CDC says bug-borne illnesses on the rise

The number of illnesses in the U.S. caused by mosquito, tick and flea bites has made a dramatic jump in the last decade, raising concerns that a changing climate could lead to more widespread viral outbreaks.

New data from the Centers for Disease Control and Prevention show more than 640,000 cases of illness caused by mosquito, tick and flea bites between 2004 and 2016, with a three-fold increase over that span. 

The numbers of confirmed new transmissions jumped from just 27,000 in 2004 to more than 96,000 in 2016, the CDC said.

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And the number of diseases those bugs spread is growing, too. The CDC said it had identified nine new pathogens transmitted by insects within the U.S. over the 13-year stretch, including diseases like the Zika and West Nile viruses and chikungunya, a virus that attacks the joints and can cause extreme pain. 

“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,” CDC Director Robert Redfield said in a statement. “And we don’t know what will threaten Americans next.”

The CDC warned that the U.S. public health system is not fully prepared to fight back against bug-borne illnesses. The increasing number of transmissions is worrying to some scientists who say those pathogens represent a growing risk to the country.

The CDC said local public health departments need to do more to control mosquito, tick and flea populations. 

Mosquito-borne infections are most likely to hit sunnier states and territories. California, Colorado, Arizona, Texas, Florida and Puerto Rico had among the highest rates of infection over the last 13 years, though states like Illinois, New York and New Jersey also had high rates. Tick-transmitted diseases are more likely to affect Northeastern states.  

Those tick-borne pathogens are most prevalent, accounting for about three-quarters of the 640,000 cases. Lyme disease is the most common tick-borne illness, and the CDC researchers found the area where Lyme disease exposure is a risk has been growing in recent years.

Among mosquito-borne illnesses, West Nile virus occurred most frequently, while dengue fever, chikungunya and the Zika virus hit hardest in U.S. territories. Puerto Rico experienced four dengue outbreaks, the worst hitting in 2010 and from 2012 to 2013.

Zika, named for the forest in Uganda where it was first discovered, moved north from Brazil through Latin America and into Puerto Rico in 2016. Later, the Zika virus showed up in limited cases in Texas and the Miami area.

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

Recent research has suggested that Lyme disease alone strikes up to 300,000 Americans every year, as much as 10-times higher than the number of diagnoses actually made. Similarly, only 840 cases of West Nile virus were diagnosed in 2016, but data suggests as many as 91,000 Americans may have been infected but not diagnosed.