West Nile virus and Mosquito Mania

By | July 5, 2021

Worried about West Nile Virus? Here are the facts about risk and your kids

By John Hoffman

Back in the fall, when the final few mosquitoes were packing up their stingers and making a last buzz, it seemed as if West Nile Watch would die down and disappear from Canadians’ radar screens for a few months. But in fact the cold weather brought a steady increase in the sense of dread over this latest disease scare.

It began in 2001 with the tally and location of infected birds. Then last summer there were daily, even hourly, updates on suspected human cases. It was scary enough as the first deaths were reported, then came the discovery in November that West Nile Virus (WNV) could be transmitted via blood transfusion, prompting the Canadian Blood Services to recall all blood donated in Ontario during the summer months. Another report concerned a pregnant woman in New York State who apparently passed the virus on to her baby. (The child was born with brain damage and experts have not be able to rule out a link to WNV; however, there have been at least three cases of pregnant women with WNV whose babies were born without complications, according to the US Centers for Disease Control.) Meanwhile the count of confirmed cases in Canada kept clicking upward through fall and winter, due in part to the seven-week waiting period for diagnostic test results. Then a study of Toronto patients sparked allegations that public health authorities had underestimated both the spread and the severity of WNV infections.

Now, with mosquito season fast approaching, Canadian parents are wondering what threat WNV poses for their children. Here’s what you need to know.

Kids’ risk is low

First, it’s unlikely your child will get sick from WNV. Data from several jurisdictions show that, thus far, the disease rarely strikes young people, or, to be more accurate, it seldom makes them ill. At press time in March, the numbers from Ontario were 305 confirmed and 82 probable cases, and 11 deaths in 2002. The average age was 57, and none of the patients was under 14. The proportions were similar in Illinois, which experienced the most severe outbreak in 2002. Statistics from the Illinois Department of Public Health show that of 877 confirmed or suspected cases of WNV, only 18 were in children 14 or under. Most of the 62 Illinois residents who died were over the age of 60. In other words, with respect to WNV, parents should be more worried about their children’s grandparents than the children themselves.

Infected doesn’t mean sick

Although some people have become severely ill with WNV, experts say that most people who get WNV probably won’t even know it. “They will have either no symptoms or mild flu-like symptoms,” says Allison McGeer, an infectious diseases specialist at Toronto’s Mount Sinai Hospital. “The people for whom West Nile is the greatest problem are the elderly, and adults with compromised immune systems,” such as those with leukemia or who have undergone organ transplants. However, younger, healthy adults have also been affected. At present little is known about the very small number of children who get sick from WNV, although health authorities are studying the 18 Illinois children who contracted the disease. So why does this potentially deadly disease tend to spare children? No one knows for sure, but McGeer says it’s common for diseases to have different manifestations in different age groups.

The urban factor

One apparent oddity is that WNV strikes city dwellers most often, although we think of mosquitoes as a rural or cottage country phenomenon. This is because the mosquito that does most of the spreading — Culex pipiens or Northern House mosquito — likes to live near human habitation, according to Fiona Hunter, a medical entomologist at Brock University in St. Catharines, Ontario. “They prefer to breed in rain barrels or other small containers of standing water that are commonly found around houses.” Culex pipiens doesn’t bite humans, only birds, but the virus is then transferred from bird to human by other mosquitoes.

The advice about avoiding WNV boils down to, “Don’t get bitten.” In practical terms, that’s hard to do, especially for people who love the outdoors. However, we can all do our bit to reduce the number of breeding grounds for Culex pipiens on our properties. “Getting rid of pockets of standing water in bird baths, clogged eavestroughs or anywhere else rainwater collects, would help reduce the spread of the virus,” says Hunter.

Hunter expects to see the bird population developing some immunity over the next several years, which should help decrease the impact of West Nile. Whether or not that proves to be the case, in the short term — especially until we learn more about this nasty disease — we can expect to hear lots more about West Nile Virus.

West Nile by the Numbers

* Virus first identified in the West Nile region of Uganda in 1937.
* First appeared in North America in 1999 in New York City.
* First confirmed Canadian case of an infected bird was in southwestern Ontario in 2001.
* Most confirmed Canadian human cases in 2002 were in Ontario (305 as of press time).
* An estimated one in 20 people infected with WNV will develop symptoms including headache, body aches, fever and, sometimes, a rash. An estimated one in 150 will develop more serious illness.
* The incubation period is three to 14 days.
* WNV rarely causes noteworthy illness in children.
* Most Ontario cases in 2002 occurred in August and September, after prime mosquito season. That’s because the virus has to spread among birds first.

The Nursing Factor

Last fall, news reports implied that a baby in Michigan had contracted West Nile Virus by breastfeeding. The mother had acquired WNV via a blood transfusion shortly after giving birth. Although viral genetic material from WNV was detected in her breastmilk, it was never confirmed that the virus could be transferred by breastmilk. Here are the facts:

* The woman recovered completely.
* The baby never got sick at all.
* Researchers tried to grow the virus in the mother’s milk but were unable to do so because the breastmilk kept killing the viral genetic material.
* Even if the mother did transfer the virus to her baby, she would have also transferred antibodies to WNV, which would have protected the child.
* For most infections, including WNV, the best protection a woman can give to her baby is to continue breastfeeding.

To learn more:
These sites can help you keep up with WNV developments this season:

Health Canada: hc-sc.gc.ca/english/diseases/west_nile.html

US Centers for Disease Control: cdc.gov/ncidod/dvbid/westnile/index.htm

May 2003