The Centers for Disease Control and Prevention is warning that after years of climate change, the global incidence of dengue fever has reached a record peak this year – reaching several parts of the U.S.
In a recent Health Alert Network Health Advisory, the CDC reported that nearly 9.7 million dengue cases were spotted in the Americas for the first half of 2024, double the number of cases in 2023. According to the Pan American Health Organization, Latin America is experiencing significant outbreaks of dengue virus infections, with more than 11 million cases in 2024 as of this month, a 401% increase from the 5-year average. In a statement for NBC News, Dr. Albert Ko, a professor of epidemiology of microbial diseases at the Yale School of Public Health, said the trends were “concerning for places where dengue hasn’t occurred before in recent history: North America and Europe.”
With the global rise in cases, health official have also noted a significant uptick in the number of cases in the United States. Earlier this year, Puerto Rico declared a public health state of emergency due to a rise in dengue virus infections. While locally transmitted cases of dengue fever in the continental United States continue to be relatively rare, the CDC cautions Americans traveling overseas of the possibility of infection. In a May report from Florida’s Department of Health, the number of dengue cases in Florida spiked to more than 150 cases, mostly from traveling Americans returning to the United States. Cases have also been reported in Texas, Arizona, California, and Hawaii.
Dengue fever is caused by four types of dengue viruses (DENV 1-4). The virus is spread through the bites of infected Aedes aegypti mosquitoes. Those who are infected with the dengue virus can be bitten by female mosquitoes of this species. When that mosquito bites a healthy person, the virus enters the bloodstream and leads to disease. These mosquitoes are commonly found in tropical environments and southern parts of the United States, but in a 2017 study published by the CDC, these mosquitoes have been found in more northern parts of the country, such as Delaware.
Many experts believe that climate change and global warming are partially responsible for the increase in the number of dengue virus infections. Global temperatures have increased to record highs in recent years. In 2023, the National Oceanic and Atmospheric Association released an annual climate report that the summer months had reached more than 1.0°C higher than the previous long term average. According to an National Institute of Health study in 2018, temperature is an essential requirement for the survival of Aedes aegypti mosquitoes, which thrive in the temperature range of 77 to 86 degrees Fahrenheit. With the increase in global temperatures, more areas of the world than ever are now habitable for these mosquitoes.
In addition, Aedes aegypti mosquitoes thrive in wet and warm climate conditions. Due to climate change, in recent years, the El Niño weather pattern has resulted in more severe weather events. This weather pattern occurs every 3 to 5 years, leading to humid and rainy seasons that are conducive to the spread of mosquitoes. As a result of this pattern, more people in the future may be at risk for insect-borne illnesses, such as dengue fever.
According to the CDC, about one in four cases of dengue fever are symptomatic. Symptoms usually manifest about 5-7 days after the infection occurs. Mild cases of dengue fever cause flu-like symptoms such as fever (up to around 104 degrees Fahrenheit), headache, nausea, vomiting, and rashes. For mild cases, most people recover within a week. Notably, people who are infected with one strain of the virus are usually protected for life against reinfection, but are still susceptible for the other variants of the virus. For some people, depending on the type of second infection, the disease can become severe and deadly in a phenomena known as “original antigenic sin.”
Severe cases of dengue fever, also known as dengue hemorrhagic fever or dengue shock syndrome, can be life threatening. According to the Mayo Clinic, this occurs when blood vessels become leaky and the number of clot-forming cells, also known as platelets, drop. The result is a risk for internal bleeding, which is life-threatening. Symptoms of dengue hemorrhagic fever include severe abdominal pain, difficulty breathing, and blood in urine. People who are experiencing any of these symptoms, especially after traveling overseas, should seek immediate medical attention.
Dengue fever can be diagnosed through a blood test and is otherwise difficult to differentiate from other conditions with similar symptoms. Currently, there is no treatment available for dengue fever outside of supportive care. There is no available antiviral medication to treat the disease. The Mayo Clinic recommends that if during the process of recovering from dengue fever, a patient shows signs of dehydration, such as decreased urination or lack of tears, a doctor should be called immediately. Over-the-counter medications such as Tylenol or Advil can also be used to mitigate the effect of symptoms. In more severe cases, intravenous fluid can be administered in a hospital and blood pressure can be monitored.
There are many ways that people can protect themselves from being infected with the dengue virus. Using Environmental Protection Agency-approved repellents is recommended by the CDC, especially during travel to tropical areas. The CDC provides a list of areas with high levels of dengue outbreaks, and travelers should be especially cautious when traveling to these areas. In addition, people can use mosquito screens, wear loose clothing, and remove still-standing sources of water to prevent mosquito bites.
