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aegypti mosquito
Dengue fever is a nasty, viral disease transmitted by the Aedes mosquito, usually the Aedes aegypti , the same mosquito that often carries yellow fever. Sometimes called "breakbone fever" or "break-heart" because of the intense pain it can produce, the disease is characterized by sudden onset of fever; intense pounding, frontal headaches; aching bones and joints; nausea and vomiting; and a feeling of being too sick to eat anything. Other symptoms include severe sweats, symptoms: eye pain, rash, chills, and excruciating chest pains. Tests foe dengue rely on the presence of antibodies, which can take up to a week to develop.

Dengue fever is found in 100 countries and kills about 20,000 people annually. Nine out of 10 people who get dengue fever don’t even feel it or get a mild case in which they feel something akin to a slight flu. People who get full-blown dengue fever are sick for a week or more. Many patients have a rash, which appears 3 to 5 days after the onset of the disease, and experience severe emotional and mental depression during the recovery period. Most cases of the disease are benign and self-limiting although convalescence may take a long time.

A few people with dengue fever suffer gastrointestinal bleeding. Fewer still suffer brain hemorrhages. In about 1 percent of cases dengue fever can cause a severe and often fatal hemorrhagic disease called dengue hemorrhagic fever (DHF) that occurs when capillaries leak and the circulatory system collapses.. Those that die of dengue fever often get DHF hemorrhaging in the final stage of the sickness. Failing to realize they are infected, they go don’t get treatment soon enough and lose blood plasma and go into shock after the initial fever passes. Some victims die within 10 hours of developing serious symptoms if they don’t get appropriate treatment.

There are several strains of dengue fever (the four main one are immunologically related). Those who get the disease develop an immunity to the strain they were infected by but are more likely to get DHF and get seriously sick if they get infected with a second, different strain. Scientists are not sure why this happens but think it may be because the immune system reacts the second time as if the invader were the first strain, wasting precious energy and leaving the body vulnerable to an attack by the second strain. Many doctors believe that since so few people show symptoms the when get dengue those that do display symptoms probably have gotten the disease a second time from a second strain. Getting the disease twice for two different strains seems to provide immunity for life from all strains of dengue fever.

History of Dengue Fever

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Where dengue fever is found in Africa, Asia and Oceania
Dengue fever and yellow fever are so closely related they are regarded as sister diseases. Dengue was first identified about 300 years ago but remained an isolated problems until it was spread around Asia and Pacific by troops during World War II. Both dengue and yellow fever were thought to have been close to eradication in the 1940s but have since made comebacks. The disease took off in crowded conditions in Asia. By 1975 it was a leading cause of hospitalization and death among children in the region.

From Southeast Asia dengue fever made its way to India, Africa, the eastern Mediterranean and finally to the Americas where it emerged as a threat in the 1970s just as campaigns to stamp out yellow fever in Latin America were declared a success.

Several new strains of the dengue virus have emerged in Asia and Latin America since the mid-1970s. The disease was a problem in Latin America and the Caribbean in the 1980s and 90s. It first took hold in Central and South America and progressed into Caribbean and the southern United States. There were 116,000 infections in Latin America alone in 1990. Cases have been reported in Florida and Hawaii.

In recent years there have been severe outbreaks of nasty forms of dengue fever and of DHF in Southeast Asia.

A dengue fever pandemic swept across the Western Pacific in 1991 and 2004, peaking with 350,000 cases in 1998, according to the WHO. In the early 2000s, tens of thousands of people were infected with dengue fever in Thailand. More than a hundred people died in 2001. Particularly hard hit were Bangkok and the central provinces of Chonburi and Nakhon Sawan. In some places outbreaks occur every two or three years as immunity after not getting the disease only lasts a year. The disease has also made its presence known in Southeast Asia in the late 2000s and early 2010s. In 2007, the number of cases of dengue fever in Thailand rose 36 percent . As of mid-2007 the disease had killed 17 people and affected more than 21,000 people. The increases was blamed on the early arrival of the rainy season. See Thailand, Indonesia, Vietnam, Singapore and Southeast Asian countries.

One Person’s Experience with Dengue Fever

Dengue fever often begins with a headache and an achy feeling. The headaches seems to migrate towards the eyes behind the sockets as fever takes hold rises. If full-blown symptoms take hold the pain spreads throughout the entire body.

