Climate Change Bringing More Than Heat — Malaria And Dengue On The Rise

As Americans gathered for Fourth of July celebrations this past week, many had to endure sweltering heat as the planet hit an unofficial record for the highest temperature in recorded history, a record that has already been broken twice since then. The average global temperature has increased by approximately 1 degree Celsius since the pre-industrial period, and has consistently been rising by more than 0.2 degrees each decade.

This has not only impacted human activity, but also the geographical distribution of animals — e.g., mosquitos and ticks — that may carry and transmit a range of infectious diseases, including malaria and dengue. Climate change is likely attributable to the resurgence of certain diseases that were previously considered eradicated in the United States.

Malaria Transmission In The Southern United States

When you think of malaria, you likely associate the disease with equatorial locations in Central America, Africa and Asia. But many are surprised to learn that malaria was endemic in temperate regions of the United States in the late 1800s, and it was only after a national program was initiated in 1947 that local transmission of the disease was eradicated. However, with rising temperatures, increased international travel and urbanization, the conditions are favorable for re-emergence of the disease. In fact, the Centers for Disease Control and Prevention (CDC) recently reported seven cases of locally acquired malaria in Texas and Florida. This marks the first time in over 20 years that non-travel related malaria has been diagnosed in the country, raising alarm among physicians and public health officials.

Why should this be a cause for concern? Malaria — caused by the parasite, Plasmodium — can be a serious and life-threatening disease. Globally, 240 million cases occur each year, with more than 600,000 deaths being reported. Infected individuals may develop a fever, headache, body aches and vomiting/diarrhea. Given the lack of endemic transmission of malaria in the U.S. for several decades, there is an absence of existing population-level immunity. This may facilitate future outbreaks and potentially increase the severity of cases, when they occur.

Dengue Virus Poised To Increase In Prevalence

Each year, approximately 400 million cases of Dengue fever are estimated to occur, resulting in nearly 36,000 deaths worldwide. Dengue — also known as break bone fever due to the severe body aches that can occur — is a viral infection spread through the bite of a mosquito belonging to the Aedes genus. Although most cases are mild and resolve without complications, severe disease can occur, potentially resulting in hemorrhagic fever, shock and death.

Although travel-associated dengue is relatively common in the United States, local transmission has been rare over the past several decades. However, endemic disease has been identified in several states and U.S. territories, including Florida, Texas, Arizona and Puerto Rico. In 2022, 57 cases of locally-acquired dengue fever were reported in Florida, and Puerto Rico experienced an outbreak resulting in over 800 cases. In 2015, the state of Hawaii reported 200 cases of local transmission. These numbers point toward a rising incidence of the disease in the U.S. as the distribution of the transmission-competent mosquito vector increases.

Vector-Borne Diseases Likely to Become More Common

Malaria and dengue are just two vector-borne diseases that are showing signs of re-emergence in the United States. As climate and environmental factors promote the increased distribution of mosquitos and ticks, other infectious diseases, such Powassan virus, Zika virus and Chikungunya virus may also rise in prevalence.

So what can you do protect yourself and others from these diseases? First, use insect repellant when outdoors, and if possible, wear long pants when walking through tall brush and grass. Second, remove any standing water near your home, such as in bird baths, old tires or planting pots. Standing water is a breeding ground for mosquitos and promotes the spread of diseases, such as malaria. And if you are exposed to mosquitos or ticks and subsequently develop a high fever, body aches or rash that does not resolve in a few days, seek medical attention.

There are multiple reasons to urgently address the climate change crisis, and the increased spread of vector-borne diseases is an unfortunate outcome we can add to this growing list. We must act now.