To begin this continual series of medical discussions, I think the topic of Dengue Fever is an excellent example of something we should be thoroughly familiar with as residents in Grenada - not to mention the fact that there is the possibility of a future epidemic occurring right now in the country of Paraguay.  Let us start with a little background.

        Dengue is an arbovirus (meaning it is transmitted by an arthropod) in the flavivirus family.  Flaviviruses have an icosahedral nucleocapsid surrounded by an envelope, and a single stranded positive sense RNA genome.  Because it is a positive sense RNA, this is used directly as their messenger RNA, making the genome infective.

         There are four related serotypes of dengue.  The fact that there are four serotypes can lead to a more severe presentation of the illness (hemorrhagic fever/shock) which will be discussed momentarily.  The known transmission cycle is human-mosquito [Aedes aegypti/albopictus/scutellaris/niveus/furcifer-taylori]-human, although a sylvatic cycle involving monkeys may also exist.  Although not endemic in the USA, tourists who visit the Caribbean are known to return inflicted with the disease.  One such case occurred in 1998 at a hospital I worked at in Connecticut.  At first there was uncertainty about what the patient may have been suffering from.

         “Classic” dengue presents suddenly with flu-like symptoms consisting of fever, malaise, cough, headache, GI disturbances, and retroorbital pain.  Severe pains in muscles and joints occur, the source of the illness’ name “breakbone fever.”  Lymphadenopathy, leukopenia, minor bleeding, and a generalized maculopapular  rash are commonly observed.  After a week or so, the symptoms regress and recovery is associated with fatigue and depression.  Epidemics can be explosive but classic dengue is very rarely fatal and has few sequelae.

         Dengue hemorrhagic fever/shock is a much more severe disease which presents in the same fashion as classic dengue, but also has the added features of increased vascular permeability, hemorrhage (especially in GI tract and skin), and abnormal clotting mechanisms.  This more severe form of the disease is due to the production of large amounts of cross-reacting antibodies in the blood after a previous exposure to the virus.  A patient recovers from classic dengue, and antibodies are produced against that particular serotype.  If a patient gets infected with a different serotype of dengue a heterotypic response occurs, and large amounts of cross-reacting antibody to the first serotype are produced.  Immune complexes consisting of the virus and the antibody activate complement, leading to thrombocytopenia, hemorrhage, and shock.

         Differential diagnosis includes yellow fever, measles, rubella, malaria, leptospirosis, and other systemic febrile illnesses – especially those accompanied by rash.

         The treatment for dengue illness is basically mother’s love.  If you are stuck down here and your mom can’t get a flight down, fluids (lots of hydration), NSAIDS, and lots of rest.  There is no vaccine or specific anti-viral therapy for the disease.  In the case of hemorrhagic dengue, more aggressive hydration therapy is required, possibly to the point of using colloids.
 

        This is definitely an illness to become familiar with.  We are in an area where the disease frequently makes itself known.  This is also the type of illness that if you identify it in a patient during your clinicals or residency, it will make you and your school look quite solid.
 

  (References:  Levinson, W. Medical Microbiology & Immunology; Chin, J. Control of Communicable Diseases; Ryan, K. Medical Microbiology.)