Street dogs keep the developing world from going to the rats
From ANIMAL PEOPLE, July/August 2001:
MUMBAI, NEW DELHI–“Some bloody idiot,” Indian minister of state for social justice and empowerment Maneka Gandhi e-mailed to ANIMAL PEOPLE on July 26, “has come forward to say dogs give leptospirosis to humans. So the Brihanmumbai Municipal Corporation (city of Mumbai, also called Bombay) has gone to court to restart the killing of strays,” halted repeatedly by judicial order in recent years as executive health officer Alka Karande and other local officials have sought pretexts to continue.
Rabies, the previous pretext, killed 35 of the 18 million Mumbai residents in 2000. Leptospirosis, mostly a rat disease, killed 17, is believed to have killed another 19 people in
unconfirmed cases, and killed 19 more during the first half of 2001. “Drains are overflowing, garbage accumulating, and people are defecating in the open–and the city wants to find someone to blame for their inability to keep the city clean,” charged Susi
Wiesinger of Ahimsa/Mumbai.
“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,” confirmed the Times of India–but added, “The stray dog population has also risen, which is believed to have led to the spread of the disease.”
The Times of India did not point out that if the dog population is up, an assertion disputed by humane groups which have escalated their pace of sterilizing street dogs, the increase may be because more rats mean more protein for the dogs, the major rat predator in Mumbai and most cities of the developing world. Rather than spreading leptospirosis, the dogs may be why the disease isn’t killing more people than about one per half million per year.
Preparing a brief against the latest proposed dog purge, Mrs. Gandhi requested copies of “any specific information with a big name behind it .”
Medical literature on leptospirosis agrees that the usually mild but sometimes deadly illness is carried almost exclusively by rats and mice. Transmission typically occurs in humid weather, especially after floods in tropical climates, which tend to put humans and rodents in closer proximity, increase the risk that people with few options will eat contaminated food, and drown many of the street dogs, feral cats, snakes, mongooses, and other
predators who normally keep rats in check.
Any mammal can become infected with one or more of the 250-plus leptospirosis strains, some of which kill about 25% of their hosts. Dogs in the developing world are usually infected by eating diseased rats and mice, or by drinking water polluted by rodent urine. Yet the chance of mammals other than rats and mice spreading leptospirosis to people is slight, because transmission requires intimate direct contact with infected urine. Rat-and-mouse puddles are not always obvious, but puddles from dogs and other large mammals tend to be seen and avoided.
Researching leptospirosis outbreaks in 12 nations of Asia, Europe, and the Americas since 1995, involving thousands of humans who recovered and 252 fatalities, ANIMAL PEOPLE found just six documented cases in which humans were infected by species other than rodents. Four Ontario trappers caught leptospirosis by skinning raccoons. A Texas man caught it while nursing his terminally ill dog. The dog is believed to have become infected by contact with either rodent or cattle urine at a rodeo.
Most recently, leptospirosis hit a volunteer and two dogs at the now closed Miaouf no-kill shelter in Ste. Justine-de-Newton, Quebec. All 175 resident animals were killed by provincial vets, with 3-2 board approval, on April 12, 2001. Louise Gagnon, who founded Miaouf in 1976, was ousted from the organization in September 2000, partly for failing to prevent rat infestation.
Pets and hooved stock are often vaccinated against common forms of leptospirosis in the U.S., suppressing transmission even though a 1996 study by University of Texas Medical Branch at Galveston professor Joe Vinetz found that leptospire spirochetes which occur in up to 90% of the rats in Baltimore and 40% of the cattle at a Texas slaughterhouse.
Fewer than 100 human cases of leptospirosis per year are reported from the mainland U.S. to the Centers for Disease Control and Prevention, plus 50-75 cases from Hawaii. But leptospirosis has increased tenfold among dogs in the northeast quadrant since 1996, to about one case detected per 21,000 veterinary visits, according to data collected by the Long Island Veterinary Medical Society and University of Pennsyvlania School of Veterinary Medicine.
Including New England, New York, and the Atlantic Seaboard, the northeast quadrant has had no street dogs in generations, and has relatively few feral cats, as this region is where the neuter/return method of feral cat control was introduced in the U.S. and has been used the longest.
Other diseases carried mainly by rodents are also increasingly common in the northeast quadrant, including tularemia on the island of Martha’s Vineyard, which was among the first places to virtually eliminate feral cats; hantavirus; and Lyme Disease, carried mainly by “deer ticks,” whose main hosts are actually mice. Coinciding with falling feral cat numbers have been local rat population explosions, as wild predators have not fully bred up to
the abundance of prey–although hawks, owls, foxes, and coyotes are all doing well.
