Cholera-Modern Pandemic Disease of Ancient Lineage
Cholera-Modern Pandemic Disease of Ancient Lineage
Cholera has affected humans for at least a millennium and persists as a major cause of illness and death worldwide, with recent epidemics in Zimbabwe (2008–2009) and Haiti (2010). Clinically, evidence exists of increasing severity of disease linked with emergence of atypical Vibrio cholerae organisms that have incorporated genetic material from classical biotype strains into an El Tor biotype background. A key element in transmission may be a recently recognized hyperinfectious phase, which persists for hours after passage in diarrheal feces. We propose a model of transmission in which environmental triggers (such as temperature) lead to increases in V. cholerae in environmental reservoirs, with spillover into human populations. However, once the microorganism is introduced into a human population, transmission occurs primary by "fast" transmission from person to person (taking advantage of the hyperinfectious state), without returning to the aquatic environment.
Cholera has been an unwanted companion among human civilizations for at least a millennium, with suggestions that it has existed in India "since immemorial times". Its impact in Bengal society was sufficient to have resulted in recognition of a goddess of cholera, Oladevi (or Oola Beebee), who required propitiation to protect villages from the disease. Global pandemic spread of cholera from its ancestral home in Bengal was first documented in 1817, the beginning of what has been designated as the first pandemic. In the intervening 2 centuries, cholera has continued to ebb and flow from southern Asia to other parts of the known world, with 6 additional pandemics identified. During the third pandemic, which ravaged London in 1854, John Snow conducted his pioneering epidemiologic studies (and gained fame for removal of a pump handle). We are currently in the throes of the seventh pandemic (caused by V. cholerae of the El Tor biotype), which originated almost 50 years ago in the Celebes. In contrast to the earlier 6 pandemics, at no time in these past 50 years has cholera retreated to its southern Asian home. It has instead established endemicity at multiple sites around the globe and continues to trigger major localized epidemics, including the epidemics in Zimbabwe during 2008–2009 and Haiti during 2010.
In 2009, the most recent year for which data are available, 221,226 cholera cases were reported to the World Health Organization (WHO) from 45 countries. This number includes 4,946 deaths, for a case-fatality rate of 2.24%. Although the disease was reported from all continents, 98% of cases reported during 2009 were from Africa, driven in part by large numbers from the latter part of the 2008–2009 Zimbabwe epidemic. However, these numbers should be interpreted with caution because of well-recognized problems with underreporting in the WHO system, particularly because cholera is no longer a notifiable disease and countries can choose whether to report cases. In 2 examples, no cholera cases were included in the annual WHO cholera summary report for 2009 from India or Bangladesh, despite anecdotal evidence to the contrary.
Cholera today takes advantage of breakdowns in sanitation and health infrastructure, often in the setting of natural and complex disasters. More notably, cholera has survived the transition from ancient to modern world, with the establishment of endemic foci in virtually every continent. We have learned a great deal about cholera during the past few decades. Major advances have been made in therapy, which has decreased expected case-fatality rates to <0.5%. However, we are just coming to appreciate the evolutionary capabilities of the microorganism and the complexity of transmission pathways, an understanding of which is essential to ultimate control of the disease.
Abstract and Introduction
Abstract
Cholera has affected humans for at least a millennium and persists as a major cause of illness and death worldwide, with recent epidemics in Zimbabwe (2008–2009) and Haiti (2010). Clinically, evidence exists of increasing severity of disease linked with emergence of atypical Vibrio cholerae organisms that have incorporated genetic material from classical biotype strains into an El Tor biotype background. A key element in transmission may be a recently recognized hyperinfectious phase, which persists for hours after passage in diarrheal feces. We propose a model of transmission in which environmental triggers (such as temperature) lead to increases in V. cholerae in environmental reservoirs, with spillover into human populations. However, once the microorganism is introduced into a human population, transmission occurs primary by "fast" transmission from person to person (taking advantage of the hyperinfectious state), without returning to the aquatic environment.
Introduction
Cholera has been an unwanted companion among human civilizations for at least a millennium, with suggestions that it has existed in India "since immemorial times". Its impact in Bengal society was sufficient to have resulted in recognition of a goddess of cholera, Oladevi (or Oola Beebee), who required propitiation to protect villages from the disease. Global pandemic spread of cholera from its ancestral home in Bengal was first documented in 1817, the beginning of what has been designated as the first pandemic. In the intervening 2 centuries, cholera has continued to ebb and flow from southern Asia to other parts of the known world, with 6 additional pandemics identified. During the third pandemic, which ravaged London in 1854, John Snow conducted his pioneering epidemiologic studies (and gained fame for removal of a pump handle). We are currently in the throes of the seventh pandemic (caused by V. cholerae of the El Tor biotype), which originated almost 50 years ago in the Celebes. In contrast to the earlier 6 pandemics, at no time in these past 50 years has cholera retreated to its southern Asian home. It has instead established endemicity at multiple sites around the globe and continues to trigger major localized epidemics, including the epidemics in Zimbabwe during 2008–2009 and Haiti during 2010.
In 2009, the most recent year for which data are available, 221,226 cholera cases were reported to the World Health Organization (WHO) from 45 countries. This number includes 4,946 deaths, for a case-fatality rate of 2.24%. Although the disease was reported from all continents, 98% of cases reported during 2009 were from Africa, driven in part by large numbers from the latter part of the 2008–2009 Zimbabwe epidemic. However, these numbers should be interpreted with caution because of well-recognized problems with underreporting in the WHO system, particularly because cholera is no longer a notifiable disease and countries can choose whether to report cases. In 2 examples, no cholera cases were included in the annual WHO cholera summary report for 2009 from India or Bangladesh, despite anecdotal evidence to the contrary.
Cholera today takes advantage of breakdowns in sanitation and health infrastructure, often in the setting of natural and complex disasters. More notably, cholera has survived the transition from ancient to modern world, with the establishment of endemic foci in virtually every continent. We have learned a great deal about cholera during the past few decades. Major advances have been made in therapy, which has decreased expected case-fatality rates to <0.5%. However, we are just coming to appreciate the evolutionary capabilities of the microorganism and the complexity of transmission pathways, an understanding of which is essential to ultimate control of the disease.