Key Diagnostic Tests.
The disease is typified by the sudden onset of a severe fever, chills, headache, pain behind the eyes (retro-orbital pain), photophobia, and joint and muscle pain. The victim may appear flushed at the onset of the fever and a rash may appear on the torso after 3-4 days and spread to the rest of the body. Lymph nodes are often inflamed.
- Virus isolation by infection of new-born mice with blood or infected mosquitoes
- Detection of antigens or antibody to the agent in the blood (serology)
- ELISA is available
- Raised hematocrit
- Symptoms and effects.
Dengue shows a number of atypical forms without fever or clinically significant symptoms.
The commonest form has an incubation period of 5-8 days followed by the onset of a fever, violent headache, chills, retroorbital pain, with a rash developing after 3-4 days. The fever usually lasts 4-7 days and most people make a complete recovery without complications. Some individuals may take several months to recover. Fatalities are rare.
Complications can arise in areas where the disease is endemic and repeated infection is possible. These are dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). They are most often found in children who have been previously had Dengue fever. DHS appears first with the child developing internal hemorrhages that lead to the onset of DSS. The condition is fatal in 10-20% of cases.
The virus is killed by heat and is susceptible to common disinfectants; 70% ethanol, 1% sodium hypochlorite, 2% glutaraldehyde.
Agent Properties and Potential Uses
The virus is relatively stable and can survive for up to two days in dried body fluids, e.g. blood. It is not easily transmitted between individuals and is normally only transmitted by mosquito bites. The virus can be carried by several members of the widely distributed genus Aedes and by the genus Stegomyia. It takes several days for a mosquito to become a vector after biting an infected individual, but it remains infected for life.
In its native environment, the virus uses other mammals as a reservoir with occasional transmittal to man. In urban areas, it can use man as a reservoir for human to human transmission.
Response to an attack has therefore to include treatment with insecticides and continued monitoring of local mosquito and wild animal populations for the presence of the virus, even after the instant crisis is past.
The most worrisome aspect of the resurgence is that it has come with an increase in the frequency and severity of dengue hemorrhagic syndrome, a severe complication of the disease normally only arising upon re-infection. Typically, when diseases first crossover to man they are at their most severe (syphilis is the prime example of this) and over the years they become less severe as they adapt themselves to a new host. Dengue appears to be running against the stream, making it a greater public health and weapons threat.