Spatial Risk Analysis of Water Borne Diseases (Bovine Leptospirosis) in the Rive Nile State-Sudan

doi:10.4236/jgis.2014.61001

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Journal of Geographic Information System, 2014, 6, 1-10

Published Online February 2014 (http://www.scirp.org/journal/jgis)

http://dx.doi.org/10.4236/jgis.2014.61001

OPEN ACCESS JGIS

Spatial Risk Analysis of Water Borne Diseases

(Bovine Leptospirosis) in the Rive Nile State-Sudan

Rania Salah Eldien Bashir Abass, Mutafa Yousif Mohamed Abd Alla,

Ali Mohammed El-Hassan El-Eragi

Field Operation Division, General Directorate of Animal Health and Epizootic Diseases Control,

Ministry of Animal Resources and fisheries, Khartoum, Sudan

Email: [email protected]

Received October 3, 2013; revised November 3, 2013; accepted November 10, 2013

tribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is prop-

ABSTRACT

Geographical Information Science (GIS) technologies have been used increasingly for ecology and epidemiology

of water-borne diseases, providing approach for animal health issues. This study was set up to investigate the

geographical distribution of Bovine that was affected by Leptospira hardijo, in River Nile state, on October 2012.

Locations of targeted cattle were delimited using GPS. Fifty three (53) of blood samples were collected, and

screened in the laboratory for Leptospira hardijo specific antibodies using indirect ELISA. 15.09% had evidence

of infection as determined by the presence of anti-leptospira antibodies. It was inferred that no incidences were

recorded in 45 locations out of the 53 selected locations in the state. Leptospirosis risk area for transmission was

mapped using 5 km buffer distance. Animals’ movements routes were mapped with their contacts area and pos i-

tive samples locations, hafair locations where animals contacts were mapped. This study demonstrated the value

of GIS and GPS in disease mapping for animals’ health, and this might help veterinary authorities to implement

strategic interventions for animal disease control.

KEYWORDS

GIS; Water Borne Diseases; Risk Analysis

1. Introduction

Leptospirosis is an infectious disease caused by patho-

genic leptospires that are transmitted directly or indirect-

ly from animals to humans. Leptospires are bacteria

which can be either pathogenic (i.e. having the potential

to cause disease in animals and humans) or saprophytic

(i.e. free living and generally considered not to cause

disease). Pathogenic leptospires are maintained in nature

in the renal tubules of certain animals. Saprophytic lep-

tospires are found in many types of wet or humid envi-

ronments ranging from surface waters and moist soil to

tap water [1].

The causal agent of leptospirosis is aspiral-shaped

aerobic spirochete bacterium of the genus Leptospira in

the family Leptospiraceae, order Spirochateales. The size

of this organism is 6 - 20 μm long and 0.1 μm in diame-

ter with 18 or more coils per cell. The coils tend to stain

poorly with common laboratory stains and are best visua-

lized by dark field microscopy, silver stain or fluorescent

microscopy. Before 1989, the genus Leptospira was di-

vided into 2 species, Leptospira interrogans and Leptos-

pira biflexa [2]. WHO has identified leptospirosis as a

neglected tropical disease, and estimates the median

global incidence of leptospirosis to be at least 5.1 cases

per 100,000 per year in endemic areas, and 14 cases per

100,000 per year during epidemics. However, inci-

dences vary significantly between regions, with esti-

mated annual incidences per 100,000 per year ranging

from 95.5 in Africa, 66.4 in the Western Pacific, 12.5

in the Americas, 4.8 in South-East Asia, to 0.5 in Eu-

rope [2].

The species L. interrogans comprises all pathogenic

strains while L. biflexa contains the non-pathogenic

strains. Recently, taxonomic studies based on DNA hy-

bridization divided the genus Leptospira into 20 species

[3]. The species that causes illness to man is L. interro-

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gans. More than 200 serovars of L. interrogans have

been identified. Animals that are natural hosts to a par-

ticular serovar usually show no or comparatively few ill

effects after infection with that serovar. However, they

may develop illness after infection with another serovar.

