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Issues Of The Environment: Protecting Yourself From Zika And West Nile During Mosquito Season

Jul 13, 2016

Mosquito
Credit Wikipedia Media Commons / wikipedia.org

Summer brings hordes of mosquitos and several diseases along with them, including the Zika virus.  In this week's "Issues of the Environment," WEMU's David Fair talks to Emily Toth Martin, assistant professor of epidemiology at the University of Michigan School of Public Health, about ways to protect ourselves from Zika, West Nile virus, and more. 


Overview

   *   The Zika virus is an emerging mosquito-borne disease that has caused miscarriages and severe, permanent brain defects and damage in unborn babies. So far in 2016, four cases of Zika virus have been found in Michigan, two of them in Washtenaw County.  All are travel related.  Pregnant women are advised not to travel to areas where Zika is active and to avoid sexual contact with those who travel to Zika-infested areas.

   *   For now, the mosquito that transmits Zika (also dengue fever and chikungunya.) appears to be unable to survive in Michigan due to the non-tropical climate.

   *   Researchers are concerned that climate change could allow the Zika carrying mosquitos to expand their range, and that means they could potentially reach Michigan.  In addition, the recent spread of Zika may be in part due to warming temperatures, which allow the mosquito to quickly breed and the population to explode.

   *West Nile Virus has been detected in mosquitos in Oakland County this summer.  There have been no reported cases of West Nile in humans, to this point.  A hot, dry summer provides the conditions that may allow for a more widespread outbreak of West Nile than in recent summers. 

Zika Risk in Michigan - 2016

Four people in Michigan have shown signs of infection from the Zika virus, state health officials said today. "None of them were acquired locally," said Jennifer Eisner of the Michigan Department of Health and Human Services.  "All of them were travel-related."  Eisner didn't have details on the patients or their current conditions but said none of them were pregnant women, a population that raises special concerns because the virus has been linked to miscarriages and birth defects.

The increased Zika caseload comes at the start of the summer travel season and as the Centers for Disease Control and Prevention reports 544 cases in the continental U.S. and another 832 in U.S. territories.  The CDC warns that the virus is spreading throughout the Caribbean and from Mexico south to Brazil.  "We would recommend that people check the CDC website and look up information about their travel destination and the precautions they should take to protect themselves from Zika virus," said CDC spokeswoman Candace Hoffmann.

The virus is mostly commonly transmitted through bites from specific types of mosquitoes, which are typically found in the tropics.  "We have not found the mosquitoes that carry the Zika in Michigan, " Eisner said, adding Michigan's cold winters may be too harsh for them to survive.

The Zika virus was first identified in humans in 1952 in Uganda, according to the World Health Organization. Last year, it was found in Brazil, which will host the 2016 Summer Olympics.  People who get it may experience fever, rashes, muscle aches and joint pain. "Most people don't even know they are significantly sick," said  Dr. Marjorie Treadwell, a professor of obstetrics and gynecology at the University of Michigan Medical School.  The bigger danger, Treadwell said, is the risk the virus poses to pregnant women. "The issue with Zika is really the effects on the fetus," Treadwell said. "Even if that child doesn't die from the condition, they are going to have severe, potentially life-long, effects."  Treadwell said the virus can cause microcephaly, a condition that halts brain development in a fetus, limiting its potential for the rest of its life.  "The smaller the brain, the worse the impact on your long-term quality of life," Treadwell said.

"Pregnant women should not travel to areas where Zika virus is spreading and if they have to travel, we would recommend that the they talk to their health care provider first and strictly follow steps to prevent mosquito bites," Hoffmann said.  The virus also can be sexually transmitted, raising concerns for women trying to get pregnant, Hoffmann said.  "Both they and their male partners should talk to their doctor or healthcare provider before they travel," she said.

At least 157 pregnant women in the continental United States — and 122 in its territories — have tested positive for the virus,  according to a CDC report posted on its website Friday.  The report notes that all of the currently reported cases in the continental United States are travel-related, not locally acquired.

Travelers Beware

The Centers for Disease Control and Prevention urges people traveling to places where Zika is spreading to take precautions to avoid Zika exposure such as:

   *   Wear insect repellent containing at least 20% DEET.

   *   Wear long sleeves and pants, socks and hats to limit exposed skin.

   *   Consider using clothing and gear treated with Permethrin, an insecticide.

   *   Seek accommodations with air conditioning or good screening to keep out insects. 

