About Dengue Fever
- Dengue fever is an acute communicable disease caused by the dengue virus, which is transmissible to humans via mosquitoes. There are four serotypes of dengue virus (I, II, III, and IV), and each is infectious and pathogenic.
- Patients infected with
a certain type of dengue virus gain lifelong immunity against that virus type, but only have brief immunity against other types of dengue virus, and may still be infected with other viral serotypes.
- Clinically, repeated infections of different dengue virus types may cause different degrees of reaction in the hosts, ranging from mild or unnoticeable symptoms to typical dengue fever symptoms such as fever and rashes, or alarm symptoms such as drowsiness, agitation, and hepatomegaly, and even severe dengue fever leading to serious hemorrhage or severe organ damage.
- Hotspots of dengue fever around the world are mainly in tropical and sub-tropical zones, in countries where the Aedes aegypti and Aedes albopictus mosquitoes are found. As globalization develops bringing increased convenience, more frequent interactions and travel between countries are resulted, and thus dengue fever has begun to spread among different countries since the 1980s, posing a major public health issue. Taiwan is located in the subtropics, where warm and humid environment is the favorite habitat of mosquitoes, making it a high-risk area to develop dengue fever outbreak.
Disease Information
- Mode of Transmission
In Taiwan, dengue fever spreads mainly through the Aedes aegypti and Aedes albopictus mosquitoes. Morphological characteristics of these mosquitoes are: dark body with white stripes on its legs. The Aedes aegypti tends to dwell in indoor containers or human-caused puddles, while the Aedes albopictus prefers outdoor habitat.
Biting peaks around 1-2 hours after sunrise and 2-3 hours before sunset in a day. People should take self-protective measures for outdoor activities during these hours.
- Incubation Period
Typical dengue fever has an incubation period from 3 to 8 days (up to 14 days at maximum). The “infectious period” spans from one day before onset to five days thereafter, which is called the “viremia” because the virus exists in the blood. If the infected person is bitten by the Aedes during this period, the mosquito will be infected with dengue virus. As the virus proliferates inside the mosquito’s body for 8-12 days, the mosquito will have lifelong ability to transmit the virus. When it bites another person, the dengue virus inside its body will be passed on to this other person.
- Symptoms
Depending on people’s different constitution, some may have mild symptoms or even no ailing symptoms when infected with dengue fever. Symptoms of typical dengue fever include sudden high fever (≧38℃), headache, pain behind the eyes, muscle pain, joint pain, and rashes. However, if a person is infected successively with different dengue virus types, he/she is more likely to develop severe clinical symptoms, which may result in a mortality rate above 20% if timely medical intervention or treatment is not given. Therefore, people are advised not to take it lightly! If the patient’s condition suddenly intensifies on the 3rd to 5th days after onset, for example having severe pain, convulsion, loss of consciousness, consciousness disturbance, and blood pressure change, it must be put on the alert for developing into a severe case.
- Preventive Measures
Dengue fever is a “community disease” or “environment disease.” Once the vector mosquitoes carrying the dengue viruses enter the community, where there are breeding grounds for the vector mosquitoes in the living environment, there is a possibility of developing into a dengue epidemic. Therefore, it is advised that people should wipe out the breeding grounds for the vector mosquitoes. In addition, people should also stay alert and understand the symptoms of dengue fever, so that they may seek timely medical care at the time of disease onset, ensure early diagnosis and appropriate treatment. Also, they should avoid being bitten by vector mosquitoes again, so as to reduce the possibility of further transmission of the dengue virus.
(1)General household preventive measures
Screen windows and screen doors should be installed at home; mosquito nets should be hung up when sleeping in order to avoid mosquito bites. Unnecessary containers should be removed; vases and containers that are not in use should be placed upside down. Dim places at home or in the basement should be regularly inspected, and mosquito killer lamps can be used. Vases and water containers at home must be cleaned weekly, and the interior should be scrubbed when cleaning. Discarded tires, water-holding containers, and similar articles placed outdoors should be removed immediately, or the cleaning team should be contacted to remove them if one cannot deal with them on his/her own. Wear light-color long-sleeve clothes and apply MOHW-approved mosquito repellent on exposed skin when going to the market, park, or other outdoor places.