In the initial stage of an infection, animals may show

mild symptoms, such as malaise and a drop in milk

production in cows. Chronic infections may lead to re-

productive problems, such as abortion and low fertility in

cattle or pigs. Mild leptospiral infection in domestic ani-

mals may pass unnoticed. Occasionally, calves and pig-

lets may suffer from an icterohaemorrhagic syndrome

with potentially fatal outcome. As in humans, animals

that are incidental hosts may become ill with severe dis-

ease. Infections can be fatal. Dogs may suffer from a

chronic disease leading to kidney damage, but may also

suffer from an acute Weil’s-like disease syndrome after

infection with certain serovars. The disease is found

mainly wherever humans come into contact with the

urine of infected animals or a urine-polluted environ-

ment. Leptospirosis is endemic in many countries. It of-

ten has a seasonal distribution, increasing with increased

rainfall or higher temperature. However, the disease can

occur throughout the whole year. Epidemics may be as-

sociated with changes in human behavior, animal or se-

wage contamination of water, changes in animal reser-

voir density or follow natural disasters such as cyclones

and floods [4].

Leptospirosis is found throughout the world, but is

particularly common in tropical and subtropical regions

where environmental conditions favour the survival and

transmission of leptospires. An estimated 500,000 severe

cases occur each year (accounting for only 5% to 15% of

all clinical infections), and case-fatality rates of over

30% have been reported in some areas [5].

Predicting epidemics is a great challenge for epidemic-

ologists regarding the emergence or reemergence of in-

fectious diseases. Remote sensing and GIS are tools of

great potential for a near real-time linkage between epi-

demiology and environmental characteristics. Beside dis-

ease incidence and prevalence in vectors and hosts, geo-

graphy is a main source of information for epidemiologi-

cal studies, making a link between environmental and

social approaches. Space technologies, therefore become

more widely used in this field, especially for the mo-

toring of tropical diseases [6].

Person, place, time: these are the basic elements of

outbreak investigations and epidemiology. Historically,

however, the focus in epidemiologic research has been

on person and time, with little regard for the implica-

tions of place or space even though disease mapping

has been done for over hundreds of years [6,7].

The development of GIS has provided a more power-

ful and rapid ability to examine spatial patterns and

processes. This, in turn, has fostered the discussion of

such policy relevant issues as health services and plan-

ning as well as the use of GIS for epidemiologic investi-

gations and disease surveillance [8].

The main objective of this study is to investigate the

spatial distribution and ecology of bovine leptospirosis in

River Nile state to locate the positive cases using Global

Positioning System (GPS) and determine leptospirosis

risk areas through mapping the factors that encourage the

spreading of disease.

2. Materials and Methods

2.1. Study Area

The present study was conducted in River Nile State

which located between longitude 32˚N - 35˚N and lati-

tude 16˚E - 22˚E, (Figure 1). The most important cli-

matic feature of the State is the occurrence of a long dry

season extending for eight months from November to

June, with a rainy season from July to September/Octo-

ber with an average annual rainfall of 150 mm in the

southern part to 25 mm in northern part. The average

temperature ranges from 8˚C to 47˚C.

The vegetation of the State is poor and sparse. In the

desert zones, it is virtually absent except along the banks

of the Nile River and water sources where ephemeral

herbs and grasses occur after the occasional rainfall.

The numbers of animals in the River Nile State are

modest compared to other States of the country. Sheep

and goats constitute the majority of the animal wealth

with an estimated population of 1,034,655 sheep,

1,211,095 Goat, 100,701 Cattle and 114,103 camel

Figure 1. Study area (River Nile State).

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(Ministry of Animal Resources, River Nile State).

2.2. Samples Collection

Fifty three blood samples were collected randomly from

cattle in River Nile state, on October 2012, locations

identified using GPS (GARMIN-GPSMAP 60CSx).The

blood samples were collected in plain vacutainers, cen-

trifuged to separate the serum and stored at –20˚C till

used. Collected sera were tested for the presence of lep-

tospira antibodies using indirect Leptospira hardijo

ELLISA kit (Cat. No.79038923, prioCHECK L. hardijo

AB, Germany).

