Thursday, July 21, 2016

Mass. General physicians outline ways to avoid contracting Zika virus, other mosquito-borne illnesses

While the hazards associated with the Zika virus – particularly the risk that infection in pregnant women can cause brain damage to unborn children – have been in the news this summer, Zika virus is only one of several potentially serious illnesses transmitted by mosquitoes. In their article published earlier this month in Annals of Internal Medicine, two Massachusetts General Hospital physicians describe the best ways to prevent mosquito bites and the illnesses that might be contracted from them.

“The recent emergence of Zika virus has increased attention to mosquito-borne illnesses, but the approaches to avoiding these illnesses has not changed,” says Regina LaRocque, MD, of the MGH Division of Infectious Diseases. “Many areas of the U.S. have mosquito-borne illnesses, so avoiding mosquito bites is a good practice for everyone.”

She and her co-author Edward Ryan, MD, MGH Division of Infectious Diseases, note that different groups of mosquitoes carry different illnesses. The highly prevalent Culex mosquitoes can transmit West Nile virus and several forms of encephalitis, and Anopheles mosquitoes in tropical areas outside the U.S. can carry malaria. Aedes mosquitoes can transmit dengue fever, yellow fever, eastern equine encephalitis and chikungunya, as well as Zika virus, and unlike most other species are active and can bite during the day. Zika virus recently emerged in Brazil, and has now been reported throughout Latin America and the Caribbean.

The physicians’ recommendations – based on U.S. Centers for Disease Control and Prevention (CDC) guidelines – are as follows:

  • Trip planning – everyone should consult a physician prior to travel to regions with active transmission of illnesses such as malaria, dengue, chikungunya and Zika virus; and pregnant women should not travel to regions where Zika virus has been reported. Travel notices from the CDC are available at
  • Personal measures – limit exposure to mosquitoes by wearing long-sleeved shirts and long pants and covering feet when outside. Children especially should be dressed in clothes that cover their arms and legs; and cribs, strollers and carriages should be covered with mosquito netting. CDC-approved mosquito  repellents containing DEET, picaridin, IR3535, oil of lemon eucalyptus or its refined form called paramenthane-3,8-diol (PMD) should be carefully applied according to the label instructions.  repellents should not be used on children under 2 months of age, and oil of lemon eucalyptus/PMD should be avoided for children under 3 years. All of these  repellents are safe for pregnant and breastfeeding women.
  • Household measures – since mosquitoes can lay eggs in even small containers of standing water, remove or empty and clean containers such as vases, flower pots, buckets, or birdbaths at least weekly. Insect sprays or foggers should be used following label instructions and repeated as necessary, with particular attention to dark or humid locations where mosquitoes are likely to rest.

The authors note that those traveling to areas where malaria is endemic should take anti-malarial medications. To avoid spreading pathogens to uninfected local mosquitoes, anyone who has or may have acquired a mosquito-borne illness should follow these precautions. Those who have traveled to areas where Zika virus is present should do so for at least three weeks after returning, even if they do not develop symptoms. Men exposed to Zika virus should avoid sexual transmission either by avoiding sexual contact or by correct use of condoms. More detailed information for preventing Zika virus transmission is available at

“Properly using insect repellent and covering exposed skin are probably the most important recommendations for everyone to follow,” says Ryan. “And when used as directed, all of these CDC-recommended and EPA-registered repellents are safe and effective.” Ryan is a professor of Medicine at Harvard Medical School and a professor of immunology and infectious diseases at Harvard School of Public Health; LaRocque is an assistant professor of Medicine at Harvard Medical School. Their work was supported by CDC grant U01CK000175.

Massachusetts General Hospital, founded in 1811, is the original and largest teaching hospital of Harvard Medical School. The MGH Research Institute conducts the largest hospital-based research program in the nation, with an annual research budget of more than $800 million and major research centers in HIV/AIDS, cardiovascular research, cancer, computational and integrative biology, cutaneous biology, human genetics, medical imaging, neurodegenerative disorders, regenerative medicine, reproductive biology, systems biology, photomedicine and transplantation biology. The MGH topped the 2015 Nature Index list of health care organizations publishing in leading scientific journals, earned the prestigious 2015 Foster G. McGaw Prize for Excellence in Community Service and returned to the number one spot on the 2015-16 U.S. News & World Report list of "America's Best Hospitals."

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