Armação dos Búzios, Brazil, March 19, 2024 --  

South America's summer has featured huge swarms of mosquitoes and related diseases. As summer approaches in the USA, southern residents may soon get a taste of these troubles.

As Brazil's public health authorities race to catch up with an unprecedented outbreak of dengue fever, scientists are predicting the caseload will more than double last year's all time record.¹ So far this year, 1.6 million suspected dengue cases have been documented, with a confirmed death toll of 491 and an additional 889 deaths suspected.²

The mosquito-born virus has long plagued the tropics, but this year the problem has also spread to more temperate areas like Buenos Aires, fueled by unusually high temperatures and unusually heavy rains. 74,555 cases were registered in Argentina this year through March 5 (including one each for the author and his wife.) This is 43 times as many cases as the same period last year.

Huge clouds of "flood" mosquitoes twice struck Buenos Aires and the surrounding province in January and February after storms flooded the region during the peak of summer heat. The swarms covered windows and sent residents fleeing indoors. Fortunately the aedes albifasciatus species that drove the swarms does not spread dengue. But the same conditions that lead to its swarms also boost the more dangerous aedes aegypti mosquito that spreads not only dengue, but chikungunya, zika and yellow fever.

Disease outbreaks spread by aedes aegypti mosquitoes have been plaguing Brazil for centuries. Brazilian health officials targeted the mosquito in the early 20th century by eliminating breeding areas, educating people to avoid bites, and using newly invented chemical insecticides. By 1958, the Pan-American Health Organization declared the mosquito eradicated in Brazil.³ Outbreaks of dengue and yellow fever became a distant memory.

But then in the 1960s, the mosquito made a comeback. The rapid growth of urban slums created new breeding areas. The mosquitoes became resistant to insecticides like DDT. By the 1970s, Brazil gave up plans to eradicate the mosquito, and the first new dengue outbreak came in 1981.⁴

Since then, the mosquito has been spreading steadily southward toward Argentina, and is now present not only in Buenos Aires but along the coast all the way to Patagonia.

In North America, the same period has seen the aedes aegypti mosquito spread north and west from a historic population reservoir on the Gulf Coast. It is now found throughout the southeast up to Washington DC and lives along the coast as far north as New York City.

Americans don't fear dengue and other tropical diseases because cases in America are rare, much like they were in Argentina in years past. Of the 700,000 worldwide deaths by mosquito-borne diseases last year, the vast majority were caused by malaria, and most of those deaths happened in Nigeria, Congo, Niger and Tanzania.⁵

But just because most mosquito borne disease deaths are in Africa, doesn't mean Americans can be complacent. if Argentina's experience is anything to go by, the American south may also start experiencing serious outbreaks. Last year, both Florida and Texas actually recorded not only dengue cases, but locally-transmitted malaria as well. Even Maryland reported one case.⁶

Unsurprisingly, it is in South Florida where cases of mosquito-borne tropical diseases are most common. The Florida Keys Mosquito Control District has been leading the way in fighting the aedes aegypti mosquito in the United States. In 2016, it got Environmental Protection Agency approval to allow British biotech company Oxitec to do trials with genetically modified aedes aegypti mosquitos that pass fatal genes to their female offspring.⁷ But trial attempts were stalled by public opposition until 2021, because of fears of potential environmental harm and general apprehension of genetic engineering.⁸

Even if Oxitec can get EPA approval for commercial sales, public fears of genetic engineering may slow governments from releasing these mosquitoes in other parts of the United States. An alternative strategy that avoids this fear has been piloted in Brazil by infecting aedes aegypti mosquitoes with the wolbachia bacteria. That bacteria is commonly found in many insects, but normally not in the aedes aegypti mosquito.

When the bacteria is present, it stops the mosquito from transmitting the virus to humans it bites. And when they breed with other mosquitoes, they pass the wolbachia bacteria to their offspring, quickly reaching virtually the entire mosquito population in the area.

Technicians in Brazil, grew thousands of these "wolbitos" in the lab, then released them into the wild in the city of Niteroi across the bay from Rio de Janeiro. So far this year, that city has a 90 percent lower dengue case rate than its more famous neighbor across the bay.⁹

The lab has since increased production of the wolbitos and is planning to seed six other cities in Brazil this year.¹⁰

Such alternate technologies offer hope to Americans at risk from the northern spread of aedes aegypti and its related diseases. While science-averse Americans may fight against genetically engineered mosquitoes, the more benign sounding wolbitos might sneak by while opponents are looking the other way.

Notes:

1. Telegram, Unprecedented Outbreak of Dengue Surges Across Brazil, March 18. 2024

2. Guardian, Brazil to Release Millions of Anti-Dengue Mosquitoes as Death Toll From Outbreak Mounts, March 15, 2024

3. American Journal of Public Health, Leaking Containers: Success and Failure in Controlling the Mosquito Aedes Aegypti in Brazil, April 2017

4. Ibid.

5. World Health Organization, World Malaria Report 2023, November 30, 2023

6. National Public Radio, New gene-editing tools may help wipe out mosquito-borne diseases, January 26. 2024

7. USA Today,The first genetically modified mosquitoes released in the U.S. to buzz in the Florida Keys, April 29 2021

8. National Public Radio, Florida Keys Opposition Stalls Tests Of Genetically Altered Mosquitoes, August 19, 2016

9. Guardian, Ibid.

10. Ibid.