“I arrived at the conclusion in the latter part of 1848, that cholera is communicated by the evacuations from the alimentary canal.” - John Snow
Everybody knows that “water is life.” After all, up to 60% of the adult human body is water, and without water, survival is limited to about three days. But many people don’t realize that according to the World Health Organization (WHO), one in three people doesn’t have access to safe drinking water. Every year, more than 3.4 million deaths are attributed to waterborne diseases, making it the leading cause of disease and death around the world. What’s worse is that most of these deaths are young children, about 4,000 a day.
Globally, at least 2 billion people use a drinking source contaminated with human feces. As you would imagine, gastroenteritis is the most common waterborne disease, and most cases and deaths occur in the developing world. As an infectious diseases specialist in the state of Minnesota –the “Land of 10,000 Lakes”—I’ve taken a special interest in waterborne diseases. I’ve long recognized the inequity between the developing and the developed world, where most waterborne infections aren’t linked to drinking unsafe water but rather to exposure to recreational water, like swimming and hot tubs.
I’ve also known about the close relationship between many waterborne and foodborne infections. For example, I often caution friends who, like me, love raw oysters, that there are “Nine Reasons Not to Eat Raw Oysters.” Of the many bacterial, viral, and parasitic pathogens that occasionally accompany raw or undercooked shellfish, the bacterial genus Vibrio is most dangerous. One species, Vibrio vulnificus, causes a fulminant necrotizing skin infection that kills about 16 Americans per year.
But it is another species, Vibrio cholerae—the cause of cholera—that is the biggest problem and is the focus of this blog. Cholera sickens an estimated 3-5 million people worldwide a year and kills 58,000-130,000. While it can be picked up by eating raw shellfish, it is unsafe drinking water (contaminated with human feces) that is the most common vehicle of infection.
V. cholerae is a diabolical pathogen. It is not only transmitted by water, but it causes copious, watery diarrhea. And by copious, I mean three to five gallons a day. Not surprisingly, patients quickly become severely dehydrated. The dehydration can result in sunken eyes and wrinkling skin of the hands and feet, which take on a bluish color—thus its nickname “the blue death.” Rehydration with water and electrolytes is the mainstay of treatment.
Cholera outbreaks and pandemics
Outbreaks of cholera likely originated in the Indian subcontinent four or five centuries ago. Subsequently, the disease spread by trade routes to Russia, Europe, North America, and the rest of the world. The first cholera pandemic (defined by the WHO as the worldwide spread of a new disease) occurred in the Bengal region of India in 1817. Since then, there have been six additional pandemics. The seventh pandemic which originated in Indonesia in 1961 is marked by the emergence of a new strain of V. cholerae, nicknamed El Tor, which still persists in developing countries.
In developed countries, due to nearly universal water treatment and sanitation practices, cholera is no longer a major threat. The last major outbreak of cholera in the U.S. occurred in 1910-1911. But in October 2010, the worst outbreak in recent years hit less than 700 miles off the coast of Florida; in Haiti. By the summer of 2017, this outbreak had sickened 1 million people and taken the lives of 10,000. Despite a major outpouring of humanitarian and medical aid, and a national cholera vaccination campaign spearheaded by the WHO, more than 13,000 cholera cases occurred in 2018.
In 2016 and 2017, WHO also sent cholera vaccine to combat large outbreaks in the poverty-stricken horn of Africa—Sudan, Somalia, and Yemen, where more than 300,000 people had been infected and 1,700 died. On top of lacking safe drinking water, the intersection of war and political upheaval severely complicated efforts to contain these outbreaks.
Discovery of the cause of cholera
Cholera has special meaning for public health and infectious disease professionals because of the 1854 epidemic in London, where a total of 10,675 people died of the disease. It was during a particularly violent outbreak in or around Broad Street that evidence was gathered supporting the hypothesis that the disease was waterborne. The discoverer, an anesthesiologist named John Snow, was skeptical of the conventional wisdom that cholera was airborne (transmitted by miasma, a bogus form of noxious air emanating from poverty-stricken neighborhoods). The techniques used by Snow to trace the source of the outbreak resulted in the removal of the now-famous Broad Street pump handle to quell the disease. It later led to the recognition of John Snow as the founder of the field of epidemiology.
In the same year as Snow’s discovery in London, an Italian anatomist, Filippo Pacini, was the first to observe with a microscope comma-shaped bacteria that he isolated from the intestines of a cholera victim. Although Pacini described his findings clearly, Robert Koch is often credited with the discovery of V. cholerae in 1883.
Impact of climate change on cholera
Despite the declaration by the United Nations General Assembly in 2010 that access to clean water and sanitation is a human right, cholera, and other waterborne diseases continue to sicken and kill millions around the world. Results of a study in Bangladesh, published in the journal Nature, indicate that extreme climate conditions enable V. cholerae to spread more easily. Floods caused by heavy monsoons can contaminate drinking water with the bacterium. During droughts, V. cholerae grows more readily in the stagnant water found in ponds and rivers.
Adding to concerns about increased waterborne infections, a major United Nations report in 2018 revealed that the goal to bring safe water and sanitation to everyone by 2030 is not on track. By 2050, it is forecast that half the world’s population may no longer have safe drinking water. Some experts predict that such severe water shortages could make fighting over access to fresh water an even more deadly threat than drinking water that is contaminated with V. cholerae.