Shigella bacteria cause an infection of the bowel known as shigellosis, which results in diarrhoea. There are four main species: Shigella sonnei, Shigella flexneri, Shigella boydii, and Shigella dysenteriae. Shigella is a major cause of moderate to severe diarrhoea globally, with an estimated 80-165 million cases each year, mostly in low or middle-income countries. It is estimated that there are around 200,000 deaths due to shigella infection every year, with 60,000 of these occurring in children under the age of five.
Shigellosis is highly contagious; it only takes a small number of bacteria to cause infection. People can continue to spread the bacteria for several weeks after they have recovered.
Symptoms usually appear one to two days after infection and last for about seven days. However, symptoms can sometimes take up to a week to develop.
Most people experience:
Shigella can be dangerous, particularly for children. The disease can cause severe bloody diarrhoea (dysentery), known as shigellosis, and can spread beyond the gut leading to blood poisoning, and in some cases sepsis and death. In places with poor sanitation and limited access to clean water, repeated infections can lead to stunted growth and impaired brain development.
Drug-resistant Shigella infections have increased significantly and a study in Nature Communications in 2023 showed that the number of cases of extensively drug resistant infections – meaning they cannot be treated with first and second line antibiotics – are growing, particularly among gay and bisexual men. In 2023 UK public health officials reported 97 cases compared to three the previous year.
Shigella spreads easily because it is found in faeces, and swallowing just a small amount of the bacteria can cause illness. The bacteria can be transmitted through:
People who travel to areas with poor sanitation and unsafe water are more likely to get sick. Children under five years old are also at high risk of contracting the disease. Outbreaks often occur in schools and nurseries.
In recent years it has been recognised that shigella can also be transmitted through sexual activity as there have been outbreaks among men who have sex with men.
Most people with shigellosis will recover without antibiotic treatment within five to seven days with rest and fluids. It is important to drink plenty of fluids to avoid dehydration. Antibiotics may be used against the most severe form of shigella, although the threat of antibiotic resistance means that these should be administered with caution.
There is currently no vaccine against shigella, although nine are currently in development. However, there is unlikely to be any available until the 2030s. In the meantime the best way to avoid getting or spreading shigella is to follow these steps:
Reports of dysentery date back to ancient times but in 1897 in Japan 20,000 people died from the disease in six months. During this outbreak, Dr Kiyoshi Shiga isolated and identified the bacteria responsible for the disease, which we now know as Shigella.
While antibiotics and improved sanitation have reduced the frequency of dysentery, Shigella still causes many deaths, particularly in lower-income countries. Scientists have been trying to develop vaccines against Shigella for over 100 years. There are currently nine vaccine candidates in clinical trials. A vaccine could reduce the reliance on antibiotics, therefore helping to reduce the growing problem of antimicrobial resistance.
While it is not classed as a sexually transmitted infection, since about 2012 the number of cases spread by men having sex with men has risen. The numbers grew after the pandemic with UK public health agencies reporting 230 cases in 2022 and 432 in 2023.
gavi.org/vaccine-profiles-shigella
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