Dengue viruses are transmitted to humans through the bites of infective female Aedes mosquitoes. When the mosquitoes feed on the blood of the infected person, they acquire the virus. Once infective, a mosquito is capable of transmitting the virus to susceptible individuals for the rest of its life, during probing and blood feeding. Infected female mosquitoes may also transmit the virus to the next generation of mosquitoes by transovarian transmission i.e. via its eggs. Humans are the main amplifying host of the virus, although studies have shown that in some parts of the world monkeys may become infected. These monkeys can serve as a source of virus for uninfected mosquitoes. The virus circulates in the blood of infected humans.
Dengue and dengue hemorrhagic fever (DHF) are caused by one of four closely related, but antigenically distinct, virus serotypes (DEN-1, DEN-2, DEN-3, and DEN-4), of the genus Flavivirus. Infection with one of these serotypes does not provide cross-protective immunity, so persons living in a dengue-endemic area can have four dengue infections during their lifetimes.
The incidence of dengue has grown dramatically around the world in recent decades. Some 2.5 billion people - two fifths of the world's population - are now at risk from dengue. WHO currently estimates there may be 50 million dengue infections worldwide every year.
In 2007 alone, there were more than 890 000 reported cases of dengue in the Americas, of which 26 000 cases were DHF.
The disease is now endemic in more than 100 countries in Africa, the Americas, the Eastern Mediterranean, South-east Asia and the Western Pacific. South-east Asia and the Western Pacific are the most seriously affected. Before 1970 only nine countries had experienced DHF epidemics, a number that had increased more than four-fold by 1995.
Not only is the number of cases increasing as the disease is spreading to new areas, but explosive outbreaks are occurring. In 2007, Venezuela reported over 80 000 cases, including more than 6 000 cases of DHF.
Sudden onset with chills and high fever, intense headache, muscle and joint pains, whichprevent all movement, characterize the disease. Within 24 hours retro-orbital pain (pain at theback of the eye), particularly on eye movements or eye pressure and photophobia develops.Other common symptoms include extreme weakness, loss of appetite, constipation, alteredtaste, colicky pain, dragging pain in the inguinal region, sore throat
and general depression.Fever is usually between 39-40 deg. C. Fever is followed by a phase of remission lasting afew hours to a few days after which it reappears.The skin eruptions usually appear either during the remission or on the reappearance offever. The rash starts on the body and then spreads to the limbs and rarely to the face. Feverlasts for 5-7 days after which usually complete recovery occurs. Convalescence is prolonged.
DHF is a sever form of Dengue fever, caused by infection with more than one type of dengue virus. The disease is much more common in children below 15 years ascompared to adults.The onset is abrupt with high fever accompanied by facial flushing and headache, loss of appetite, vomiting, abdominal pain and discomfort are common. Patient has ableeding tendency and spontaneous bleeding into the skin may be apparent. In sever cases there may be a collapse of the circulatory system characterized by aweak and rapid pulse
, fall in blood pressure and a cold and clammy skin. If diagnosedand treated early, death rate can be lower than 5%; otherwise it can be upto 30%.
Causes and Risk factors:
Dengue fever is a disease caused by a family of viruses that are transmitted by mosquitoes. It is an acute illness of sudden onset that usually follows a benign course with headache, fever, exhaustion, severe joint and muscle pain, swollen glands (lymphadenopathy), and rash. The presence (the "dengue triad") of fever, rash, and headache (and other pains) is particularly characteristic of dengue.
Dengue strikes people with low levels of immunity. Because it is caused by one of four serotypes of virus, it is possible to get dengue fever multiple times. However, an attack of dengue produces immunity for a lifetime to that particular serotype to which the patient was exposed.
Dengue goes by other names, including "breakbone" or "dandy fever." Victims of dengue often have contortions due to the intense joint and muscle pain, hence the name breakbone fever.
Dengue hemorrhagic fever is a more severe form of the viral illness. Manifestations include headache, fever, rash, and evidence of hemorrhage in the body. Petechiae (small red or purple blisters under the skin), bleeding in the nose or gums, black stools, or easy bruising are all possible signs of hemorrhage. This form of dengue fever can be life-threatening or even fatal.
Dengue is prevalent throughout the tropics and subtropics. Outbreaks have occurred in the Caribbean, including Puerto Rico, the U.S. Virgin Islands, Cuba, and Central America. Cases have also been imported via tourists returning from areas with widespread dengue, including Tahiti, the South Pacific, Southeast Asia, the West Indies, India, and the Middle East.
Dengue fever is common and may be increasing in Southeast Asia. Thailand, Vietnam, Singapore, and Malaysia have all reported an increase in cases. According to the World Health Organization, there are an estimated 50 million cases of dengue fever with 500,000 cases of dengue hemorrhagic fever requiring hospitalization each year. Nearly 40% of the world's population lives in an area endemic with dengue.
