaria.
The areal expansion of Warri metropolis is now over 100 sqr.km [22] with a population that has grown from 19,526 in 1933, 55,256 in 1963, 280,000 in 1980, 500,000 in 1991 to 536,023 in 2006 having a high population density that is concentrated in the core areas of the city.These areas include; Warri-Sapele road, Agbassa, Okere, Okumgba Avenue, Igbudu, Iyara, Jakpa and Airport road, P.T.I. road, Udu and Ekpan.This has resulted to an increase in the incident of anthropogenic activities in these areas.

CONCEPTUAL ISSUES
The success of spatial distribution of disease requires accurate information on vector biology and ecology, malaria transmission and epidemiology, in relationship to local environmental conditions, and a good stratification of control areas with respect to time and space [25].Epidemiology concept is concerned with the study of the occurrence, distribution, determinants of diseases and injuries in human populations.Thus, it concerns with the types and frequencies of illnesses, injuries, and other health-related conditions or problems in groups of people and with the factors that influence their distribution and to discover the factors essential for diseases to occur within groups.Furthermore, finding the best methods to reduce or prevent those factors and other conditions detrimental to the health of communities [14].Malaria control is based on the three main functions which epidemiologists perform, more or less successfully, namely, in order of increasing difficulty and uncertainty: 1) To describe and measure the distribution of disease, e.g. who gets malaria, how much of it, when and where?
2) To explain that distribution by its determinant factors: biological, environmental, social, behavioural and economic.
3) To predict the changes expected in that distribution from human interventions, in particular from control measures.
These three epidemiological functions constitute important inputs into the planning of malaria control, with the aim of adopting the control strategy to the epidemiological situation.Within an epidemiology approach, the diverse set of factors associated with malaria is considered in the context of Epidemiology Triangle, linking the environment with disease transmission and health.The epidemiologic triangle consists of three components, with the Agent at the top point and the Host and the Environment at the other two points of the triangle.Each component must be analysed and understood to comprehend and predict patterns of disease (see Figure 2).
The complex nature of the host-vector-agent characteristics of the disease in relationship to the environment has been recognised as the primary cause of malaria illness over the years [26].Changes in any component will alter the existing equilibrium to increase or decrease the frequency of a disease.In a steady state of the triangle, each leg of the component is affecting and being affected by the other components.Any influence among the triangle relationship will impact the epidemics of vectorborne infectious disease.

MATERIALS AND METHOD
The data utilized for this study was generated from the archives of hospitals medical records of malaria in-patient and out-patient diagnosis in Warri metropolis.The data contains recorded cases by place of diagnosis which was obtained from the two (2) central hospitals (Central Hospital, Warri and central Hospital, Ekpan) and one (1) renowned hospital each from the three (3) local Government Areas; (Numa Clinic, Odion Road) Warri, (Twins Clinic, Udu Road) Udu and (NNPC Clinic, Ekpan) Uvwie respectively.The choice of these three hospitals was for data consistency.The medical records contain the number of patients treated for malaria in 2011.ANOVA was used to ascertain the spatial variation of malaria in Warri metropolis.
Malaria is at its peak in the month of June and minimal in September (see Table 1).It is worth noting that the mosquito breeds well in flooded environment.During the month of June, Warri metropolis is heavily flooded.Malaria transmission in the Warri metropolis is characterized by substantial inter-monthly variation.Minakaw [27] asserted that the wet season presents favourable environmental conditions that enhance mosquito breeding and survival.
Table 2 reveals that in Warri metropolis the high prevalence of malaria are found in areas of Okumagba layout, Jakpa, Airport road, Pessu market, Warri main market, and Igbudu market (see Figure 3).However, the low malaria prevalence area represented by SPDC, Edjeba, Ubeji, Ugbomro, DBS express, G.R.A at Warri and Effurun.Succinctly, the highest episode of malaria prevalence was recorded in Okumagba layout areas (see Table 2).The increased malaria prevalence is attributed to increase flooding which results from increased rainfall there by creating breeding sites for mosquitos.
Table 3 shows a calculated F of 7.857 at P < 0.05 and thus, the model is significant.Therefore, there is a statistically significant difference in the spatial spread of malaria between the three locations (Warri, Uvwie and Udu) that are being compared.Looking at the Sig.column in the Turkey's post hoc test, there are values lesser than 0.05 (see Table 4).However, there are two values that are 0.042 and 0.026.These values correspond with the comparison between the prevalence of malaria in Udu and Warri, and malaria prevalence in Warri and Uvwie conditions.Conclusively, the prevalence of malaria in Warri is significantly different from the prevalence of malaria in Uvwie and Udu.However, the prevalence of malaria in Uvwie and Udu are not significantly different from one another.This finding corroborates with study of spatial and temporal distribution of falciparum malaria in China by Lin [28] showing that stable falciparum malaria transmission occurs in the bordering region of Yunnan and the hilly-forested.

MALARIA MANAGEMENT MEASURES
Integrated Vector Management encourages a multi-disease control approach, integration with other disease control measures and the considered and systematic application of a range of interventions, often in combination and synergistically (WHO, 2004).This management serves to maximize cost effectiveness and extend the useful life of insecticides and drugs by reducing the selection pressure for resistance development.Integrated Vector Management harnesses precise scientific knowledge of the vector ecosystem and its inter-relationship to human ecosystems to address the following issues in more environmentally sustainable ways.However, environmental modification has been used successfully to destroy either vector or reservoir host habitat, particularly at the fringes of disease transmission.Although destructive locally, careful targeting can minimize environmental impacts.Furthermore, efforts to address the issue of malaria resulting from environmental changes have to be strengthened.Preventive public health could also be initiated by warning and the education of public and local communities to conduct relevant health promotion cam-    burdens from malaria disease.

CONCLUSION
Findings of this study demonstrate increased exposure to malaria in areas near water bodies serving as mosquito vector breeding sites.Malaria transmission in the Warri metropolis is characterized by substantial inter-monthly variation.The prevalence of malaria is high in Okumagba layout, Jakpa, Airport road, Pessu market, Warri main market, and Igbudu market areas of the metropolis.Succinctly, there is a significant difference in the prevalence of malaria in Warri metropolis.These findings may be useful for the planning of malaria control activities, as they may induce the design and implementation of more reliable malaria policy and intervention in the region.It is therefore recommended that vulnerable mapping should be carried out to identify areas in which malaria is likely to invade.Entomological and parasitological surveillance

Figure 3 .
Figure 3. Spatial distribution of malaria in Warri metropolis.

Table 2 .
Malaria distribution in Warri metropolis.

Table 3 .
ANOVA on the spatial spread of malaria.