The Effects Of Cholera

A pandemic is a term used to describe the widespread outbreak of an infectious disease that affects a large geographical area, such as an entire country or multiple continents, and has a significant impact on a substantial number of people. Commonly, pandemics exhibit a pattern where they initially experience a sharp increase in the number of fatalities, but then either subside to safe levels or eventually disappear altogether. This pattern is evident in historical records of pandemics. However, there is one notable exception to this trend – cholera.

Cholera stands out as an extraordinary case among pandemics. It has maintained one of the longest-running pandemics in recorded history, spanning over 140 years and spreading across five continents through seven distinct pandemics. Cholera is characterized as an intestinal disease that leads to severe symptoms including intense diarrhea, vomiting, fever, and abdominal cramps. It is caused by the ingestion of Vibrio cholerae, a gram-negative bacterium.

Vibrio cholerae is primarily transmitted through the consumption of contaminated water and, to a lesser extent, through the consumption of contaminated food, particularly shellfish such as oysters. Cholera bacteria colonize the human small intestine and are subsequently released into the environment through fecal contamination of food and water sources. This cycle of contamination is especially prevalent in areas with high population density and poor sanitation practices, where sewage often mixes with natural or municipal water supplies, leading to the consumption of the bacterium.

What is particularly remarkable about Vibrio cholerae is its ability to survive the harsh acidic conditions of the human stomach. In the stomach, most ingested bacteria are typically destroyed by the strong hydrochloric acid, which acts as a protective barrier against pathogens. However, Vibrio cholerae employs various strategies to endure this hostile environment.

When Vibrio cholerae is discharged in fecal matter, it does so in extraordinarily high numbers, often forming protective structures known as biofilms. A biofilm is essentially a sticky mass of bacteria that creates a thick, multi-layer structure, serving as a physical barrier to external threats, such as proteins, acids, bases, and even heat. An everyday example of a biofilm is dental plaque, consisting of millions of bacteria that release sticky proteins and sugars to bind together, forming a protective layer. This biofilm acts as a shield against the acid in the stomach, where it survives the acidic conditions.

Moreover, Vibrio cholerae can also survive the stomach's acidity by increasing the pH or making the environment less acidic. It achieves this by utilizing an enzyme called lysine decarboxylase to convert the amino acid lysine into cadaverine. Cadaverine is then released into the stomach, where it acts to neutralize acids, thereby making the environment less acidic. In this way, the bacterium ensures its survival in the stomach.

Upon surviving the stomach's acidic conditions, Vibrio cholerae continues its journey into the small intestine, where it embeds itself into the thick mucus lining the intestinal walls, using whip-like extensions called flagella. It then begins to colonize the small intestine. During this colonization, Vibrio cholerae releases a toxic protein known as cholera toxin, which plays a pivotal role in causing the characteristic intense diarrhea associated with cholera. The toxin binds to receptors on the surface of the intestinal walls, leading to the engulfing of the toxin by the cells. Once inside the cells, the cholera toxin catalyzes a signaling protein called the G-protein, locking it into an active state. In this active state, the G-protein continually signals a series of biochemical reactions that lead to the activation of the enzyme protein kinase A (PKA). PKA, in turn, signals the intestinal cells to release large amounts of sodium and chloride ions into the intestine.

The high concentration of ions in the intestines, in turn, draws in significant volumes of water through osmosis, resulting in what is termed "purgative diarrhea." During a cholera infection, an individual can excrete as much as six liters of water per day due to this aggressive inflow of water. This substantial loss of water becomes a severe problem when considering that the daily requirement for water intake is approximately 3.7 liters. In fact, individuals suffering from cholera lose nearly double the amount of water required for their daily needs.

The consequences of such water loss are severe. Dehydration is a significant risk, and individuals can become severely dehydrated in just a few hours. The diarrhea associated with cholera is so frequent and watery that patients are often placed in specialized beds known as cholera cots. These cots are designed with a hole cut in the middle to allow patients to excrete while lying down. Given the frequency of excretion and the accompanying fatigue caused by cholera, it is often more practical for patients to remain lying down rather than making frequent trips to the bathroom. The diarrhea also takes on a milky white appearance, known as "rice water diarrhea," due to the shedding of mucus and tissue from the intestines.

Despite the severe effects of cholera infection, the treatment is relatively straightforward. It primarily involves the replacement of fluids and essential nutrients. In cases of severe cholera, antibiotics may also be administered. However, it's important to note that in the 19th and early 20th centuries, medical science was not aware of these treatments, and cholera often led to horrific levels of dehydration and fatalities.

The persistence of cholera from the 19th to the 20th centuries, unlike other pandemics such as the Black Plague and influenza, which had shorter and more aggressive lifespans, can be attributed to specific factors. Unlike communicable diseases, which spread from person to person and are influenced by factors like isolation and changing population size, cholera transmission is primarily driven by water contamination. As a result, it is largely unaffected by isolation measures or fluctuations in population size. The failure to understand and address the transmission of the disease via contaminated water sources allowed cholera to persist.

A significant breakthrough occurred during the third cholera pandemic of 1846. In London, John Snow, a physician, was investigating patterns of cholera cases in the Soho neighborhood. The neighborhood experienced a severe cholera outbreak, which claimed the lives of 500 people in just ten days. Snow's meticulous investigation revealed that the outbreak was centered around the Broad Street water pump. Upon interviewing residents, Snow discovered that those who consumed water from the pump were falling ill with cholera.

Further investigation revealed that the pump had become contaminated by a nearby cesspool, which served as a dumping pit for sewage and waste. This cesspool was located just three feet from the pump and was leaching into the groundwater, contaminating the water source. Snow's findings were instrumental in identifying the role of contaminated water in cholera transmission.

In 1896, German microbiologist Robert Koch successfully cultured the Vibrio cholerae bacteria from various sources, including water supplies, cadavers, and infected cholera patients. This groundbreaking discovery confirmed that cholera was caused by a bacterial agent. Subsequent improvements in water sanitation and hygiene practices led to a significant reduction in cholera pandemics. Following Koch's discovery and the adoption of improved water sanitation practices, cholera pandemics ceased for nearly 38 years. This marked a stark contrast to the previous pattern, where pandemics recurred every 5.2 years on average.

However, a seventh cholera pandemic has been ongoing since 1961, with the World Health Organization defining the current cholera outbreak as endemic in regions such as Yemen, Africa, and parts of Western Asia. The persistence of cholera in these regions is attributed to poor sanitation management and limited access to medical interventions. Efforts to combat this ongoing pandemic have included the development of a cholera vaccine and robust sanitation initiatives aimed at improving water quality and hygiene practices.

In conclusion, cholera represents a unique case among pandemics due to its longevity and distinctive mode of transmission through contaminated water sources. It is characterized by severe symptoms and dehydration, but with effective treatment involving fluid and nutrient replacement, fatalities can be significantly reduced. The understanding of cholera transmission and improvements in sanitation have played a crucial role in mitigating its impact on public health. Despite these advances, the ongoing seventh cholera pandemic in some regions underscores the importance of continued efforts to ensure safe water sources and access to medical interventions.