Protecting Workers against
ZIKA
Long Clothing, Repellent among Preventive Measures
BY ROBERT N. PHALEN AND PENGFEI GAO
The association between Zika virus infection during pregnancy and severe birth defects has led to worldwide efforts to prevent more infections. Zika was first identified in 1947, with a geographical distribution primarily in tropical regions of Africa, Southeast Asia and the Pacific Islands. However, since 2015 we have seen the virus spread through South America, Central America, and the Caribbean. Spread to the southern half of the United States is possible, because the Aedes aegpti and Aedes albopictus mosquitoes that can transmit the virus to humans live in these regions as well. In late July 2016, the Florida Department of Health identified an area in one neighborhood of Miami with active transmission of Zika virus. Locally acquired cases have also been reported in the U.S. territories of Puerto Rico, Virgin Islands and American Samoa, as well as neighboring Mexico.
Although most infected people are asymptomatic, the critical issues with Zika infection are with its associated risks, namely severe birth defects and Guillain-Barré syndrome. The primary birth defect is microcephaly, a condition that reduces head size and is a sign of incomplete brain development, which can be accompanied by a host of severe outcomes, such as hearing loss, vision problems, developmental delays and intellectual disability. Guillain-Barré syndrome is an autoimmune disease that attacks the nervous system and can lead to muscle weakness, paralysis, and even death in about 5 percent of those affected. Several countries that have experienced Zika outbreaks recently have reported increases in people who have Guillain-Barré syndrome. This potential relationship is under further investigation by the U.S. Centers for Disease Control and Prevention (CDC). These potential complications of Zika infection are the impetus behind efforts to control and prevent the spread of Zika.
From an occupational health standpoint, industrial hygienists play an important role in protecting workers, their families, and their community from Zika. This is especially true for employees who work outdoors, travel to areas with Zika, or work in the healthcare sector. The focus of this article is on the preventive measures that can be taken by an organization whose workers may be at risk. MODES OF TRANSMISSION Zika virus is an arbovirus (transmitted by arthropods) in the same Flavivirus genus as dengue fever, yellow fever, and West Nile viruses. Mosquito-borne transmission from an infected human to another human is similar to dengue and other similar Flavivirus species. The signs and symptoms of Zika infection are often mild if present at all, and only about 20 percent of infected individuals show any symptoms. Two to seven days following exposure (for example, a mosquito bite), mild fever, a rash, and/or joint pain may be observed. In addition, headache, conjunctivitis (red eyes), and muscle pain may be reported. The symptoms, if any, typically only last up to a week. Thus, Zika infections are largely underreported, facilitating its spread both regionally and worldwide.
Zika virus transmission is primarily associated with the Aedes aegypti and Aedes albopictus mosquitoes. Aedes aegypti and Aedes albopictus bite primarily during the day. These species are most active for approximately two hours after sunrise and several hours before sunset, but they can bite at night in well-lit areas. Aedes aegypti is common to urban tropical areas and many parts of the southern half of the United States. Aedes albopictus, known as the Asian tiger mosquito, is also common to urban areas and similar regions of the U.S., but the potential for transmission of Zika to humans is lower compared to Aedes aegypti
In addition to mosquito-borne transmission to humans, Zika virus can likely be transmitted as a blood-borne pathogen. Zika can also be transmitted sexually from an infected person to his or her partners. Blood transfusions, needle sticks, and contact with blood can transmit the virus. The virus can be found in the blood for about a week after initial infection. Zika remains in semen longer than in blood. Unfortunately, the actual period of communicability is unknown at this time. Lastly, the virus can be transmitted in the blood from a pregnant mother to her fetus, during pregnancy or at delivery. Protecting pregnancies from the devastating impact of Zika virus infection and potential severe outcomes is our primary concern.
Local measures to disrupt the mosquito life cycle can be effective. The mosquitoes require standing water to lay eggs, and the life cycle can take as little as one week.
PREVENTATIVE MEASURES: THE ESSENTIALS Zika is of worldwide concern and everyone will need to do their part to control its spread. This is especially true for those living in areas where the Aedes aegypti and Aedes albopictus mosquitoes thrive. The essential preventive measures in the workplace include:
  1. Staying up-to-date. As the public health community learns more about the disease, new and important information related to transmission, geographic distribution, prevention and treatment will continually become available. Preventative measures will need to address new developments as they arise. The CDC provides updated information on Zika.
  2. Control mosquito populations outside. The flight range of these mosquitoes is typically less than a mile; thus, local measures to disrupt the mosquito life cycle can be effective. The mosquitoes require standing water to lay eggs, and the life cycle can take as little as one week from egg to development of an adult. Several control measures are discussed below.
  3. Keep mosquitoes outside. Keeping windows and doors closed or using screens can help keep mosquitoes out of buildings.
  4. Educate workers. Those at risk need to know about the disease, how it is transmitted, and how they can protect themselves. 
