1. Ecology of Vibrio cholerae, epidemiology of cholera: What role for climate?
Guillaume Constantin de Magny
University of Maryland
Institute for Advanced Computer Studies

2. Outline Ecology of Vibrio cholerae
Seasonality and inter-annual variability of cholera outbreaks
Comparative study of recent cholera cases dynamics in three locations in Asia in regards to local environmental conditions.
Conclusions

3. The Cholera Today
Cholera: Acute intestinal infection causing copious, painless, watery diarrhoea, with vomiting. Contamination by ingestion of food or water contaminated with the bacterium Vibrio cholerae. Few hours to 5 days of incubation period.
In 2008, 56 countries affected, for a total of 190,130 cases including 5,143 deaths, Case Fatality Rate of 2.7% (WHO).
According to WHO, these numbers represent only 10% of the actual cases. It means closed to 2.0M of cases and over 50,000 deaths.
This figure excludes the estimated 500– cases labeled as acute watery diarrhoea.

4. Ecology of Cholera
Data on the association between plankton, either phytoplankton or zooplankton, and V. cholerae have been gathered over the last 20 years and strongly support the hypothesis of a commensal or symbiotic relationship between chitinous zooplankton and most particularly copepods and this bacterium. Because V. cholerae can be highly concentrated on zooplankton carapaces and in their gut, the risk of ingesting an infectious dose increases when untreated surface waters are used for consumption, leading to the well known human to human transmission. In this way, cholera shares some properties of a vector-borne disease.

5. How climate affects cholera?
Physical & Chemical
Characteristics of Water
temperature
sunlight
rainfall pH
dissolved oxygen
salinity & nutrients
Biological Characteristics
algae bloom
phytoplankton bloom
Zooplankton bloom
(enters into non-culturable state)
V. Cholerae
viable but non-culturable state in the water
column & attached to particulates. Commensal
or symbiotic relationships
Fecal shedding
returns V. cholerae
to the water
Transmission of V. cholerae
to humans via ingested water containing
colonized copepods or other vectors.

6. Cholera outbreaks frequency
Seasonal cycle: - Single peak per year typically found Africa and in Latin America. - Two peaks per year in the surrounding regions of the Bay of Bengal, lands of cholera.
Interannual cycle: - In endemic context, cholera appears to wax and wane from 3 to 8 years.
Most of these studies were focusing on one geographical area at a time, using historic data.
Today, what about cholera outbreak dynamics in three contrasted locations in Asia?

7. Comparative study of cholera outbreak dynamics in Asia.
Cholera cases due to V. cholerae, confirmed by culture.
Rainfall data: Global Precipitation Climatology Project
Land Surface Temperature: NCEP global reanalysis.
NEW DELHI
1999
2008
10 years
KOLKATA
1996
2007
12 years
MATLAB
1966
1998
33 years
1990
2007
18 years

8. Methods and Designs Wavelets analysis: Coherency: Phase Analysis:
Because epidemiological and climatic time-series are typically noisy, complex and strongly non-stationary, Wavelet time series analysis, that decompose the variance of a time series into different frequencies at different localities in time, is particularly adapted.
Wavelets analysis:
Decomposing the variance of a time series into different frequencies at different localities in time. The Morlet wavelet function was used.
Data treatments:
1. Square root transformation of epidemiological data only.
2. Normalization (mean=0, variance=1) all time series.
Coherency:
Coherency is similar to some classical correlation but for the oscillating components in a given frequency mode.
Phase Analysis:
When coherency is significant, the extraction of oscillatory component and phase calculation of the signal in a periodic band is used to quantify synchrony or delay.

9. New Delhi ( )
Period Time series Wavelet power spectrum Spectral analysis
0.3 – 5 yrs
2 – 5 yrs
0.3 – 2 yrs

10. Matlab ( )
Period Time series Wavelet power spectrum Spectral analysis
0.3 – 15 yrs
2 – 15 yrs
Detection of seasonal cycle composed by 2 peaks, but not so regular along time.
Surimposed of a 3 and 5 years cycle during 70 through mid-80s with a drift of the 4-5 year cycle to 6-7 year.
0.3 – 2 yrs

11. Cholera dynamics
Seasonal pattern The bi-modal (6 and 12 months) cycle is observed in Bangladesh, but is not stationary along time. The 6 months cycle is detected but not significant in Kolkata and is absent in New Delhi.
Interannual Variability: 3 year cycle for New Delhi, Kolkata (also, but not so clear). 3 and 4 year cycles for Matlab between 1970 and 1985 with a progressive increase from 4 to 6 years for the last two decades.

12. Coherency and Phases Analyses New Delhi vs. Kolkata (1999-2007)
yrs
Phases
1 year
New Delhi annual outbreak 1 month in advance on Kolkata

13. Asynchrony of cholera outbreaks
Annual cycle
2 Months
KOLKATA
1 Month
MATLAB
1 Month
NEW DELHI
What about patterns in environmental parameters?

14. Coherency and Phases Analyses New Delhi
Rainfall vs. Cholera
Land Surface Temperature vs. Cholera

15. Cholera and Environment
Annual cycle
KOLKATA
NEW DELHI
MATLAB
1 Month
2 Months
LST
1 month lag
Rainfall
Synchronous
LST
2 months lag
Rainfall
Synchronous
LST
3 months lag
Rainfall
3 months lag

16. Conclusion
Annual or bi-modal cycles but are not always stationary along time, as for example for very long time series, as shown for Matlab.
Asynchrony of cholera outbreaks in India and Bangladesh,
But dynamics are highly coherent with environmental parameters at different time lags.
First approach will be to issue early warnings by using direct observations of LST to support preventive actions against cholera transmission.
The next step will be to use climate seasonal forecast model outputs for rainfall and land surface temperature to setup a more developed early warning system in endemic settings.
But what about cholera and climate in Africa…

17. Point of discussion
How to integrate outputs of climate forecasting models at seasonal scale into a mechanistic SIRS model of cholera transmission?
How to integrate social sciences in the cholera equations?

18. Collaborators
Dr N.C. Sharma from Maharishi Valmiki Infectious Diseases Hospital, New Delhi, India
Dr G.B. Nair, and Dr K. Rajendran from National Institute of Cholera and Enteric Diseases, Kolkata, India
Dr M. Yunus from International Centre for Diarrhoeal Disease Research, Dhaka, Bangladesh
Dr R.B. Sack from Johns Hopkins Bloomberg School of Public Health, Baltimore, USA
Dr R. Murtugudde, Dr M. Sapiano, and Jim Beauchamp from Earth Science System Interdisciplinary Center, College Park, USA
Dr R.R. Colwell, and Dr A. Huq from University of Maryland, College Park, USA

19. Thank you for your attention
Guillaume Constantin de Magny
University of Maryland Institute for Advanced Computer Studies
College Park, MD USA