Climate change and global travel have brought a reemergence in the United States of viral diseases spread by mosquitos.
In 1905, Florida’s public health officials were dealing with several outbreaks of mosquito-borne diseases, including 572 cases of yellow fever and 82 deaths, and 42 deaths from malaria. Miami saw 6,000 cases of dengue while Tampa dealt with 5,000 cases of dengue.
Window and door screenings, air conditioning and organized mosquito control have all worked to significantly decrease infections and death from what we now think of as exotic diseases. But these measures have not completely eradicated viral infections that are transmitted by mosquitos. This summer, Florida’s Department of Health issued an advisory after seven cases of locally acquired malaria were detected in one county in the state. And so far this year, the CDC is reporting 380 cases malaria in the state.
People with malaria often experience fever, chills, and flu-like illness. In 2020, an estimated 241 million cases of malaria occurred worldwide and 627,000 people died, according to the CDC. The United States sees about 2,000 cases each year.
Many of these cases where people have traveled outside the United States and have been exposed to malaria or dengue, Andrea Morrison, Ph.D., Vector-Borne Disease Surveillance Coordinator at the Florida Department of Health, said in a session at ID Week in Boston. “With the increased globalization, you can have an outbreak in a different country that can keep you busy locally,” she said. “That’s especially evident with these exotic mosquito-borne diseases.”
For dengue, Florida health officials have found that patients’ exposure occurred in Cuba, Puerto Rico, Dominican Republic, Haiti and Jamaica.
But as Morrison highlighted in her presentation, locally acquired transmission is possible in the United States. Florida, she said, has a locally acquired case of dengue every month of the year, although activity is greater in the summer months. “We already have the right environmental conditions,” she said.
Each year, up to 400 million people get infected with dengue. About 100 million people get sick from infection, and 40,000 die from severe dengue. In the United States, so far this year there have been almost 1,200 cases of dengue, with 380 cases in Florida and 475 cases in Puerto Rico. About one in four people infected will get sick and many times symptoms are mild, according to the CDC. But about one in 20 who get sick will have severe symptoms, including internal bleeding and shock.
Temperature, rainfall and humidity can influence the spread, but Morrison also pointed that different species of mosquitos have different habits and preferences that can affect the transmission of disease.
Prompt diagnosis, treatment and reporting is critical for addressing these diseases. Addressing locally acquired cases is a concerted effort that requires coordination with mosquito control.
For malaria, treatments are available, including Coartem (artemether-lumefantrine) and Malarone (atovaquone-proguanil). For dengue, there is no treatment, but vaccine, Dengvaxia, was approved by the FDA in 2015 for children 9 through 16 years old. It is approved for those who have been previously infected with dengue and living in areas where dengue is common. Another vaccine was developed by Takeda, but the company pulled its review application in July for TAK-003. The company said could not address issues related to aspects of data collection; Takeda officials indicated they are evaluating next steps for the vaccine.