An outbreak of shigella infection has created panic in Kerala after an 11-year-old died in Kozhikode district. According to the authorities, six out of 56 suspected cases in the area have been confirmed as shigella infections. These cases of Shigellosis have been spotted in Feroke, not far from the border with the Malappuram district.
Classification of shigella
Shigella is an antigenically diverse pathogen. As per the latest accepted taxonomy, there are four species (or groups) and 49 serotypes for the genus Shigella. The four groups are Shigella dysenteriae, Shigella flexneri, Shigella boydii and Shigella sonnei. In addition, more than a dozen new serotype or subtype strains are now being considered for possible official classification.
Shigellosis typically arises in developing countries experiencing an upheaval of civil society or just after a natural disaster. The problem is that it disappears suddenly, and reappears just as abruptly when an opportunity presents itself. Ingestion of a very minute inoculum of about 10 microorganisms is enough to induce shigellosis. This makes the illness very contagious. Shigella flexneri serotypes are the major agents of endemic shigellosis. Shigella sonnei is the predominant serotype in human settlements in transitional countries.
The signs and symptoms of the disease range from mild abdominal discomfort to full-blown dysentery characterised by cramps, diarrhoea with slimy-consistent stools, fever, blood, pus or mucus in stools, abdominal pain and the feeling to pass stools even when the bowels are empty. The most common neurological symptom is seizures. These symptoms appear within 12 to 96 hours, and recovery takes 5 to 7 days.
The probability of being infected by the above four strains of Shigella varies around the world. The bacteria is transmitted through the faeces of individuals infected with the disease, whether or not they are exhibiting symptoms. Long-term carriers of the bacteria are rare.
Apart from humans, they can also infect primates. Upon ingestion, the bacteria pass through the gastrointestinal tract to reach the small intestine where they begin to multiply until they reach the large intestine. In the large intestine, the bacteria cause cell injury and the early stages of Shigellosis, including (1) the direct invasion of the epithelial cells of the large intestine, and (2) the production of enterotoxin 1 and enterotoxin 2.
The diagnosis of shigellosis is made by isolating the bacteria from diarrheal faecal sample cultures. Shigella species are generally not lactose fermenters, but S. sonnei can ferment lactose. They typically do not produce gas from carbohydrates (with the exception of certain strains of S. flexneri) and tend to be overall biochemically inert. Shigella are also urea hydrolysis negative.
Treatment & precautions
Bismuth subsalicylate may help with the symptoms. In severe cases, antibiotics such as ciprofloxacin, trimethoprim-sulfamethoxazole and azithromycin can be used when the person is very young or very old. Ampicillin (but not amoxicillin) was observed to be effective, but now, the first drug of choice is pivmecillinam. Medications such as loperamide should not be used.
Simple precautions can be taken to prevent getting shigellosis: wash hands before handling food, and thoroughly cook all food before eating. The primary prevention methods are improved sanitation and personal and food hygiene.