Lyme at Forefront of Vector-Borne Disease Explosion in U.S.

New Jersey Hit Hard; Weather Extending Ticks’ Range
By RICK MELLERUP | May 23, 2018

Ticks are the Rodney Dangerfield of the vector-borne disease world.

They don’t get no respect.

The Centers for Disease Control and Prevention released a report earlier this month that showed that the number of reported vector-borne diseases in the U.S. have tripled in the past 13 years. Some 642,602 cases of 16 diseases caused by bacteria, viruses or parasites transmitted through the bites of mosquitoes, ticks or fleas were reported to CDC from 2004 to 2016.

Over that time period mosquitoes have gotten most of the attention in the media and perhaps deservedly so. After all, West Nile disease can be fatal – according to a preliminary CDC report issued in January it killed 121 persons in the U.S. in 2017, including two in the Garden State. And the Zika virus can lead to horrible birth defects.

But the fact is that tick-borne diseases accounted for 77 percent of all vector-borne disease reports over that 13-year period. And the most common tick-borne disease, Lyme, accounted for 82 percent of all of the tick-borne cases described in the CDC report.

Lyme, although some activists strongly disagree, isn’t generally considered fatal. But thousands, maybe hundreds of thousands, of Lyme sufferers can testify that it can be extremely debilitating and can ruin lives if not take them.

There were 3,322 laboratory confirmed cases of Lyme reported in New Jersey in 2016, and an additional 1,018 probable cases. That’s out of 26,203 confirmed and 10,226 probable cases in the entire country. Only one state, Pennsylvania, had more than the Garden State, checking in with a whopping 8,988 confirmed cases and 2,455 probable.

Nationwide there were 402,502 cases of Lyme disease reported to CDC from 2004 to 2016. Its nearest competitor was dengue, a group of mosquito-transmitted viruses, with 46,692 reported cases. But dengue was mostly reported in Puerto Rico, where it is endemic; rarely is it found in the continental U.S.

The number of reported cases is just the tip of the iceberg.

“We know that the number of Lyme disease cases that actually occur each year (in the U.S.) are approximately 300,000 or 10 times higher than what is nationally reported,” said Lyle Peterson, director of the CDC’s Division of Vector-borne Diseases in a teleconference with reporters accompanying the report’s release.

Why, one reporter asked, is there this undercounting?

“So, one of the reasons that Lyme disease is undercounted is the fact that many Lyme disease cases are treated as outpatient,” answered Peterson. “So people go to the local doctor to get treated. Diseases that are treated by local doctors, you know, particularly when the doctor sees many, many, many cases in a day, they all may not be reported. So as an outpatient disease like this, they’re typically underreported to a certain extent. But it’s important to note the other reason is that there are so many reports coming in to certain state health departments where it’s endemic that the state health department has a difficult time keeping up with the sheer number of case reports.”

The trend line, even for just reported cases, is also not encouraging. In 2004 there were 19,804 reported cases of Lyme in the country. In 2016 there were 36,429. The line on the chart hasn’t gone straight up – in 2009, for example, 38,468 Lyme cases were reported nationwide but that number fell to 30,158 in 2010. But by 2015 that number had climbed again to a record-threatening 38,069 reported cases.

All the other tick-borne diseases that are reported to CDC – Anaplasmosis/Ehrlichiosis, spotted fever Rickettsiosis, Babesiosis, Tularemia and Powassan virus, have followed a similar trend line since 2004, dipping in some years but generally heading upward.

Interestingly, the trend lines for reported mosquito-transmitted diseases – dengue, West Nile, malaria, Chikungunya, California sereogroup viruses, St. Louis encephalitis, eastern equine encephalitis and yellow fever (yes, yellow fever! – more on that later) have not followed suit. Zika, by the way, was nonexistent, or at least undetected, in the U.S. until 2016 when it arrived in a big way with 41,680 cases, mostly in Puerto Rico and the U.S. Virgin Islands.

“It’s important to note that overall figures are really two distinct trends,” said Peterson. “One is the tick-borne diseases that are steadily going up every year, year by year [that’s actually a misstatement, as already shown, but he’s right about the trend]. And so that’s almost a monotonic increase in cases every year as the tick-borne diseases expand to new areas around the country and as the number of cases in areas where the tick has been established has gone up as well.

“For the mosquito-borne diseases, they tend to be more episodic. For example, in 2012 there was a large increase in West Nile cases because there was a large epidemic. In 2016 we had the Zika epidemic, many cases associated with that. So the mosquito-borne diseases tend to be more episodic, causing those numbers to fluctuate up and down whereas the tick-borne diseases are generally increasing year by year over time.”

Global Warming

To Blame?

Some of the reporters on the teleconference were practically asking Peterson to blame the dramatic increase in reportable vector-borne diseases on global warming, returning to that line of questioning time after time. The director tread carefully when discussing that possible correlation. Wading into the global warming debate would involve the CDC in a political controversy.

In any case, the, uh, uptick in vector-borne diseases defies simple explanation.

“As I mentioned, these are very complicated diseases in nature,” said Peterson, answering a reporter’s question. “Does it have to do with global warming or other factors?”

“And there are many, many different factors which affect where these diseases occur and how frequent they are,” he continued. “And so for the mosquito-borne diseases, in particular, they’re very sensitive to patterns of travel and trade and how we live. So, for example, the fact that Zika virus or Chikungunya viruses or the fact that the West Nile Virus came to our shores in 1999, these are diseases that are spread by the movement of people. Or the movements of animals or occasionally the movements of the vectors and the way we transport them. So right now we’re in a situation with the expanding global travel and trade that all these diseases are basically a plane flight away.”

He went on, “For the tick-borne diseases, there are many factors involved with those as well, including the way we live. So, for example, there is many more deer in the area – areas where people live and with more deer you have more deer ticks and with more deer ticks you have more Lyme disease or a number of other diseases that spread.”

Still the director came close to wading into the global warming debate.

“In addition, we know that temperature is very important. And so if you increase temperatures in general, what will happen is that the tick populations will move farther north, expanding their range, as well as increase the length of tick season which puts more people at risk for a longer period of time.”

Another reporter asked, “What I hear you saying, Dr. Peterson, is climate change does play a role here with the tick-borne disease?”

“What I can say,” answered the director, “is that any of these diseases are very sensitive to temperatures. And so when there are increasing temperatures, it promotes several things. One is the mosquito-borne diseases tend to get worse during heat waves. West Nile Virus major outbreaks that have happened in the United States have all happened during heat waves. So temperatures tend to make mosquitoes more infectious and infectious faster, thus promoting outbreaks. For the tick-borne diseases, as I previously mentioned, increasing temperatures will tend to expand the range of the ticks farther north as well as increasing the length of the tick season.”

Whatever the reason, tick-borne diseases in the U.S. are becoming more common. But there’s a chance the focus of the media this summer will be turned to yellow fever. Yellow fever, most people think, is a deadly disease that was conquered back in the days of the building of the Panama Canal.

In March the CDC warned travelers to several states in Brazil to be vaccinated against yellow fever.

“There is a large, ongoing outbreak of yellow fever in multiple states of Brazil,” read a CDC travelers’ health alert. “Since early 2018, a number of unvaccinated travelers to Brazil contracted yellow fever. … Several have died.”

Stay tuned to CDC updates, especially if you plan to travel abroad.

rickmellerup@thesandpaper.net

 

 

 

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