Cases of illnesses transmitted by insect bites have increased significantly in recent years, according to a new report from the Centers for Disease Control and Prevention (CDC) published in May 2018. The agency emphasizes a need for the public to be vigilant in avoiding insect bites to lower the risk of these infections, especially during the summer months when biting insects are more active and/or when traveling to areas where the diseases are common.
The Morbidity and Mortality Weekly Report (MMWR) details the number of reported insect-borne diseases in the United States and its Territories between 2004 and 2016. During this 13-year period, there were more than 600,000 reported cases of 16 different mosquito-, tick- and flea-borne diseases, with most cases coming from the bites of ticks and mosquitos. The most commonly reported infections were Lyme disease, Rocky Mountain spotted fever, West Nile virus, dengue, and Zika virus diseases.
Infections from tick bites accounted for over 76% (491,671) of the total number of reported insect-borne infections in the U.S. The annual incidence more than doubled between 2004 and 2016, going from less than 22,000 in 2004, to over 48,000 in 2016, with Lyme disease making up 82% of all reported tick-bite infections. Most of these reports were from the continental U.S. and were concentrated in the East and along the Pacific Coast. In addition, the CDC says reports from this time-period identified seven new tick-borne microbes in the U.S. that can infect humans.
Viruses predominated among the more than 150,000 cases of mosquito-borne diseases reported between 2004 and 2016. Puerto Rico, the U.S. Virgin Islands, and American Samoa reported the highest incidence of dengue, chikungunya, and Zika virus diseases. Travelers to the U.S. Territories and Latin America accounted for about 90% of the dengue, chikungunya, and Zika virus disease cases identified in the continental U.S. In Puerto Rico, dengue virus was endemic (there was a reported constant presence of this infection). In the continental U.S., West Nile virus was endemic, but outbreaks (epidemics) of the disease occurred in 2012—especially in Texas.
The CDC identified several possible reasons for the rise in reported insect-borne infections, including climate change, an increase in the number of people travelling by plane, suburban reforestation, lack of vaccines, and the need for more support for state and local health departments. In order to reduce the transmission of insect-borne diseases, the CDC concludes in its report that the U.S. will need a "major national improvement of surveillance, diagnostics, reporting, and vector [insect] control, as well as new tools, including vaccines."
Representatives from the CDC note that the number of reported cases in the MMWR is likely a substantial underestimate of the actual number of infections occurring in the U.S. Many infected people do not experience noticeable sign and symptoms, so they do not seek care and are not diagnosed. Others, who develop signs and symptoms and consult their healthcare practitioner, may not be tested to confirm the diagnosis. Finally, some cases may not be reported to a public health agency.
While some cases of insect-borne diseases cause no symptoms or mild illness, some cases can potentially progress to more serious illness and complications. It is important to reduce the risk of these infections by avoiding insect bites. The CDC strongly recommends that everyone protect themselves from biting insects by taking precautions, such as:
- Using an insect repellent that contains DEET
- Wearing long-sleeved shirts and long pants
- Staying indoors during dawn and dusk when mosquitos are most active
- Treating clothing and camping gear with permethrin or buying permethrin-treated clothing and gear
- Controlling ticks and fleas on pets
- Finding and removing ticks every day from family and pets
- Controlling mosquitoes, ticks, and fleas inside and outside the home