Caitlin Mollison, Senior Editor

Illnesses from flea, mosquito, and tick bites tripled in the United States, with more than 640,000 cases reported from 2004 through 2016, according to the CDC.

Nine new germs spread by mosquitoes and ticks were discovered or introduced into the United States during this time, according to the CDC’s

This is the CDC’s first summary collectively examining data trends for all nationally notifiable diseases caused by the bite of an infected flea, mosquito, or tick. It provides detailed information on the growing burden of mosquito-borne and tickborne illnesses in the United States.

“Zika, West Nile, Lyme, and chikungunya—a growing list of diseases caused by the bite of an infected mosquito, tick, or flea&mdash;have confronted the US in recent years, making a lot of people sick, and we don’t know what will threaten Americans next,” CDC Director Dr. Robert R. Redfield said in a statement. “Our nation’s first lines of defense are state and local health departments and vector control organizations, and we must continue to enhance our investment in their ability to fight against these diseases.”

Difficult to control and widespread, diseases from flea, mosquito, and tick bites are major causes of death and sickness worldwide. The growing number and spread of these diseases pose an increasing risk in the United States. The report found that the nation needs to be better prepared to face this public health threat.

CDC scientists analyzed data reported to the National Notifiable Diseases Surveillance System for 16 notifiable vector-borne diseases from 2004 through 2016 to identify trends. Many infections are not recognized or reported, so it is difficult to truly estimate the overall burden and cost of these diseases. In 2016, the most common mosquito-borne viruses in the United States were West Nile, dengue, and Zika. The most common tickborne diseases were Lyme disease and ehrlichiosis/anaplasmosis. Although rare, plague was the most common disease resulting from the bite of an infected flea.

The increase in diseases caused by the bite of an infected flea, mosquito, or tick in the United States is likely the result of many factors. Mosquitoes and ticks and the germs they spread are increasing in number and moving into new areas. As a result, more people are at risk for infection. Overseas commerce and travel are more common than ever before. A traveler can be infected with a mosquito-borne disease, such as Zika, in one country, and then unknowingly transport it home. Finally, new germs spread by mosquito and tick bites have been discovered and the list of nationally notifiable diseases has grown.

Caitlin Mollison, Senior Editor

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CDC: Illnesses from Flea, Mosquito, and Tick Bites Surge in the US