  5. Provide workers with the means to protect themselves. This includes providing proper clothing, insect repellents, and permethrin-treated clothing, if needed.
Each of these essentials is covered in more detail below for those workers most at risk, including outdoor workers, workers in areas with Zika, workers traveling to areas with Zika, and healthcare workers. PROTECTING OUTDOOR WORKERS Two factors must first happen for a mosquito to transmit a virus to a human. First, according to a 2015 published article in Current Biology, the mosquito must be attracted to the person, which is dependent on a number of factors such as body heat, exhaled carbon dioxide, and various odorous volatile organics from the skin. Second, the mosquito must have access to the skin. Because outdoor workers are more likely to come in contact with mosquitoes, both of these factors are relevant to protect outdoor workers. Outdoor workers should:
  1. Use an insect repellent on exposed skin. The most effective way to deter mosquitoes is to use an Environmental Protection Agency (EPA)-registered repellent with one of the following ingredients: DEET (N, N-diethyl-meta-toluamide), picaridin (KBR 3023), or oil of lemon eucalyptus or para-menthane-diol. DEET is one of the more effective repellents against mosquitoes, and as the strength or percentage increases, so does the protection time before reapplication is required. However, concentrations greater than 50 percent typically do not show added protection. DEET and similar repellents are designed to be applied directly on the exposed skin. Since mosquitoes can penetrate thin materials, it is recommended that workers treat clothing as well, especially socks and where clothing is in close contact with the body. Application must always be in accordance with the manufacturer’s guidelines.
  2. Treat hands and feet with a repellent. According to a 1998 published article in the Journal of Vector Ecology, it has been shown that the hands are a strong attractor to Aedes aegypti mosquitoes, followed by sweaty socks. The hands and feet are two areas that may often go untreated if a worker is focused solely on exposed skin and his/her hands are busy applying the repellent. Thus, workers should be instructed to ensure these critical areas are well covered.
  3. Cover skin with clothing. Outdoor workers need to be adequately covered by clothing. This includes a long-sleeved shirt, long pants, socks, and possibly even gloves. Loose pant legs should be tucked into the socks to prevent access to the skin. In addition, soiled clothing should be laundered regularly to prevent the buildup of sweat and scents that may attract mosquitoes. Since sweaty socks have been used to effectively bait mosquitoes, workers should exchange soiled socks for fresh ones more regularly, even at daily breaks if needed.
  4. Wear clothing treated with permethrin. When exposure to mosquitoes potentially harboring Zika is expected, the use of permethrin-treated clothing is highly recommended. Permethrin is a pesticide that kills many mosquitoes and ticks. The military has effectively used treated clothing for more than 20 years. Both sprays and pre-treated clothing are readily available. When using sprays, permethrin should never be sprayed directly on the skin or inside clothing. Instead it must be applied to the outer surface and allowed to air dry before putting on the clothing. Application and re-application must always be in accordance with the manufacturer’s guidelines. Use of insect repellents on exposed skin and even clothing is still necessary, as permethrin is not an effective repellent.
The hands and feet are two areas that may often go untreated if a worker is focused solely on exposed skin and his/her hands are busy applying the repellent.
MOSQUITO CONTROL IN AREAS WITH ZIKA In addition to personal protection for outdoor workers, mosquito control in areas with Zika is equally important. Mosquito control involves removing or treating nearby standing water to reduce mosquito populations, treating mosquito resting areas with appropriate insecticides, and keeping mosquitoes outdoors.
Mosquitoes lay their eggs near standing water or areas or containers with standing water from rain or sprinklers. Some mosquitoes, such as the Aedes genus, may require only small amounts of water for growth and development. Nevertheless, standing water that cannot be drained, dumped out or covered should never be left for periods longer than five to six days. The following preventive measures can help control mosquito populations:
  1. Use mosquito netting to block entry of mosquitoes into areas where standing water is continually present (for example, drains, piping, shallow basins, and so on).
  2. Empty standing water at least once every week.
  3. Treat non-potable standing water that cannot be drained or dumped with mosquito larvicides (for example, mosquito water treatment tablets).
  4. Contact the vector control staff or staff who conduct mosquito control operations within your local public health department for assistance in evaluating and controlling mosquito populations. A variety of treatment methods may be readily available in your area and at no additional cost.
  5. Lastly, common outdoor and indoor resting areas for mosquitoes can be treated with insecticides. Mosquitoes often prefer to rest in dark, humid areas, such as under furniture, under dense vegetation, within tree cavities, or even within animal burrows. Both the CDC and EPA provide useful information on effective insecticides for adult, flying mosquitoes. However, in the workplace, pest control professionals should be consulted on the matter.
