“The virus infects about 400 million people worldwide each year, and about 40,000 people die annually from severe dengue.”
- USA Today, August 16, 2023, Ken Alltucker, American health reporter
“Considering their impact, you might expect mosquitoes to get more attention than they do. Sharks kill fewer than a dozen people ever year, and in the U.S. they get a week dedicated to them on TV every year.”
- Bill Gates
In the U.S., locally acquired cases of dengue fever are rare. Nonetheless, during the second week of August, Florida health officials reported four new cases of locally acquired dengue fever. This brought the total to 10 cases this year, a new record for locally-acquired cases for the U.S. The fact that these four dengue cases occurred in one week prompted Florida health officials to consider the situation a wake-up call.
Dengue is not endemic in the U.S.—yet. Florida’s environment, however, is a suitable breeding ground for the mosquito that carries the dengue virus. In today’s Germ Gems post, I present a brief overview of the disease and then focus on what’s new with the villainous Aedes mosquito. (I previously discussed the topic of dengue fever in my June 16, 2021 Germ Gems post, “Putting the Brakes on Break-bone Fever (Dengue).”)
Dengue fever (a synopsis). DENV-1, DENV-2, DENV-3, and DEN-4 are four closely-related arboviruses that cause the disease called dengue fever. All four are mosquito-borne (carried by Aedes aegypti or Aedes albopictus mosquitoes), and they all cause the same symptoms, most notably severe muscle, bone, and joint pain. Other symptoms include high fever, headaches, and nausea and vomiting.
When treated, severe dengue has a mortality rate of 2-5%. When left untreated the mortality rate is as high as 20%. Children are at greatest risk of severe (hemorrhagic) dengue, but in recent years deaths have increased disproportionately in adults over 50 years of age.
Given the huge global burden of dengue (almost 400 million cases worldwide per year), a number of innovative approaches have been implemented to stop its onslaught. In my June 2021 post on dengue, I mentioned several of these approaches, e.g., vaccines and the release of genetically modified or Wolbachia-infected mosquitoes. But despite man’s best efforts, to date, the dengue viruses and the mosquitoes that carry them are winning.
What’s new? In November 2022, Arizona reported the first case of locally acquired dengue in a man in Maricopa County. This triggered a concerted environmental assessment of potential breeding habitats of Aedes-bearing mosquitoes. To date, a source for the 2022 case has not been discovered, and no further locally acquired dengue cases have cropped up in Arizona.
The number of cases of dengue fever is, however, mounting worldwide and in the U.S. According to the World Health Organization, the number of dengue cases worldwide this year is the highest ever compared to the same periods recorded since 2000.
Bangladesh has been hit especially hard. An August 3 article in Lancet, “Bangladesh faces record dengue outbreak,” reported that 51,832 cases, 251 deaths, and 2,694 hospitalizations were recorded to date. Health officials expected this surge given a severe monsoon season and increased temperatures in southeast Asia fueled by El Nino—conditions feared by Homo sapiens, but warmly welcomed by Aedes aegypti, the main mosquito vector in the area.
In the U.S., the Centers for Disease Control and Prevention (CDC) manages ArboNet, a national arboviral surveillance system that tracks human cases of dengue throughout the country that are either travel-associated or locally acquired. Florida is the hotspot for locally acquired dengue cases (11 total so far this year). Additionally, Florida has recorded 190 travel-associated cases—cases in people who brought dengue virus with them to Florida from a foreign site.
Why is Florida such a magnet for nasty mosquitoes? Florida’s warm humid weather is the perfect environment for mosquitos to breed and thrive. In dengue virus infections, the culprit is Aedes-carrying mosquitoes. In the case of indigenous cases of malaria, mosquito species belonging to the genus Anopheles are the villain. (See July 19, 2023 Germ Gems post “Homegrown Malaria in the United States: Should You Worry,” highlighting the invasion of Florida by Plasmodium vivax—the parasite that causes malaria.)
Dengue and malaria kill more than 1 million people per year worldwide. The mortality of these infections is the reason the mosquito is considered the most lethal animal in the world.
Let’s hand it to the entomologists. Our warming climate is a major factor that is changing the geography of mosquito-borne infections. But entomologists are coming up with different ways to eradicate these pesky mosquitoes.
Many of the clever technologies aimed at eradicating Aedes and Anopheles mosquitoes target male mosquitoes, even though only female mosquitoes bite (they need proteins from human blood to produce their eggs). The latest article I’ve read on this topic appeared in an August 18, 2023 report in NPR’s global health blog Goats and Soda, “Hairy ears of male mosquitoes help them find the ladies. Can we disrupt their hearing?” It must be a wonderful time to be an entomologist.
What can you do to protect yourself? The CDC’s website “Prevent Mosquito Bites” (http://www.cdc.gov>mosquitoes) is an excellent reference source. And right now, protecting yourself from getting bitten by a mosquito is the best way to avoid contracting dengue fever.
wow !