a. Signs/Symptoms and Reservoir. The fever lasts about 5 to 7 days, during
which time there is intense headache, pain in the joints and muscles, and a rash. Fatal
termination is rare. Humans are the only known vertebrate hosts for dengue and serve
as the reservoir as well as definitive host.
b. Period of Infection for Man and Mosquito. Patients usually are infective for
mosquitoes from the day prior to onset through the fifth day; accordingly, keeping
patients in enclosures that are screened or treated with residual insecticide will reduce
but not halt transmission to vector mosquitoes. The Aedes mosquito vector becomes
infective for life 8 to 11 days after a blood meal from an infectious person. Incubation
time from mosquito bite to onset of symptoms is 3 to 15 days, with 5 to 6 days the
c. Military Significance. The military significance of dengue rests on its
explosive nature, resulting in a high percentage of casualties in a short time, and in the
prolonged convalescent period. There is no specific therapy. Recovery confers limited
d. Prevention. Prevention lies in control and avoidance of mosquito vectors.
5-23. THE ENCEPHALITIDES
a. General. The mosquito-borne viral encephalitides are acute
inflammatory diseases of comparatively short duration that involve the
central nervous system (CNS). These disease occur in widespread
areas of the world and are not confined to the topics. The mosquito
vectors considered most important in the transmission of these
diseases to man are listed in Table 5-1.
b. Natural Cycle of Infection and Diagnosis. Most vectors seem to feed by
choice on birds or small rodents. Hence, the primary natural cycle of infection probably
is one of bird-mosquito-bird or rodent-mosquito-rodent, with the infection of man being
only accidental. Each of these encephalitides is caused by a specific virus. Specific
diagnosis is by serologic tests for which laboratories smaller than major overseas
laboratories or area laboratories in the United States usually are not equipped.
c. Prognosis. The clinical syndrome produced in man varies with the severity
of the infection and with the infecting agent. Murray Valley, St. Louis, and Western
equine, with fatality rates approximately 5 percent, may be considered mild in
comparison to Japanese B and Eastern equine, which have fatality rates ranging up to
Death, when it terminates, one of these infections usually occurs in the
first 7 to 10 days after onset of frank CNS signs.