Spatio-temporal Spatio-temporal changeschanges

of tick-borne of tick-borne encephalitis (TBE) encephalitis (TBE)

incidence in the Baltic incidence in the Baltic States: possible States: possible

causes?causes?D.SumiloD.Sumilosupervised by Prof S.E. Randolphsupervised by Prof S.E. Randolph

Department of Zoology, University of Oxford, Department of Zoology, University of Oxford, UKUK

EDEN PhD meetingEDEN PhD meeting, , 88th th JuneJune, 200, 20066,, CIRAD CIRAD, , ParisParis

EstoniEstoniaa

LatviLatviaaLithuaniLithuani

aa

EstoniEstoniaa

LatviLatviaaLithuaniLithuani

aaUKUK

SpainSpain

ItalyItaly

GermaGermanyny

PolanPolandd

RomaRomaniania

HungaHungaryry

Czech Czech RepubRepub

liclicSlovakSlovak

iaia

SlovenSloveniaia

0300600

1960 65 70 75 80 85 90 95 2000 2005

0

200

400

1960 65 70 75 80 85 90 95 2000 2005

0

150

300

1960 65 70 75 80 85 90 95 2000 2005

Estonia

Lithuania

Poland

0

400

800

1200

1960 65 70 75 80 85 90 95 2000 2005

Latvia

Rec

ord

ed a

nn

ual

cas

es o

f T

BE

0

200

400

1960 65 70 75 80 85 90 95 2000 2005

Hungary

0

200

400

1960 65 70 75 80 85 90 95 2000 2005

0

500

1000

45 50 55 1960 65 70 75 80 85 90 95 2000 2005

Czech Republic

0

50

100

1960 65 70 75 80 85 90 95 2000 2005

Slovakia

Slovenia

0

200

400

1960 65 70 75 80 85 90 95 2000 2005

0

10

20

1960 65 70 75 80 85 90 95 2000 2005

Italy

Germany

no data

ChangeChangess in in the the recorded recorded annual cases of TBE annual cases of TBE over over

timetime

1985-901985-90lowlow

19199393--9898highhigh

19199999--0404mod highmod high

Randolph SE (2001) Phil. Trans. Roy. Soc. Lond. B 356, 1045-56Randolph SE (2001) Phil. Trans. Roy. Soc. Lond. B 356, 1045-56

1993 - 19981993 - 19981985 - 19901985 - 1990 1999 - 2001999 - 20044

Spatial heterogeneity of Spatial heterogeneity of TBETBE

within the Balticswithin the Baltics

Data source: Official Public Health statistics, Estonia, Latvia, LithuaniaData source: Official Public Health statistics, Estonia, Latvia, Lithuania

EstoniaEstonia

LatviaLatvia

LithuaniaLithuania

The driving factors?The driving factors?

Just an artefactJust an artefact – – change in public health change in public health activities?activities?

General consensus: General consensus: possibly exaggerated, but nevertheless real possibly exaggerated, but nevertheless real increaseincreaseBiologicalBiological abiotic - climatic & habitat abiotic - climatic & habitat

conditionsconditions

biotic - tick & host biotic - tick & host populationspopulations

Non-biologicalNon-biological socio-economic changessocio-economic changes

human behaviour changeshuman behaviour changes

increased hincreased humanuman-tick contact -tick contact

ratesrates

Spatial and temporal Spatial and temporal analysisanalysis

SpatialSpatialRegression analysis to identify abiotic Regression analysis to identify abiotic predictorspredictorsof TBE incidence of TBE incidence at the ‘county’ level at the ‘county’ level across across all Baltic Statesall Baltic States

Variables for spatial Variables for spatial analysisanalysis(1993-1998)(1993-1998)

AbioticAbiotic - - climatic and habitat conditionsclimatic and habitat conditions

• Surrogate climate variablesSurrogate climate variables (LST, NDVI, MIR)(LST, NDVI, MIR)

extracted from meteorological satellitesextracted from meteorological satellites

Temporal Fourier analysis used to yield Temporal Fourier analysis used to yield summary statisticssummary statistics

• ElevationElevation - digital elevation model (DEM)- digital elevation model (DEM)

• Land coverLand cover – CORINE database– CORINE database

Classified in according to suitability for the tick-Classified in according to suitability for the tick-

habitathabitat

Spatial analysisSpatial analysis – – linear regressionlinear regression BalticsBaltics (1993-1998) (1993-1998)

Dependent Dependent variablevariable

Independent Independent variablesvariables

Variables selectedVariables selected RR22

(n=85(n=85))

