Dengue fever, malaria, yellow fever, those are diseases found in third world countries, right? Places like Africa and Malaysia, where people are poor and can’t afford screens and air conditioning and medicine and vaccines, and the mosquitoes swarm like angry bees. Think so? Think again.
While it’s true that of the estimated 207 million malaria cases and 627,000 deaths reported in 2013, 90% were in Sub-Saharan Africa, malaria cases in the United States climbed to a 40-year high of 2,000 in 2011. Increasing globalization means that eradicating diseases on our own soil is not enough; until we eradicate it globally we will continue to be at risk.
In the 1950s and 60s, the Pan American Health Organization organized a major campaign to eliminate the Aedes aegypti mosquito, responsible for transmission of yellow fever and dengue fever in the Americas. Concurrently, programs were working to finally eradicate malaria in the Southern United States, using extensive spraying of DDT to control the malaria-transmitting Anopheles mosquitoes.
When DDT was banned in the U.S. in 1972, eradication efforts were considered successful and largely abandoned. Since then, both Aedes aegypti and Anopheles quadrimaculatus mosquitoes have returned in force. Fortunately, malaria medications and yellow fever vaccines have kept those diseases at bay. Dengue fever, however, has no vaccine and no treatment.
Once considered a mild tropical fever, the more sinister side of dengue, called dengue hemorrhagic fever (DHF), reared its ugly head in Cuba in 1981. DHF is an often fatal complication of dengue, involving severe abdominal pain, persistent vomiting, hypothermia, shock, plasma leakage and a drastic drop in blood pressure. Researchers soon isolated four different serotypes of the disease, with exposure to more than one serotype increasing a patient’s risk of contracting the hemorrhagic version of the disease. Scientists now believe they may have identified a fifth serotype of the disease in Malaysia.
Over one-third of the world’s population live in areas where there is risk of infection, and dengue is a leading cause of disease and mortality in the subtropics and tropics. An estimated 400 million people contract dengue every year, and while most cases in the U.S. are acquired during travel outside the country, 28 people contracted the virus in Key West in 2009 and 2010 , causing experts to speculate whether the virus would become endemic in the area’s mosquito population.
Also called “breakbone fever” due to the debilitating muscle and joint pain, dengue fever is spread by the Aedes aegypti mosquito and its cousin, Aedes albopictus, or Asian Tiger Mosquito. Thanks to globalization that largely began with the slave trade back in the 19th century, both species of mosquito can be found in a significant portion of the coastal and southeastern United States.
Symptoms of dengue usually begin four to seven days after infection and typically last from three to ten days. Some people may be asymptomatic, however they can still infect mosquitoes that bite them during a five-day period when large amounts of the virus are in their blood. The virus must incubate in the mosquito for 8 to 12 days before it can be transmitted to another human, which might explain the relative absence of dengue in more arid climates such as Arizona, where a mosquito’s lifespan may be significantly shortened due to the lack of humidity.
The number of dengue cases in the Americas increased five-fold between 2003 and 2013, with 2.3 million cases reported in 2013 and 1,289 deaths. With such devastating outbreaks so close to our borders, it seems inevitable that the disease will regain a foothold here. Since the beginning of 2014, some 24 cases of travel-related dengue have been reported in Florida alone, three of them in Hillsborough County.
Chikungunya – the New Dengue?
Still another virus to make its way to our shores is chikungunya, pronounced chik-en-gun-ye. Like dengue, its major symptoms are fever and joint pain -- in fact the name means “that which bends up” in Makonde, a reference to the agonized posture of the afflicted. Other symptoms may include headache, muscle pain, swelling of the joints and rash. Most people recover to some extent within a week, but joint pain may persist for months or even years, in some cases. The good news is that once you get it, you do seem to develop some immunity. There is no treatment and no vaccination available, however.
Although outbreaks have occurred in Africa, Asia, Europe and countries in the Indian and Pacific Oceans, chikungunya did not arrive in the Americas until late 2013, first detected on islands in the Caribbean. While no locally acquired cases have yet occurred in the United States, anywhere from 5 to 65 travel-related cases have been reported annually since 2005, climbing to 80 so far in 2014, 34 of them in Florida. In Puerto Rico, there have been 23 locally-acquired cases so far this year.
As with dengue, there is no vaccine or treatment for chikungunya. And unlike West Nile and other mosquito-transmitted arboviruses monitored here in Florida by mosquito control organizations and health departments, there is no way to monitor for dengue or chikungunya in the mosquito population. Where antibodies in the blood of sentinel chickens give us early warning of the presence of West Nile Virus (WNV), Eastern Equine Encephalitis (EEE) and Saint Louis Encephalitis (SLE), there is no sentinel for dengue and chikungunya, except the very humans we strive to protect.
Mosquito control efforts are further complicated by the breeding and feeding habits of these two species of mosquito. They both lay their eggs on the sides of household containers, where they hatch once the container fills with rainwater. Mosquito control organizations do not have sufficient manpower to go house to house emptying these containers, and must rely on homeowners to do so. Adult mosquitoes do not fly far from where they emerge from the larval state, generally feeding on the homeowners who so generously provided their nursery. Preferred feeding times are dawn and dusk, whereas mosquito control spraying is done at night when people are largely inside, for obvious reasons.
Anything that holds water is capable of playing host to larval mosquitoes, from pet dishes to trays under potted plants, sagging boat covers and even bromeliads. These items should be rinsed and/or emptied every four to five days as a minimum.
Dengue fever and chikungunya will no doubt provide a tremendous challenge to mosquito control organizations in the coming years. The good news is, these mosquitoes CAN be controlled. The bad news is, we can’t do it. It’s up to YOU. What’s in YOUR water?