Public Health Biting questions

Public Health Biting questions
Posted on 04/10/2016

As a mosquito species known to transmit Zika virus ranges north, is there a threat to Lane County?

By Diane Dietz

The Register-Guard


This unseasonably warm spring may bring an early awakening to wrigglers and pupae now in rain barrels, pet bowls and riverside marshes — and put newly hatched and hungry mosquitoes on the wing.

“As soon as the temperature reaches 62 degrees, mosquitoes start hatching,” said Emilio DeBess, the Oregon Health Authority’s expert on mosquito-borne illness. “As soon as they hatch they need a blood meal so they can lay eggs.”

In recent decades in Oregon, this annual rite has been a mere nuisance — requiring no more than a swift slap. But in the age of climate change-driven migration of diseases such as Zika, West Nile, chikungunya and dengue fever, the awakening of mosquitoes each spring is increasingly sinister.

In the past week, the Centers for Disease Control and Prevention revised its range map for mosquitoes capable of transmitting the birth defectlinked Zika virus. Before the revision, the terrain marked in shadow on the map was in the Deep South. On the new map, the shadow ranges to New Hampshire, Minnesota — and up the West Coast north of San Francisco.

“You would be a fool to think they’re not going to come here,” Lane County health officer Patrick Luedtke said. “You’d also be a fool to prognosticate when they will come here.”

This doesn’t mean the mosquitoes will necessarily be carrying Zika when they arrive; it means they could be, the CDC hastens to add.

At a recent White House summit on the Zika virus, CDC officials looked out across the nation and saw a patchwork of local mosquito control districts that leaves many communities ignorant about whatever mosquitoborne illness might be coming their way. Lane County is an unmonitored patch of the map since county government eliminated its vector control efforts about 30 years ago.


“There’s a lot of water this year, so this may be a good year for mosquito activity, especially if it gets warm very quickly and they hatch,” DeBess said. “It’s important to keep on reminding ourselves that we need to protect ourselves against mosquito bites,” he said.

Zika symptoms

Zika is just the latest mosquito-borne illness to capture the world’s attention. The virus is associated with a severe birth defect — microcephaly — that develops while a fetus is in the womb. The fetus’s head stops growing because the virus interrupts brain development so the brain and the head don’t get bigger, according to the CDC. An affected newborn emerges with a tiny head, which makes his or her regular-sized features look odd.

Researchers have yet to prove that it’s Zika that arrests brain development, but areas of Brazil where the virus is strongest experienced a spike in microcephaly. Since October, about 4,000 Brazilian babies have been born with the affliction, compared with about 150 in the previous year.

“We know there’s an association,” DeBess said. “It’s been found in the brains of children who have died of microcephaly.

“You’ve got to take it very seriously, right?”

The governments of Ecuador, Colombia and El Salvador have advised women not to get pregnant.

In adults, the virus can cause other temporary mild symptoms, such as a fever, rashes or joint pains that are treated with rest. Zika — first identified in Uganda — spreads like wildfire wherever the mosquito species Aedes aegypti and Aedes albopictus live.

After sweeping through countries in Southeast Asia and the Pacific Islands, the virus was detected in the Americas, in Brazil, in May 2015. A year later, it’s been found in 33 Latin American countries.

“As the climate warms, the Aedes aegypti and Aedes albopictus are ranging ever farther north, drawn by longer warm summers, longer growing seasons and shorter, milder winters,” said University of Oregon research associate Chris Holzapfel, who, with her husband, UO professor Bill Bradshaw, studies mosquitoes.

The longer growing season “provides more time for pathogens to complete their life cycle within the mosquito so they can be transmitted by that mosquito, not just carried by it,” Bradshaw said.

Warmer summer nights “increase the length of (mosquito) biting behavior,” Luedtke said.

Aedes aegypti, the most effective known Zika carrier, has been found in the past two years at Menlo Park near San Franciso.

This mosquito — commonly called the yellow fever mosquito — is capable of transmitting several viruses, including dengue fever and chikungunya, which causes high temperatures and joint pain.

Aedes albopictus — aka the Asian tiger mosquito — is as far north as Los Angeles. It’s “very, very vigorous. It’s not a mosquito to be taken lightly,” Holzapfel said.

In March, DeBess met with the Jackson
County Vector Control District to initiate surveillance for the southern intruders.

One especially disturbing idea to public
health officials is that the Zika virus would hop into a species of mosquito such as Culex pipiens that’s common in North America, including in Oregon.

Tropical or subtropical diseases carried by mosquitoes seem a long, long way from the Pacific Northwest. Mosquito- borne malaria, for example, kills 800,000 people a year, mainly children in Africa.

But historically, mosquitoes brought death to thousands of people right here in Western Oregon.

“The Indians called the Willamette Valley the ‘Valley of Death’ because of the malaria,” Bradshaw said. Malaria hitched a ride to the New World via European settlers and spread across the continent. Malaria outbreaks, carried by the Anopheles freeborni mosquito, in the early 1830s killed 90 percent of about 14,000 Oregon Indians who lived in the lower Columbia and Willamette river valleys, according to Oregon Historical Society documents.