2.3. Detection of Leptospira Antibodies

Briefly; the test uses 96-well microtitration plates sensi-

tized by purified antigen Leptospira hardjo. The plate’s

odd columns (1, 3, 5, 7, 9, and 11) contain the LPS,

whereas the even columns (2, 4, 6, 8, 10, and 12) contain

a control antigen.

The sera were diluted in the dilution buffer. The plate

was incubated and the LPS washed, then the conjugate,

protein G peroxidase-labelled, is added to the wells. The

plate was incubated a second time at 21˚C +/− 3˚C. After

the second incubation, the plate was washed again and

the chromogen (tetramethylbenzidine) is added. This

chromogen has the advantages of being more sensitive

than the other peroxidase chromogens and not being car-

cinogenic. If specific Leptospira hardjo immunoglobu-

lins are present in the test sera, the conjugate remains

bound to the microwell that contains the bacterial antigen

and the enzyme catalyses the transformation of the

colorless chromogen into a pigmented compound. The

intensity of the resulting blue color is proportionate to the

titer of the specific antibody in the sample.

All the reagents were brought to 21˚C +/− 3˚C before

the use. For sera, one milliliter aliquots were placed of

the dilution buffer, prepared as instructed in the “Com-

position of the Kit” section, in 5 or 10 ml hemolysis

tubes. 10 ml of the serum samples was added to each of

these tubes (dilution 1/100) and were shacked briefly on

a mechanical agitator.

Positive and negative sera were diluted 1/100 in dilu-

tion buffer. Sera samples were distributed and the posi-

tive and negative sera (100 ml/well) as follows: positive

serum in wells A1 and A2, negative serum in wells B1

and B2, sample 1 in wells C1 and C2, sample 2 in wells

D1 and D2 etc. The plate was incubated at 21˚C +/− 3˚C

for one hour. The plate was rinsed with the washing

solution, was prepared as instructed in the “Composition

of the Kit” section, as follows: the microplate was emp-

tied of its contents by flipping it over sharply above a

sink. Tap the microplate upside down against a piece of

clean absorbent paper to remove all the liquid. The used

wells were filled with the washing solution using a

squeeze bottle or by plunging the plate in a vessel of the

right dimensions, then empty the wells once more by

turning the plate over above a sink. Repeat the entire

operation two more times, taking care to avoid the for-

mation of bubbles in the microwells. After the plate has

been washed three times the conjugate was diluted 1:50

in the dilution buffer. 100 ml of the conjugate solution

was added to each well. Incubated for 1 hour at 21˚C

+/−3˚C, the plate was washed as described in step 6

above.

100 ml of the chromogen solution was added to each

well on the plate and incubated for 10 minutes at 21˚C

+/− 3˚C protected from the light and uncovered. 50 ml of

stop solution was added to each microwell.

The optical densities in the microwells were read using

a plate reader at 450 nm. Results were read fairly soon

after the stopping solution has been added since the

chromogen may cristallize in the wells with strong sig-

nals and thereby distort the data.

The test can be validated only if the positive serum

yields a difference in optical density at 10 minutes that is

greater than 0.8 and the negative serum yields a differ-

ence in optical density that is lower than 0.3.

Divide the signal read for each sample well by the

corresponding positive control serum signal and multiply

this result by 100 to express it as a percentage.





ValDelta OD Sample100Delta OD positive

Table 1 can be used to determine the serum’s degree

of positivity.

2.4. GIS Software

An Arc View 9.3 software system was used to map sam-

ples locations. The data used were: animals population

2011(Ministry of Animal Resources-River Nile state),

human population 2008 (Sudan Central Bureau of Statis-

tics), Samples location by GPS (River Nile State), hafairs

locations where animals contacts, Animals routs. The

buffering method was used to determine the risk area.

3. Results

This study demonstrated the use of GIS in the study of

Table 1. The serum’s degree of positivity.

0 + ++ +++ ++++ +++++

Val <= 20% < Val <= 40% < Val <= 60% < Val <= 80% < Val <= 100% < Val

R. S. E. BASHIR ABASS ET AL

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leptospirosis in River Nile State. The results of this study

supported the evidence that leptospirosis is a burdensome

disease of animals and human health in the Sudan just as

in other countries in the tropics where there are the ap-

propriate environmental conditions for the survival of the

infective agents. In some developed countries, leptospi-

rosis is a disease of economical significance in animal

husbandry (Levett, 2001) rather than a human illness.