Mean Mean annual TBE annual TBE incidence incidence per ‘county’per ‘county’

• ElevationElevation• LSTLST Fourier factorsFourier factors• NDVINDVI Fourier factorsFourier factors• MIRMIR Fourier factorsFourier factors

• Land cover typeLand cover type

• 3 LST3 LST variables variables• 2 MIR2 MIR variables variables• ElevationElevation

0.470.4700

Spatial analysisSpatial analysis – – linear regressionlinear regression BalticsBaltics (1993-1998) (1993-1998)

IInteraction between tick habitatnteraction between tick habitat and human and human contact with that habitatcontact with that habitat

Precise seasonal patternsPrecise seasonal patterns of of vegetation vegetation andand temperaturetemperature are important are important

Dependent Dependent variablevariable

Independent Independent variablesvariables

Variables selectedVariables selected RR22

(n=85(n=85))

Mean Mean annual TBE annual TBE incidence incidence per ‘county’per ‘county’

• ElevationElevation• LSTLST Fourier factorsFourier factors• NDVINDVI Fourier factorsFourier factors• MIRMIR Fourier factorsFourier factors

• MMarginalarginal suitability suitabilitytick habitattick habitat

• 2 LST 2 LST variablesvariables• 2 MIR 2 MIR variablesvariables• 1 NDVI 1 NDVI variablevariable

0.0.555555

• Land cover typeLand cover type

Spatial analysis (1993 – 1998)Spatial analysis (1993 – 1998)

1

85

RanksRanks

to

No statistical difference betweenNo statistical difference betweenobserved and predicted TBE incidence observed and predicted TBE incidence

(p>0.05)(p>0.05)

TBE incidenceTBE incidence

observedobservedpredictedpredicted

Tick suitability habitat Tick suitability habitat mapmap

Tick habitat suitability:Tick habitat suitability:

high high (woodland/forests)(woodland/forests)

marginal (marginal (green urban areas, green urban areas,

pastures etc.)pastures etc.)

zero (zero (built-up areas, water bodies,built-up areas, water bodies,

arable land etc.)arable land etc.)

Data source: CORINE Land Cover national databasesData source: CORINE Land Cover national databases

Currently working withCurrently working withEDEN High Resolution EDEN High Resolution RS team to integrate RS team to integrate land-cover structure land-cover structure variables in the model variables in the model

Conclusions from spatial Conclusions from spatial analysisanalysis

Abiotic factors (temperature, vegetation Abiotic factors (temperature, vegetation index, land cover) are importantindex, land cover) are important

Account for 55% of variation in mean Account for 55% of variation in mean annual TBE incidence across the Baltic annual TBE incidence across the Baltic States States

There appear to be other important factors There appear to be other important factors

e.g. hosts, public health, human factorse.g. hosts, public health, human factors

Temporal analysis Temporal analysis Have these predictors changed at the right Have these predictors changed at the right time, place and direction to explain time, place and direction to explain the upsurge the upsurge in TBE incidence since 1993in TBE incidence since 1993??

Biologically most significant Biologically most significant increase in temperature increase in temperature occurred in Apriloccurred in April

Analysis of temperature data Analysis of temperature data by 10-day periods by 10-day periods fromfrom 1970 1970 toto 2004 2004

Šiauliai

JelgavaGulbene

Rezekne

TBE relative increase (log scale)

Liepaja

Dagda

Biržai

Utena

Klaipėda

Kaunas Vilnius

Jõgeva

Jõhvi

Stende

Lääne-Nigula

Pärnu Sõrve

Tallinn-Harku

Tartu-Tõravere

Võru

0

7

14

21

19

70

19

75

19

80

19

85

19

90

19

95

20

00

Me

an

ma

xim

um

air

te

mp

era

ture

(°C

)

Pärnu county

Lääne county

Harju county

April, last 10-day period

Temporal changes in TBE and Temporal changes in TBE and temperaturetemperature

LarvaeLarvaeNymphsNymphs

Temperature thresholds for tick acitvity

0

50

100

19

70

19

75

19

80

19

85

19

90

19

95

20

00

TB

E in

cid

en

ce

(p

er

10

0,0

00

)

0

7

14

21

19

70

19

75

19

80

19

85

19

90

19

95

20

00

Pärnu county

Lääne county

Harju county

Changes in precipiationChanges in precipiation

20

40

60

80

100

120

Jan Mar May Jul Sep Nov

Mo

nth

ly t

ota

l pre

cip

ita

tio

n (

mm

)

