Canadians Brace for West Nile Virus
STRESSED-OUT, Canadians are more than ready for summertime, when the living is, well, easier. The last, lingering vestiges of winter - the Stanley Cup playoffs - are well on their way to a final reckoning, as sure a sign as daffodils in bloom that long days of lounging by the lake are just around the corner. And about time. Winter overstayed its welcome in many parts this year, then spring sprung fears of a global epidemic. Since then, we've grudgingly learned to live with the viral scourge from China called SARS as it landed a body blow on the health-care system and our economy. We need a break.
The coming Victoria Day weekend is just the ticket, a chance to kick back, hoist a cold one, perhaps, spark up the barbecue and catch up with a neglected novel or kibitz with the kids. Enjoy it: it's probably your last MOSQUITO-free long weekend for a few months. As the weather warms, the backyard and the lakeshore by the cottage could become hazardous to your health. Relax in the great outdoors, urban or otherwise, and you'll hear it - that unmistakable, high-pitched whine of the winged bloodsucker looking for a free lunch. Your muscles tense and a hand cocks instinctively, ready to strike the mosquito as it burrows through the fine hairs of an exposed, tender forearm. SMACK! Gotcha!
Or maybe, as with Mark Little, it got you.
Little was one of the 307 confirmed victims of the West Nile VIRUS in Ontario last year, a figure some experts consider a gross underestimate. Seventeen Ontarians are known to have died. Quebec, the only other province hit hard, had 16 cases and one death, while Alberta reported treating two patients who contracted West Nile outside its borders. This year, health authorities across southern Canada are girding for an assault by the insect world's equivalent of a dirty syringe. An emerging and poorly understood health threat in North America, West Nile put Little, a fit, then 37-year-old electrician in the Lake Erie town of Port Colborne, out of commission for a month.
He doesn't recall being bitten all that often last year, but he won't forget what the virus did to him. For a week last September, Little was so overcome by weakness that he slept as much as 19 hours at a stretch. "The most I could stay up was probably an hour at a time." Then came the excruciating headaches, prompting his girlfriend to take him to the hospital. "I just wanted the pain to go away."
Little was leading an active life, eating well, enjoying regular bike rides with his daughter, Tamara, now 9, and getting out on weekends as the member of a race car crew. Like most of us, he did not fully appreciate the risks of West Nile as the virus moved into the Canadian population for the first time last summer. When he got sick, he had no idea what hit him. Authorities in Ontario were saying West Nile affected mainly the elderly and those with compromised immune systems. Clearly, that wasn't the whole story. "We must remember that disease and fatalities do occur in all age groups," says Harvey Artsob, Health Canada's Winnipeg-based chief of zoonotics diseases (transmitted from animals) and special pathogens. "Anyone in an area where West Nile virus is active is at some risk."
A study of 64 adults in the Toronto area hospitalized because of West Nile, published last week in the on-line edition of the Canadian Medical Association Journal, backs up that conclusion. "Before, the emphasis was, if you're not some old, decrepit person waiting to die, you won't get sick," says Dr. Jim Brunton, one of the study's authors. "That's definitely not true because we've had middle-aged people, even 20- and 30-year-olds, who've gotten sick." What's more, many of the elderly who were affected were physically active, adds Brunton, director of the infectious diseases division in the University of Toronto's department of medicine, and an outspoken critic of Ontario's decision to cut lab staff in 2001.
While that study did not include children, others have found that, for some reason, the young may have an advantage. They don't seem to be "particularly vulnerable," says a fact sheet issued by the Cornell Center for the Environment in Ithaca, N.Y. "Few cases of serious illness," it notes, "have involved children."
Making a diagnosis can be tricky. Little's family doctor suspected the virus, but his hospital physician was almost certain it wasn't West Nile. Medical staff drained fluid from his spine, relieving his headache slightly, did some blood work and sent him home, where he recovered on his own. Two months later the blood tests finally came back showing he'd developed an antibody to the virus - confirming he'd had West Nile. Test results were taking that long, many say, because the response to the outbreak was mismanaged in an overburdened health-care system. Last week, Ontario promised to add 26 technicians so West Nile tests can be done locally, not just in Winnipeg.
Today, eight months after coming down with the disease, Little is strong enough to go to work but still dogged by fatigue. "After an eight-hour day, I pretty much have had it," he says. "I'm exhausted - 38 years old and I'm having afternoon naps again." As someone who's been infected, Little is immune to West Nile, doctors say, but they don't know for how long. Hedging his bets, he'll be taking many of the recommended precautions to ward off bites this year, including getting hooded bug jackets for himself and his daughter. "You just can't take a chance," he says.
