Like robins, the advent of cooler temperatures, drier air and the cessation of afternoon thunderstorms are precursors to two important events in Naples. Rather than springtime, however, they foretell the beginning of “snow-bird” season and the end of mosquito season.
At least one of these is eagerly anticipated each year by Naples area residents.
While mosquito season in Naples was typical, meaning there was no real rhyme or reason to mosquito numbers, the mosquito-borne disease situation was quite atypical. And this disease problem was not limited to Naples, but struck the entire state.
A scary new trend
Statewide there are three regularly occurring, mosquito-borne diseases that can infect humans: St. Louis encephalitis (SLE), West Nile virus (WNv), and Eastern equine encephalitis (EEE), with dengue fever being a new kid on the block. Naples residents should be familiar with SLE and WNv, as these two diseases, transmitted from infected birds to humans by mosquitoes, periodically impact local residents, and, in the case of WNv, horses. On the other hand, EEE has not been detected in the Naples area for at least the last 50 years.
Until this year, that is.
Normally, EEE is found north of a line from Tampa, across the peninsula, to Vero Beach on the east coast. This year that line moved completely down the peninsula and included Collier County and Miami-Dade County. Collier had four equine cases of EEE from June 9 to July 9, but was fortunate in not having any human cases. All four infected horses died as a result of the disease, which is preventable by having horses vaccinated.
This is the most severe type of mosquito-borne encephalitis in the state, with higher mortality rates in both horses and humans.
While Collier County had four horses infected this year, there have been a total of 93 horses and four human infections in Florida through Nov. 6. There is a vaccine for horses, but not for humans, so personal protective measures are the primary way to avoid contracting EEE.
SLE, the predominant mosquitoborne disease in the Naples area before the introduction of WNv, was detected in five sentinel chickens in Miami Dade County but no human cases have been reported. WNv, however, has caused illness in 11 Floridians and 22 horses. Two of the human cases were in Naples, with one case being fatal. The human cases in Naples were both in areas of historically low mosquito numbers, making it difficult to understand how the individuals were infected. These cases, coupled with the low mosquito density, serve to reinforce the fact that, while the Collier Mosquito Control District (CMCD) can reduce mosquito numbers significantly, it cannot completely eliminate mosquitoes and the final responsibility for preventing mosquitoborne diseases lies with the individual.
Because of the presence of mosquito-borne disease, the CMCD greatly increased both mosquito and disease surveillance, especially in those areas where humans or equines were affected. In addition to the nearly 60 permanent light traps used to monitor mosquito numbers throughout the district, 16 new sites were sampled using portable traps. These new sites were located so the mosquito collections could be used to better target control efforts.
Disease presence was monitored using laboratory techniques that identify WNv infected mosquitoes. A total of 9,811 mosquitoes, in 459 pools of mosquitoes, were tested, with only three pools being positive for WNv. This low level of infection is just another indication people need to take personal precautions against mosquitoes, in addition to what the CMCD can provide.
EEE, SLE, and WNv should be familiar to most residents, but how about dengue fever? Dengue, also known as break-bone fever because of the extreme joint pain it can produce, seems to have come back home to Florida, at least to Key West. There have been 57 human cases of dengue in Key West and one in Broward County, as of Nov. 6. These are all cases that were acquired in Key West and Broward, not brought back from some tropical vacation spot.
Two very closely related mosquito species can be responsible for dengue transmission. One or both of these mosquitoes are found throughout Florida and are known as “domestic” mosquitoes because they breed in manmade containers such as cans, bottles, buckets, rain barrels, rain gutters, and kiddy pools, as well as natural sites, like tree holes.
Like Key West, we have the mosquito, the climate and the potential breeding sites for continued mosquito production. All we lack is the dengue virus, and that could show up any day. So far this year there have been 118 cases of dengue brought into Florida by people arriving from other countries. All it takes is for one of those infected individuals to be bitten by the right mosquito, and we could very well be having our own dengue fever problem in Naples.
And now, malaria
And how about malaria? There have been 103 cases of malaria imported into Florida this year. As with dengue, we have the mosquito and the climate for malaria, all we lack is the right mosquito biting the wrong person. If that happens we could have malaria circulating in Naples again.
The threat of mosquito-borne diseases to Naples area residents is real, and worrisome in its potential. It will take the combined effort of the CMCD and local citizens to prevent these diseases from becoming even more of a threat.
Jeffrey C. Stivers, Ph.D. is director of research for Collier Mosquito Control District. Contact him at JStivers@colliermosquito. org or by phone at 436-1000. The district website is www.collier-moquito.org.