Warning over rise in highly infectious parasite that’s reached 10 year high in Britain

Cases of a diarrhea causing parasite have reached their highest levels since 2016, health officials have warned. 

Giardia is an infection caused by a microscopic parasite. The most common symptoms include diarrhoea, abdominal cramps, flatulence, unexplained weight loss and fatigue. 

If left untreated, in rare cases it can trigger malnutrition and stunted growth in children. 

The infection can also cause serious complications in the elderly and those with weakened immune systems. 

Cases in England have significantly risen by 11 per cent in the last year, the UK Health Security Agency (UKHSA) has revealed, from 5,450 in 2024 to 6,069 in 2025. 

London has seen the highest number of cases, totalling 1,568 followed by the North West, where 1,029 cases have been confirmed. 

Cases peaked in autumn, with the 599 people falling ill in October. 

Health chiefs continue to investigate potential reasons for the unprecedented rise but believe it could be due to more effective testing, increased travel since the pandemic and climate changes. 

Although it is found throughout the world, it is most prevalent in developing countries and is one of the most common foodborne illnesses caught by backpackers.  

Infections are most commonly seen in people returning from Southern Asia, South-Eastern Asia, Africa and South America, but it can also be caught in the UK. 

Giardia spreads through direct contact with infected people or animals, or by swallowing contaminated food or water. Once treated symptoms should stop in about a week but can sometimes last longer. 

The UKHSA says international travellers should take precautions when travelling abroad to reduce the risk of infection. 

This includes drinking bottled water rather than tap water, and consuming cooked food rather than raw items such as salad vegetables washed in tap water. 

Travellers are also advised to care when swimming where water may be contaminated, for example in rivers, lakes and the sea.  

Giardiasis is generally not considered to be a serious risk to health and can be treated easily with antibiotics. 

However, about half of those who get the parasite experience no symptoms.  

The bug can be prevented by washing hands with soap and water, especially after using the toilet and before handling and eating food. Children should be encouraged to wash their hands regularly. 

Nicola Love, Senior Food Safety Surveillance Lead at UKHSA, said: ‘We are seeing a rise in giardiasis in the UK.

‘Symptoms can last from weeks to several months and if left untreated, it can cause serious complications especially in young children, the elderly and those with weakened immune systems.

‘There are some simple precautions everyone can take to reduce their risk, whether you are planning an autumn getaway somewhere warm or staying in the UK.

‘Good hygiene can help prevent giardiasis and other common gastro illnesses. 

‘Wash your hands with soap and water after using the toilet, after changing nappies, and before preparing food. Encourage children to wash their hands regularly too. 

‘If you have a Giardia infection, continue to hydrate yourself and see your GP, do not go swimming until 2 weeks after your diarrhoea has stopped. 

‘Parents should contact their GP or NHS 111 if they or their children are ill with dehydration, or if diarrhoea worsens or lasts longer than 3 days,’ she added. 

It comes following the tragic death of two children who were pupils at Millstead primary school in 2024. 

The school was dealing with an outbreak of giardia at the time – though the UKHSA said it was unlikely the deaths were linked to the outbreak.