(2)Four tips to remove breeding grounds – “Inspection, Removal, Cleaning, Scrubbing”
“Inspection” – Make frequent inspections to check possible water-holding containers both indoors and outdoors.
“Removal” – Pour out water and discard unused articles.
“Cleaning” – Minimize containers and clean containers that are in use thoroughly.
“Scrubbing” – Eliminate insect eggs, clean up or reverse containers to avoid waterlogging and breeding of mosquitoes.
(3)Guidelines for individuals infected with dengue fever (Controls of patients, contacts, and surrounding environment)
People infected with dengue fever should prevent themselves from being bitten by vector mosquitoes within 5 days of onset. Screen windows and screen doors should be installed in the hospital ward, and patients should sleep inside a mosquito net. Disease control units should wipe out breeding grounds and determine whether it is necessary to implement chemical control on adult mosquitoes after integrated assessment of the relevant data. Infectious vector mosquitoes may have existed in the surroundings of a dengue fever patient. Therefore, patients’ travel history (or locations of activities) two weeks before onset and one week thereafter should be investigated to identify suspected cases.
(4)Temporary suspension of blood donation to prevent possible transfusion-transmitted infection (TTI) of dengue fever
- Suspend blood donation for 4 weeks after departing from dengue fever endemic regions.
- For confirmed dengue fever cases, patients can only donate blood 4 weeks after recovery and with no symptoms.
- Contacts of confirmed cases (including those with dengue fever patients at home or at work, or those whose home or workplace has been subject to mandatory spraying) should suspend blood donation for 4 weeks.
Medical Treatment and Medical Care Information
There is currently no specific medicine for dengue fever. Therefore, dengue fever patients are strongly advised to follow the doctor’s advice, rest well, drink more water, and take antipyretic as prescribed. Patients will usually recover by themselves in about two weeks’ time after infection. Furthermore, severe dengue fever patients should be hospitalized, accept timely interventions, and be given comprehensive, intensive, and consistent care. In this way, the mortality rate will drop from more than 20% to below 1%.
FAQs on Dengue Fever:
＊Precautions for dengue fever patients as diagnosed by physician:
1. Follow the physician’s instructions and take medicine as prescribed, take rest, and drink more water.
2. Within 5 days from onset, pay particular attention to avoid being bitten by mosquitoes and thereby spread the virus.
3. Suggested mosquito control measures:
(1) Install screen windows and screen doors at home;
(2) wear light-color long-sleeve clothes and long pants;
(3) hang up a mosquito net when sleeping;
(4) use mosquito killer lamps or electric mosquito swatters (mosquito coils only drive mosquitoes away);
(5) apply DEET-containing mosquito repellent when necessary;
(6) stay at home and take rest when falling ill.
＊Guidelines for dengue fever patients as diagnosed by physician:
1. Department of Health (DOH) or Public Health Center will pay visits to the neighboring households around your residence (for epidemic investigation) to check if there are people with similar symptoms in other households. If your family members or friends show similar symptoms, please ask them to go to a medical care institution for medical consultation as soon as possible.
2. DOH or Public Health Center will conduct inspection on breeding grounds in neighboring households around your residence. Households and communities will be required to remove all water-holding containers. Necessary water storage containers should be put upside down when not in use and be sealed with a cover when in use; containers must be cleaned and replaced at least once a week, and the interior should be scrubbed clean to eliminate insect eggs.
3. If a breeding ground is found in or outside a person’s residence, and he/she fails to remove it upon the government’s notice or public announcement, the person shall be fined between NT$3,000 and NT$15,000 pursuant to Article 70 of the Communicable Disease Control Act when it is identified.
＊What is “dengue fever”?
Dengue fever is commonly known as “tengu fever” or “breakbone fever.” It is an acute infectious disease caused by the bite of a vector mosquito. Major symptoms include fever, headache, pain behind the eyes, muscle and joint pain, and rashes. Dengue fever can be distinguished into four types (DENV-I, DENV-II, DENV-III, DENV-IV) based on antigenicity.
＊How do people get infected with dengue fever?
Infection is mainly caused by the bite of a vector mosquito, which transmits the virus to the human body. Infection is not caused by human-to-human transmission, airborne transmission, and contact transmission.