One suffer who was struck by dengue fever in Singapore wrote in the New York Times, “Not for nothing is dengue also known as breakbone fever...I, for one, felt as though someone had tied a Brink’s truck to my lower back. My skin was flushed, I could not eat, and I slept 12 to 14 hours at stretch. When I went to my doctor two days later, I could hardly open my blood-stained eyes...The doctor had little choice but to send me home with the painkiller Panadal and some muscle relaxants.”

“A week after my first feverish night, a doctor looked at the tiny pinpricks of blood under the skin on my shoulders, and sent me for a blood test, which confirmed that I had dengue...My first blood tests also revealed that my platelets---the cells that allow blood to clot and prevent hemorrhaging---had dropped to almost half of what doctors consider normal. They weren’t low enough for me to be hospitalized for transfusions, fortunately, but they were low enough to earn me daily blood tests to make sure.”

“The virus had inflamed my liver, as well, sending liver enzymes into my bloodstream, another mysterious symptom. For weeks after my fever subsided and my platelets returned to normal, I was still laid out, lethargic and giddy. My appetite returned slightly, but food and even water tasted strangely unpleasant...A month of afternoon naps later I was completely recovered.”

Dengue Fever Mosquitos

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spread in Western Hemisphere
Aedes aegypti is a small, dark mosquito with white markings and banded legs. It originated in Africa and made its way around the globe centuries ago when it hitchhiked on transoceanic voyages.

Aedes aegypti mosquitos prefer to feed on humans during the daytime and are most frequently found in or near human habitations. They are most likely to bite during a period of several hours in the late afternoon before dark and for several hours after day break.

In 2007, scientists published the genome---a map of all the DNA---of the Aedes aegypti, the mosquito that carries yellow fever and dengue fever. It turns out the genetic make up of this mosquito is more complex than the one that carries malaria. Both Aedes aegypti and the mosquito that carries malaria have about 16,000 genes but the genome for Aedes aegypti is about five times larger.

Dengue Fever Treatment and Prevention

Dengue fever has no vaccine and no cure. Most victims that show symptoms recover on their own with rest and hospital care. Dengue fever can be avoided by staying out of endemic areas (the Center of Disease Control can tell you where they are) and protecting oneself against mosquitos.

Dengue outbreaks often have followed unusually hot, rainy and humid conditions. The danger of dengue fever rises when there is a lot of stagnant water for mosquitos to breed in. In some places where it rains a lot people get infected every two or three years as their immunity from the previous illness lasts only a year and they get infected again..

Developing a vaccine against dengue fever is difficult because one a vaccine has to be developed that can work on all the strains.. Scientists are tinkering with the genetic material of 17D to come with a vaccination for dengue fever. See Yellow Fever.

Scientist were able to wipe out mosquitos that carry Dengue fever in a village in northern Vietnam by using a one-eyed crustaceans that lives in ponds where mosquitos breed and has a large appetite for the larvae mosquitos that carry Dengue fever.

There are concerns dengue fever could spread northwards, even becoming common place in the United States, as result of global warming. Already species capable of carrying the disease have been found in 28 states in the U.S. and as far north as the Netherlands in Europe. Cases of dengue fever have been reported in all 50 U.S. states but people who had it contacted the disease abroad and brought it home.

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Avoiding Insects

For protection from insects use an insect repellant with at 30 percent DEET (some people recommend 95 to 100 percent), wear long pants and long sleeve shirts, treated with "Coulston's Duranon Tick, spray, and sleep under an insecticide-impregnated insect netting. Periodically check your body for ticks. If a tick penetrates your skin, remove the entire tick with tweezers or a tick removal kit by grasping the head and slowly backing it out.

Disease-carrying mosquitos, like most mosquitos, generally bite at night between dusk and dawn, and are particularly fierce around sunset. An exception to this rule are mosquito that carries dengue fever. They generally bite in the day. Mosquitos generally go for the lower extremities of the body. People with a high skin temperature and high moisture-transpiration rates sometimes attract more mosquitos.

The best way to avoid disease-carrying mosquitos and insects is avoid the places where the diseases are known to exist. The Center of Disease Control can provide information on countries and regions where diseases are found. Rural areas are generally more risky than urban areas. Local people can often provide information on specific risky places in their area.

