ARBO VIRUS DISEASE : CLINICAL ASPECTS
The arboviruses may be isolated in various culture systems including intracerebral inocu-lation of newborn mice, which often results in encephalitis and death. The viruses may be found in the blood (viremia) from a few days before onset of symptoms through the first 1 to 2 days of illness; attempts at isolation from the blood are generally useful only when viremia is prolonged, as in dengue, Colorado tick fever, and some of the hemorrhagic fevers. Virus is not present in the stool and is rarely found in the throat; viral recovery from cerebrospinal fluid (CSF) is also unusual. Virus can be detected in CSF or affected tissue by reverse transcriptase polymerase chain reaction, and sometimes by culture dur-ing the acute phase of illness. Specific diagnosis is usually accomplished by serologic techniques using acute and convalescent sera. Various tests have been used including hemagglutination inhibition, complement fixation, virus neutralization methods, and en-zyme immunoassay. Early rapid presumptive diagnosis can sometimes be made by the detection of IgM-specific antibodies that often appear within a few days of onset (except in Colorado tick fever, where they may be delayed by 1 to 2 weeks), and persist 1 to 2 months.
There is generally no specific treatment for arboviral infections other than supportive care; ribavirin has been used on occasion, but controlled studies have not been reported to support or refute its effectiveness. Prevention is primarily avoidance of contact with potentially infected arthropods, a task that can be extremely difficult even with the use of adequate screening and insect repellents. In some settings, vector control can be accomplished by elimination of arthropod breeding sites (stagnant pools and the like) and sometimes by attempts to eradicate the arthropods with careful use of insecticides. Such measures have been highly effective in the control of urban yellow fever, in which elimination of urban breeding sites and other measures to eradicate the principal mosquito vector species (Aedes aegypti) have been used. Viruses maintained in complex sylvatic cycles are infinitely more difficult to control without risking major environmental disruption and inestimable expense.
Vaccines are available for immunization of horses against western, eastern, and Venezuelan equine encephalitis virus infections, and the latter has also been used for some laboratory personnel who work with the virus. The only other arbovirus vaccine in general use for humans is a live attenuated yellow fever virus vaccine (17-D strain), which is used to protect rural populations exposed to the sylvatic cycle and international travelers to endemic areas. In fact, many countries in tropical Africa, Asia, and South America require proof of yellow fever vaccination before allowing travelers to enter.