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DYNAMICS OF CHOLERA OUTBREAKS IN THE GREAT LAKES REGION OF AFRICA

Wednesday, 2nd of November 2011

Is cholera predictable? If so, then with two prequalified oral cholera vaccines now available, it may be amenable to control.

•  DYNAMICS OF CHOLERA OUTBREAKS IN THE GREAT LAKES REGION OF AFRICA

From Emerging Infectious Diseases

 

Good reading.

BD

 

Abstract below. Full text, with figures, is at

http://wwwnc.cdc.gov/eid/article/17/11/11-0170_article.htm

 

Volume 17, Number 11—November 2011

Research

Didier Bompangue Nkoko, Patrick Giraudoux, Pierre-Denis Plisnier, Annie Mutombo Tinda, Martine Piarroux, Bertrand Sudre, Stephanie Horion, Jean-Jacques Muyembe Tamfum, Benoît Kebela Ilunga, and Renaud Piarroux  

Author affiliations: Université de Franche-Comté, Besançon, France (D. Bompangue Nkoko, P. Giraudoux, M. Piarroux, B. Sudre); Ministère de la Santé Publique, Kinshasa, Democratic Republic of Congo (D. Bompangue Nkoko, A. Mutombo Tinda, J.-J. Muyembe Tamfum, B. Kebela Ilunga); Royal Museum for Central Africa, Tervuren, Belgium (P.-D. Plisnier); Joint Research Centre of the European Commission, Ispra, Italy (S. Horion); Université de Kinshasa, Kinshasha (J.-J. Muyembe Tamfum); Université de la Méditerranée, Marseille, France (R. Piarroux); University Hospital La Timone, Marseille (R. Piarroux)

Suggested citation for this article

Abstract

Cholera outbreaks have occurred in Burundi, Rwanda, Democratic Republic of Congo, Tanzania, Uganda, and Kenya almost every year since 1977–1978, when the disease emerged in these countries. We used a multiscale, geographic information system–based approach to assess the link between cholera outbreaks, climate, and environmental variables. We performed time-series analyses and field investigations in the main affected areas. Results showed that cholera greatly increased during El Niño warm events (abnormally warm El Niños) but decreased or remained stable between these events. Most epidemics occurred in a few hotspots in lakeside areas, where the weekly incidence of cholera varied by season, rainfall, fluctuations of plankton, and fishing activities. During lull periods, persistence of cholera was explained by outbreak dynamics, which suggested a metapopulation pattern, and by endemic foci around the lakes. These links between cholera outbreaks, climate, and lake environments need additional, multidisciplinary study.

In Asia, the endemic and seasonal character of cholera largely depends on human exposure to the aquatic reservoirs of Vibrio cholerae (1). Culturable V. cholerae as well as viable but nonculturable V. cholerae (i.e., those that have entered into a dormant stage because of conditions unfavorable for growth or reproduction) attach to zooplankton and phylankton, especially in estuarine areas (2). In these areas, the incidence of cholera is influenced by local factors, such as rainfall and plankton blooms, and by global climatic conditions, such as increased sea surface temperatures linked to El Niño Southern Oscillation events (3,4). This link between cholera, the aquatic environment, and climate, named the “cholera paradigm” by Colwell (5), was highlighted by numerous studies in coastal areas.

Except for Haiti, where an epidemic of cholera began in mid-October 2010 (6), the area experiencing the worst cholera epidemics is sub-Saharan Africa. During 1995–2005, a total of 632 cholera outbreaks were reported worldwide; 66.0% of the total cases and 87.6% of fatal cases were reported from sub-Saharan Africa (7). Specifically, according to the World Health Organization (WHO), only 5 countries (Burundi, Cameroon, the Democratic Republic of the Congo [DRC], Ghana, and Tanzania) have reported cases of cholera every year since 1990 (8). Three of these countries—Burundi, DRC, and Tanzania—are partially or totally located in the African Great Lakes region (AGLR), an area including Lakes Tanganyika, Victoria, Kivu, Edward, and Albert. This region also includes Rwanda and part of Kenya and Uganda, which have also reported cases of cholera nearly every year since 1991 (except for 3 years for Kenya and 2 years for Rwanda and Uganda). Except for some limited epidemics, AGLR was long free from cholera, which emerged in 1977–1978 when the 6 countries were simultaneously affected (9). Since then, AGLR has become one of the most active foci of cholera, declaring 322,532 cases during 1999–2008 (20% of all cholera cases officially reported worldwide to WHO for these 10 years). Nevertheless, these numbers are widely underestimated because many patients cannot access health care facilities (10). This worrying evolution of cholera outbreaks in AGLR went unnoticed in the scientific community, and no serious attempts have been made to describe these new endemic foci of a waterborne disease originating from coastal marine environments.

Considering the established link between rainfall, El Niño events, sea surface temperature, plankton, and cholera in the coastal areas, the emergence of cholera and its spread in AGLR can be hypothesized to have been facilitated by global climatic and local environmental factors. However, the AGLR environment differs widely from estuarine environments, which are known to harbor favorable ecosystems for V. cholerae survival during interepidemic periods (1–5). Our study aimed to describe 1) cholera outbreak dynamics in the AGLR, 2) the modes of persistence of V. cholerae during lull periods, and 3) the role of specific climatic conditions that might trigger widespread epidemics.