The best way to avoid mosquitos is to: 1) stay inside when they are most active (in the late afternoon, early evening, and early morning); 2) sleep under a mosquito net (tucked under the mattress and treated with an insecticide); 3) cover as much of your body with clothing as possible, wearing long sleeve, light-colored, loose-fitting clothing; 4) use a repellant and your skin and a toxicant on your clothing; and 5) stay in hotels that are well-screened or air-conditioned, if screens are insufficient ask for mosquito netting. Fans and mosquito coils are also effective in keeping mosquitos away. Sandals should be avoid and pants should be tucked into socks in places with lots of ticks. White or light clothing makes ticks easier to spot.

Many Africans who live malaria-endemic areas use nets but still get the disease. Many people in hot countries don't like them because the keep out the breeze.

Websites and Resources on Health and Diseases: Centers for Disease Control and Prevention ; Disease Pictures ; World Health Organization (WHO)statistics and data ; World Health Organization (WHO) disease outbreak alert ; Third World Traveler ; Health Map ; Medline Plus medlineplus/healthtopics ; Merch Manuals (detailed info many diseases) ; Health Images Directory

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mosquito stages of development

DEET and Permethrin

Use a DEET insect repellents on your skin. DEET is a strong chemical that interferes with the tiny sensory hairs and pits in the antenna and body it uses to detect carbon dioxide.. DEET is toxic if ingested; stings eyes severely; and can blister the skin in high concentrations. Repellents with 30 to 35 percent DEET are good. They the usually only last for around five hours. Higher concentrations, such a 95 percent to 100 percent, don’t add any more protection but they last longer. Aerosol insecticides and mosquito coils help to clear rooms but they sometimes contain DDT. Non-DEET repellants generally work 1½ hours or less.

The Centers for Disease Control and Prevention recommend products containing DEET, picaridin, IR3535 and the oil of lemon eucalyptus. They say put some on you clothes for greater protection. If you wear sun screen, apply the insect repellant on top of it.

Use a spray or repellent with Permethrin or Permanone (such as Coulston's Duranon Tick Repellent) on your clothes, shoes, tents, camping gear and bed netting. Permethrin often maintains its potency through ten or more washing. It bonds tightly with cotton fabric and It is effective enough to knock out a mosquito by the time sticks its probe through the cloth and it aims it towards the victims skin.

Some people are turned off by the odor of DEET and the chemical os not suited for all ages. Alternatives include the chemical Picaridin and the plant-based oil of lemon eucalyptus.

Preventive Measures Used in Singapore During the Dengue Fever Outbreak in 2005

Singapore launched a number of measures to contain the dengue outbreak, including public awareness campaigns and regular fogging with insecticides. 4,200 volunteers, 970 environmental control officers hired by construction sites, 350 so-called "mozzie busters" made up of girl guides and scouts, have participated in the preventive efforts. [Source: Wikipedia +]

The Ministry of Health stepped up its monitoring of common mosquito breeding sites and launched an online map listing "hotspots" for the insects. Residents who allow mosquitoes to breed in their homes can be fined between S$100 to S$200, and heavier penalties may be issued for construction sites found with standing water. The number of officers conducting such checks have tripled since the start of the year to 360, and may increase to 510 by December. The National Environment Agency has allocated an additional S$7.5 million on top of its existing S$2.5 million budget to clear drains of stagnant water where mosquitoes breed. Singapore Land Authority has also stepped up its checks on vacant state properties. +

On 10 September, National Environment Agency started collecting blood samples from residents of Sims Avenue, a dengue hotspot, to help track the infection. The residents were asked to provide voluntarily 5 millilitres of blood sample and a swab of saliva for the study. The samples were to be analysed for antibodies against dengue infection in the last 2 months.

The National Parks Board (NParks) considered removing broad-leafed plants which may breed mosquitoes. These plants like palm trees or any plants with axils capable of trapping water, are potential breeding sites. Holes in tree trunks were also a concern, and NParks workers filled these holes with sand. NParks engaged 16 pest companies to stop mosquito breeding in the parks it manages. Due to the dengue threat, some schools cancelled excursions to the parks.

Health Minister Khaw Boon Wan urged the public to help in the fight against the disease. As households are common breeding grounds for mosquitos and are less accessible for fogging, residents were told to check for stagnant water in their households and neighbourhoods and ensure there as no blockage of drains. Due to the short life cycle of Aedes aegypti mosquitos (7 to 10 days), frequent checks were necessary to eradicate dengue. These checks only took several minutes. Singapore residents also armed themselves with anti-mosquito products including insecticides, repellents and electronic mosquito traps. For repellents, experts recommend those with DEET which provides more effective and lasting protection. Some residents bought a potted plant called Citronella. The perennial grass plant, imported from Cameron Highlands, gives off a strong lemon-like fragrance which repels mosquitoes. To prevent the spread of the virus, those who were already infected with dengue were encouraged to use mosquito repellents, wear long-sleeved clothing and sleep under mosquito nets to prevent mosquitoes from biting them again and spreading the virus to others.

