Dengue fever (pronounced "deng gay") is the most common mosquito vectored disease in the world affecting upwards of 100 million people each year. As Earth's climate increases globally, the mosquitoes that transmit this disease are spreading both north and south from the tropics and it is estimated that by the year 2030 approximately fifty percent of the world's population will be exposed to this disease.
Dengue Fever in the United States
Although new locally obtained cases of dengue fever, also known as "break bone fever," had not been recorded in the United States since 1934, vacationers sometimes return to the U.S. with dengue fever after being infected in areas where this viral disease is endemic. In 2009 and 2010, almost fifty cases of dengue fever were brought into the U.S. by vacationers who were bitten in an endemic area – most often Latin America.
During the same period, twenty five cases of dengue fever originated in Key West with no locally obtained cases being recorded for other areas of the US. In 2011, however, two cases of locally obtained dengue fever were recorded in the Miami area by August. With mosquito activity continuing through the autumn, it is possible that more cases will have developed by the end of 2011.
To keep mosquito populations down in 2011, Key West sprayed and removed mosquito breeding sites. The Key West County Health Department's Bob Monroe said they were acting on the principle of: "No bugs, no dengue." Since Key West was the focus of dengue fever in 2009 and 2010, and no new cases were recorded for 2011, the spraying program appeared to accomplish what the health department set out to do. Unfortunately, spraying programs of this nature often kill much more wildlife than the targeted mosquitoes, but that is another story.
Transmission of Dengue Fever
Although mosquitoes are not the only means of transmitting dengue fever from person to person, they are the only insect vectors for the disease. Day biting tropical species such as the Egyptian mosquito, Aedes aegypti, and the Asian tiger mosquito, Aedes albopictus, are the primary vectors, and there is some indication other mosquito species may also transmit this virus. Both of these mosquitoes are widespread throughout the southern United States and have recently been found in regions with cold winters – although they probably repopulate places such as New York and Chicago each year as the result of human movements. Unlike bacterial infections like Lyme disease, dengue fever virus does not need to mature in its vector. Thus, a mosquito can transfer the virus from one person to the next individual it bites.
A second mode of viral transmission is via blood transfusion and use of blood products. If a person with an undiagnosed case of dengue fever gives a blood transfusion to another person, the second person may experience a full-blown case of the fever. The virus can also cross the placenta to an unborn fetus.
Frequency of Dengue Fever Infections in the U.S.
Most people who have been bitten by a mosquito carrying the dengue fever virus produce antibodies against the virus whether or not they show symptoms of the fever. These antibodies can be identified from blood samples. In 2009 and 2010, twenty five people were diagnosed with dengue fever in Key West. In the same period, the health department estimated about 1000 people carried antibodies against the disease – showing that they had recently been exposed to dengue fever but had not developed symptoms. Thus, about ninety seven percent of those infected are not symptomatic and never know they have had the disease.
Symptoms of Dengue Fever
Dengue fever has two forms. The first, affecting muscles and joints, is extremely debilitating but of short duration; the second, dengue hemorrhagic fever, causing massive hemorrhaging throughout the circulatory system as well as attacking the muscles and joints, is often fatal. In either case, symptoms first appear from three to fourteen days after being bitten by an infected mosquito. Both forms begin with a sudden high fever; headaches; pain behind the eyes; intense muscle, joint and bone pain; and bleeding. Many patients also experience vomiting and diarrhea. The symptoms usually last four days to a week. Dengue fever is often misdiagnosed because its symptoms resemble those of influenza and other viral infections. Thus, the incidence of dengue fever may be much higher than the actual number of cases reported.
It appears that dengue hemorrhagic fever occurs when a person is infected with a second strain of the dengue fever virus having first developed antibodies against the disease after an earlier infection. Less than one percent of people suffering from dengue fever experience dengue hemorrhagic fever. According to the CDC, most cases of dengue hemorrhagic fever also resolve – usually after a single day of intense bleeding, the "crisis day," but fifty percent of the people who go into shock on the crisis day die without medical intervention.
Dengue fever is a debilitating disease with no known cure – yet a tea made of the leaves of the Tawa Tawa plant appears to offer relief of symptoms of dengue fever, dengue hemorrhagic fever, and the fatal shock associated with Dengue hemorrhagic fever. Because of its debilitating affect on people and a remote chance of it being fatal, a vaccine is being developed, but it will be some time before that is ready for distribution.
Albert Burchsted - Ph.D. in animal behavior, field biologist, and photographer. Al leads nature study walks and is an environmental consult in SE ...
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