Yard dogs are consequently coming into more contact with leptospirosis-carrying rats, getting infected, and often dying before the symptoms are recognized. Since 1996 more than 1,000 dogs have died from leptospirosis on Long Island alone. Yet few if any of the dogs passed leptospirosis on, as yard dogs rarely have the requisite close contact with either humans or other animals.
An investigation 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,” summarized Associated Press.Still, the CDCP warned that humans can become infected from contact with dog urine, which may occur if like the Texas victim they personally attend their sick dogs.
Because the U.S. has relatively few rats compared to the leptospirosis hot spots in the developing world, and because most U.S. dogs share human homes, some references suggest that canine-to-human transmission has been the most common identified
avenue of infection among U.S. cases in recent decades. But canine-to-human cases occur mainly in veterinarians and vet techs, who can accurately trace their exposure. The people most often infected are farm workers and sewer workers, who become ill through suspected contact with rat urine that they cannot trace because they were unaware of it at the time.
“You cannot get leptospirosis just by patting or playing with your dog, or even by having the dog lick your face. You have to come into contact with an infected dog’s urine,” explained Tufts University School of Veterinary Medicine expert Linda Ross, DVM, to Boston Globe reporter Vicki Croke.
Passage to India
After the CDCP warning was amplified by U.S. news media, in accounts often omitting the qualifiers, the Times of India– often editorially critical of street dogs–began telling readers that street dogs may be causing the monsoon-season leptospirosis outbreaks in Mumbai which have occurred for as long as public health records have been kept.
Similar outbreaks are routine elsewhere in India, including Kerala state, where at least 40 people died from leptospirosis last year, and Chennai, where 40% of the local waterways, 80% of the slaughterhouse runoff, and 60% of the rodents carried leptospires according to research by K.S. Venkatraman of the Leptospirosis Laboratory.
The prevalence of leptospires in Chennai, one of India’s cleaner cities, may indirectly reflect the success of the Blue Cross of India and People For Animals-Chennai in reducing the Chennai street dog population via the world’s first and oldest Animal Birth Control program, begun in 1964. Fewer dogs, in India, means less control of rats, even if sanitation is good by developing world standards.
“I would think that if dogs are involved in the outbreaks, you would be seeing some symptomatic dogs,” opined Roland Lenarduzzi, DVM, of the Manvel Animal Clinic in Manvel, Texas, via the TexVetMed electronic bulletin board, when Rita Vazirani of PfA-Mumbai sought strategic advice. “If leptospirosis is being seen there,” Lenarduzzi continued, “free-roaming unvaccinated dogs would certainly be an important source of disease transmission to humans.”
That would be true if humans and dogs had the same relationship in India that they do in the U.S.–but Indian street dogs rarely share human homes. In a nation where lack of refrigeration makes food waste abundant, and work animals still fill the streets with excrement, dogs, rats, and pigs remain vital parts of the public sanitation system. Among them, street dogs are minor vectors for zoonotic diseases other than rabies, but are the major rat predator, and help to control pigs by competing for food and habitat.
The Times of India has called street pigs “one of the most dangerous threats in recent times” despite their role in garbage removal. Street pigs are believed to be proliferating wherever street dogs are fewer. They also compete with rats for food, and kill poisonous snakes, but rarely attack rats. Street pigs do, however, bite and sometimes kill humans (especially small children and the elderly). Of greater recent concern, pig waste forms the
breeding habitat for the mosquitoes who carry the often fatal Japanese encephalitis, which kills an average of 220 children per year in Andhra Pradesh alone, state health minister S. Aruna said during a November 1999 outbreak. The outbreak led to street pig massacres in many cities which had earlier purged steet dogs. Street pigs also carry leptospirosis, along with cattle– whose urine, in India, is widely believed to have purifying qualities.
Mumbai officials would like to get cattle as well as dogs and pigs off the streets, to ease traffic flow, but calling cattle leptospirosis carriers may be politically awkward. Pigs may be
villified and killed in India (only lower-caste Hindus commonly eat them), and dogs may be villified and killed if animal defenders do not notice (killing healthy dogs is illegal), but cattle can only be rounded up on the pretext of doing it for their own good. Thus every city in India has a cow-shelter–some exemplary, and others run by corrupt subcontractors who sell impounded cattle out the back door to slaughter, or starve them to death to sell their hides.
Jack & Jerry
The real issue in Mumbai and many other places where leptospirosis and other rodent-carried diseases are a resurgent problem is a persistent failure of public officials to understand the fundamentals of urban ecology. And Maneka Gandhi, who began her adult life by writing and translating fables, might appropriately recite to the Bombay High Court and Mumbai city executives the nursery rhyme “The House That Jack Built.”