Vietnam Releases Mosquito with Bacteria That Blocks Dengue Fever

In November 2013, Associated Press reported from Tri Nguyen Island: “Nguyen Thi Yen rolls up the sleeves of her white lab coat and delicately slips her arms into a box covered by a sheath of mesh netting. Immediately, the feeding frenzy begins. Hundreds of mosquitoes light on her thin forearms and swarm her manicured fingers. They spit, bite and suck until becoming drunk with blood, their bulging bellies glowing red. Yen laughs in delight while her so-called "pets" enjoy their lunch and prepare to mate. [Source: Associated Press, November 15, 2013 |:|]

“The petite, grandmotherly entomologist -- nicknamed Dr. Dracula -- knows how crazy she must look to outsiders. But this is science, and these are very special bloodsuckers. She smiles and nods at her red-hot arms, swollen and itchy after 10 minutes of feeding. She knows those nasty bites could reveal a way to greatly reduce one of the world's most menacing infectious diseases. All her mosquitoes have been intentionally infected with bacteria called Wolbachia, which essentially blocks them from getting dengue. And if they can't get it, they can't spread it to people. |:|

“So how can simple bacteria break this cycle? Wolbachia is commonly found in many insects, including fruit flies. But for reasons not fully understood, it is not carried naturally by certain mosquitoes, including the most common one that transmits dengue, the Aedes aegypti. The germ has fascinated scientist Scott O'Neill his entire career. He started working with it about two decades ago at Yale University. But it wasn't until 2008, after returning to his native Australia, that he had his eureka moment. |:|

“One of his research students figured out how to implant the bacteria into a mosquito so it could be passed on to future generations. The initial hope was that it would shorten the insect's life. But soon, a hidden benefit was discovered: Wolbachia-infected mosquitoes not only died quicker but they also blocked dengue partially or entirely, sort of like a natural vaccine. "The dengue virus couldn't grow in the mosquito as well if the Wolbachia was present," says O'Neill, dean of science at Monash University in Melbourne. "And if it can't grow in the mosquito, it can't be transmitted." The Australians tapped 58-year-old Yen at Vietnam's National Institute of Hygiene and Epidemiology, where she's worked for the past 35 years. Their plan was to test the Wolbachia mosquitoes on a small island off the country's central coast this year, with another release expected next year in Indonesia. |:|

“Just getting the mosquitoes to Tri Nguyen Island was an adventure. Thousands of tiny black eggs laid on strips of paper inside feeding boxes had to be hand-carried inside coolers on weekly flights from Hanoi, where Yen normally works, to Nha Trang, a resort city near the island. The eggs had to be kept at just the right temperature and moisture. The mosquitoes were hatched in another lab before finally being transported by boat. Yen insisted on medical checks for all volunteer feeders to ensure they weren't sickening her mosquitoes. She deemed vegetarian blood too weak and banned anyone recently on antibiotics, which could kill the Wolbachia. "When I'm sleeping, I'm always thinking about them," Yen says, hunkered over a petri dish filled with dozens of squiggling mosquito pupae. "I'm always worried about temperature and food. I take care of them same-same like baby. If they are healthy, we are happy. If they are not, we are sad." |:|

“Vietnam has logged lower numbers this year overall, but the country's highest dengue rate is in the province where Yen is conducting her work. At the area's main hospital in Nha Trang, Dr. Nguyen Dong, director of infectious diseases, says 75 of the 86 patients crammed into the open-air ward are infected with the virus. Before jabbing his fingers into the stomach of one seriously ill patient to check for pain, he talks about how the dengue season has become much longer in recent years. And despite the government's increased education campaigns and resources, the disease continues to overwhelm the hospital. |:|

“If the experiment going on just a short boat ride away from the hospital is successful, it eventually will be expanded across the city and the entire province. The 3,500 people on Tri Nguyen island grew accustomed to what would be a bizarre scene almost anywhere else: For five months, community workers went house-to-house in the raging heat, releasing cups of newborn mosquitoes. And the residents were happy to have them. "We do not kill the mosquitoes. We let them bite," says fisherman Tran To. "The Wolbachia living in the house is like a doctor in the house. They may bite, but they stop dengue." |:|