For the data-starved men and women in lab coats, predicting the severity of this summer's outbreak is a crapshoot. "I don't want to say anything because I don't know what the truth is," concedes Brunton. "It could be worse, it could be the same, it could be better." It's a common theme. "In 2002, we had the largest mosquito-transmitted epidemic ever documented in North America," says Artsob at Health Canada. "The big question, of course, is why?"
STUDIES SO FAR give just crude estimates, but it seems that about two per cent of residents in West Nile areas get infected. In a city of one million inhabitants, that means 20,000 are exposed to the virus. But 80 per cent of them - 16,000 - never get sick. The others will experience a flu-like illness with such symptoms as fever, headache, body aches and possibly a mild rash or swollen lymph glands. Among that 4,000, roughly 130 will get really sick, suffering so-called neuro-invasive conditions that include encephalitis (brain swelling) and meningitis (an inflammation of the lining of the brain or spinal cord). Symptoms in these cases can include severe headache, high fever, stiff neck, nausea, difficulty swallowing, vomiting, drowsiness, confusion, loss of consciousness, lack of coordination, muscle weakness, profound fatigue and even paralysis. Roughly 10 per cent of these patients die.
To get a better fix on those numbers, researchers at McMaster University in Hamilton are looking for signs of the virus in the blood of 1,500 residents in Oakville, Ont., a particularly hard-hit community between Hamilton and Toronto. Lab results, delayed by the SARS outbreak, won't be ready until the end of June at the earliest, says Susan Elliott, the geographer who designed the survey. "We have no idea what proportion of people have actually been bitten and carry the antibody," she notes. "Is it a big problem or is it a little one? We don't really know yet."
With West Nile, some perspective is useful. While the virus killed at least 18 people in Ontario and Quebec last year, that figure pales in comparison, say, to the 2,000 Canadian fatalities from flu each year, and the 40,000 who die from smoking. But West Nile cannot be brushed off. The virus can paralyze and kill, and it has the potential to overwhelm the health system.
Just look at what Brunton and his colleagues found in seven hospitals in the Toronto area. Among their 64 patients, they noted encephalitis in 55, including 24 who also suffered from a kind of neurological damage called acute flaccid paralysis that causes profound weakness. "It wasn't just, 'I feel tired and weak today,' that sort of thing," explains Brunton. "Some of them had all four limbs paralyzed, some had one leg paralyzed, and some who left the hospital had to use a walker." And some may never make a complete recovery, he notes. Patients in the study took up 1,856 hospital days - an average of almost a month each. As grave as the situation was, though, it wasn't without hope. "A lot of people made very significant recoveries," says Brunton, "but it took a long time to do so."
The list of West Nile's unpleasant consequences is growing. Health Canada says that in 2002, newly recognized symptoms seen in patients in North America included movement disorders, Parkinsonism (characterized by shaking, rigidity and loss of motor control), a polio-like syndrome and muscle degeneration.
DISEASES LIKE West Nile used to fall under the heading of geographic medicine, says Dr. Kevin Kain, director of the Centre for Travel and Tropical Medicine in Toronto. That meant they were restricted to certain areas. "A theme that we've been talking about for at least 20 years, and people are starting to wake up to," says Kain, "is that there are no geographically restricted diseases anymore."
Scientists first identified West Nile virus in Uganda in 1937. Epidemics occurred in Israel in the early 1950s and in '57. The virus popped up in France's Rhone delta in 1962, South Africa in '74, and Romania in '96. Israel's and Romania's outbreaks were particularly large, then just fizzled out. In South Africa, West Nile made about 75,000 people sick, but serious cases involving encephalitis were extremely rare. The latest epidemiological incarnation of West Nile debuted in New York City in 1999. And it does seem more virulent, says Dr. Anthony Marfin, a Colorado-based epidemiologist with the U.S. Centers for Disease Control and Prevention (CDC).
West Nile could have been carried to New York by infected migratory birds blown off course, or perhaps by birds smuggled into the country, part of the illegal pet trade. Possibly, infected mosquitoes found their way on a plane or ship. Once in New York, the virus found conditions particularly good for establishing a foothold in the northeastern United States. A series of mild winters had allowed mosquitoes to flourish, explains Dr. Paul Epstein, an associate director of the Center for Health and the Global Environment at Harvard Medical School. In fact, Epstein expects that global warming will facilitate the spread of many warm-climate diseases to historically cooler parts.
West Nile turned up in birds, mosquitoes, humans and horses in parts of New York, Connecticut, New Jersey and Maryland by late 1999. In all, 62 cases were identified in humans, causing seven deaths, all in New York state. Three years on, in 2002, West Nile was in 39 states and the District of Columbia. They recorded 4,156 cases, including 284 deaths. The CDC expects to see the virus in all the lower 48 states this summer.