＊What kinds of vector mosquitoes for dengue fever exist in Taiwan?
In Taiwan, vector mosquitoes that transmit dengue fever are the Aedes, mainly Aedes aegypti and Aedes albopictus, whose characteristics are dark body with white stripes on their legs. Adult Aedes aegypti has a pair of lyre-shape vertical lines on both sides of its thorax and a pair of yellow lines in the middle, prefers to inhabit indoors; Aedes albopictus has a prominent white line running down the middle of it thorax scutum, and mostly inhabits outdoors.
＊How long is the incubation period of dengue fever?
In general, onset of the disease begins after an incubation period of 3-8 days from infection, but a small number of people may have an incubation period up to 14 days.
＊What is the mode of transmission for dengue fever?
Dengue virus exists in the blood of dengue fever patients during the period from one day before onset to five days thereafter (it is called the “viremia”). If the patient is bitten by the Aedes during this period, the Aedes mosquito will be infected with the virus. After 8-12 days’ proliferation in the mosquito body, the virus will reach the vector mosquito’s salivary gland and the mosquito will become infectious. When it bites other healthy people, the virus will be transmitted. The mosquito thus gains lifelong ability to transmit the virus.
＊What is the mortality rate of dengue fever?
1. Typical dengue fever: Mortality rate below 1%.
2. Dengue hemorrhagic fever: Mortality rate may exceed 20% if no proper treatment is given, but with early diagnosis and appropriate treatment, mortality rate can drop to less than 1%.
＊When an infected person recovers from dengue fever, will he/she be infected again?
A patient infected with a type of dengue virus gains lifelong immunity against that virus type, but only has brief immunity against other virus types, generally for about 2-9 months. The patient may still be infected with other virus types thereafter. For example, a person infected with DENV-I before will never be infected by DENV-I again, but he/she may be infected by DENV-II, DENV-III, or DENV-IV.
＊How is dengue fever treated? Is there a vaccine?
There is currently no specific medicine for dengue fever. Supportive treatment is generally given. There is currently no effective vaccine either.
＊In what condition would a person be most likely infected with dengue fever?
Incidences of dengue fever around the world are mainly found in tropical and sub-tropical zones, in countries where distributions of the Aedes aegypti and Aedes albopictus are found, especially in areas with a lot of Aedes aegypti mosquitoes, including Asia, Central and South America, Africa, and northern Australia, as well as some Pacific islands. Therefore, infection of dengue fever is possible when traveling overseas, visiting friends, and going on business trips to the abovementioned areas. Hence, when suspected dengue symptoms such as fever, joint and bone pain, pain behind the eyes, and rashes show up after a person returns to the home country, please consult a doctor as soon as possible, and take the initiative to report one’s travel history. Moreover, if a city or county in Taiwan has a dengue epidemic, one may also be infected with dengue fever when going to that area without taking good protective measures.
＊What are the hosts of dengue viruses?
There are currently three known natural hosts of dengue viruses, i.e., human beings, primates, and the Aedes mosquitoes. Primates, including chimpanzees and gibbons, generally have shorter viremia than human beings, approximately 1-2 days. Human beings are the only hosts that show clinical symptoms.
＊Where do vector mosquitoes of dengue fever breed their larvae?
Larvae (wigglers) of dengue vector mosquitoes breed inside man-made containers and natural containers. Indoor man-made containers include vases for Nippon lily (Rohdea japonica) and Golden Pothos, flower pot saucers, refrigerator drip pans, and waterlogging in the basement. Outdoor containers include water storage tools such as water buckets, ceramic urns, and concrete troughs. Discarded items include small items such as beverage cans, paper cups, paper bowls, plastic bags, etc.; medium items such as plastic buckets, washbasins, bathtubs, pots, bowls, ladles, basins, tires, etc.; large items such as discarded bathtubs, toilets, refrigerators, washing machines, various furniture items, etc. Natural containers include tree hollows, bamboo tubes, and rachises, etc.
＊Where do adult vector mosquitoes including the Aedes aegypti and Aedes albopictus inhabit?
The Aedes aegypti prefers to inhabit indoors, for example inside the kitchen, usually in dim, moist, and poorly ventilated corners; in the bedroom, usually staying at wall corners, on curtains, or dark-color hanging clothes. The Aedes albopictus mainly inhabits outdoors, and the mosquitoes’ areas of activity are usually close to their breeding grounds, for example in dim places of a forest or bamboo grove.