To keep mosquitoes outdoors, windows and doors should be kept closed or fine mesh window and door screens should be used. Mosquitoes are attracted to carbon dioxide and heat; thus, significant gaps around doors and windows need to be sealed. Operation of the building under a slight negative pressure may preclude the escape of carbon dioxide from around doors, which are likely entry points for mosquitos as workers come and go. PROTECTING WORKERS TRAVELING TO AREAS WITH ZIKA It is also highly recommended that anyone traveling visit a healthcare provider at least four to six weeks prior to travel, to ensure they receive proper advice, medicines and vaccines. There is no vaccine for Zika at this time. Clinics and county health departments providing services are listed on the CDC Travelers Health website. The key is to receive up-to-date information and advice prior to travel. 
Workers traveling internationally are advised to visit the CDC Travelers’ Health website, especially those traveling to South or Central America, the Caribbean, Africa, Asia, or the Pacific Islands. The website provides vital information on how travelers can protect themselves from infection. 
CDC recommends that pregnant women not travel to an area with active Zika virus transmission. Consider delaying travel to areas with Zika, especially for workers who are or may become pregnant or whose sexual partners are or may become pregnant. For the most up-to-date information and recommendations on Zika and sexual transmission, visit the CDC website. Pregnant women, women who may become pregnant, and people with sex partners who are or may become pregnant should consult with their healthcare providers about risks associated with Zika virus infection during pregnancy. PROTECTING HEALTHCARE WORKERS Healthcare workers should follow standard and universal precautions for blood-borne pathogens. Zika virus can be found in the blood, saliva, vaginal fluids, breastmilk, and semen of infected individuals. Protective measures in accordance with the OSHA blood-borne pathogens standard (29 CFR 1910.1030) apply in the U.S. Similar protections should be followed outside the U.S. These general protective measures include:
  1. Establishment of an effective exposure control plan and program.
  2. Use of standard and universal precautions with the treatment of all blood and bodily fluids as infectious.
  3. Initiation of effective engineering and administrative “work practice” controls to prevent contact with blood and bodily fluids.
  4. Use of effective personal protective clothing and equipment (for example, gloves, masks, face shields, and gowns) as needed to prevent blood and bodily fluid contact with the skin, eyes, mucus membranes, and respiratory tract.
  5. Implementation of adequate worker education and training on blood-borne pathogens and protective measures.
  6. Well established post-exposure evaluation, treatment and follow-up policies and procedures in place in the event of a needle stick or exposure.

ROBERT N. PHALEN, PhD, CIH is an associate professor of Industrial Hygiene at University of Houston-Clear Lake. He can be reached at (281) 283-3753 or phalen@uhcl.edu.
PENGFEI GAO, PhD, CIH is a research physical scientist at the NIOSH National Personal Protective Technology Laboratory. He can be reached at (412) 386-6885 or pcg9@cdc.gov.
RESOURCES CDC: “Zika Virus” (June 2016).
CDC: “Travelers’ Health” (June 2016).
Current Biology: “Mosquitoes use vision to associate odor plumes with thermal targets” (August 2015).
Journal of Vector Ecology: “Olfactory responses and field attraction of mosquitoes to volatiles from Limburger cheese and human foot odor” (December 1998).
WHO: “Standard Precautions in Health Care” (June 2016).
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Disadvantages of being unacclimatized:
  • Readily show signs of heat stress when exposed to hot environments.
  • Difficulty replacing all of the water lost in sweat.
  • Failure to replace the water lost will slow or prevent acclimatization.
Benefits of acclimatization:
  • Increased sweating efficiency (earlier onset of sweating, greater sweat production, and reduced electrolyte loss in sweat).
  • Stabilization of the circulation.
  • Work is performed with lower core temperature and heart rate.
  • Increased skin blood flow at a given core temperature.
Acclimatization plan:
  • Gradually increase exposure time in hot environmental conditions over a period of 7 to 14 days.
  • For new workers, the schedule should be no more than 20% of the usual duration of work in the hot environment on day 1 and a no more than 20% increase on each additional day.
  • For workers who have had previous experience with the job, the acclimatization regimen should be no more than 50% of the usual duration of work in the hot environment on day 1, 60% on day 2, 80% on day 3, and 100% on day 4.
  • The time required for non–physically fit individuals to develop acclimatization is about 50% greater than for the physically fit.
Level of acclimatization:
  • Relative to the initial level of physical fitness and the total heat stress experienced by the individual.
Maintaining acclimatization:
  • Can be maintained for a few days of non-heat exposure.
  • Absence from work in the heat for a week or more results in a significant loss in the beneficial adaptations leading to an increase likelihood of acute dehydration, illness, or fatigue.
  • Can be regained in 2 to 3 days upon return to a hot job.
  • Appears to be better maintained by those who are physically fit.
  • Seasonal shifts in temperatures may result in difficulties.
  • Working in hot, humid environments provides adaptive benefits that also apply in hot, desert environments, and vice versa.
  • Air conditioning will not affect acclimatization.
Acclimatization in Workers