Canadians found West Nile in dead birds and mosquito pools for the first time in 2001, in southern Ontario. It reached the human population last year, and has been detected in mosquitoes, birds and horses in Saskatchewan, Manitoba and Nova Scotia, as well as Quebec. Health authorities in British Columbia expect to see infected birds this season.
ALTHOUGH OTHER MEANS, such as blood transfusions and organ transplants, present minor risks, by far the most likely way of getting the disease is through mosquito bites. The linchpin seems to be Culex pipiens, the common northern house mosquito, one of approximately 80 mosquito species in Canada. Early in the season, thirsty females suck in crimson bellyfuls of blood, targeting birds solely. As their contaminated saliva spreads the virus through the avian population bite by bite, other mosquito species - as many as 10 - that feed on both birds and humans become infected. Some of these then spread their viral seed to mammals and people - where it incubates for three to 14 days before causing illness. Infected humans aren't contagious - they can't pass it on to either humans or mosquitoes.
West Nile has been detected in more than 130 species of birds, proving particularly fatal to crows and blue jays. Studies now underway will determine the long-term effect on birds, but there's room for optimism. "We're expecting some populations, at least locally, to dip for a few years," says Audrey Heagy, who monitors avian migration for Bird Studies Canada in Port Rowan, Ont., "and then they'll rebound."
While West Nile can kill horses, cats and dogs don't seem to get sick. Just how many horses have died from the disease isn't known, but Scott Weese, a veterinarian at the Large Animal Clinic at the University of Guelph's Ontario Veterinary College, estimates a few hundred in that province alone. "We saw quite a few two- or three-year-old race horses last year that should have been at the peak of fitness getting quite severely sick," Weese recalls.
The virus can spread in various ways. Last year, Health Canada scientists found it in adult Culex mosquitoes that had hibernated through the winter. When Culex take flight in the spring, the mosquitoes may reintroduce the virus into the bird population. (It's not known whether other mosquito species that spend the winter as larvae can carry West Nile.) And, of course, birds migrating from the U.S. carry West Nile into Canada. The virus spreads to humans once a critical mass of infected birds and mosquitoes is reached. That has tended to be between mid-July and September. But there's some evidence from the U.S. to suggest that human infections could start as early as next month.
As for other risks, blood transfusions tainted with West Nile virus appear to have infected two Canadians, killing at least one in Ontario. While organ transplants have the potential of transmitting the disease, there have been no recorded cases. Last December, Canadian Blood Services directed hospitals to withdraw frozen blood products collected in Ontario between June and October. The agency will continue to stockpile extra supplies until the mosquito season starts, to carry it through the summer. It also hopes a test to screen for the actual virus, and not just antibodies in blood, will be available by July. In any case, Health Canada says, transfusions and organ transplants will continue because their benefits "outweigh the risk of becoming infected with West Nile virus."
Two other, particularly unnerving ways of transmitting West Nile - through breast-feeding and pregnancy - are suggested by just one recent case each, both in the U.S. The breast-fed infant showed no sign of disease and, with the health benefits of breast milk well established, the CDC concludes there's no need for nursing mothers to change their ways. The birth of a child with profound brain damage in New York last December sent up another red flag. "Although the newborn in this case was infected with West Nile virus at birth and had severe medical problems," says the CDC, "it is unknown whether the West Nile virus infection itself caused these problems, or whether they were coincidental."
There is no sure treatment for West Nile, that much is clear. One New York researcher is investigating the potential effectiveness of interferon, a drug used to treat hepatitis C. A vaccine is a possibility, especially as West Nile is similar to the virus that causes Japanese encephalitis, for which a vaccine already exists. Meanwhile, Health Canada has trained lab technicians in most provinces to screen patients, hoping to speed up case identification. Municipalities across the country are broaching the prickly topic of using pesticides to battle mosquitoes. Winnipeg, for instance, has already started its larvicide program and plans to spray malathion in neighbourhoods to kill adult mosquitoes, a controversial practice known as fogging, as a last resort. In Toronto, officials have set aside $1.4 million to battle West Nile this year, and plan to administer larvicide pellets in storm-water catch basins in late June and again in late July to coincide with peak periods of mosquito reproduction. Similarly, the Ontario government has readied $7 million to take the sting out of summer.
Those defensive measures come too late for Susan, a stay-at-home mom, and her husband Philip, a waiter - both of whom requested anonymity to protect their family's privacy. In less than a week last September, Susan, 46, went from enjoying a barbecue on the deck of her home just north of Toronto's downtown core to being consigned to a ventilator for the next 10 weeks. She's still in hospital, she still can't walk, and needs help to get into a wheelchair.
