United States: California has recently registered its fourth instance of locally transmitted dengue fever, a worrisome escalation in a potentially fatal affliction, with experts pointing to climate change as a possible accelerant.
The Los Angeles County Department of Public Health verified the latest case of this mosquito-borne virus in a resident of Panorama City, nestled in the San Fernando Valley. Notably, the individual had not ventured to regions where dengue is endemic, suggesting that this case, like three earlier ones in the county, originated locally, as reported by The Hill.
“The occurrence of locally transmitted dengue is unprecedented in Los Angeles County,” stated Dr Muntu Davis, the county’s health officer, emphasizing the anomaly.
Although local transmission remains an infrequent phenomenon, officials strongly urged the public to take preventative measures against mosquito bites and eliminate breeding grounds.
Dengue, a viral infection propagated through the bites of specific mosquito species, as defined by the World Health Organization (WHO), predominantly inhabits tropical and subtropical zones. While the majority of cases present mild, flu-like symptoms, severe manifestations can prove fatal.
Globally, dengue cases have skyrocketed, rising from 505,430 in the year 2000 to a staggering 6.5 million by 2023, according to WHO.
The organization attributes this exponential growth to a redistribution of the virus-carrying mosquitoes, exacerbated by climate phenomena and rising global temperatures. Warmer climates, increased precipitation, and heightened humidity create ideal breeding conditions for these vectors.
Since 2010, Florida has regularly experienced locally acquired dengue cases, as reported by the Centers for Disease Control and Prevention (CDC). Other states, including Texas, New York, West Virginia, North Carolina, Hawaii, and Arizona, have also seen sporadic occurrences of locally contracted cases in recent years, as per The Hill.
California, however, recorded its first two instances of locally transmitted dengue only in 2023, placing it alongside Florida as the two states with domestic dengue cases this year.
Before the latest case on September 25, the Department of Public Health had disclosed two cases in Baldwin Park on September 18 and one earlier in the month on September 9.
“This year and last have been among the years with the highest burdens for dengue globally, with climate change likely playing a significant role,” Erin Mordecai, an associate professor of biology at Stanford University, explained in an email.
As dengue’s global reach intensifies, more cases are being imported into California, Mordecai elaborated, noting that travelers bring the virus into the state after being infected abroad.
When local populations of Aedes aegypti and Aedes albopictus mosquitoes are present in California, these imported cases may trigger localized transmission chains, she added.
Although the scale of these outbreaks remains minor compared to endemic regions, Mordecai warned that increasing local transmission could eventually entrench the virus more deeply within California’s ecosystems, according to The Hill.
Mordecai further explained that climate change is likely expanding the seasonal window for dengue transmission by making temperatures more conducive to the mosquito vector’s survival.
Extreme weather events, such as floods, can also trigger outbreaks by causing damage to infrastructure, as witnessed in Peru following Cyclone Yaku in 2023, she noted.
In the US, climate change has similarly fueled a rise in the transmission of West Nile virus, a mosquito-borne disease with broader domestic reach. Unlike dengue, West Nile can thrive at lower temperatures and is sustained by a reservoir of infected birds and mosquitoes, creating a stable source of transmission.
While dengue’s impact in the US remains dwarfed by West Nile, Mordecai warned that “we could be on a trajectory toward more widespread dengue transmission domestically.”
To mitigate the worsening trend, Mordecai emphasized the potential benefits of reducing greenhouse gas emissions, which could temper the expected rise in dengue cases due to climate-driven factors.
In her research, she and her colleagues have demonstrated that climate change has already increased dengue incidence by 18 percent across the Americas and Asia, with projections estimating a further surge of 40 to 57 percent by mid-century. However, scenarios involving lower emissions could significantly curtail this future burden.
Despite this potential reprieve, Mordecai cautioned that many of the future increases in dengue are now inevitable, given the ongoing climate trends already set in motion, as per The Hill.
In the short term, Californians should remain vigilant, avoiding mosquito bites and reporting large mosquito populations to local control agencies, particularly during the day when dengue-carrying mosquitoes are most active.
Dr Davis reinforced this guidance, recommending that residents utilize insect repellents, remove standing water, and ensure homes are equipped with screens.
Davis concluded that these straightforward steps can “substantially reduce the risk of mosquito-borne disease for both you and your neighbors.”