Effects of Zika

Zika is a disease that seems to keep evolving, and escalating. The mosquito-borne virus many thought would be a milder version of dengue has turned out to be a serious neurological threat, causing the birth defect microcephaly (which often includes brain damage), and Guillain-Barré, an autoimmune disorder that attacks the nervous system.  It’s also been linked to inflammation of the brain and spinal cord, and it may be that the virus specifically targets nerve cells.

Though Zika is not a super-new virus—it was first discovered in 1947 in Uganda’s Zika forest—the scope and seriousness of this outbreak is unusual in the disease’s history.  For the first 60 years, scientists were aware of it, the virus just caused “mild illness across equatorial Africa and Asia,” according to a timeline of Zika published by the World Health Organization.  “Human Zika virus infection appears to have changed in character while expanding its geographical range,” the WHO paper concludes.  “The change is from an endemic, mosquito-borne infection causing mild illness across equatorial Africa and Asia, to an infection causing, from 2007 onwards, large outbreaks, and from 2013 onwards, outbreaks linked with neurological disorders.  Zika, in most cases, is a very mild disease.”

Zika is an epidemic on delay, with the worst of the outbreak’s effects trailing in the wake of the mosquitoes that carry the virus.  Which means the problem is not the suffering inflicted by the initial infection; there probably won’t even be any suffering for most, since four out of five people never experience any symptoms.  The danger is what might happen later—the fetuses that get microcephaly, the people whose brains and spinal cords swell and possibly sustain damage, the people temporarily paralyzed by Guillain-Barré, the ones who die because the Guillain-Barré stops their breath (as it can sometimes do) and they’re unable to get to a hospital with a respirator.

In Brazil, [there have been] more than 7,000 cases of microcephaly or central nervous system malformation reported between October 2015 and early April 2016.  And as the summer approaches, the Aedes aegypti mosquito is expected to gallop north, with Zika riding along.  With no vaccine on the near-term horizon (Espinal says one is slated to go to clinical trial in September), the only real option to get out in front of the outbreak is mosquito control, which is difficult.  There are at least 15 companies or academic groups around the world trying to create a vaccine.

Zika Damage Found at All Stages of Pregnancy

Fetuses are vulnerable to many diseases that infect the mother, but for most infections long-lasting, devastating, or deadly impacts are more common in the early trimesters of pregnancy, with the impacts being less severe or nonexistent in the final trimester.  Although with Zika the risk for miscarriage or the complete retardation of brain development is highest in the first trimester, the risk of severe outcomes appears to be great at any stage of pregnancy.  Babies exposed to Zika in the later stages of pregnancy may not be as likely to show outward signs of brain abnormalities (such as microcephaly), but there is alarming evidence that when mothers are infected, catastrophic brain damage may occur at any time prior to delivery, and possibly even after birth.  Researchers are predicting a future epidemic of mental illness related to Zika outbreaks because of the permanent brain damage that occurs in utero.  Doctors are advising American women who are pregnant or may become pregnant not to travel to regions where Zika is active.  In some countries where Zika is epidemic, women are being advised to avoid pregnancy. 

Zika Escalating and Expanding Range with Climate Change

Zika, the global public health emergency involving deformed babies emerged in 2015, the hottest year in the historical record, with an outbreak in Brazil of a disease transmitted by heat-loving mosquitoes.  Can that be a coincidence?  Scientists say it will take them years to figure that out, and pointed to other factors that may have played a larger role in starting the crisis.  But these same experts added that the Zika epidemic, as well as the related spread of a disease called dengue that is sickening as many as 100 million people a year and killing thousands, should be interpreted as warnings.

Over the coming decades, global warming is likely to increase the range and speed of the life cycle of the particular mosquitoes carrying these viruses, encouraging their spread deeper into temperate countries like the United States.  Aedes aegypti is present across the southern tier of the United States.  Brief outbreaks of dengue have occurred recently at the warmest margins of the country, and one is underway in Hawaii.  But with pervasive window screens and air-conditioning, the risk of disease transmission is far less for most Americans than for people in poorer countries.

Coming to Michigan?  The mosquito does not thrive in areas with cold winters.  Some research suggests that continued climatic warming could allow the mosquito to colonize more of North America in coming decades, though how much of a disease risk that would represent is anybody’s guess.  The yellow fever mosquito competes with a cousin, the Asian tiger mosquito, that has also colonized the United States and is more tolerant of cold weather.  Whether one would beat out the other in a hotter climate is unclear.  Likewise, it is unclear how effective the Asian tiger mosquito might become at transmitting Zika or dengue viruses.