Samples locations layer was prepared and overlaid

with possitive samples layer using GIS software, a map

was created as shown in (Figure 2).

The animals and human population layers were over-

laid with positive samples locations layer to compare the

distribution of the disease as shown in (Figure 3).

To estimate the probable risk from animal movement,

buffer tool was used to create buffer zone of risk area

from positive samples locations, 5 km distance was de-

termined according to animals movement the previous

studies (Weise et al., 2006). The buffer zone layer was

overlaid with an urban area to estimate the risk map as

shown in (Figure 4).

Hafair is a main source of water for animal use, hence

it has an affect the disease spreading, locations of Hafairs

were determined using GPS and has been overlaid it with

animals population layer, positive samples locations

layer and negative samples locations as shown in (Figure

5).

Animal’s tracks were mapped, routes for searching for

water and grazing, overlaid with Hafair layer and posi-

tive samples locations layer (Figure 6).

Figure 2. Spatial distribution of leptospirosis in the study area.

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Figure 3. Distribution of animals, human population and disease.

4. Discussion

Incidences survey was confirmed through indirect

ELISA test. This is used to visually interpret the spread

of incidences according to their intensity in the localities.

From (Figure 2), it was inferred that no cases were

recorded in 45 locations out of the 53 locations present in

the state, this study, as far as we are aware, is the first to

describe leptospira hardijo infection. This study, per-

formed in zone (A) for cattle leptospirosis, identified

positive samples distribution of leptospira infection with-

in cattle in River Nile state shown in (Figure 2). Among

numbers of cattle which move in rural area as index cas-

es of leptospirosis, 15.09% had evidence of infection as

determined by the presence of anti-leptospira antibodies

in the indirect ELISA as shown in (Table 2).

Animal’s population layer shows the numbers of each

species through the localities, it has been found that goats

have the highest numbers and cattle the lowest. This

layer has been overlaid over the human population layer.

From population layer it appears that Eldamer locality

has the highest population.

Our finding indicate that positive cases of leptospirosis

are found in Eldamer locality which is the highest popu-

lation and Elmatama which is the fourth in order, the

location of positive samples near Atbara River that pass

through ELdamer and Atbara, and near river Nile which

divide Elmatama and Shendi, movement and migration

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Figure 4. Buffer zones for the positive sample location.

of animals and humans through Atbara river and river

Nile increase risk for leptospira infection in Atbara and

Shendi localities.

It can be suggested that infection risk varies over short

distances within theses rural areas. These risk differences

may relate to differences between animals husbandry

with respect to rodent population densities and proximity

to environmental source of contamination such as surface

water, larger buffers (5 km) often included other valleys,

watersheds, a buffer distance of 5km was chosen for

analysis because it provided the best prediction of risk

area.

Leptospirosis has latency period of 10 - 14 days be-

tween contact and development of clinical signs of infec-

tion; we predict that animals are able to travel during this

latency period. By maintaining a portion of the popula-

tion in a latent disease state, the distribution of infected

animals perpetuated as animals disperse across a board

geographical area.

In higher temperature human and animals may partici-

pate in water based activities such as swimming, bathing

or drinking, these activities increase contact probability

of human and animals and leptospires where hafair lo-

cated in rural areas as shown in (Figure 4). The cases of

leptospirosis mostly occurred during the rainy season, the

highest average of rainfall in August 26 - 35 mm (Figure

5) shows this. The inability of leptospires to survive out

of water is the single most important control factor in the

natural environment, as it means they are unable to create

infection risks from dry surfaces.

The cases of leptospirosis mostly occurred during the

rainy season, the highest average of rainfall in August 26

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Table 2. Serum samples result.