Around the globe, humans have removed many of the dogs and cats who killed the rats who live in the House That Jack Built, and inhabit in even greater numbers the jerry-built shacks of the poor. There are still street dogs and feral cats enough to be seen as a nuisance, an alleged threat to native species, and a possible vector for rabies, but in some developing world cities with dog and/or cat sterilization programs and growing traffic, roadkill
mortality may already challenge the dog and cat birth rate.
Mrs. Gandhi has pointed out often since the city of Surat poisoned street dogs in August 1994 that for India, as for much of the developing world, the price of dog extirpation includes rat-borne disease. After the dog poisoning, when the Surat rat population predictably exploded, the city poisoned rats.
Bubonic plague, like dog predation, is normally a brake on rats, killing 95% to 98% of the rats who get it, explained Matthew J. Keeling and Chris Gilligan in the October 2000 edition of the journal Nature. The survivors become resistant, passing immunity to their offspring while continuing to carry the fleas who carry the plague bacteria.
“When most rats are resistant, plague sort of peters away. You can’t get big epidemics,” Keeling explained to Henry Fountain of The New York Times. But when resistant rats are poisoned en masse, Keeling continued, the plague-carrying fleas must seek new hosts.
Then, said Keeling, “The main alternative is going to be humans. If you kill the rats, you remove the food source and make human exposure much worse.”
The result in Surat was the deadliest outbreak of plague anywhere in the world during the past 50 years. At least 693 people were infected; 57 people died. As vivid as the example of Surat should have been, however, the notion that a community can kill its way to perfection dies hard–and not just in India, where half the electorate cannot read or write, and dog-catching and selling dog leather traditionally provide patronage jobs for illiterates. The same idea underlies the existence of USDA Wildlife Services, the official U.S. exterminating agency, and obsesses restoration biologists who think endangered species can be recovered by killing “invasive” species that have taken hold in altered habitat.
Surat offered an extreme example of the fallacy of killing street dogs where rats abound, but there are others:
* China, with virtually no street dogs, suffers half a million cases of leptospirosis per year. The next most afflicted nation is Brazil, with 30,000. Rat-carried disease outbreaks are
expected to be worse than usual in China this year because many Chinese greeted the Year of the Snake by eating snakes, despite an official campaign against snake-killing begun in January.
* Street dog reduction in Fiji last year was followed by a leptospirosis outbreak that killed 23 people.
* A rapid reduction of the Taiwanese street dog population through official catch-and-kill and nonprofit sterilization efforts sent the island rat population soaring this year to an estimated 80 million. Two people died from the Seoul strain of hantavirus.
* Kuching, the capital of Sarawak state, Malaysia, is named with the Malay word for “cat.” A cat museum, cat temples, and cat statues are the symbols of the city. Yet the cats of Kuching were not enough to prevent the worst rat infestation anyone could remember in mid-2000, after officials purged unlicensed dogs in 1999. Dogcatchers reportedly darted dogs with blowpipes at first, then killed them with iron bars. amid public outcry, the city
allocated funds to build a new pound alongside the Sarawak SPCA shelter.
The cats come back
Some residents in cities in which sterilization campaigns have markedly reduced dog and cat populations now want them back–as in Santiago, Chile, where a local politician recently campaigned for re-election by giving 1,500 free cats to constituents, and local humane society president Luis Navarro told Associated Press that cat adoptions were up 60% after an outbreak of hantavirus.
Vietnam, another nation with virtually no street dogs because dogs are often eaten, but afflicted by rats who may eat or contaminate 20% of the rice harvest each year, in 1998 closed cat meat restaurants and forbade harming either cats or snakes.
The dog population of northeastern Thailand has been depleted in recent years by the growth of a dog meat-and-pelts export industry among Vietnamese refugees of ethnic Chinese descent, who were driven out of Vietnam during a 1978-1979 border war with China. Leptospirosis killed 136 Thais during the 1999 monsoons, mostly in the northeast, and 180 Thais in 2000, 152 of them (84%) from the northeast. The Thai government has tried to discourage the dog-killing, which offends the Buddhist majority–but gently, to avoid ethnic violence.
Meanwhile, on July 24, Bangkok governor Samak Sundaravej celebrated completing his first year in office by announcing a plan to sterilize 100,000 of the estimated 633,814 dogs in Bangkok during the next 12 months, and to sterilize all 115,084 homeless dogs before the end of his four-year term. Earlier, Samak halted dog poisoning as “inhumane and contrary to Buddhism.” Openly fond of animals, Samak in June introduced an effort to buy all of the 70-odd ex-logging elephants that roam the city streets, begging with their mahouts, and return them to a jungle sanctuary.
Bangkok can do without street elephants, who at times run dangerously amok, but whether the city sanitation is ready to do without street dogs has yet to be seen.