Dengue
                                   ======

Short incubation, severe malaise

Found in urban areas, including Bangkok

Carried by tiger mosquitoes, found in urban areas.

A few basics: There are 4 distinct dengue viruses (which are small,
single-stranded enveloped RNA viruses belonging to the Flavivirus family),
referred to as types 1-4 (DEN-1, DEN-2, etc).  These show significant genetic
variation in different geographical regions.  The existence of these 4
distinct types of virus has clinical importance.

Classic Dengue Fever occurs in non-immune populations, and is primarily
diagnosed in adults.  In children, DF usually presents as a mild illness
characterized by pharyngitis, fever, rhinitis, and cough, and is essentially
indistinguishable from other viral syndromes that kids get.  In older kids
and adults, "break-bone fever" is the rule, with the sudden onset of high
fever, headache, backache, arthralgias and myalgias after a 2 - 7 day
incubation period.  The illness generally lasts for 2-6 days, after which the
well-known maculopapular rash occurs, and fever may re-occur.

Dengue Hemorrhagic Fever (DHF) and Dengue Shock Syndrome (DSS) usually occur
only in areas where two or more dengue virus types are endemic (or epidemic).
 DHF/DSS *usually* occurs in children, and is thought to require
*non-neutralizing* antibodies from a previous infection with a different
dengue serotype (or from trans-placental transfer).  The current thinking, as
best I can remember, is that the viral-antibody complexes are taken up into
mononuclear cells in lymph nodes and cause the release of cytokines and other
compounds that activate the coagulation and complement cascades.
 Unfortunately, my Int'l Health notes and references are out on loan right
now; I know there is a literature on this that is more explicit.

The viruses are spread by the Aedes aegypti and Aedes albopictus mosquitoes,
which primarily bite during the day (as opposed to Anopheles sp, which bite
primarily at night).  A mosquito that bites a person infected with dengue can
then transmit the disease to other humans. The mosquito remains infected for
the rest of its life. There are also viral reservoirs in non-human primates.

    Because mosquitoes that carry the virus only travel a few hundred feet
from where they are hatched, health officials feel that the best way to
control the spread of the disease is to eliminate hatching grounds by
emptying sources of standing water such as old tires, tin cans, barrels, jars
and birdbaths.

As far as transmissability is concerned, I am not aware of person-to-person
transmission, although I know of no reason why such transmission could not
occur via blood products. As far as a vaccine is concerned, there is not an
available vaccine for any of the 4 viruses at the moment, although work
continues on a live, attenuated vaccine against DEN-2.  An alternative
approach was published in Science last year - a genetically engineered virus
that makes the Aedes mosquito unable to transmit dengue.  Neat stuff.

Hope this helps.

--Richard

Richard A. Wagner, MD, PhD
PGY-1, U. of Arizona
Tucson