With rising temperatures, “You’re actually speeding up the whole reproductive cycle of the mosquitoes,” said Charles B. Beard, who heads a unit in Fort Collins, Colorado, studying insect-borne diseases for the Centers for Disease Control and Prevention in Atlanta.  “You get larger populations, with more generations of mosquitoes, in a warmer, wetter climate.  You have this kind of amplification of the risk.”

Several experts said in interviews that a main reason for the disease outbreaks was most likely the expansion of the number of people at risk, through urbanization, population growth, and international travel.  They see the changing climate as just another stress on top of a situation that was already rife with peril.  While they do not understand to what degree rising temperatures and other weather shifts may have contributed to the outbreaks, they do understand some of the potential mechanisms.

The mosquitoes mostly live on flower nectar, but the female of the species needs a meal of human blood to have enough protein to lay her eggs.  If she bites a person infected with dengue, Zika, or any of several other diseases, she picks up the virus.  The virus has to reproduce in the mosquito for a certain period before it can be transmitted to another person in a subsequent bite.  The higher the air temperature, the shorter that incubation period. Moreover, up to a point, higher temperatures cause the mosquitoes to mature faster. 

Other Mosquito-borne Diseases in Michigan

Mosquito-borne disease probably have been present in Michigan since before the arrival of European settlers and in the early years they created many more serious interruptions to daily activities than they do now.  Mosquito-borne diseases are not as prevalent in Michigan today as many other pathogenic infections, but the emotional stress associated with their occurrence and the media publicity that inevitably has been associated with them create intense public concern that must be dealt with by health professionals.

West Nile Virus (WNV) -  Thus far in 2016 there have been no reports of WNV in Washtenaw County, and none were reported in 2015 or 2014.  However, there was an uptick in occurrence in 2013, and in 2012 there were a handful of cases and one death, so the threat is there. 

West Nile (WN) virus was first reported in the United States in 1999.  It has since spread throughout much of the U.S. Transmission Cycle: West Nile virus exists primarily as an infection of bird populations is transmitted from bird to bird by several species of mosquitoes.  Humans become infected through the bites of mosquitoes which have previously fed on birds carrying the virus.  The birds most commonly associated with WNV in the U.S. are members of the Corvid family (Crows and Blue Jays).  Mosquitoes serve as primary vectors of WN virus.  [Several species of mosquitos that occur in Washtenaw County can transmit WNV.]

The risk of getting West Nile encephalitis is limited to persons in areas where virus activity occurs, and the risk is higher in persons 50 years of age or older.  The chances you will become severely ill from any one mosquito bite are extremely small.  Even in areas where mosquitoes do carry the virus, very few mosquitoes are infected.  Most people infected with West Nile virus have no symptoms of illness, but some may become ill 3-15 days after the bite from an infected mosquito.  Studies have shown that about 1 in 4 infected persons will experience mild illness with fever, headache, and body aches, sometimes with a skin rash and swollen lymph glands.

Less than 1% of people who get bitten and become infected with West Nile virus will develop a severe illness like encephalitis or meningitis.  More severe infection may be marked by headache, high fever, stiff neck, disorientation, convulsions, muscle weakness, and paralysis.  In a few cases, mostly among the elderly, death may occur. 

Eastern Equine Encephalitis (EEE) - Eastern equine encephalitis (EEE) virus causes acute encephalitis in horses and man.  The clinical disease is severe with a case fatality rate of 50 to 75 percent (90 to 95 percent in horses).  The case fatality rate is especially high in children.  The disease occurs in horses each summer along the Gulf Atlantic coasts as well as in such states as Massachusetts, New York, New Jersey, Maryland, and Michigan.  Human cases are rare.  Most human cases in Michigan have been in the southern Lower Peninsula.  Eastern Equine Encephalitis occurs regularly in Michigan horses.  For more information on EEE Horse Cases in Michigan by County, click here.  

