I often get asked about mosquito-borne dengue fever in the context of climate change. One of the first things I tell people is that it’s actually quite common outside the United States. Between 50 and 100 million cases occur each year, including about 500,000 of the really severe hemorrhagic fever type, and the numbers continue to increase. This increase is due to the usual suspects: more people moving into cities with poor sewage and scattered water containers that breed mosquitoes, increased international travel spreading the mosquito and viruses, and poor public health systems to control the mosquitoes.
The second thing I tell people is that dengue caused outbreaks here in the United States in the 1800s and beginning of the 1900s – and we still have the right mosquitoes to spread disease in the southeastern United States. And yet, despite at least 100 travelers diagnosed with dengue each year in the United States and frequent epidemics right across the US border with Mexico, we have seen only a handful of local cases in Texas. [Note: We are also seeing an epidemic in Puerto Rico, but that’s for another post.] This all changed last summer when a local outbreak of dengue emerged in the Key West area after a 70-year absence; the outbreak affected an estimated 5% of the population (see report). Most recently, a 41-year-old man in Key West was confirmed to have dengue. He went to a military medical facility on April 6th, was referred to Lower Keys Medical Center, and from there was referred to a hospital in Miami, FL. The doctors there diagnosed him with dengue on the basis of his symptoms, and lab results later confirmed their diagnosis. The man reported not having traveled outside the country in the last year, suggesting that he contracted dengue virus locally.
After being hospitalized for five days, the patient fully recovered. Public health authorities in Key West and elsewhere in Florida are advising that people avoid mosquito bites and eliminate mosquito breeding sites in their homes. Florida’s public health authorities are working with the Florida Keys Mosquito Control District to try and decrease the local mosquito population.
So the big question is whether this case represents a persistence of last year’s outbreak or a new introduction of dengue from an outside traveler. What do our readers think?
Dengue: the Facts
Dengue is caused by a virus (to make matters worse, there are actually four separate but related dengue viruses, all of which cause disease) and is often called “breakbone fever” because its main identifying symptoms are high fever and aching bones or joints. Other symptoms include intense headache, pain behind the eyes, minor bleeding (for example, nose or gum bleeding), and sometimes a rash. The symptoms can last for about a week. There is no vaccine or antiviral medicine for this disease, so those who have dengue-like symptoms should see a physician. In about 1 to 5% of all cases, a person’s condition can actually worsen when the fever comes down. These patients need to be hospitalized for frequent monitoring of their blood pressure, administration of intravenous fluids, and other supportive therapy.
The viruses are spread through the bite of infected mosquito species belonging to the genus Aedes. These mosquitoes are black with white stripes on their bodies and legs, so they’re pretty easy to spot. Almost everything about these mosquitoes makes them ideally suited for life with humans. For example, they like to feed at dusk or dawn but will feed during the day in shady areas or at night if the lights are on. They also tend to live inside or around houses and lay eggs wherever there is standing water (which could be in flower vases, pet water bowls, or on the surface of outdoor trash that has collected rainwater). These pests tend to live in tropical and subtropical regions, but these regions include areas of the southeastern United States and surrounding territories like Key West and Puerto Rico (see WHO map).
Methods to prevent contact with mosquitoes include:
- Remove any sort of standing water from in and around your home
- Wear long-sleeved shirt and long pants and use mosquito repellent
- Make sure screens are in place and don’t have any holes by which mosquitoes can enter
- Use air conditioning whenever you can (mosquitoes don’t like the cold, dry air)