Remotely-sensed Enviroclimatic patterns and Ebola outbreaks:

linkages and early warning

Dan Slayback

Jorge Pinzon

Compton Tucker

8 September 2004

Biospheric Science Branch, Code 923NASA Goddard Space Flight CenterGreenbelt MD 20771 USA

Outline

• Ebola outbreaks: facts and hypotheses• Environmental links to remotely sensed data• Spatial & temporal specificity of

environmental trigger events• Conclusions

From: Trigger events: enviroclimatic coupling of Ebola hemorrhagic fever outbreaks. 2004. JE Pinzon, JM Wilson, CJ Tucker, R Arthur, PB Jahrling, and P Formenty, American Journal of Tropical Medicine and Hygiene. (in press)

•Many Ebola outbreaks have occurred Many Ebola outbreaks have occurred in African closed tropical forestin African closed tropical forest

•Some Ebola outbreaks have occurred Some Ebola outbreaks have occurred in African gallery tropical forest in African gallery tropical forest within a savanna matrixwithin a savanna matrix

Outbreak Severity

385 21079 47

Outbreak Locations

Community Epidemic Scenario Secondary transmission within species.Secondary transmission within species.Reciprocal transmission between species.Reciprocal transmission between species.

APES/HUMANS

INTERMEDIATEHOST

RESERVOIR

“Cul de Sac” Hosts

Cul de Sac HOST--Cul de Sac HOST--HUMANSHUMANS?

RESERVOIR

APESAPES

Just because a species tests positive for virus or Just because a species tests positive for virus or antibodies does not mean that it is a link in the antibodies does not mean that it is a link in the chain of transmission to apes.chain of transmission to apes.

Peter Walsh et al. Peter Walsh et al. NatureNature (2003) (2003)

Transmission Scenarios

Possible Ebola Transmission(s)no usual suspects!

It is unknown where the virus dwells…

NOAA 11AVHRR

1980 200019901985 201020051995

NOAA 7AVHRR

NOAA 9AVHRR

NOAA 14AVHRR

SeaWiFS

SPOT

MODISes

NOAA-16AVHRR NPOESSNPOESS

NOAA9NOAA9

Moderate-resolution (1-10’s kms) environmental satellites

Environmental Links withRemotely Sensed Data:

available datasets

NOAA AVHRR 8-km NDVI Data Set

Radiation

VIS/NIR/SWIR Band Comparison

AVHRR

SeaWiFS

SPOT-VGT

MODIS

New, improved 8-km AVHRR NDVI data set 1981-present

2003

pal: est ndvi = 0.002*year - 0.020

gimms: est ndvi = 0.0007*year - 0.007-0.04

-0.03

-0.02

-0.01

0.00

0.01

0.02

0.03

0.04

1982 1984 1986 1988 1990 1992 1994 1996 1998 2000

GIMMS-E

PAL

Ye

Major Dataset Differences

Global NDVI anomalies

Are there unique environmental characteristics at outbreak sites, during the outbreak year?

Hypothesis: very extreme change from rainy to dry season

1994 Ebola Outbreak Locations NDVI Time Series

Mean time series and anomalies

Spatial signatures and risk

CCA is a method that maximizes the variance between two datasets. Here, we use CCA to identify areas and times that exhibit enviroclimatic signals typical of those at known outbreak sites and dates.

CCA(A) = [U,S,V]

A: paired-mode correlation matrix between yearly NDVI signals and corresponding NDVI signals from the outbreak sites at outbreak years.

U: orthonormal vector of satellite NDVI signals

S: percentage of covariance explained by canonical factors

V: orthonormal vector of Ebola sites

The analysis conducted only over areas with high enviroclimatic correlation to previous outbreak sites (r2 > 0.95)

Canonical Correlation Analysis (CCA)

Trigger Trigger event event

summarysummary∑

=

Nc

j

NcjVNcNcSNcU1

)':1,():1,:1():1(:,

the the hot hot

zonezone