1985-1990

1993-1998

Dryer summers Dryer summers duringduring 1993-19981993-1998 might might have have encourageencouragedd more leisure activity outsidemore leisure activity outside

Changes in average Changes in average I.ricinusI.ricinus nymph nymph abundanceabundance

((I.ricinusI.ricinus monitoring site, Riga’s county, monitoring site, Riga’s county, Tireli)Tireli)

0

10

2030

40

50

6070

80

90

Apr May Jun Jul Aug Sep Oct

1993-1998

1985-1990ti

cks p

er

1 k

m

Data source: Latvian Public Health AgencyData source: Latvian Public Health Agency

0102030405060708090

100

Apr May Jun Jul Aug Sep Oct

1999-2004

1993-1998

ticks p

er

1 k

m

Changes in other factorsChanges in other factors

Data source: Data source: National Statistical offices and Forest agencies in Latvia, Lithuania and EstoniaNational Statistical offices and Forest agencies in Latvia, Lithuania and Estonia

% of area % of area sownsownfor field cropsfor field crops

0

5

10

15

20

25

301

97

8

19

80

19

82

19

84

19

86

19

88

19

90

19

92

19

94

19

96

19

98

20

00

20

02

20

04

Latvia

Estonia

Roe deer per 1000 haRoe deer per 1000 ha

0

5

10

15

20

25

30

35

40

45

19

70

19

75

19

80

19

85

19

90

19

95

20

00

Latvia

Lithuania

Estonia

0

5

10

15

20

25

30

35

40

45

50

55

Cas

es/ 1

00 0

00

1970 75 80 85 90 95 2000

Year

Latvia

Estonia

Lithuania

Change in recorded TBE incidence Change in recorded TBE incidence over timeover time

Data source: Official Public Health statistics, Estonia, Latvia, LithuaniaData source: Official Public Health statistics, Estonia, Latvia, Lithuania

TBE incidence and vaccination TBE incidence and vaccination coveragecoverage

by counties inby counties in Lithuania Lithuania and and LatviaLatvia

Relative change (log Relative change (log scale) of mean TBE scale) of mean TBE incidence 1993-98 to incidence 1993-98 to 2002-042002-04

% of fully immunised people 2002-04% of fully immunised people 2002-04

Data source: Latvian and Lithuanian official public health Data source: Latvian and Lithuanian official public health statisticsstatistics

1.0

0.5

0.0

-0.5

-1.0

0.0 5.0 10.0 15.0 20.0

Who Who goesgoes to to the the forest?forest?

Data source: Data source: SKDS Research Centre, LatviaSKDS Research Centre, Latvia

Secondary analysis of cross-sectional Secondary analysis of cross-sectional survey data of survey data of 18-74 year olds in Latvia 18-74 year olds in Latvia in 2001in 2001

Who are more Who are more likely to go?likely to go?

69% (701/1022) had been to the forest at least once during 69% (701/1022) had been to the forest at least once during tick-activity seasontick-activity season

<55 years of age<55 years of age

With the lowest With the lowest and the highest and the highest incomeincomeLiving in rural Living in rural areas and small areas and small townstowns

From those who From those who go, who are more go, who are more likely to go likely to go frequently?frequently?MalesMales

With the lowest With the lowest incomeincome

Who are more Who are more likely to be likely to be vaccinated?vaccinated?

35 – 54 years of 35 – 54 years of ageageWith higher With higher incomeincome

Those who go to Those who go to the the forestforest

Next stepsNext steps

Further analyses of biotic factors,Further analyses of biotic factors,socio-economic conditions and humansocio-economic conditions and human behaviourbehaviourto explain the epidemiological patterns to explain the epidemiological patterns in the Baltics in the Baltics more fullymore fully

Thank you!Thank you!

To test the findings on the pan-To test the findings on the pan-European scaleEuropean scale

AcknowledgmentsAcknowledgments

II would like to thank would like to thank EDEN-TBD partnersEDEN-TBD partners in the in the Baltic StatesBaltic States::

Antra Bormane, Antra Bormane, Public Health Agency (Latvia)Public Health Agency (Latvia)

Loreta Asokliene, Loreta Asokliene, Centre for Communicable Centre for Communicable Diseases Prevention and Control, (Lithuania)Diseases Prevention and Control, (Lithuania)

Veera Vasilenko, Veera Vasilenko, National Institute for Health National Institute for Health Development and Health Protection Development and Health Protection Inspectorate (Estonia)Inspectorate (Estonia)

for their help with providing data for this for their help with providing data for this studystudy