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1. Disease description
Dengue fever is also called classic dengue or primary dengue. It is a type of acute viral fever propagated by mosquitoes such as Aedes aegypti or Aedes albopictus. The major symptoms are high fever, head, muscle, bone, joint, orbital pain and eruption.
There is another type of unusual Dengue fever which was discovered in the Philippines, Thailand, Malaysia, Singapore, Indonesia, India, Sri Lanka, Myanmar and Vietnam in 1953; it attacks mainly children between the age of 3~10 and is characterized by severe to potentially deadly hemorrhage symptoms or even shock, posing a serious threat to public health. Its subject of infection, symptoms and prognosis are entirely different from the original dengue fever: it is called dengue hemorrhage fever (DHF) or dengue shock syndrome (DSS) and it is also referred to as secondary dengue. Dengue fever mentioned below refers to traditional or classic dengue fever.
2. Infectious agent
This is caused by the Flavivirus of Flaviviridae, which is comprised of four different types of dengue fever viruses that are called type I, II, III or IV according to their antigenic characteristics.
3. Epidemiology
Dengue fever occurs mostly in tropical and subtropical regions where Aedes aegypti or Aedes albopictus is present. but especially where there is infestation of Aedes aegypti, including Asia, South/Central America, Africa and Northern Australia, or parts of the Pacific islands.
However, after the 1980s, the disease exhibited trends of propagating across the globe and has become a local infectious disease in areas such as Sri Lanka, India, Bangladesh, Myanmar, Thailand, Laos, Cambodia, Vietnam, Malaysia, Singapore, Indonesia, Papua New Guinea, Philippines, Micronesia, the Caribbean and several countries in Central and South America.
4. Reservoir
Conventionally, people believe that the only path of infection transmission is through the vector mosquitoes. However, in western Malaysia and western Africa, reports of a transmission cycle between monkeys and mosquitoes have been filed; it is known as the forest transmission cycle.
Recently, it has been discovered that dengue fever is able to be transmitted to the next generation of Aedes aegypti or Aedes albopictus through eggs under natural conditions in Trinidad-Tobago and Yangon, Myanmar, albeit the positive rate is relatively low (1/158 and 5/199 respectively). In addition, dengue fever has also been identified in male mosquitoes in western Arica, indicating that dengue fever is able to be transmitted through eggs in nature. However, the significance of this vertical transmission cycle in the natural ecological cycle of dengue fever still needs to be evaluated.
5. Mode of transmission
When a person is stung by a dengue fever vector mosquito, viral activities occur in the person’s blood between one day before and five days after falling ill; this is called viremia. The most influential vector mosquitoes in Taiwan are the Aedes aegypti and Aedes albopictus. After 8~12 days of stinging a person with viremia, a mosquito will be endowed with the ability to transmit viruses throughout its lifespan.
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6. Case definition
| A |
Dengue fever, sudden fever (≧38℃) and is accompanied by at least two of the following |
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symptoms
Headache
Orbital pain
Muscle pain
Joint pain
Measles
hemorrhagic manifestations and
leucopenia
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| B |
DHF (All four of the following symptoms are required) |
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(a) Fever
(b) Hemorrhage (Conform to one or more of the following symptoms):
(c) Tested positive for tourniquet test
(d) Petechial hemorrhage, bruising, purpura
(e) Mucous membrane, gastrointestinal tract hemorrhage or bleeding at the place of intravenous drip
(f) Bloody stool, haematemesis
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| C |
Reduction in platelet count (less than 100,000)
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| D |
plasma leakage |
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Plasma leakage: Due to the increase in permeability of the blood capillaries, one or more of the following must be confirmed:
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(a) Increase of hematocrit to above 20%
(b) Reduction of hematocrit to less than 20% after transfusion treatment
(c) Pleural effusion or ascites
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DSS: Exhibits symptoms of dengue fever and DHF, together with skin clamminess, cold limbs, uneasiness, weak pulse (pulse pressure ≦20mmHg). |
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Healthcare
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Preventative measures:
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Educate the public to clean up breeding sources and prevent being bitten by vector mosquitoes, including adding screen windows, screen doors, wearing long sleeve tops and trousers when entering areas with high infection levels, and also to apply anti-mosquito spray on exposed skin.
Conduct vector density investigation in communities, monitor vector mosquito density and ascertain the breeding sources in the community in order to facilitate breeding source cleaning work.
Control over patients, contacts and surrounding environment.
Report to the local health authorities.
Before the patient’s fever is brought down, avoid being bitten by vector mosquitoes; wards should install screen windows, doors or spray insecticides. Patients should sleep inside mosquito nets.
Spray insecticide at the residents’ place of residence, work or temporary stay (more than one hour) in order to eradicate vector mosquitoes and execute the cleaning work of the breeding sources.
Quarantine: None.
Contact inoculation: None
Investigation of the contacts and source of infection: Stay in location two weeks prior and one week after falling ill while the causes are investigated; furthermore, investigation of other suspicious cases should also be conducted.
If you have any questions or for further details, please visit the CDC website.
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