Shigella | Virulent bacterium: The Hindu update
Stained, and viewed under a microscope, Shigella is a captivating sight. The rod-shaped bacteria resemble fat, furry cartoon caterpillars. In reality, however, this gram-negative, contagious
Stained, and viewed under a microscope, Shigella is a captivating sight. The rod-shaped bacteria resemble fat, furry cartoon caterpillars. In reality, however, this gram-negative, contagious bacterium, which causes shigellosis, can be remarkably dangerous. Shigella is back in the news, after an outbreak in Kerala that was first detected in late March 2026 and has continued into June. According to the Kerala health department, 132 confirmed cases and about 75 probable cases of shigellosis had been reported till June 12. Three deaths have been linked to the disease this year, two of which were children under five. Shigellosis is a diarrhoeal disease marked by fever, abdominal cramps, and bloody diarrhoea (dysentery). It was bacteriologist Kiyoshi Shiga, who isolated the shigella dysenteriae, in 1897, after Japan experienced a severe dysentery epidemic. The genus eventually took his name. Transmission is mostly through the faeco-oral route, when people ingest tiny amounts of faecal matter through contaminated food, water or hands. As low as 10-100 bacteria can cause the infection, and even an outbreak.
It is estimated that globally, shigella causes 80-165 million infections annually and about 6,00,000 deaths, particularly among children under five in sub-Saharan Africa and South Asia. In an article in the Indian Journal of Medical Research, Neelam Taneja and Abhishek Mewara write about the epidemiology of shigella in India. “Though humans and primates are the primary reservoir of shigella, it has been isolated from various sources — aquatic bodies (rivers, surface waters as well as coastal waters), free living amoebae, insects, birds and wild animals.” Taneja and Mewara explain that several aquatic bodies in India have been found to show the presence of shigella. So a potential source of infection could be fish if it is harvested from sewage-contaminated water. Even ingesting small amounts of contaminated water while swimming or bathing, or the consumption of crops cultivated in soil/water contaminated by shigella can cause severe infection. The paper argues that while no individual can be considered immune to shigellosis, “certain individuals are at increased risk.
Globally, the incidence of shigellosis is highest among children under five. The incidence of shigellosis has been reported to increase steadily after the age of 40.” Outbreak in Kerala In late March 2026, Kerala reported a shigellosis outbreak in Kuttikkattoor, Kozhikode, where a three-year-old girl died and over 60 residents (mostly children) fell ill. Soon, clusters came up in Wayanad, Malappuram and Kannur. A major cluster emerged at a Wayanad school where over 300 children were hospitalised. So far, experts have traced the infections to contaminated water and food sources, alongside poor hygiene practices in communal environments such as schools. Explained: What is Shigella infection? This is not Kerala’s first brush with shigellosis. In 2009, over 300 people reportedly contracted a food-borne shigella infection across the State. In December 2020, an outbreak, again in Kozhikode, killed an 11-year-old and infected 40 others; in May 2022, shigella was said to be behind a mass food poisoning incident, in Kasaragod, where 30 people were hospitalised and a 16-year old girl died.
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