A parasitic outbreak, known to cause explosive diarrhoea, has now spread to the UK.

On Wednesday, the UK Health Security Agency (UKHSA) reported a notable increase in cyclosporiasis infections, primarily affecting travellers returning from Mexico.

It comes after thousands of people fell sick with the bug across the United States.

Cyclospora cayetanensis, a microscopic parasite, is the culprit behind cyclosporiasis. The illness is contracted by consuming contaminated food or water.

Once ingested, the parasite's eggs release spores that invade the small intestine, triggering an immune response and leading to a range of unpleasant symptoms.

Here’s what to look out for and what to know about the illness.

When do symptoms of cyclosporiasis begin?

Symptoms typically manifest around a week after exposure, though they can appear as quickly as two days or take up to two weeks, according to New York health officials.

The delay occurs because the parasites require time to multiply and damage the intestinal lining before symptoms become apparent.

What are the symptoms of cyclosporiasis?

The primary symptom is diarrhoea, which many have reported as “explosive”.

“You’re barely able to make it to the toilet,” Dr. Alejandro Macías, an epidemiologist and physician at the University of Guanajuato in central Mexico, told The New York Times.

That can often be accompanied by loss of appetite, flatulence, cramps, nausea, fatigue, body aches, and fever.

While some people may experience no symptoms at all, the illness can be particularly severe for young children, older adults, and those with weakened immune systems.

How long do symptoms of cyclosporiasis last?

Even after the parasite is eliminated, the intestinal lining needs time to heal, meaning symptoms can persist for several weeks, State University of New York experts say.

What is the treatment for cyclosporiasis?

Currently, there is no vaccine available to prevent cyclosporiasis. Diagnosis relies on testing stool samples, which can also help identify other causes of infectious diarrhoea.

The recommended treatment involves a course of antibiotics, usually taken for seven to ten days.

Most healthy adults can eventually overcome the parasite, but those with compromised immune systems face a higher risk of severe or prolonged illness.

How can you avoid getting cyclosporiasis?

According to the NHS, cyclospora is not found in the UK, but there is a risk of picking it up while travelling to places it is common, such as Central and South America, south and south-east Asia, the Middle East and Africa.

There is a major outbreak of the infection in the US, which has spread to 45 states.

The most effective way to minimise exposure to Cyclospora is to avoid potentially contaminated sources and ensure food is thoroughly cooked and cleaned.

Heating food to 70 degrees Celsius (158 degrees Fahrenheit) is known to kill the parasite.