Cholera epidemics in 2010: respective roles of environment, strain changes, and human-driven dissemination

Abstract

The cholera burden has grown strikingly during the past 4 years, and has spread to countries previously spared by this disease. The current spread has proved especially violent, as illustrated by the recent deadly epidemics around the Lake Chad Basin, in East Africa, and in Haiti. This onset of severe cholera epidemics is part of the overall dynamic of the current seventh cholera pandemic, composed of successive epidemic waves. The current wave is attributable to new atypical El Tor strains, which spread from the Bay of Bengal to Papua in the east, Africa, and the Caribbean Sea in the west, and caused hundreds of thousands of cases and thousands of deaths during each of the last 4 years. The particular severity of the resulting epidemics is partially attributable to the specific characteristics of the atypical El Tor strain involved. Besides the abilty of El Tor to spread easily, this strain is associated with more severe clinical findings, because of elevated levels of toxin secretion resulting from a genetic content originating from classical strains. Conversely, recent studies of these deadly outbreaks raised hope by illustrating their relationship with human-borne dissemination rather than with the resurgence of environmental strains. As human-borne dissemination can be more easily targeted than ubiquitous environmental contamination, accurate and comprehensive epidemiological studies are essential to better understand the dynamics of the disease and to optimize future cholera responses.

Spatio-Temporal Dynamics of Cholera during the First Year of the Epidemic in Haiti

“…This booster effect of rainfall on cholera outbreaks has been observed in many other countries [13], [14], [36]–[38], where rainfall has caused latrine overflow or the washing up of waste with subsequent contamination of wells and surface waters. However, the relationship between rainfall and cholera likely involves other mechanisms, such as the seasonal modification of human water sources or human behavior such as rice culture activity.…”

“…The explosive spread of the disease overwhelmed the humanitarian response and the initial attempts to broadcast awareness and hygiene messages. People who fled from the Artibonite Delta to neighboring communes [36] also played an aggravating role in cholera diffusion, thereby favoring the spread of cholera even in remote rural areas. The violent nature of this outbreak spread may also have been promoted by Hurricane Tomas, which reached Haiti on November 5 with rapid flooding in some areas already affected by cholera, such as Gonaives.…”

Cholera Outbreaks in Nigeria Are Associated with Multidrug Resistant Atypical El Tor and Non-O1/Non-O139 Vibrio cholerae

“…Nigeria is in one of the three major current cholera foci in the world [9]. In 2009, outbreaks began in Nigeria and other countries at the Lake Chad basin [8] with the first reports coming from Maiduguri, a city in the far north-east of the country.…”

Nepalese origin of cholera epidemic in Haiti

“…Within 2 months, cholera cases were observed throughout the country [1], with dozens of deaths per day, peaking at more than 100 per day by mid-December, 2010 (MSPP, Haiti, 4 January 2011). When the outbreak was first observed, immediate focus was on case management, water chlorination and hygiene awareness.…”