CRUISING HEALTH
Dengue: You Give Me Fever

by Marybeth Ellison

As the rainy season approaches again, it brings with it foes both large and small. As you strategize about hurricane preparedness, don't forget to protect yourself from the horde of hungry mosquitoes that may carry disease your way. In previous issues of the Compass, Malaria and Yellow Fever, which are also spread by mosquitoes, were discussed. Of all of the mosquito-borne diseases, the most prevalent by far in the Caribbean is Dengue Fever.
Dengue is endemic in all of the Caribbean and the Americas, as well as the South Pacific, Asia, and Africa. An increase in air travel has been cited as a factor in the rapid transmission of Dengue throughout the world. In the past 20 years, Dengue transmission has skyrocketed in most tropical countries of the Americas, corresponding with the cessation of mosquito-control programs throughout much of the region. There have been especially noteworthy outbreaks recently in Mexico, Venezuela, and Ecuador.
Dengue Fever and Dengue Hemorrhagic Fever (DHF) are caused by one of four serotypes of arboviruses. While these four strains are closely related, they don't provide cross-protective immunity: a person may be infected by all four of these viruses; and, in fact, subsequent infections are more likely to result in a more clinically severe case.
Dengue is transmitted mainly by the Aedes aegypti mosquito, which has a preference for daytime feedings and human victims.  Most tropical urban centers, in fact, have come to be designated as "hyper endemic"; that is, they have multiple Dengue viral serotypes circulating in their populations, and multiple strains of mosquitoes able to spread them. This high level of multiple infections is responsible for the increase in the potentially fatal DHF. This more severe form often occurs during a second or third infection from a Dengue arbovirus, and seems to occur at intervals of every three to four years in most tropical countries. The epidemics most often correspond to the rainy, mosquito breeding season.

Classic Dengue Fever most often presents with the sudden onset of high fever, significant body aches, and lethargy, following an incubation period of three to 14 days. It is often accompanied by a frontal headache, pain around the eye sockets, nausea and vomiting. Patients may also develop a rash on the torso which appears three to five days after the onset of fever, then slowly spreads to the extremities and face. Most commonly this week of acute symptoms is followed by a two-week period of convalescence which is characterized by fatigue, weakness and loss of appetite, as well as a gradual recovery. Unfortunately some patients, at the end of the first week of illness, begin to develop signs of DHF. In these cases, just as the fever is beginning to subside, the patient begins to bleed either internally or externally. Severe bruising, palpable dark rashes, and tiny, bright red dots may be distributed throughout the skin. The patient may also have signs of bleeding from the nose, gums, or gastro-intestinal tract. Severe abdominal pain, protracted vomiting, changes in mental status, and temperature instability are all ominous signs. This may be followed rapidly by signs of shock, which include restlessness, cold and clammy skin, and a rapid weak pulse. At this point in the illness, according to one CDC report, fatalities are as high as 44 percent.
Dengue has a variety of presentations, and the diagnostic and treatment modalities will vary according to the severity of the illness. Dengue can be so mild that in one Asian study, children ages three to 15 missed only one or two days of school on average. In such mild cases, Dengue may not be differentiated from any other viral illness, and the patient will probably not seek medical help. In the most common presentation illustrated above, with a week of fever followed by convalescence, it would be prudent to seek medical care when the fever lasted more than three days, especially if one is feeling particularly ill. Early diagnosis and treatment are essential to survival if it progresses to DHF, and one can't possibly know during that first week if it will progress or not. Risk factors for DHF include previous infection with Dengue, as well as the immune status and age of the host (in this area of the world, it is more common for older children and adults to develop DHF).
To manage pain and fever in one suspected of having Dengue, acetaminophen products are recommended over aspirin or ibuprofen, since the latter classes of drugs can aggravate the bleeding tendencies which may occur with Dengue. Unequivocal diagnosis of Dengue requires a laboratory test. Unfortunately, these tests require specialized equipment which may not be available in many tropical locations. The best site in the Caribbean is the Dengue Branch of the CDC, located in San Juan, Puerto Rico (phone 787-706-2399). To effectively treat DHF, intense supportive care and IV fluid resuscitation is the cornerstone. Careful fluid management can reduce the risk of death to one percent.

"Staying out of trouble is always easier than getting out of trouble," is a favorite medical quip. There are no antivirals currently known to be effective against Dengue. The only realistic way of avoiding Dengue is by eluding mosquitoes. Aedes aegypti mosquitoes are most active during the day, and are most prevalent in urban areas, so protecting yourself in that setting is paramount.

· Keep exposed skin to a minimum. Long sleeves, long pants, socks, and hats all make it more difficult for the mosquito to have access to your skin.
· Use chemical repellents for clothing. Clothing can be treated with Permethrin-containing repellents such as Permanone or Deltamethrin. These are highly effective, last through a number of washings, and are more easily available outside the US. Some clothing companies also make pre-treated clothing: Buzzoff.com provides an on-line catalog.
· Use chemical repellents for skin judiciously. DEET (N,N-diethylmetatolumide) is the most effective substance on the market to repel insects. In general, the higher the percent, the more effective, up to a maximum of 50 percent. A micro-encapsulated sustained release formula will protect longer, though the time will depend on water exposure and sweating. No definitive studies have been done regarding safety in children with DEET, so exercise caution when using this on them. DEET is toxic when ingested, can cause blistering in high concentrations, and should never be used on open or abraded skin. Application to a child should be done by the parent, being careful to avoid the face, eyes, and mouth; it should never be used on infants. All users should wash their hands well following application, and avoid inhaling any preparations with DEET.
On April 28th the CDC  announced the licensing in the US of two "new" chemoprophylactics. One is Oil of Eucalyptus, otherwise known as P-menthane 3,8-diol, or PMD, and is (obviously) plant-based. It has not been approved for children under three years of age, and its duration of efficacy is notably shorter than standard products. The other product is Picaridin, also known as KBR3023. This chemical has been used in Europe and Latin America for years, and has an efficacy similar to DEET. The new product marketed by Cutter is called Advance; the one used in Europe is known as Autan.

Other commercially marketed products, including Citronella cream and Avon's Skin-So-Soft, have not produced compelling data for their efficacy as a repellent when compared with the others.

Explore this beautiful planet, but protect yourself and those you love!
Mary Beth Ellison, MD, FAAP, is US-trained physician with extensive experience in Tropical Medicine. She enjoys cruising the Caribbean on S/V Promise with her family.