Defeating Zika - More Common Sense, Less Toxic Chemicals

Am I the only one that thinks the mosquito populations have skyrocketed this season?! All the rain is good for the garden, and unfortunately great for mosquitos. Uugh. I confess to moments where I thought about dousing my whole yard with insecticide products stamped with gigantic skull-and-crossbones images. But, I don’t – and, you shouldn’t either.

Mosquitos are a serious problem, especially because of the diseases that they may be carrying – West Nile Virus, Dengue, Chikungunya, and now Zika to worry about. But, poisoning ourselves and our lawns and gardens with highly toxic insecticides will kill off all the beneficial wildlife like birds, butterflies, bees, and bats that eat mosquitoes. Toxic insecticides poison the lawns that our pets and children play on, the vegetables that we eat from our gardens, and the pollinators that bring all our trees and flowers into bloom.

So, what’s a person to do? Routinely, and especially after every rain, dump out all the little water puddles and pockets around your home, and use a mosquito spray on yourself before heading outside. I like to use a lemon and eucalyptus repellant, or one called Wildthings that a friend of mine makes that works wonderfully and smells great.  If convenient, I wear long pants and shirt-sleeves, and put the spray on my clothing instead of my skin.  Here is a list from the Environmental Protection Agency of pesticide ingredients that are minimal risk, so try to pick products with these ingredients if possible.

Mosquito-borne viral illness Chikungunya, Dengue fever and  Zika all can cause similar symptoms, including fever, muscle and joint pain, and rash (see CDC for more info). Four of five people infected with Zika are either asymptomatic, or have symptoms so mild they might go unnoticed. There is currently no vaccine or treatment for Zika virus.

On February 1, 2016, the World Health Organization (WHO) declared the Zika a public health emergency amid growing concerns about its links to Brazil’s substantial increase in cases of microcephaly, a devastating developmental abnormality. Babies with microcephaly can have severe defects, including cognitive deficiencies, deafness, blindness, difficulty swallowing, and speech problems. This permanent condition can range from mild to severe, and may be life-threatening (see CDC Facts About Microcephaly). They were also concerned about Zika’s links to Guillain-Barré syndrome in adults, a condition in which the body’s immune system attacks its own nerves to potentially cause paralysis (see WHO info and WHO on Zika complications). New research in 2016 has almost definitively linked microcephaly with pregnant mothers infected with Zika in their first trimester (Johansson et al 2016). Outside of Zika, microcephaly is rare, occurring in approximately 2 to 12 babies per 10,000 live births in the United States (see CDC Facts about microcephaly).

High-risk populations for Zika-induced microcephaly include pregnant women, women who may become pregnant, and their male partners who may pass it through infected sperm. As of July 13, 2016, 62 countries and territories reported Zika transmission from mosquitos to people (see WHO Zika complications).

While Zika is not a widespread threat in the United States yet, climate change is likely to make much of the southeastern United States more susceptible to this and other mosquito-borne pathogens in the future (Weaver and Reisen 2010). Mosquito-borne disease is a real threat to public health, but widespread pesticide use may not be the best approach. There are commonsense, low-chemical measures we can all take to limit our exposure to mosquitos and protect ourselves from the pathogens they carry.

A Virus on the Move: How Does Zika Travel?

Zika is carried by Ae. aegypti and Ae. albopictus mosquitoes, which bear a distinct white striping on their bodies and legs.  Ae. albopictus is more widely found throughout the United States and its range is expanding rapidly. Ae. aegypti is currently found mainly—but not only—in the southern half of the country (CDC Integrated Mosquito Management). Increased heat, precipitation, and humidity can allow mosquitoes to thrive in new places (Knowlton et al 2009, NYT 2016).

female Aedes aegypti mosquito
James Gathany/CDC, 2006

Warmer temperatures enable mosquitoes to develop more quickly, and to incubate viruses that can infect people faster. Thus, climate change has hastened the spread of many infectious diseases, including Zika.

The main Zika carrier, Ae. aegypti, may migrate to new cities because of favorable summertime weather. During the summer, many U.S. cities may risk low, moderate, or high populations of the Zika-transmitting mosquitos (colored circles). The circles are color-coded to show July projections for Ae. aegypti populations. In addition, Zika risk may be elevated in cities that receive more air travelers from Latin America and the Caribbean (larger circles) who may have been exposed to Zika. As of March 2016, 26 states and the District of Columbia reported populations of Ae. aegypti, and Ae. albopictus was found in 40 states and the District (Hahn et al 2016; See a high-resolution map).