“A child dies from malaria every minute in sub-Saharan Africa,” Bradshaw said. “(Islamic State fighters) are real pikers by comparison.”

Anopheles freeborni still is biting valley dwellers. It’s the most common two-winged picnic guest — with piercing-sucking mouthparts — found all over
Lane County. All that it needs in order to become a menace is a source of a parasite to transmit.

“People do travel a fair amount, and there’s a lot of movement from Central and South America in the United States that potentially, if one person comes to Oregon infected, and a mosquito bites (and spreads malaria), we could find ourselves in a significant problem,” DeBess said.

Malaria wouldn’t be as much trouble, however, as Zika or some other virus, Bradshaw said.

“Anopheles cannot give you malaria unless it has bitten someone who has malaria,” he said. “Viruses, on the other hand, travel through the mosquito, through the (mosquito’s) ovarian wall, into the ovaries, and infect a female’s eggs, so that when she lays her eggs, her daughters are already capable of spreading that virus,” he said.

Surely, not here

Viruses can move quickly. West Nile virus, for example, visited Egypt before landing in Queens, N.Y., in 1999, when 62 people were sickened (seven died) — marking a single dot on the U.S. map. The virus, which causes fever, rash and swollen glands, began spreading across the Midwest, but
Lane County officials were doubtful it would come the full 2,500 miles to the Northwest coast.

In August 2002,
Lane County Public Health Program Manager Karen Gillette told Register-Guard readers not to worry. “This issue has generated a degree of disquiet and concern,” she said. “At this point we’d like the public to know ... that the virus has not been found in the Western coast states and is not likely to occur anytime soon.”

Twenty-three months later, Oregon got its first
human case. Oregon has seen outbreaks most years since then. The biggest was in 2006, with 73 cases. The state saw 16 human cases in 2013, eight cases in 2014 and one in 2015.

For most people, West Nile disease is mild, but every year some people die from it. Last year, California reported 730 West Nile cases with 45 deaths, according to the CDC.

For public
health officials, West Nile was a dress rehearsal, said John Parrott, a Master Gardener who Lane County hired during summers until 2013 to trap and test mosquitoes for the virus. Parrott said he never found a West Nile-bearing mosquito in Lane County, but he’s sure they’re here. “It’s billions and billions of mosquitoes and one trapper, half-time for 10 weeks,” he said.

Vector control

In 2015, some 59 batches of mosquitoes from a half-dozen Oregon counties tested positive for West Nile virus. No virus-laden mosquitoes were found in
Lane County, but only because “Lane County Public Health is not currently collecting or testing,” the county makes clear on its website.

Thirteen Oregon counties have launched — or voted for — mosquito control districts, including the state’s most populous counties, Multnomah, Washington and Clackamas.

Mosquito control districts capture, identify and deliver mosquitoes to an Oregon State University lab for testing. Some of the districts offer free home visits to identify and eliminate mosquito breeding grounds. The agencies distribute mosquitoeating fish for ponds or livestock tanks. Some district personnel are trained to put larvicide in ponds or fog the air to kill adult mosquitoes —
services that could avert a public panic.

“The last thing you want is for people to start buying pesticides over the counter ... and spraying without having any knowledge,” Parrott said.

In Clackamas
County, homeowners pay 2.5 cents per $1,000 of assessed value for mosquito and other pest control (or $5 a year for the owner of a $200,000 house). Jackson County homeowners pay 4.29 cents per $1,000 annually (or $8.58 a year for a $200,000 house).

For similar service in
Lane County, you’d have to look back to the 1970s, when the county conducted annual summer mosquito spraying.

Low-flying aircraft sprayed around lakes — Fern Ridge, Cottage Grove, Dorena — and sloughs at the confluence of the McKenzie and Willamette rivers and flooded fields west and south of Junction City. By 1979, the
county stopped, because of fears the pesticides were harming fish.

Since then, whenever the subject arose,
Lane County officials have taken a wait-and-see approach.

With the arrival of Zika, CDC Director Tom Frieden at the recent White House summit urged state and local agencies to prepare for mosquito season, “to protect our next generation from this newly discovered threat.”

Luedtke, the
Lane County health officer, said that “it would be reasonable to have some sort of ongoing surveillance system. Then, when all hell breaks loose, you’d have a little bit of infrastructure in place. It’s a lot easier to make it bigger fast.”

But Jeff Lang, supervisor at
Lane County government’s environmental health unit, said he’s not expecting any local move against mosquitoes.

“That would be a decision made by the (
county) commissioners and the public at large based on some real evidence of Zika or West Nile virus — and to date there’s been none, so I don’t see any pressure that way currently. If we started seeing some outbreaks in counties surrounding us from the south, the pressure might increase to do something — but until that happens, I don’t see anything happening,” he said.

Said Faye Stewart, chairman of the
Lane County Board of Commissioners: “If a health concern arises or is brought forward by our experts, we will discuss and address that concern publicly.”

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