It may have been overshadowed by Zika, the disease du jour, but a dengue outbreak has plagued Hawaii's Big Island since October 2015, afflicting over 250 people with fever, joint aches, and rash — the largest outbreak in the state's recent history.
The diseases share the same transmission vector: Aedes mosquitos. And now experts are saying that Hawaii's limited capacity to manage its mosquito population, thanks to austerity cuts a few years ago, set the stage for dengue — and still threatens the rest of the country's biosecurity.
Pingjun Yang is one of the two entomologists on staff at the Hawaii State Department of Health. During the 2009 recession, staff in the state's vector control program, which monitors and, when necessary, acts to reduce mosquito populations, were slashed from 56 to 17.
After 2009, there were no people in vector control, Yang says. Without staff to trap, identify, and test the archipelago's mosquitoes, it was impossible to detect changes in populations that posed a human threat. "That's why, here and right now, [if someone were to ask,] 'what's the mosquito population?' That's difficult to answer," he said.
That answer, if Hawaii had known it, could have helped prevent its current outbreak, experts believe.
Now under a different administration, the Hawaii governor's office is supporting the health department's efforts to rapidly scale up vector control staff using previously restricted funds.
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Dengue virus infects about 100 million people worldwide each year, mostly in South and Central America and Southeast Asia, and CDC estimates about one million people die annually from the disease.
Dengue was eliminated from Hawaii in 1945, before it was even a state — so when a Tahitian strain mushroomed into an outbreak involving 122 people in 2001, health authorities responded aggressively; mosquito repellent was handed out at highway checkpoints, and staff went door-to-door to educate the public on mosquito abatement.
They also did the sweaty legwork of mosquito surveillance: setting and collecting mosquito traps in remote areas, and categorizing mosquitoes according to their wing shape and coloring patterns under microscopes. They would have noticed if the efficient dengue transmitter Aedes aegypti was outnumbering the comparatively doddering Aedes albopictus, heralding conditions ripe for human disease clusters.
But after the 2009 cuts, there weren't enough of the staff to notice the conditions that resulted in a small 2011 dengue cluster in Oahu, says Yang — and although a few were hired in subsequent years, there were still only 25 vector management staff at the health department in late 2015.
Would more resources have prevented the current outbreak? "You'd like to think so," says state epidemiologist Sarah Park. Being aware of heavier mosquito activity and changes in mosquito populations could have provoked targeted pesticide spraying and standing water mitigation to head off the outbreak.
But surveillance isn't failsafe prevention when it comes to dengue, says Roberto Barrera, who leads dengue entomology and ecology activities at the Centers for Disease Control and Prevention. Because these Aedes like to live in urban houses, trapping them is complicated. Nevertheless, knowing the true mosquito density landscape on the Big Island would have allowed for better-targeted elimination, says Park. Their current strategy makes it easy to miss environmental disease reservoirs.
Other reservoirs that are easy to miss are the ones that leave on airplanes before they even get sick. Over eight million tourists travel to Hawaii annually, and if they are infected before leaving for another warm coastal area where Aedes live, they can become the patient zero of new outbreaks.
Although mosquitoes are often characterized as the villains in such diseases, viral spread requires human reservoirs of infection. When an infected human leaves Hawaii for, say, coastal Florida, dengue-compatible mosquitoes may bite her while she orders a margarita, then bite – and infect – her bartender, who's later bitten by another mosquito that then snacks on a busboy. Before long, there's an outbreak much like the 90-person epidemic that plagued Key West, Fla. from 2009 to 2011. Humans are as much a problem as mosquitoes — if not more — when it comes to spreading dengue across the world.
Barrera still maintains that the mainland US is not very susceptible to massive outbreaks. "However," he wrote in an email, "dengue viruses could become endemic in some southern areas, which would then act as a domestic source of viruses," resulting in cooler areas of the country developing seasonal outbreaks. This hasn't happened — yet.
As people travel internationally at ever-rising rates, though, there is an increased risk of importing not just dengue, but other mosquito-borne diseases. Although Zika has recently made headlines, chikungunya, yellow fever, and countless other infections are all spread by the same Aedes vector, and other diseases spread by other mosquitoes abound. The only sustainable solution, many argue, is eliminating mosquitoes.
The Obama administration seems to agree: on February 8, the president requested $1.8 billion USD for mosquito elimination efforts in the Americas, most of it earmarked for domestic programs.
Does Hawaii know how much of that it will see?
"No," wrote a health department representative, "not yet."
Follow Keren Landman on Twitter: @landmanspeaking