Cholera

Cholera is a severe infectious disease caused by the bacterium Vibrio cholerae.

This infection specifically targets the small intestine. It is a significant global health concern because it can cause rapid, life-threatening dehydration. While some people show no symptoms, others experience severe illness. The most classic symptom is profuse, watery diarrhea. This discharge is often described as looking like "rice water" and may have a fishy odor.

Because the disease can spread so quickly through water, it has caused several major global outbreaks.

The mechanism of infection is a complex biological process. It begins when a person ingests a large number of bacteria. A healthy adult typically needs to swallow about 100 million bacteria to become ill.

Most bacteria perish in the acidic environment of the stomach. However, survivors reach the small intestine and use flagella to swim through mucus.

Once they attach to the intestinal wall, the bacteria stop using flagella to conserve energy. They then produce the cholera toxin, which is an oligomeric complex. This toxin consists of one A subunit and five B subunits. The B subunits bind to the surface of intestinal cells. This allows the A subunit to enter the cell and trigger a chemical reaction. This reaction causes the cell to secrete water, sodium, potassium, and bicarbonate into the intestine, leading to rapid fluid loss.

Symptoms of cholera can appear very suddenly. They usually manifest between two hours and five days after exposure. The massive loss of fluids leads to severe dehydration and electrolyte imbalances. This can cause sunken eyes, dry mouth, and cold, clammy skin. In extreme cases, a person's skin may turn bluish-gray, earning the disease the nickname "the blue death." Patients may also experience muscle cramps, weakness, or seizures. Severe dehydration can lead to a drop in blood pressure and decreased urine output. In very serious cases, the loss of bicarbonate can cause acidosis, resulting in deep, labored breathing known as Kussmaul breathing.

Cholera is primarily transmitted through the fecal-oral route. This happens when water or food is contaminated with human feces containing the bacteria. In developing countries, unsafe water is the most common source of infection. In developed countries, transmission is more often linked to food. Undercooked shellfish are a common source because they can accumulate bacteria from the water.

Humans are the only known host for these bacteria. However, Vibrio cholerae can also exist in natural water sources by interacting with plankton. Climate change is currently increasing the occurrence and intensity of cholera outbreaks.

The history of cholera research includes significant scientific milestones. Descriptions of the disease exist in Sanskrit literature as early as the 5th century BCE. In Europe, the term was originally used for any kind of gastroenteritis. It was not specifically applied to this disease until the early 19th century. A major breakthrough occurred in England between 1849 and 1854. During this time, John Snow studied the disease and discovered it was spread via contaminated water. His work led to the first recorded use of epidemiological tracking through mapping.

Today, cholera remains a major global health challenge. It affects an estimated 3 to 5 million people every year. This results in between 28,800 and 130,000 deaths annually. The most recent pandemic began in 1961 and is still ongoing. Areas with ongoing risks include Africa and Southeast Asia. The risk of death is highly dependent on medical access. Without treatment, the death rate can be as high as 50%. However, with improved treatment, the risk of death usually falls below 5%.

Prevention and treatment focus on replacing lost fluids and improving sanitation. The primary treatment is oral rehydration salts (ORS). These are solutions that are slightly sweet and salty to replace electrolytes. Rice-based solutions are often preferred for rehydration.

In children, zinc supplementation can also improve health outcomes. For severe cases, doctors may use intravenous fluids like Ringer's lactate or antibiotics. Vaccines are also available to provide protection. In 2017, the FDA approved Vaxchora, a single-dose oral vaccine for adults traveling to high-risk areas. While it offers limited protection to young children, it remains a vital tool for public health.