Vibrio is a genus of gram-negative, rod-shaped, facultative anaerobic bacteria. There are more than a 110 species of Vibrio and Vibrio-like organisms. Less than 15 percent of those are human pathogens. Here I list some of the important pathogenic species, and the most important one is Vibrio cholerae. So we're going to talk about cholera in a few minutes. Most Vibrio species live exclusively in saltwater, but there are two species that live either in saltwater, brackish water, or freshwater, endo, and those are Vibrio cholerae and Vibrio mimicus. Of concern here is the Vibrio cholerae. So very important point is that coastal ecosystems and estuaries in warm climates provide an ideal habitat for Vibrio cholerae. These are environmental correlates of elevated Vibrio presence and abundance. Now we're still talking about any Vibrio not just Vibrio cholerae. Those are high sea surface temperature, low salinity, but still seawater, and high plankton abundance. The reason for the plankton abundance is that Vibrio like to attach to and basically live on plankton. Now let's turn to cholera, as mentioned the infectious agent is Vibrio cholerae. The primary site of infection is the small intestine. The cholera toxin produced by the organism causes acute watery diarrhea, and it's transmitted person to person through the fecal-oral route via water or food. So that's a very important mode of transmission, but it's more complicated than that as we'll see due to the environmental reservoir for Vibrio cholerae in coastal waters. The treatment of cholera. If the symptoms are mild, it's treated with simple oral rehydration solution. When there are severe symptoms, it's very important to have rapid treatment with intravenous fluids and antibiotics to avoid a quick death. So severe cholera is a very serious acute disease. So importantly, there's an environmental reservoir for Vibrio cholerae which is coastal ecosystems and estuaries, and we'll get back to that. We're now in the midst of the Seventh Cholera Pandemic which started in 1961. The serogroup is called O1, biotype is El Tor. Note that serogroup 0139 has emerged as a possible eighth pandemic, but it's not yet considered. It's only been sporadic. Give some examples of how explosive cholera epidemics could be. In South America in 1991, there was an epidemic that was probably initiated by plankton blooms triggered by El Nino. That resulted in Peru alone and 300,000 cases and 3,000 deaths. In a Rwandan refugee camp in Goma, during one month in 1994, there were 48,000 cases and 24,000 deaths. There was a cholera epidemic in Haiti between 2010 and 2013 with about 660,000 cases more than 8,000 deaths in a population of about 10 million, and we continue to see cholera in Haiti. You've probably heard about the most recent severe cholera epidemic which has been and still is occurring in Yemen. So between April 27th, 2017 and July 1st, 2018, there were about 1,115,000 suspected cases, more than 2,300 deaths in a population of 27.6 million. Of course, that particular cholera epidemic was caused by the Yemen Civil war and the destruction of sanitary infrastructure, unavailability of clean water, etc, in these severe war circumstances. Cholera prevention. The cornerstone of prevention is safe drinking water and sanitation. So if everyone in the world had safe drinking water and sanitation, there would be little or no cholera in the world. But unfortunately, everyone in the world doesn't have safe drinking water and sanitation so we have cholera. A secondary prevention measure, there are several actually oral vaccines of kind of moderate efficacy, but the WHO recommends that they be used in endemic areas, also when there are humanitarian crises with a high risk for cholera and during cholera outbreaks. Then, the third prevention measure is health education campaigns such as emphasizing hand-washing which could help protect. So based on the critical importance of poor water treatment and sanitary infrastructure in the onset in facilitating cholera incidents, vulnerable populations or populations that have poor water treatment and sanitary infrastructure. That would include residence of low-income countries, residence of crowded urban slums where there's poor sanitation, displaced populations or refugee camps, populations exposed to war like Yemen, and coastal areas in particular with poor sanitation, and that's because of the environmental reservoir of the Vibrio cholera in coastal areas. Now, what about storms flooding and cholera? So some of these, I'm just repeating what a, cholera is a waterborne infection, so we're seeing some of the same dynamics as we see for all waterborne infections. So storms and flooding could cause disruption of water treatment and sanitary infrastructure, could spread sewage in areas with disrupted poor or no sanitary infrastructure. We have the problem of poor sanitation and unsafe drinking water in shelters and camps for displaced populations such as those displaced by storms and flooding. But we have something that's unique, which is coastal storms and floods as a trigger for cholera outbreaks. So let's go through that one. So again, we have the environmental reservoir. So we could have a situation with a coastal ecosystem with a very high abundance of Vibrio cholerae due to favorable conditions such as high sea surface temperature or high plankton abundance. So then, if in that region, we have a hurricane or a flooding, that could be the trigger of the initial human infection. Suppose pre-hurricane there was no cholera. Now we have the hurricane, we have the the organism that's lurking out there on the coast living in the water, and we have a storm surge and flooding that leads to human exposure to Vibrio Cholerae from the reservoir, and that triggers some human infections. From there, we could have propagation of human infection through person-to-person transmission by the fecal-oral route, and that could be facilitated if the hurricane or flooding or storm also caused destruction of drinking water and sanitary Infrastructure. So this map shows, it's a global map of Vibrio cholerae suitability in seawater. That was generated by some investigators. The red shows high suitability. So you could see that the suitability tends to be along coastal areas, first of all. You could see that also there areas that are suitable for Vibrio cholerae and where Vibrio cholerae is undoubtedly growing, where there is no cholera, like along the Florida coast and up here in the southeast of the United States for example, up here in northern Europe for example. The reason for that, of course, is that those areas have relatively good water-treatment and sanitary infrastructure. Now, these same investigators generated, and let's focus on this top map which is more conservative than this map. They generated another global map of Vibrio cholerae suitability. This one was estimates for 2100 under the SRES B1 climate scenario. So that's a lowered emissions scenario actually, but it's still, they're projecting increase in sea-surface temperature in 2100 according to that scenario. You could see that the extension of the red, what I think is most notable is that now it's actually extending not just along the coast but it's throughout the ocean. So the significance of that if that's true and it probably is, remains to be determined, but it's very interesting that we could see essentially the expansion of this Vibrio cholerae reservoir because of increase in sea surface temperature. To summarize for climate change and cholera, we have increasing sea surface temperature and increasing plankton abundance, that could result in higher Vibrio cholerae levels in coastal ecosystems and expansion of the V. cholerae environmental reservoir. More intense hurricanes and an increasing frequency of extreme precipitation events and floods, can result in increased disruption of water treatment and sanitary Infrastructure and spread of sewage. The intersection of these two factors could cause an increased frequency of cholera outbreaks.
