Mumbai’s great rat hunt and why it matters to you
Since 2015, leptospirosis has killed 70 people in Mumbai, more than dengue and malaria. It is an uphill battle that the city’s massive rat-killing machinery has been desperately trying to win
In August, when eight-year-old Sameer Shaikh complained of muscle pain, his uncle Chand, a 32-year-old carpenter who he stayed with him in Govandi, thought the child perhaps exerted a little too much while playing that day.
However, when Sameer developed high fever, his parents who were based in Uttar Pradesh, asked Chand to get a blood test done. The test revealed that Sameer’s white blood cell (WBC) count was dangerously low, which meant he needed to be hospitalised immediately.
The first two hospitals that Chand took Sameer to couldn’t admit him - there were no Intensive Care Unit (ICU) beds available. Chand was finally able to admit him at Lokmanya Tilak Municipal General (LTMG) hospital in Sion. But by then Sameer’s condition had deteriorated considerably.
On August 19, Sameer went into an acute respiratory distress syndrome and died. The child succumbed to leptospirosis.
“We don’t know how he got the infection and how his condition deteriorated so quickly,” Chand later said, recalling Sameer’s tragic death.
Sameer is among 70 people in Mumbai who have died from leptospirosis - a bacterial infection that spreads via the urine of infected animals such as rats and cattle - since 2015, the highest mortality in monsoon-related diseases.
In comparison, dengue and malaria - both mosquito-borne viral infections - killed 55 and 38 people, respectively, during the same period.
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In congested urban areas such as Mumbai, rats are known to be the main source of leptospirosis in humans as well as in animals.
Dr Radha Gulati Ghildiyal, head of paediatrics at LTMG hospital, said muscle pain is typical of leptospirosis. When children report this symptom along with fever, doctors usually suspect leptospirosis or dengue as the cause. “Mortality is seen only in patients who come in very late, typically four to five days after symptoms first appear,” the doctor said.
Leptospirosis is caused by the leptospira bacteria that can enter the human body through cuts, abrasions or open wounds. Cases typically surface during the monsoon season, especially after floods and waterlogging.
Overflowing sewers and lack of hygiene often lead to rat urine mixing with accumulated water, which commuters are forced to wade into.
Chemical warfare
“Even one human life lost to leptospirosis is a concern for us,” said Mumbai’s insecticide officer Dr Rajan Naringrekar, who is in charge of containing the rat population in the city.
At least 1,000 rats are killed in the city every day. The civic body hires rat killers who hunt and kill rats at night. At least 14 out of the 24 wards in the city have rat killers on night duty. But the corporation’s mainstay, though, is poison baiting - poison-laden wheat balls made with chemical compounds that rats feed on and die.
Around 25gmof zinc phosphide is mixed with a kilogram of wheat flour and 300- 350 pellets are made that are then pushed into numerous burrows. Zinc phosphide works as a poison. The civic body uses 100-130kg of zinc phosphide every year as part of its mission to kill rats.
The task of mixing the chemical compound with wheat flour is done by “rat labourers”. The Municipal Corporation of Greater Mumbai (MCGM) has 137 such permanent employees who make that mix every day and put the pellets in burrows spread across the city’s 24 wards. While rat labourers cover areas assigned to them on a daily basis, they are often asked to focus on areas where residents complain of rampant rat menace. The work of the rat labourers is supervised by junior overseers in each ward.
The civic body also mixes bromadiolone, a rodenticide that is highly toxic for mammals, with the flour; it uses nearly 70kg of it every year. During the monsoon season, the poisoned wheat pellets often get washed away as water inundates the burrows.
The civic body then tries out something else: it relies on readymade tablets of aluminium phosphide that release poisonous fumes that kill rodents. Nearly 1,500kg of aluminium phosphide tablets are used annually.
Watching out for the plague
The civic body needs to be vigilant about bubonic plague, a bacterial infection caused by the bite from an infected rodent flea, which had killed millions in erstwhile Bombay at the turn of the previous century.
The first official case of plague was detected in the city on September 23, 1896. The pandemic spread like wildfire as the British authorities opened quarantine centres, and washed streets and homes with sea water in a bid to flush out rats that had overrun the city. The episode triggered a mass exodus, and in the following years, millions died from the plague.
As of now, there are no estimates of the rat population in Mumbai. But the insecticide department is certain that the numbers have not increased. “If at all, we have managed to keep the numbers plateaued despite growing congestion in the city,” said Naringrekar.
