Mosquito, Tick, and Flea Illnesses Triple in US; Nine New Germs

On May 1, 2018, the CDC published a report that found that illnesses from mosquito, tick, and flea bites have tripled in the U.S., with a total of 642,602 cases reported during the 13 years from 2004 through 2016. Nine new germs spread by mosquitoes and ticks were discovered or introduced into the U.S. during this time.


This report is the CDC’s first examination of data trends for all nationally notifiable diseases caused by the bite of an infected mosquito, tick, or flea. The report provides detailed information on the growing burden of mosquito-borne and tickborne illnesses in the U.S.


“Zika, West Nile, Lyme, and chikungunya—a growing list of diseases caused by the bite of an infected mosquito, tick, or flea—have confronted the U.S. in recent years, making a lot of people sick. And we don’t know what will threaten Americans next,” said CDC Director Robert R. Redfield, M.D. “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.”


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


The number of reported tickborne diseases more than doubled in 13 years and accounted for more than 60 percent of all reported mosquito-borne, tickborne, and fleaborne disease cases. Diseases from ticks vary from region to region across the U.S. and those regions are expanding.

From 2004 through 2016, seven new germs spread through the bite of an infected tick were discovered or recognized in the U.S. as being able to infect people.


In 2016, the most common tickborne diseases in the U.S. were Lyme disease and ehrlichiosis/anaplasmosis. Lyme disease, an inflammatory disease characterized at first by a rash, headache, fever, and chills, and later by possible arthritis and neurological and cardiac disorders, is caused by the bacterium Borrelia burgdorferi and is transmitted to humans through the bite of infected blacklegged ticks. Human ehrlichiosisis is a disease caused by at least three different ehrlichial tick species in the U.S.: Ehrlichia chaffeensis, Ehrlichia ewingii, and a third Ehrlichia species provisionally called Ehrlichia muris-like (EML). The lone star tick (Amblyomma americanum) is the primary vector of both E. chaffeensis and E. ewingii in the U.S. Typical ehrlichiosisis symptoms include fever, headache, fatigue, and muscle aches.


The most common mosquito-borne viruses in 2016 were West Nile, dengue, and Zika. Most people infected with West Nile virus (WNV) do not have symptoms; while about 1 in 5 infected people develop a fever and other symptoms; and about one out of 150 infected people develop a serious, sometimes fatal, illness. Dengue is caused by any one of four related viruses transmitted by mosquitoes. People with dengue will have a high fever and at least two of the following symptoms: severe headache, severe eye pain (behind eyes), joint pain, muscle and/or bone pain, rash, mild bleeding manifestation (e.g., nose or gum bleed, petechiae, or easy bruising), or low white cell count. Early recognition and prompt supportive treatment can substantially lower the risk of medical complications and death from dengue. Zika is spread mostly by the bite of an infected Aedes species mosquito (Ae. aegypti and Ae. albopictus). Zika can also be passed from a pregnant woman to her fetus, which can cause birth defects; through sex; and through blood transfusion. There have been increased reports of Guillain-Barré syndrome, an uncommon sickness of the nervous system, in areas affected by Zika.


Though rare, plague was the most common disease resulting from the bite of an infected flea. Plague is caused by the bacterium, Yersinia pestis, which is usually transmitted to humans by a rodent flea bite. Modern antibiotics are effective in treating plague. Without prompt treatment, the disease can cause serious illness or death.


The increase in diseases caused by the bite of an infected mosquito, tick, or flea in the U.S. is likely due to 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 travel and commerce are more common than ever before. A traveler can be infected with a mosquito-borne disease, like 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.


Reducing the spread of these diseases and responding to outbreaks effectively will require additional capacity at the state and local level for tracking, diagnosing, and reporting cases; controlling mosquitoes and ticks; and preventing new infections. The public and private sectors need support to develop new diagnostic and vector control tools.


“The data show that we’re seeing a steady increase and spread of tickborne diseases, and an accelerating trend of mosquito-borne diseases introduced from other parts of the world,” said Lyle Petersen, M.D., M.P.H., director of the Division of Vector-Borne Diseases in the CDC’s National Center for Emerging and Zoonotic Infectious Diseases. “We need to support state and local health agencies responsible for detecting and responding to these diseases and controlling the mosquitoes, ticks, and fleas that spread them.”


See the CDC Announcement


See the CDC Report


See also Medical Risk Law Report: Vectors of Risk: Zika, West Nile, and Similar Tick and Mosquito Disease Litigation