    *Transmission Cycle: EEE virus is maintained in nature through a cycle involving primarily the freshwater swamp mosquito Culiseta melanura and many species of birds.  Mosquitoes which feed on both birds and mammals are responsible for transmitting the disease to horses and humans. Horses, and probably humans, rarely develop viremia high enough to infect mosquitoes. Horses and humans are considered dead end hosts not involved in the cycle of transmission.  Human and Equine cases usually appear relatively late in the season.  Mosquito Vectors: Eastern equine encephalitis virus has been isolated from several species of mosquitoes.  The swamp-breeding Culiseta melanura, the summer flood-water breeder Aedes vexans, and the cattail mosquito Coquillettidia perturbans are probably most important, and seems to be the major vector of EEE to horses and humans in Michigan.  Cq. perturbans breeds prolifically in permanent bodies of water with emergent vegetation such as cattails.  These mosquitoes are relatively strong flyers and may migrate some distance from their breeding area.  Peak feeding occurs at dusk and dawn.

Jamestown Canyon Virus- Jamestown Canyon is an “emerging” disease, possibly expanding with the increasing deer populations in many regions of North America. The first recognized case of primary encephalitis due to Jamestown Canyon virus was seen during 1980 in an eight-year-old girl living in rural southwest Michigan.  Subsequent human infections with JC virus have been recognized from Michigan, New York, Wisconsin, Indiana, Illinois, Ohio and Canada.  

    *Transmission Cycle: With Jamestown Canyon, the white-tailed deer is the most important amplifying host.

LaCrosse Encephalitis - During the past several years there has been increasing recognition that LaCrosse represents a serious and growing infectious disease problem in the United States.  In many years, LaCrosse accounts for more human disease than SLE, WEE, and EEE combined.  The disease is most prevalent in the midwest and mid-Atlantic states.  Unlike the other arboviral encephalitides that occur in the U.S., relatively few deaths have been associated with LaCrosse virus.  The natural transmission cycles of LaCrosse virus involves mostly small mammals, such as squirrels, chipmunks, field mice, and rabbits as the primary vertebrate hosts and mosquitoes of the genus Aedes as the vector.  The primary vector of LaCrosse virus is Aedes triseriatus.  This species is the most widely distributed tree hole mosquito in North America.  Adults normally found in deciduous forests and woodlots, although they may become serious pests in residential areas near wooded localities and tire piles.

Dog Heartworm - Dog heartworm (Dirofilaria immitis) appears to be a relative newcomer to Michigan, although it has been a major problem in the southeastern United States for many years.  The severity of the disease symptoms in dogs is highly variable, depending upon the intensity of infection, the age, breed, and health of the animal, and a variety of other factors.  Transmission occurs only through the bite of a mosquito and involves a rather complicated cycle of development.  Approximately one quarter of the species of mosquitoes known to occur in Michigan are biologically capable of transmitting dog heartworm.

Malaria - Hundreds to thousands of cases of malaria continue to be reported from the U.S. annually.  With the continuous reintroduction of malaria parasites each year infection of native Anopheles species mosquitoes and subsequent local transmission remains a possibility.  Cases of local transmission have occurred in Michigan as recent as 1995. 

Prevention of West Nile (and Other Diseases)

*   Mosquitoes need water in which to lay their eggs, so eliminate standing water around your home and yard.  Get rid of old tires, tin cans, buckets, drums, bottles or any water-holding containers.  Fill in or drain any low places (puddles, ruts, etc.) in the yard.  Keep drains, ditches, and culverts free of weeds and trash, so water will drain properly.  Empty plastic wading pools at least once a week and store indoors when not in use.  Unused swimming pools should be drained and kept dry during the mosquito season.  Change the water in pet dishes, horse troughs, birdbaths and plant pots or drip trays at least once each week.

*   Use personal protection measures to prevent mosquito bites.  Wear long sleeves, long pants, shoes and socks.  Wear insect repellent containing DEET, picaridin (KBR 3023), or oil of lemon eucalyptus (p-menthane 3,8-diol or PMD).  Whenever you use an insect repellent, be sure to read and follow the label directions!  Spray clothing with repellent because mosquitoes may bite through thin clothing. Wash repellent off after coming back indoors.

*   August and September are the months of greatest risk to humans for becoming infected with WNV in Michigan.

*   High numbers of dead birds can indicate that the virus is active in a particular area, so report any dead birds you find.  Call the Washtenaw County West Nile Virus information Line at (734) 544-6750 to report dead bird(s). 

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— David Fair is the WEMU News Director and host of Morning Edition on WEMU.  You can contact David at 734.487.3363, on twitter @DavidFairWEMU, or email him at dfair@emich.edu