People in North America may be experiencing the virus differently because the strain here may be more virulent than the predominant strain in Africa.
How is it spread?
The virus is normally spread by birds and the mosquitoes that
bite migrating birds - crows seem to be affected the most. WNV has recently
killed healthy horses. Humans get WNV from a bite from an infected mosquito.
It is not contagious, but it has been discovered that the virus can be
transmitted between people via blood transfusions and breast milk
and organ transplants. There is no evidence that you can get infected
from handling infected animals, live or dead, but you probably should wear
gloves to handle suspected animals. An increase in dead crows appears to
predict an increase in infection rates in mosquitoes, followed by an increase
in human infections.
Symptoms of WNV:
Mild cases show flu-like symptoms, including fever, headache and body aches. Some people may also develop a mild rash, or swollen lymph glands.
The virus can cause the more serious West Nile neurological syndrome, which can result in weakness, paralysis, confusion, coma, and rarely death. It takes 3 to
6 days to show signs of the disease, and some people have no symptoms. There
is no treatment for the virus, so prevention is important.
Risk:
Children appear to have the lowest risk; older people seem most susceptible.
Most people recover fully, and there is only 1% risk of death, with older people
most at risk. In about 1% of cases, West Nile virus can cause a more serious
illness called West Nile neurological syndrome, which can have serious complications,
including weakness, muscle degeneration, brain damage, paralysis, coma or death.
In the Canadian Medical Association Journal (2002), it was reported only 25% of previously healthy people admitted to hospital with the virus (2002) were able to live independantly upon release.
Some patients were gravely ill with West Nile, and others had symptoms so mild they didn't know they had it. It's possible the virus strain in North America may be more virulent than the strain in Africa.
Only 20% (1 in 5) of people who become infected actually show symptoms. These are:
Species at risk:
Humans, mosquitoes, birds (especially crows), dogs, cats, squirrels,
horses, sheep, cattle, apes, wolves, reindeer and mountain goats. Dogs and cats
get WNV but without extensive illness or even symptoms. Only humans and horses
are at risk for encephalitis, which can be fatal.
How can it be treated?
There is no known treatment. Full recovery is the norm.
How can it be prevented?
Protect yourself from being bitten by mosquitoes! Use repellants
and wear clothing that covers you. Try to eliminate standing water (5-7 days
old) in bird baths, wading pools, eavestrough, old tires, patio furniture and
pool covers that mosquitoes can breed in. Hot, dry weather will cause an increase
in mosquito breeding, which will increase the spread of WNV.
Spraying or not?
Experts had said that spraying mosquitoes with malathion would
harm more people than the virus. There is evidence this chemical is not effective
in the long term and causes a variety of health problems such as difficulty
breathing in humans and hormone disruption and malformed limbs in frogs. Although
the links cannot be proven, more than 90% (11 million) of the adult lobsters
in Long Island Sound mysteriously died not long after spraying was done.
Some Larvicides such as Bti are considered safer but are very expensive. Municipalities are unwisely rushing to kill larvae or mosquitoes to try to keep voters happy.
WNV is a reportable disease in Ontario. Canadian Blood Services can test blood donations for the first time; 14 rejected donations in 2003 probably saved many lives. Some municipalities sprayed in spite of warnings about the effects of chemicals and larvicides on health.
Read more about mosquitoes, repellants, other diseases spread by mosquitoes.
1937: West Nile virus (WNV), a flavivirus, was first isolated in Uganda. The disease is common in parts of Africa, Europe and Asia.
1999: WNV was diagnosed in North America, infecting 62, 55 in New York City and 7 died - including a Canadian tourist. All the victims were over 68 years of age. The virus was found in a single dead cat.
2000: Only 21 were infected in New York, Connecticut and New Jersey; 2 died. Canada still had no cases, but was using a system of 600 "sentinel chickens" near the U.S. border, since chickens don't die of the virus, but develop antibodies that can be tested. By autumn WNV had been identified in a dead bird in southern Ontario.
2001: WNV survived the mild winter and arrived in Canada via migratory birds such as crows (dead birds near the border tested positive for the virus). 19 cases were confirmed with 2 deaths. Tests confirmed WNV in 9 mosquito pools and 128 dead birds, mostly in Ontario. In the U.S. 66 were infected, 9 died along the east coast.
2002: WNV spread with 2,000 seeking treatment, 416 cases "probable and confirmed" concentrated in Ontario and Quebec, and 20 deaths. Ontario had 307 confirmed (1 travel related), 85 probable cases, and 17 deaths (3 directly attributed to the virus). In Toronto, about 1,000 sought treatment, with 292 confirmed cases, 64 severely ill, and 10 deaths. Quebec had 16 confirmed cases; Alberta had 2 (both travel related).
555 dead birds had confirmed WNV, 3 in Nova Scotia, 139 in Quebec, 88 in Manitoba, 44 in Saskatchewan, the rest in Ontario (none in PEI, NB, AB, BC). 315 mosquito pools tested positive.
The U.S. had 4,161 cases, with 277 deaths in 39 states and D.C - the worst mosquito-borne epidemic in U.S.history.
2003: 1,481 cases (852 probable 462 confirmed). The prairies were hardest hit with over 1,000 cases. Saskatchewan cases were up sharply with 947 infections with 7 deaths. Manitoba and Ontario both had 2 deaths. Cases in Ontario and Quebec were down. Nova Scotia, New Brunswick, British Columbia and the Yukon reported human cases, but it was believed they were contracted during travel.
2004-2005: There was little West Nile virus activity. In 2004 there were 25 cases in all of Canada, and 224 in 2005. Experts disagree about the reason, but possibly weather conditions or humans becoming immune.
2006: 151 total cases Manitoba: 50, Ontario: 42, Alberta: 39, Saskatchewan: 19, Quebec:1. There were 2 deaths nationally. (The U.S. had 4,269 cases, 177 deaths.)
2007 reported cases: 2,215 Saskatchewan: 1,285 (4 deaths), Manitoba: 542 (3 deaths), Alberta: 93, Ontario: 2.