Susan's recollections are vague, but Philip says everybody "was getting eaten alive" on the deck that Sunday night. Just as Susan was going into the house, a mosquito got her on her right foot. Over the next couple of days, pain spread from her right leg to her back and left leg. Her family doctor prescribed an anti-inflammatory drug for arthritis but by Friday, she went to bed feeling ill. Saturday morning, she couldn't get up. "She started screaming that she couldn't move," says Philip.
Now Susan can raise her left leg about 15 cm off the bed and bend her left arm at the elbow. Her right side is weaker. She's making progress each day, but it is excruciatingly slow. "You just don't have a life anymore," she sighs. The prognosis? "Nobody knows," says her husband. "Nobody's willing to venture a guess because that's all it is at this point - guesswork."
Coming so quickly on the heels of the SARS scare, this year's West Nile season bolsters our awareness that we're living in a brave new world of viruses without borders. "I guess the take-home message is that the illusion we're safe from global diseases in Canada should be shattered," says Kain at Toronto's tropical medicine centre. "That doesn't mean we should panic," he adds - it means we need to develop appropriate ways of dealing with outbreaks. And that requires new diagnostic tests, without which doctors are blind to the threat they face. "Knowledge in medicine is being able to determine what someone actually has," says Kain. "After that, things are easier." Just like the living in summer is supposed to be.
Four Habits of the Highly Successful Mosquito
Feast on flower nectar, plant juices, not blood The males have no use for us; the females just need a shot of blood to produce each batch of eggs. Although many mosquitoes gravitate to other animals, they'll settle for humans if we're available.
Don't whine about poor eyesight Mosquitoes can't see well, but they use a keen sense of smell (mainly for the carbon dioxide we exhale) and sensitive heat receptors on their antennae to zero in on us from as far away as 10 m.
Live long and propagate Males die within three weeks, but those pesky females live up to five weeks in the summer, time enough to lay multiple batches of hundreds of eggs, new generations all set to breed and bite within weeks.
Always know where to find stagnant water That's where mosquitoes lay their eggs. Some species are less interested in rural ponds and marshes, actually preferring small pools of water like the ones that collect around household settings - in eavestroughs, the saucers under flowerpots, birdbaths, cans and tires.
As if SARS and West Nile weren't enough...
We've seen how sick passengers aboard airplanes can spread a disease like SARS around the world. Lyme disease, another debilitating ailment threatening Canadians, also depends on air travel, but in a different way. The flightless larvae and nymphs of the tiny blacklegged tick that carries the ailment hitch rides on migratory birds, says Robbin Lindsay, an entomologist with Health Canada's National Microbiology Laboratory in Winnipeg. Once engorged with blood, they fall off, delivering their bacterial baggage to new destinations. Ticks with Lyme disease are on the move this spring, spreading inexorably from their hot zone in the northeastern and north-central U.S. "The overall risk of being infected in Canada is low," says Lindsay, "but it's persistent. These ticks can show up wherever birds can fly."
Lyme disease is caused by Borrelia burgdorferi, a bacterium that infected ticks transmit to animals - and people - by latching painlessly onto the skin. While scientists have found infected ticks across most of southern Canada, human cases have been rare so far - 15 to 40 a year in Ontario, only a handful elsewhere. But the situation could get worse. The U.S. records about 15,000 cases each year, mostly between Minnesota and New Jersey.
The ticks, just the size of a sesame seed, develop from larvae feeding on birds and small animals one year, to nymphs that drink the blood of birds and larger mammals the next, and then, by fall, to adults. Capable of surviving the winter with the disease, they're found in decaying leaves, rotting logs and low-lying vegetation, especially in hardwood forests, brush and overgrown grass. The ticks are particularly prevalent around suburbs, where urban sprawl has pushed out foxes and other predators, leaving an unchecked mouse population for the insects to feast on.
Visitors to potentially infested areas should take precautions - tucking pants into socks and using a repellent containing DEET. At the end of the day, check your body thoroughly for the little ticks. If you find one, remove it with tweezers, grasping it close to your skin and pulling straight out, making sure to extract the embedded mouth parts. It's unlikely a tick will transmit bacteria within the first 36 hours. When it does, symptoms usually appear within a week or two - a rash like a bull's eye around the bite, accompanied by fever, malaise, fatigue, headache, muscle ache and joint discomfort. Unchecked, it can lead to neurological damage. The good news: Lyme disease responds to antibiotics.
Maclean's May 19, 2003