CDC: Diseases from mosquito, tick, flea bites more than tripled from 2004

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Diseases transmitted by ticks, fleas, and mosquitoes are becoming more risky and far more numerous: Between 2004 and 2016, they tripled to almost 650,000 cases, a new CDC report finds.

While Zika stood out as the latest emerging threat in the report, it also showed a long-term increase in cases of tick-borne Lyme disease, which can attack the heart and nervous system if left untreated.

In the time period covered by the study, nine new diseases showed up in the USA, including seven carried by ticks, and Zika and chikungunya, which are carried by mosquitoes.

Climate change, although not explicitly mentioned in the report, is thought to be a major factor in the spread of vectorborne illnesses, especially Lyme disease, as ticks move northward into areas that were previously too cold for their survival.

Other factors leading to the spread of mosquito-borne diseases like Zika include global travel, the CDC said.

Overall, the researchers tallied a little more than 642,600 cases of disease transmitted by insect bites between 2004 and 2016. The actual burden is thought to be "substantially higher", researchers wrote.

The findings were published May 1 by the CDC as a Vital Signs report.

While the increase in tick-borne illnesses was gradual, rising steadily each year, the increase in mosquito-borne diseases was more sudden, driven by recent epidemics of West Nile virus and Zika virus.

They include Lyme disease, anaplasmosis, Rocky Mountain spotted fever, babesiosis, rabbit fever and Powassan virus.

The report found that during the 13-year study period, the number of reported illnesses from mosquito, tick and flea bites more than tripled, going from about 27,300 cases in 2004 to 96,000 cases in 2016.

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Mosquito-borne infections are most likely to hit sunnier states and territories. That's enough to help nine states to increase their ability to manage vector-borne disease, Petersen said. Petersen said higher temperatures also raise the risk for mosquito-borne diseases.

"Many of these diseases are sensitive to increasing temperatures", he told reporters on a conference call. "Mosquito-borne diseases tend to get worse during heatwaves".

Most of the increase comes from the arrival of Zika virus in 2015 and from ticks. He added that increasing temperatures can expand the range of ticks further north.

The most common tick-borne diseases in 2016 were Lyme disease and ehrlichiosis, a serious illness that infects white blood cells.

Warmer weather is an important cause of the surge in cases reported to the Centers for Disease Control and Prevention, according to the lead author of a study in the agency's Morbidity and Mortality Weekly Report.

"It will take all of us to prevent this", Dr. Redfield stressed. "Second, CDC is working with state and local health departments to build or rebuild comprehensive vector programs that have eroded over time", he said.

The Infectious Diseases Society of America (IDSA) seconded that conclusion, calling for more federal funding of research into the development of new vaccines to battle these diseases. The longevity, distribution, biting habits, and proliferation of the vectors all affect disease transmission, and, according to the report, they're all dependent on environmental factors such as rainfall, temperature, and shelter.

"While all possible efforts must be made to prevent vector-borne diseases, we also wish to ensure rapid, accurate diagnosis and optimal treatment for patients who are sickened", he said.

The CDC said it is likely that the 640,000 cases of bug-borne illnesses grossly understates the actual number of cases around the USA because many other cases are never diagnosed or treated properly.

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