MUMBAI, India; ORLANDO, Florida—Fifteen human residents of Mumbai, India’s richest and largest city, died during the first 10 days of July 2015 from leptospirosis, a preventable but little recognized disease mostly associated with rat and dog urine. Another 30 patients were reportedly hospitalized with advanced leptospirosis infections.
Outbreak News Today and ProMED-mail warned health workers worldwide to look out for leptospirosis symptoms, and to beware of the conditions associated with outbreaks.
Leptospirosis in the developing world mostly occurs during flooding, especially the summer monsoons, but Malaysia had 753 suspected cases with 126 confirmed in flooded areas during the first three weeks of January 2015.
Human cases in the U.S., Canada, and Europe over the past several decades have mostly been associated with summer outdoor recreation.
Dog rescuers vulnerable
Animal rescuers involved in transporting dogs from tropical nations, especially flood disaster areas, and adopters of former street dogs from the developing world are also among the categories of people who are at greatest risk of exposure in the U.S., Canada, and Europe.
The United Kingdom has about 250 identified canine cases of leptospirosis per year, some of indigenous origin, others suspected of arriving with imported dogs.
Animal shelters have seldom reported leptospirosis outbreaks, possibly through lack of vigilance for a disease not familiar to most U.S., Canadian, and European veterinarians.
In April 2001, however, leptospirosis hit a volunteer and two dogs at the Miaouf no-kill shelter in Ste. Justine-de-Newton, Quebec. To keep the Miaouf outbreak from spreading, provincial veterinarians euthanized all 175 resident animals. Louise Gagnon, who founded Miaouf in 1976, had been ousted from the organization in September 2000, partly for failing to prevent rat infestation.
The kennels, built in the 1960s by Ayerst Laboratories, then the world’s leading maker of hormone products derived from pregnant mares’ urine, later housed an alleged puppy mill that was the target of intensive protests circa 2006.
High exposure potential worldwide
Leptospirosis infections in dogs are most often detected in Florida and the Deep South, but leptospirosis may infect almost any mammal, and has occurred almost everywhere that anyone has looked for it. At least four Canadian trappers, for example, are known to have contracted leptospirosis from skinning raccoons.
Research done in 2000 by K.S. Venkatraman of the Leptospirosis Laboratory found that 40% of the waterways in Chennai, India, 80% of the slaughterhouse runoff, and 60% of the rodents carried leptospires. Data produced by the Pakistan Science Foundation shows that more than half of the people and livestock in Pakistan have already had some exposure to leptospirosis, if not enough to become actively infected. China has as many as half a million human cases of leptospirosis per year; Brazil has reported 30,000.
But the background potential for exposure in the U.S. may not be significantly less. A 1996 study by University of Texas Medical Branch at Galveston professor Joe Vinetz found leptospires in up to 90% of the rats in Baltimore and 40% of the cattle at a Texas slaughterhouse.
Water, food, soil
The difference between the risk of contracting leptospirosis in India and the risk of contracting it in the U.S. may simply be the difference in cleanliness of drinking water, with equal potential for serious outbreaks through other forms of exposure.
Relatively isolated islands can be as severely afflicted as mainland habitats. Tahiti had 129 known leptospirosis cases in 2014, with two human deaths; Reunion Island had 59 cases with three human deaths. Fiji in 2000 had 23 human deaths from leptospirosis after an ill-advised purge of street dogs allowed the rat population to run amok.
People and animals contract leptospirosis through either direct or indirect contact with the urine of animals who are already infected. Infection is especially likely from urine-contaminated water, but can also occur through contact with contaminated food and soil.
“The bacterium,” a form of spirochete, “enters through contact with skin, especially through cuts or breaks in the skin, and through mucous membranes like the eyes,” explained Robert Herriman of Outbreak News Today.
Most animal cases go undetected
First medically identified in the late 19th century, leptospirosis “was long considered an occupational disease,” Herriman recalled, afflicting “farmers, veterinarians, sugar cane harvesters and sewer workers.”
In recent years, however, leptospirosis “is increasingly associated with recreational water sports and camping,” Herriman continued.
Fewer than 100 human cases of leptospirosis per year are reported from the mainland U.S. to the Centers for Disease Control & Prevention, plus 50-75 cases from Hawaii––but for each human case there may be thousands among dogs and other animals, mostly going undetected.
CDC dropped notification requirement
Deeming leptospirosis to be no longer a major threat to public health, if it ever was, the Centers for Disease Control & Prevention took it off the list of “nationally notifiable” diseases in 1995, a mistake recognized in 1998 after 775 Americans were exposed and 110 fell ill after an Illinois triathlon.
The next largest U.S. leptospirosis outbreak came in 2005, when as Kate Santich of the Orlando Sentinel summarized, “a group of 43 international adventure racers competing near Tampa became infected after swimming in bacteria-laden waters.”
Thirty-six states had retained leptospirosis notification requirements. But leptospirosis was not restored to the list of “nationally notifiable” diseases until 2013.
Recognized leptospirosis cases in dogs meanwhile increased tenfold in the northeast quadrant between 1996 and 2001, according to data collected by the Long Island Veterinary Medical Society and University of Pennsylvania School of Veterinary Medicine, and more recently increased about sixfold in Florida, according to anecdotal reports.