The virus is contracted from the bite of a striped Aedes aegypti mosquito that has previously bitten an infected person. The mosquito flourishes during rainy seasons but can breed in water-filled flower pots, plastic bags, and cans year-round. One mosquito bite can inflict the disease.
The virus is not contagious and cannot be spread directly from person to person. There must be a person-to-mosquito-to-another-person pathway.
Dengue hemorrhagic fever (DHF) is a specific syndrome that tends to affect children under 10. It causes abdominal pain, hemorrhage (bleeding), and circulatory collapse (shock). DHF is also called Philippine, Thai, or Southeast Asian hemorrhagic fever and dengue shock syndrome.
DHF starts abruptly with high continuous fever and headache. There are respiratory and intestinal symptoms with sore throat, cough, nausea, vomiting, and abdominal pain. Shock occurs two to six days after the start of symptoms with sudden collapse, cool, clammy extremities (the trunk is often warm), weak pulse, and blueness around the mouth (circumoral cyanosis).
In DHF, there is bleeding with easy bruising, blood spots in the skin (petechiae), spitting up blood (hematemesis), blood in the stool (melena), bleeding gums, and nosebleeds (epistaxis). Pneumonia is common, and inflammation of the heart (myocarditis) may be present.
Patients with DHF must be monitored closely for the first few days since shock may occur or recur precipitously. Cyanotic (bluish) patients are given oxygen. Vascular collapse (shock) requires immediate fluid replacement. Blood transfusions may be needed to control bleeding.
The mortality, or death rate, with DHF is significant. It ranges from 6%-30%. Most deaths occur in children. Infants under a year of age are especially at risk of dying from DHF.
The laboratory diagnosis of dengue virus infection has been greatly improved during the last decade. The rapid detection of the dengue virus genomic sequence by real-time one-step RT-PCR has become a trend. This assay has the advantages of simplicity, rapidity, and a low contamination rate compared to the characteristics of the nested RT-PCR method, which, however, has a sensitivity similar to that of the real-time RT-PCR. For acute-phase serum samples, the real-time one-step RT-PCR by either the TaqMan assay or SYBR Green method has been developed and successfully applied to the clinical diagnosis of dengue virus infections. Future developments based on a four-color multiplex protocol may revolutionize this field and eventually replace the conventional RT-PCR as the new gold standard for the rapid diagnosis of dengue virus infection. It should be pointed out that multiple primers and probes targeted to different regions of the dengue virus gene are needed to increase the sensitivity and avoid false-negative results. In addition, good quality control should be followed to avoid false-positive results caused by sample and/or reagent contamination.
For serological diagnosis, detection of the NS1 antigen in acute-phase serum samples has shown promising results. Further studies are needed to evaluate its usefulness and to compare it with real-time one-step RT-PCR with respect to its sensitivity and specificity. For antibody detection, the E/M-specific capture IgM and IgG ELISA has become the new standard in serodiagnosis due to its high degrees of sensitivity and specificity and its simplicity. Careful analysis showed that the differential diagnosis of flavivirus infection could be made by tests with a panel of viral antigens. Finally, an easy, sensitive, and specific NS1 serotype-specific IgG ELISA has been developed and has reliably been used for the serodiagnosis and seroepidemiological study of dengue virus infection. The advantage of the NS1 serotype-specific IgG ELISA is that dengue virus serotyping is possible for patients with primary dengue virus infection if convalescent-phase or postinfection sera are available.
In conclusion, present advances in molecular and serological diagnostic methods have greatly improved the sensitivity and specificity of diagnosis of dengue virus infection. It is expected that the successful application of these assays will contribute significantly to the clinical treatment, etiologic investigation, and control of dengue virus infections.
Because dengue is caused by a virus, there is no specific medicine or antibiotic to treat it. For typical dengue, the treatment is purely concerned with relief of the symptoms (symptomatic). Rest and fluid intake for adequate hydration is important. Aspirin and nonsteroidal anti-inflammatory drugs should be avoided. Acetaminophen (Tylenol) and codeine may be given for severe headache and for the joint and muscle pain (myalgia).
Initiate supportive therapy: Intravenous (IV) crystalloids, as needed to keep systolic blood pressure above 90 mm Hg
Emergency Department Care:
IV access, O2, and monitoring are helpful.
IV crystalloids may be necessary for hypotension; central line may be needed.
Correct electrolyte abnormalities and acidemia.
Implement therapy for DIC if indicated.
Corticosteroids are not helpful.
No antiviral therapy is available.
Medicine and medications:
No specific medications are indicated for direct treatment of the dengue virus infection.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.