Sample No Result by

Percentage

Positivity

Degree Location Sample

Result by

Percentage

Positivity

Degree Location

1 4.23% 0 Atbara 23 18.93% 0 Umm Eltiuor

2 6.27% 0 Atbara 24 7.35% 0 Alsyal

3 4.07% 0 Atbara 25 1.77% 0 Alsyal

4 5.84% 0 Atbara 26 38.34% + Alsyal

5 3.38% 0 Atbara 27 4.88% 0 Alsyal

6 3.86% 0 Atbara 28 9.06% 0 Elwehaib

7 0.64% 0 Atbara 29 46.33% ++ Elmashaikha

8 1.55% 0 Atbara 30 49.87% ++ Elmashaikha

9 2.09% 0 Elaaliab 31 7.35% 0 Elremaila Ganoub

10 16.35% 0 Elaaliab 32 3.54% 0 Elgambarat

11 3.06% 0 Elaaliab 33 16.41% 0 Elgambarat

12 14.90% 0 Elaaliab 34 7.88% 0 Elgambarat

13 2.25% 0 Elfadnia 35 1.72% 0 Elhamadab

14 5.09% 0 Elfadnia 36 15.44% 0 Teiba Alkhwad

15 7.72% 0 Eldamar 37 10.26% 0 Wad Hamid

16 19.09% 0 Eldamar 38 4.77% 0 Wad Hamid

17 6.54% 0 Elkitiab 39 22.14% + Wad Hamid

18 −0.75% 0 Elkitiab 40 8.36% 0 Basabir

19 73.94% +++ Elgabrab 41 75.81% ++ Basabir

20 13.89% 0 Elgabrab 42 24.72% + Elmesektab

21 −0.05% 0 Elfadlab 43 3.27% 0 Elmesektab

22 4.08% 0 Elfadlab 44 3.38% 0 Hager Elaasal

45 2.79% 0 Shendi

- 35 mm. During this month all hafair fill in with water,

this facilitates leptospira organisms’ growth in water. The

bacteria can survive for 1 to 2 months. In the natural wa-

ter sources, leptospira spp. Can survive even with expo-

sure to UV-A radiation for 6 hours. This may lead to

greater chance for animals and people to be exposed to

leptosira organisms during their movement from and to

hafair. The positive samples of leptospirosis located near

animals routs and their contact at hafair location and this

may lead to greater chance and increase risk of exposure

animals to leptospira infection during their movements.

The potential application of GIS to epidemiological

studies has been shown by recent studies. GIS is a val-

uable tool of environmental epidemiology. GIS also

permits analysis of spatial and non-spatial information

and hence is an excellent framework for disease moni-

toring and control (Clarke et al., 1996) have reviewed

the use of GIS in surveillance and monitoring of vector

borne diseases, water borne diseases, environmental

health and modeling and the analysis of the diseases pol-

icy and planning.

5. Conclusions

This study demonstrated the value of GIS in disease

mapping for investigating the spatial distribution of lep-

tospirosis infection, identifying geographic and environ-

mental risk factors, and enhancing our understanding of

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Figure 5. Animals population and surface water resources (Hafair).

disease transmission and the ability to accurately assess,

predict, and map environmental drivers of disease trans-

mission.

The output disease maps have facilitated knowledge

on the geographical distribution of leptospirosis at the

localities level.

The epidemiology of leptospirosis is complex and va-

ries significantly in different environmental settings. Its

transmission dynamics can be influenced by climatic

events, environmental factors, animal reservoirs, as well

as human behavior and social trends.

The present study revealed that the disease is present

in most of the localities suggesting that the detected an-

tibodies were due to active or past exposure to infection

since there were no adopted vaccination progarammes

against leptospirosis all over the country.

Acknowledgements

I would like to express my sincere thanks and gratitude to

Dr. Mutafa Yousif Mohamed-Elzaem Elazhari University

for his support, encouragement and guidance.

My thanks and appreciations were extended to all the

veterinarians at the Veterinary Research Institute, espe-

cially Dr. Ali Mohammed El-Hassan El-Eragi (Head De-

partment of Pathology and Diagnosis-VRI), for their fruit-

ful discussions and inspirations that helped me to per-

form this work as well as in writing this manuscript.

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Figure 6. Animals movement and their routes in the state.

I would like also to thank Eng. Alaa Eldien Hassan

Mohamed (Department of planning, water corporation,

River Nile State) for providing some information.

I would like to thank Dr. Omiema Ahmed Abd Allah

(Head of Epizootic Diseases control Directorate—River

Nile State) for her help and support.

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