Sources & symptoms
An investigation of more than 1,000 dog deaths by New York state veterinarian Mary Jane Lis found that, “In most cases, the dogs [who died] were living in homes that had standing water in the back yard, in a wooded lot with wildlife in the neighborhood. Infected urine from wild animals taints the water or soil, and the dogs drink, swim, or walk through the water,” Associated Press summarized of Lis’ findings.
“Symptoms of leptospirosis, if present, appear up to four weeks after exposure,” Herriman wrote. “Sometimes the person will show no symptoms or mild flu-like symptoms. According to the CDC, leptospirosis may occur in two phases. After the first phase, with fever, chills, headache, muscle aches, vomiting, or diarrhea,” all of which are common and easily misdiagnosed, “the patient may recover for a time but become ill again. If a second phase occurs, it is more severe: the person may have kidney or liver failure (jaundice), or meningitis. Leptospirosis is confirmed by laboratory testing of a blood or urine sample.
“The infection can be treated with antibiotics (penicillin and doxycycline), especially if started early in the disease,” Herriman continued. “For very ill patients, intensive care support and IV antibiotics may be necessary.”
Asymptomatic in animals
Identifying infected animals tends to be much more difficult than identifying infected people.
“It’s a disease carried by wild animals who can be totally nonsymptomatic,” Orlando veterinarian Rick Marrinson told Santich of the Sentinel. “So that [infected] raccoon or opossum comes in your yard, urinates on your grass overnight, and your dog goes out the next morning and starts sniffing around and gets exposed—without ever seeing the [infected] animal.”
Marrison promotes vaccination against leptosprirosis, Santich wrote, but many U.S. and European veterinarians do not.
“That’s because, of all dog vaccines — rabies, distemper, parvovirus, kennel cough—the lepto vaccine is most likely to provoke an adverse reaction,” Santich reported, “especially in small shorthaired breeds such as shorthaired dachshunds.”
In addition, effective leptospirosis vaccination requires annual boosters. Some veterinarians believe a first leptospirosis vaccination provides effective coverage for as little as nine months.
The rat/dog relationship
Both in the U.S. and Europe and in the developing world, leptospirosis outbreaks are most often spread by rats.
In the developing world, however, the most visible carriers tend to be street dogs––who tend to become infected in part through their role as leading rat predators.
Street dogs are also major competitors with rats in consuming food waste and undigested food remnants in animal and human excrement.
Following a flood, including summer monsoons, a great deal of material that dogs and rats find edible tends to be distributed wherever the water rose and people are mucking out homes and businesses. Since rats are good swimmers and climbers, they tend to survive floods.
Because rats also breed rapidly whenever new food sources become available, rats proliferate after flooding almost as rapidly as the water recedes––and of course shed leptospirosis spirochetes.
Because flooding tends to rapidly overburden whatever latrines and ditches are used to convey human waste out of developing world shantytowns and densely populated urban areas, human water sources become contaminated, and human deaths from leptospirosis follow.
Dogs purged, rats breed
Historically, at this point municipal authorities desperate to regain public confidence blame dogs for the outbreaks, and order dog massacres, which in turn allow the rats to proliferate even faster.
Alternatively, attempts are made to poison both dogs and rats by distributing poisons among the post-flooding debris piles. Nicaragua, for example, in August 2013 responded to three human leptospirosis deaths by poisoning rats at 862 locations in 120 municipalities, using a Cuban-developed pesticide called Biorat, which is based on the bacterium salmonella.
ProMED-mail experts warned that this could potentially have become a water contamination problem in itself. Salmonella in 2011 killed 29 Americans and caused about one million human illnesses within the U.S. alone, according to the Centers for Disease Control & Prevention.
The long-term solutions to leptospirosis include better flood water containment, better drainage, better plumbing and sewage control systems, better municipal waste and refuse collection, and––as their food sources and habitat niches diminish––far fewer rats and street dogs.
Short-term, the safest practice tends to be to leave the dogs alone, let the dogs deal with the rats, and meanwhile focus on removing edible debris and restoring clean drinking water.
Some lessons learned
As of mid-July 2015, the Brihanmumbai Municipal Corporation, less formally known as the city of Mumbai, formerly Bombay, appeared to be resisting political and media pressure to order a street dog purge. Instead, Herriman reported, “The corporation has started an awareness campaign in which they have visited 14,649 houses and surveyed 57,736 people,” seeking to identify and treat leptospirosis cases and educate residents about avoidance and prevention.”
In that respect, Mumbai officials may have learned something since 2001, when leptospirosis killed at least 19 people in six months.
“The main reason for the rise in the number of leptospirosis cases has been waterlogging and the accumulation of garbage, which has resulted in an increase in the rat population,” acknowledged the Times of India then–but added, “The stray dog population has also risen, which is believed to have led to the spread of the disease,” a precise reversal of the reality that the dog population was sharply down due to the success of several of India’s first of a now national string of Animal Birth Control programs.
Under much less predation pressure and without food competition from dogs, the rat population was up, and prospered further after both official and unofficial dog purges followed the first reports of leptospirosis.
The lesson to leave street dogs alone while focusing on improving sanitation should already have been obvious from the catastrophe that hit Surat, India, following a dog purge. Bubonic plague, carried by the fleas on rats, broke out soon afterward, infecting at least 693 people, killing 57.
But while the deadliest plague outbreak since World War II grabbed the headlines, leptospirosis simultaneously killed at least 37 Surat residents. Some epidemiologists believe many and perhaps most of the purported plague cases were also misdiagnosed leptospirosis.