Cholera

Since the 19th century, there have been 7 global pandemics related to cholera. The first was a lethal outbreak stemming from contaminated rice. Cholera is one of the most known bacterial infectious diseases. Like other infectious diseases such as Tuberculosis (TB), it is caused and spread by a bacterial pathogen that enters and infects the human body causing illness. However, around 80% of people who contract the bacteria do not actually develop any symptoms.

Despite being completely curable, many people still die of cholera. According to the World Health Organisation (WHO), cholera remains a threat to global public health and a clear indicator of inequality between the developed and developing world.

The meaning of cholera: what is it?

Cholera is a disease characterised by an infection of the intestine caused by the pathogenic bacteria Vibrio cholerae. In severe cases, this infectious disease can lead to diarrhoea and death within hours if left untreated. The WHO and researchers estimate that around 3,000,000 cases and 100,000 avoidable deaths from cholera happen every year, almost exclusively in developing countries in Asia, Africa, and Latin America. Cholera infection numbers have remained high for the past few years.

Understanding how cholera transmits between people is essential to understand why it is more prevalent in developing countries. Direct personal cholera transmission is unlikely as large amounts of this bacteria typically exit the body of infected people through their faeces. The bacteria present in faeces can contaminate water and food that comes into contact with it. In other words, this infectious disease is water and food-borne.

Proper access to sanitation and basic hygiene rules are the critical factors in reducing the transmission chain of this pathogen. The infrastructure to help achieve this tends to lack more in developing countries, so cholera is more prevalent in these regions.

Fig. 1: Vibrio cholerae bacteria

The causes of cholera

Cholera disease is caused by the infection resulting from the bacteria Vibrio cholerae. People contract cholera by eating food or drinking water contaminated with Vibrio cholerae. This pathogen first passes through the stomach to reach its site of action in the wall of the small intestine. In the small intestine, Vibrio cholerae multiplies and releases choleragen, a toxin that affects the epithelium wall of the intestine. Choleragen can cause dramatic loss of fluids with water and salts leaving the blood. It causes diarrhoea which can be fatal if left untreated.

There are only two strains of Vibrio cholerae capable of causing cholera outbreaks: the O1 and O139 strains. These strains cause the same symptoms and illness, but the O139 strain appears more virulent.

The symptoms of cholera

Cholera infection is mild to moderate or even asymptomatic amongst most people after becoming infected with the toxigenic bacteria Vibrio cholerae. However, this doesn’t mean that these people are not capable of infecting others. Asymptomatic individuals can still pass the bacteria through their faeces 1-10 days after infection, potentially spreading the bacteria further into the environment.

According to the WHO, about 1 in 10 people who become infected with cholera will develop severe symptoms. Cholera affects adults and children equally. Symptom onset can take anywhere from a few hours to 5 days (the incubation period) after ingestion of the cholera bacteria but usually takes 2-3 days. This minority of people will experience:

• severe watery diarrhoea (also known as ‘rice water’ diarrhoea),

• dehydration,

• shock,

• vomiting,

• weakness,

• and leg cramps

The associated rapid loss of body fluids (water and salts) can be fatal, killing within 24 hours if these fluids aren’t replaced.

The transmission of cholera

Cholera bacteria are passed on through the faeces of an infected person. These faeces can contaminate water supplies in regions with inadequate water management/treatment and sanitation facilities. Infected people who come into contact with food or cooking utensils without washing their hands can inadvertently contaminate food supplies.

As mentioned before, individuals contract cholera by ingesting water/food that has been contaminated with cholera bacteria. Casual contact with an infected person is therefore not a risk factor for becoming infected and ill with cholera.

Cholera transmission is therefore much more common in urban slums in developing countries or refugee camps because of unsatisfactory access to clean water supplies or sanitation infrastructure. Cholera is rarely found in countries where there is a significant investment in clean piped water and sewage treatment facilities that kill any bacteria through the use of chlorine.

The treatment and prevention of cholera

Surveillance strategies are essential to contain outbreaks quickly and require effective and fast diagnostic approaches. Cholera is diagnosed by identifying cholera bacteria in a stool sample or rectal swab, usually sent to a lab. A quick diagnosis is essential to provide a rapid treatment that can be life-saving.

Treatment of cholera is very cheap and straightforward. People with mild or moderate symptoms usually receive oral rehydration therapy. This is a solution of salts and glucose that rehydrates the body, thus diminishing the impact of the fluid losses caused by diarrhoea. Patients with more severe dehydration usually receive intravenous fluids and antibiotics.

Preventative steps are also essential when visiting areas with cholera epidemics. Basic hygiene and water consumption precautions can significantly reduce the risk of becoming infected.

According to the Centres for Disease Control and Prevention (CDC) some precautions include:

• only drinking bottled water,

• disinfecting your own water (e.g., boiling or filtering),

• washing hands thoroughly before eating, cooking, or handling food,

• eating pre-packaged hot food, and never raw/undercooked food

Fig. 2: How to prevent cholera infection

Long-term resolution and eradication of cholera disease will require the development of infrastructure for sanitation and clean water supplies to areas of sub-standard housing. There should be universal access to safe drinking water and proper sanitation facilities that encourage good hygiene practices.