＊Do both male and female dengue vector mosquitoes suck blood? At what time they suck blood?
Vector mosquitoes that transmit dengue fever are female Aedes mosquitoes. They are active and suck blood mainly during the day. Male mosquitoes cannot suck blood because of their reduced mouthparts, and they usually suck plant sap. The Aedes aegypti prefers to inhabit indoors and suck human blood. Peak time for blood sucking is 4:00-5:00 p.m., and second peak at 9:00-10:00 a.m. The Aedes albopictus prefers to inhabit outdoors, and there are two blood sucking peaks in a day, one in the morning and one in the evening, usually around 1-2 hours before and after local sunrise time and 2-3 hours before sunset; blood sucking peaks higher in the afternoon than the morning.
＊In what areas are the dengue vector mosquitoes distributed in Taiwan? Does climate change cause northward migration of the Aedes aegypti?
1. The Aedes aegypti is mainly distributed in cities and counties to the south of Budai, Chaiyi, which include Tainan County, Tainan City, Kaohsiung County, Kaohsiung City, Pingtung County, Taitung County (Taitung City), Penghu County (Magong City), and the Aedes albopictus is distributed throughout the plain of the Taiwan island and mountain area below the altitude of 1500 meters.
2. Global warming may change the ecology of vector mosquitoes, but according to Taiwan Centers for Disease Control’s vector monitoring data in recent years, distribution areas of the Aedes aegypti have not changed.
＊What is the life cycle of the Aedes mosquitoes?
There are four stages in the life cycle of the Aedes mosquitoes, including egg, larva, pupa, and adult, and the time needed for its development usually varies with temperature and food condition. In general, the egg stage lasts for 1-3 days, larva stage 4-7 days, pupa stage 1-4 days, and so it takes 6-14 days for the Aedes to develop from egg, larva to pupa. Female mosquitoes can live for 15-30 days, while male mosquitoes live for 7-14 days.
＊I live on the 10th floor; why are there still mosquitoes? How high can a mosquito fly?
Mosquitoes may take the elevators too (they may enter an elevator when the door opens)! Although it is unlikely that mosquitoes fly vertically from the ground to the 10th floor, they may still reach high places with the help of the airflow or transporting tools. Therefore, please watch out for mosquito breeding grounds (water-holding containers) downstairs, in the basement, or parking lot!
＊What should people do when there is an outbreak of dengue epidemic in their community?
1. Remove all water-holding containers in the home environment to stop the breeding of vector mosquitoes.
2. Wear long-sleeve clothes and long pants, and spray mosquito repellent on exposed skin to avoid being bitten by dengue vector mosquitoes when going out in the day.
3. Install screen doors and screen windows at home.
4. Cooperate with the government and implement epidemic control measures.
＊Why is dengue fever a community-acquired disease?
Vector mosquitoes bite people indiscriminately. Once there is a dengue fever case in the community, each individual in the community would probably be bitten by the vector mosquitoes and infected with dengue fever. Taking stern actions to wipe out breeding grounds of vector mosquitoes in the community would not only benefit oneself but also help others. Always keep the community environment at its best level to make sure there is no breeding ground for vector mosquitoes, and so community outbreak of dengue epidemic would not be a concern.
＊How to prevent dengue fever?
There is currently no effective dengue fever vaccination that can prevent the disease, and no specific medicine for the disease either. Therefore, removing water-holding containers to eradicate breeding of the vector mosquitoes is the most effective way to prevent dengue fever.
＊What are the breeding grounds of the vector mosquitoes?
Breeding grounds of the vector mosquitoes are the environment where larvae and pupae of the vector mosquitoes grow. For dengue vectors, their breeding grounds are “all water-holding containers.”
＊Why should everyone work to remove the breeding grounds?
Removing all water-holding containers is the most effective way of preventing dengue fever, and the government should not do it alone. Everyone must contribute to achieve the objective in a short time.
＊How can we remove the breeding grounds for good?