While both types of Zika-spreading mosquitos are daytime biters, Ae. aegypti is more likely to spread viruses. This insect bites, rests, and lays eggs indoors and outdoors. It also prefers humans to animals, can bite several people in each “blood meal,” prefers to live near people (i.e., in homes), and can live longer under harsh conditions than Ae. albopictus. The female lays her eggs in artificial containers such as buckets, flowerpot bases, and tires in and around homes and schools (CDC 2012).

The Zika virus can survive for several months in semen, and men can transmit it to their sexual partners (CDC 2016 Zika and sexual transmission). Thus, pregnant women can become infected through mosquito bites or their infected male partners—and that infection can be transmitted to their fetus.  

Weak Testing Methods, and No Cure

Current diagnostic tools can only detect Zika within the first week of infection, after which point the virus hides within cells and becomes more difficult to detect (CDC 2016 diagnostic testing). This means that someone infected with Zika can still test as negative. There is currently no Zika vaccine, and no known treatment or cure (White House Zika response). Our best possible response is prevention where possible, followed by management of the disease, including long-term care for microcephalic children, which experts have estimated could cost up to $10 million per case (Kaiser Family Foundation 2016).

What We Don’t Know about Zika

Though we have learned a great deal about Zika since the current outbreak came to light, many questions remain unanswered. For example, we don’t know the exact point during pregnancy at which a Zika infection will lead to a birth defect. Not all infants born to mothers who have been infected with Zika immediately show signs of microcephaly. In those cases, we don’t know what health impairments may emerge. The long-term prognosis for Zika-babies born with microcephaly or other health problems is also unclear. Beyond consequences for infants, we don’t know what increases the risk of developing Guillain-Barré or other longer-term health threats for adults.

We Can’t Just Spray It Away

Drenching our homes and communities with harmful pesticides will not address Zika. Pesticides may seem like an attractive solution, but these chemicals must be used judiciously and strategically to avoid harming the very people we seek to protect (Duprey et al 2008). Aerial or even backpack spraying of ultra-low volume pesticides has had a very hard time achieving effective control of these particular mosquitoes, which have proven almost impossible to get rid of. Instead, we need a range of tactics to help prevent mosquito bites and  disease transmission (CDC 2016 prevention):

o   Wear protective clothing such as long sleeves and long pants. 

o   Apply personal mosquito repellant, such as EPA recommended formulations in the morning and early evening (CDC 2016 prevention; EWG 2016 on Zika). Try to pick products using  minimal risk ingredients, if appropriate. 

o   Use window and door screens to keep mosquitoes out of homes. 

o   Every week, inspect the inside and outside of your home for standing water and eliminate it. This includes flowerpots, tires, buckets, planters, toys, birdbaths, empty garbage cans and lids, etc.

o   Stop infected people from getting further mosquito bites to prevent spreading the disease to more mosquitoes.

Apply EPA-approved biological or chemical larvicides to standing water like birdbaths and backyard ponds, preferably using ones from EPA’s list of minimal risk ingredients.

In Puerto Rico, traps to capture and kill adult female mosquitoes are showing promise as being highly specific, with little to no impact on people or other animals (Barrera et al 2014). Other methods currently under evaluation include the introduction of genetically-modified male sterile mosquitoes to curb population growth, and new lower-risk biopesticides (Alphey et al 2010).

Widespread aerial spraying of communities and water sources alone may not fully eradicate Zika-carrying mosquitoes, and could instead promote insecticide-resistance, which often builds with exposure (PAHO 2013). This effect has been demonstrated in nearly every class of insecticide (Brogdon and McAllister 1998). Insecticide resistance can be passed from adult mosquitoes to offspring, rendering insecticide treatments ineffective with generational shifts. That means that while sprays and larvicides may be part of the solution, chemicals alone are not the answer (CDC 2015). Informed insecticide selection must be based on resistance testing results, and should be just one part of a control program (CDC 2016).

White House Response

The federal government’s coordinated Zika response includes developing a vaccine; diagnostic tests; and national tracking databases for the virus, mosquitoes, and infected people (White House 2016). Congress has yet to approve funding. Developing safe, rapid responses to the public health challenge of Zika could be an important opportunity to increase community knowledge, protection, and preparedness against emerging infectious disease threats, which are likely to increase under a changing climate.

About the Authors

Jennifer Sass

Senior Scientist, Federal Toxics, Health and Food, Healthy People & Thriving Communities Program

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