A rarely reported leptospirosis bacteria (serotype) that did not exist earlier in Mumbai killed 16 residents of the disease this year. This is the preliminary observation made by the Regional Medical Research Centre (RMRC), Indian Council of Medical Research, Port Blair, Andaman and Nicobar Islands.
The Brihanmumbai Municipal Corporation (BMC) had sent blood samples of the 16 people who died of the disease in Mumbai this year, to the RMRC. The laboratory tested 12 of the samples — the other four samples did not meet the testing standards — and concluded that the leptospirosis bacterium, which is now in circulation in Mumbai, is “relatively new” to India. The study, however, did not clarify whether the high mortality this year was because of the new type of the bacteria.
RMRC, considered the best testing centre in India for the disease, performed the microscopic agglutination test (MAT) to identify the serovars - types of leptospira bacteria - in circulation in Mumbai. MAT is the most reliable way (gold standard) to identify the serovars. There are about 250 to 260 types of serovars across the world. Of the serovars identified globally, 12 to 13 are common in India, of which seven to eight are routinely reported from western India, including Maharashtra, none of which were found in the blood samples sent from Mumbai.
The researchers found Tarassovi and Djasmin bacteria, which are unusual in this part of the country. “In six cases, the serogroup of the infecting strain was Tarassovi; in two it was Djasmin and in the remaining four, the test detected the presence of both the types,” said Dr P Vijayachari, director of RMRC.
“It seems that there may be a shift in the circulating serogroup of leptospira in Mumbai,” he said.
However, he said the test results have to be corroborated with additional studies to find out the bacteria’s host. “Such a study will also help identify the predominant animal species that is acting as the source of leptospira for human infection in Mumbai and will help devise appropriate measures to control the carrier state in these animals,” he said.
"The leptospirosis bacteria survive in animals. Many animals, including cattle, can be responsible for the spread of the bacteria. We have to identify the animals which are spreading this type of serova. The carrier of the bacteria could have changed. Once the animal is identified, we can vaccinate them accordingly and even treat them to arrest transmission,” said Vijayachari.
The researchers also found respiratory problems to be the predominant cause of death among the patients. “This trend is now seen in most parts of the world,” said Vijayachari, refuting the possibility of any mutations in the bacteria. “There are no strong indications at present to suspect mutations in the bacteria as the underlying cause for the apparent increase in the occurrence of the disease or mortality in Mumbai.”
“There is a need to study the change in the host [animals], organism and the environment. There is also a need to study if there is any other organism associated, which has resulted in higher fatality,” said Dr Om Shrivastav, infectious disease consultant.