He attributes the plateauing of numbers to a series of measures put in place by his department to rid the city of rats. About 300,000 to 400,000 rats are killed annually in Mumbai using these various interventions.
Getting his hands dirty
Every day at noon, three tempos line up at a civic compound in Lower Parel carrying dead rats from all the wards of Mumbai. Labourers unload gunny bags of dead rats, count the numbers, and update a ward-wise log.
Once counting concludes, 34-year-old lab technician Pravin Ghuge steps in. Armed with rubber gloves, a mask and a lab coat, Ghuge carefully picks up some dead rats from various wards and takes them to a room in the compound. He proceeds to dissect a rat. He places a tiny piece of rat liver on a glass slide. He stains the spot on the slide with a chemical solution and observes it under a microscope. He searches for a safety pin-like appearance of yersinia pestis, the bacteria that causes plague.
Ghuge, who holds a Master of Science in microbiology and has been working as a lab technician, dissecting rats since 2009, hasn’t seen any trace of the plague yet.
“It’s not exactly a great feeling to dig your hands through a pile of dead rats every day, but it’s the job that I have been tasked with and I have to do it,” Gughe said. “This was my first posting. I have asked for a change many times,” said the Thane-resident who is father to a five-year-old. “My biggest fear is being exposed to infections myself, and taking it back home. There could be so many pathogens on the rodents that I may be exposed to every day.”
In some ways, Ghuge is a key barrier between the city and the deadly bacterial infection that once killed millions. He has been mandated to dissect at least 10% of the daily collection of dead rats. But with just one technician for screening, won’t it be easy to miss an infected rat among the thousands?
“It’s less likely to miss such an outbreak,” argued Naringrekar. “If the infection surfaces, the first alarming signs will be a large number of rat deaths or what is known as ‘rat fall’, without any apparent reason or intervention. That would be our main signal,” he said.
In an outbreak of plague, typically an unusually high number of rodents die first as the infection spreads among them. The bacterium that causes the plague, Yersinia pestis, is found in rodent fleas that feed on the rodents’ blood. After the plague-stricken rodents die, the fleas turn to other hosts such as humans and other animals.
Community interventions
Mumbai’s civic body uses what the department head called a “4D formula” to tackle rats - deny entry (rat-proof buildings, pipes), deny shelter (discard clutter, scrap), deny food (properly dispose garbage) and destruction (trapping, poison-baiting, fumigation, which is done under the insecticide department’s watch).
“In areas such as Nepean Sea Road and Malabar Hill, one may rarely find rats other than in sewers. This is because all the buildings have rat-proofing and there is cleanliness,” said Naringrekar, who has been working at the insecticide department since 1989.
Rat-proofing involves creating stoppers (like a circular aluminium sheet) on pipes that run up a residential building, and sealing the gaps between pipes and the structure itself, so that the rodents can’t climb up and enter people’s homes. Since 2019, the department has been rat-proofing all civic-run hospitals. Work at Kandivli’s Shatabdi Hospital is over, and it is currently going on at LTMG Hospital. Next in line is Nair Hospital.
“Unfortunately, public behaviour is responsible for creating conducive environment for rats to thrive. People give them ample of food in the form of unclean premises, littering and haphazardly disposing of garbage. They provide them shelter in the clutter that accumulates everywhere,” Naringrekar said.
‘Rats breed at a great speed’
“Rats breed at a great speed. Their gestation period is only about 21 days and they have large litters - anywhere between six and 14,” Naringrekar said, adding that while his department works to ensure that the rat population doesn’t go up, a change in public behaviour is the only factor than can lead to a decline in numbers. “Cleanliness and hygiene are crucial to keeping rats at bay.”
Diseases such as leptospirosis, malaria, gastroenteritis, Hepatitis A and E, and dengue continue to flourish in Mumbai. Cumulatively, according to Brihanmumbai Municipal Corporation (BMC) data, these diseases have killed 173 people since 2015.
The civic body undertakes awareness campaigns, such as putting up hoardings to warn citizens about leptospirosis and other diseases during the monsoon season. As far as leptospirosis is concerned, the civic body’s campaigns are focused on taking doxycycline - the antibiotic drug that works against the infection - as preventive medication if someone has waded through floodwaters.
Sameer’s family is still clueless as to how exactly the child contracted the infection. Tragically, his uncle blames himself for the death.
“Doctors asked me if Sameer had walked in water. But I had been protecting him, since I was responsible for his safety. He played with some friends just outside our house. He never went far,” Chand recounted. “I don’t think he had come in contact with sewer water.”