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UM Entomologist Shares Insight on South Florida’s West Nile Virus and Dengue Fever Cases

Left: A female Aedes aegypti mosquito, which is the primary vector for the spread of Dengue fever. Right: A female Culex quinquefasciatus mosquito, which spreads West Nile virus.
In Miami-Dade County, there have been nearly two dozen locally transmitted West Nile virus cases so far this year, including eight reported in July. As of July 28, Monroe County has reported 22 cases of dengue.

The West Nile virus is the leading cause of mosquito-borne disease in the United States. Dengue fever, an important mosquito-borne disease worldwide, is also transmitted by infected mosquitoes.

John Beier, Sc.D., an internationally renowned entomologist and professor at the University of Miami Miller School of Medicine Department of Public Health Sciences, along with collaborator and postdoctoral associate Andre Wilke, Ph.D., work closely with Miami-Dade County Mosquito Control. The extensive mosquito surveillance and control activities by the county help protect residents and tourists. For local outbreaks of mosquito-transmitted diseases,  Mosquito Control deploys greater surveillance and control measures to help prevent transmission.

Here, Dr. Beier answers questions on the local vector mosquitoes, symptoms of West Nile virus and dengue, what to do if you think you have been infected, as well as what causes mosquitoes that carry the infections to linger in certain environments. Dr. Beier also discusses preventive measures, advising residents in counties with increasing cases on what to do in their outdoor areas.

How prevalent are West Nile virus and dengue fever cases in the State of Florida each year?

West Nile virus is endemic in the United States and human cases are common in Florida. Underserved communities are at a higher risk of infection due to their increased contact with night-biting Culex mosquitoes, the main vector of the West Nile virus in Florida.

Florida has the most cases of dengue in the contiguous United States. It has been disproportionally affected with 1,173 imported cases of dengue since 2010. Furthermore, of the 48 states in the contiguous United States, only four states reported locally transmitted cases of dengue, with Florida accounting for 80.5 percent (120) of these cases.

What type of mosquitoes carry West Nile virus or dengue fever? How do the mosquitoes themselves become infected?

Miami-Dade County has more than 50 different types of mosquito species. Several of the local mosquito species are known vectors of West Nile virus. The most widespread and common vector is Culex quinquefasciatus. This mosquito blood feeds on hosts at night. Female mosquitoes become infected by feeding on infected birds of many different types. Birds are reservoir hosts for the virus, and some die of the virus infection. Dead birds such as blue jays and crows are a warning sign of West Nile outbreaks.

The vector of the dengue virus is Aedes aegypti, which is abundant throughout Miami-Dade County. It is also the vector of Zika and chikungunya arboviruses. Aedes aegypti becomes infected by blood-feeding on an infected human. Local transmission generally occurs when there is an influx of infected people coming into the county from endemic areas of the Caribbean, and Central and South America.

What kinds of environments attract these types of mosquitoes the most and what would you suggest as preventive measures? What measures should counties take?

Both Culex and Aedes mosquitoes can develop in their immature stages in various types of standing water. The Culex are generalists using a wide range of aquatic habitats, such as storm drains, ditches, roadside standing water, and all types of containers holding water. The Aedes are specialists depending mostly on container habitats, such as buckets, flower pots, containers in yards, bromeliad plants, and storm drains. Residents can take action around their homes by removing or emptying containers holding water.

Throughout Florida, counties operate effective mosquito surveillance and control operations. In Miami-Dade County, the Mosquito Control Division operates around 200 traps throughout the county each week to collect and monitor adult mosquitoes. When trap catches of vector species are higher than a threshold of 10 then this triggers teams of operators to go to the specific areas and do control. There are many types of mosquito control but control of immature aquatic stage mosquitoes is best done by using Bacillus thuringiensis serotype israelensis (Bti). This is a biological control agent which is effective in killing mosquitoes while having almost no effect on other organisms.

What are the symptoms and treatment of the West Nile virus and dengue fever? What should a person do if they suspect that they have been infected?

As stated by the Centers for Disease Control and Prevention (CDC), there are no vaccines to prevent or medications to treat the West Nile virus. Usually, those who become infected with the virus do not feel sick. Approximately one in five people who are infected do develop a fever and other symptoms, and about one out of 150 infected people develop a serious, sometimes fatal illness.

The CDC also advises that mild symptoms of fengue can be confused with other illnesses that cause fever, aches and pains, or a rash. The most common symptom of dengue is fever, along with any of the following: nausea, vomiting, rash, aches and pains, including eye pain, which typically occurs behind the eyes, muscle, joint, or bone pain. Symptoms of dengue typically last two to seven days. People will typically recover after about a week.

For anyone who suspects being infected with either West Nile virus or dengue, you are advised to see your health care provider.

Can one be infected with both at the same time?

Yes, it is possible but extremely rare that an individual is infected at the same time with West Nile virus and dengue.

What are some resources for residents who want to learn more about preventing infected mosquitoes on their properties?

In Miami-Dade County, mosquitoes occur all year round, but reach peaks during the warmer, wetter months from April through November. Each week residents should remove or empty water from containers around their homes. They should also remove old tires on their property, as these hold water and are ideal habitats for dangerous mosquito vectors. Residents are also advised to use insect repellents, and wear long-sleeve shirts and long pants when possible.

Those having mosquito problems can call 311 to report their problem to Mosquito Control. The call triggers Mosquito Control to send an inspector to check the property for mosquito problems due to standing water, water-filled containers and/or bromeliads, to conduct local mosquito control, and to advise residents.

Written by Amanda Torres
Published on July 22, 2020