Change personal behaviors, properly manage containers, and avoid discarding water-holding containers, and then the breeding grounds can be removed for good. Follow the procedures below:
1. Containers for aquatic plants: Common aquatic plants include Golden Pothos, Nippon lily (Rohdea japonica), and water lettuce (Pistia stratiotes), etc. (1) Put pebbles or colored plastics into the containers and keep water level below the surface of the pebbles or plastics. (2) Put mosquitofish into the containers for growing aquatic plants. Commonly seen mosquitofish include guppy, Gambusia affinis, and paradisefish, etc.
2. Water storage containers: Common water storage containers include buckets for watering, washing, and drinking water, ceramic urns, and concrete troughs, etc. (1) Put it upside down when not in use. (2) Cover and seal up when in use. (3) Grow the abovementioned mosquitofish and put water lettuce in it if it cannot be sealed for a special reason.
3. Discarded containers: Do not pile up or dump discarded containers outdoors at discretion. Commonly seen discarded containers include beverage cans, lunch boxes, washbasins, fish bowls, bathtubs, etc.
4. Man-made structures: Avoid possible waterlogging during construction work. For example, when working on courtyard landscape design, avoid making puddles that hold water around a stream, and do not leave bamboo holes when making artificial bamboos.
5. Natural containers: These include tree hollows, bamboo tubes, etc. Tree hollows can be filled with soil for growing plants and avoid making a waterlogging environment. Bamboo tubes should be cut at the joints to avoid holding water in the tubes.
＊Is spraying pesticides an effective way of eliminating vector mosquitoes for dengue fever?
1. When there is an epidemic outbreak, pesticides would be sprayed in order to rapidly eliminate adult mosquitoes in the environment, and hence reduce the possibility of spreading dengue virus.
2. Emergency spraying of pesticides cannot eradicate larvae in water containers, and may cause emergence of pesticide-resistant strains and environmental pollution. It is a last-resort measure when there is already an epidemic. Emergency pesticide spraying must be coupled with thorough removal of the breeding grounds to be actually effective.
＊If there is an outbreak of dengue fever epidemic in the community, what should people in general do to prevent spreading of the epidemic?
In the area where there are dengue fever cases, households should work with the Public Health Center for the following dengue fever prevention work.
1. Accept visitation, provide correct and detailed information, or accept blood test.
2. Households within the radius of 50 meters from the patient’s home and workplace should accept emergency spraying of pesticides (both inside and outside their homes) to kill adult mosquitoes that may be carrying the virus and prevent the epidemic from spreading.
3. Remove water-holding containers inside and outside their homes, so that the Aedes mosquitoes have no place or opportunity to breed, and thus infection can be prevented.
＊What good does it do to report dengue fever proactively?
With early reports, the relevant authorities can take immediate preventive measures to avoid further spreading the epidemic, and this helps prevent one’s family members or neighbors from being infected.
＊Will people be punished for failing to work with the competent authority in epidemic prevention work?
1. Upon receiving report of a suspected case, the Department of Health will carry out relevant epidemic prevention work (e.g., removing breeding grounds, carrying out inspection, or spraying pesticides) within 48 hours at the patient’s residence, workplace, and other possible places of infection, as well as the locations the patient had stayed for more than 2 hours during viremia, in order to exterminate vector mosquitoes rapidly and prevent further spreading of the epidemic or emergence of other dengue fever cases.
2. Those who refuse to cooperate with the Department of Health for removal of breeding grounds and inspection shall be imposed a penalty between NT$3,000 and NT$15,000 pursuant to Article 70 of the Communicable Disease Control Act. If you fail to stay at home when the Department of Health informs you for mandatory epidemic prevention work inside your home, the Department of Health may force to unlock your residence to implement epidemic prevention work together with relevant personnel in accordance with Article 38 of the Communicable Disease Control Act. If breeding ground for vector mosquitoes is found on the spot, a fine between NT$3,000 and NT$15,000 shall be imposed pursuant to Article 70 of the Communicable Disease Control Act.
3. Those who refuse to cooperate (refusal, evasion, or hindrance) when the Department of Health arrives on the spot and implements mandatory epidemic prevention work shall be fined between NT$60,000 and NT$300,000 in accordance with Article 67 of the Communicable Disease Control Act. For the health of your family and the public, please cooperate with the health authority in the implementation of the relevant epidemic prevention work.