“Specimens collected from traps are taken back to the lab for analysis to determine how well Wolbachia mosquitoes are infiltrating the native population. The strain of bacteria used on the island blocks dengue 100 percent, but it's also the hardest to sustain. At one point, 90 percent of the mosquitoes were infected, but the rate dropped to about 65 percent after the last batch was released in early September. A similar decrease occurred in Australia as well, and scientists switched to other Wolbachia strains that thrive better in the wild but have lesser dengue-blocking abilities. The job is sure to keep Yen busy in her little mosquito lab, complete with doors covered by long overlapping netting. And while she professes to adore these pests nurtured by her own blood, she has a much stronger motivation for working with them: Dengue nearly claimed her own life many years ago, and her career has been devoted to sparing others the same fate. "I love them," she says, "when I need them." |:|

Malaysia Releases GM Mosquitoes to Combat Dengue Fever

In January 2011, AFP reported: “Malaysia has released 6,000 genetically modified mosquitoes designed to combat dengue fever, in a landmark trial slammed by environmentalists who say the experiment is unsafe. In the first experiment of its kind in Asia, about 6,000 male Aedes aegypti mosquitoes were released at an uninhabited site in the central state of Pahang, the government-run Institute of Medical Research (IMR) said. [Source: AFP, January 26, 2011]

The IMR, which was tasked with carrying out the trial, said the experiment was conducted on December 21 to "study the dispersal and longevity of these mosquitoes in the field". "The experiment was successfully concluded on January 5, 2011," the institute said in a statement dated Tuesday, adding that no further releases are planned until the trial results are analysed. The insects in the experiment have been engineered so that their offspring quickly die, curbing the growth of the population in a technique researchers hope could eventually eradicate the dengue mosquito altogether.

Females of the Aedes species are responsible for spreading dengue, a deadly disease which killed at least 134 people last year in Malaysia alone. The trial has sparked widespread concern among environmental groups and non-government organisations (NGOs), and had been postponed due to their protests as well as unfavourable weather conditions. "I am surprised that they did this without prior announcement given the high level of concerns raised not just from the NGOs but also scientists and the local residents," said researcher Lim Li Ching from Third World Network.

The network is part of 29 public health and environmental groups which have repeatedly demanded the government cancel the trial, saying it was risky and could lead to unintended consequences. "We don't agree with this trial that has been conducted in such an untransparent way. There are many questions and not enough research has been done on the full consequences of this experiment," she told AFP.

Critics have also said that too little is known about the Aedes mosquito, and how the genetically modified insects would interact with their cousins in the wild. Authorities have dismissed the fears and said the trial would be harmless as the GM mosquitoes can live for only a few days. Dengue infection leads to a sudden onset of fever with severe headaches, muscle and joint pains, and rashes, which can lead to death if left untreated.

Tiny, One-eyed Crustaceans Conquers Dengue in Vietnam Village

Scientist were able to wipe put mosquitos that carry dengue fever in a village in northern Vietnam by using a one-eyed crustaceans that lives in ponds where mosquitos breed and has a large appetite for the larvae mosquitos that carry Dengue fever. Reuters reported from Nam Dinh: “Scientists have wiped out mosquitoes that carry the potentially fatal dengue fever in a village in northern Vietnam, a feat believed to be a world first.Pivotal to their success is a microscopic, one-eyed crustacean, which is eating its way into medical history with a voracious appetite for the larvae of dengue-carrying mosquitoes. The experiment was pioneered by Australian and Vietnamese scientists, who say the results could have global implications for combating a disease for which there is still no vaccine nor specific cure. [Source: Reuters, July 30, 1999 ^^]

"Dengue-carrying mosquitoes were wiped out in the village of Phan Boi within 18 months,'' said Ahmet Bektas, country director for the Australian Foundation for Peoples of Asia and the Pacific, which oversees the scientific project. The American Society of Tropical Medicine and Hygiene recently hailed the project as the first anywhere in the world to eradicate the dengue-carrying Aedes mosquitoes. "The great fear is that it's spreading,'' Jeremy Farrar, a dengue fever expert at Britain's Oxford University, said after observing the project in Nam Dinh, south of Hanoi. But in Vietnam, which has one of the highest regional rates of dengue infection, the shrimp-like crustacean mesocyclops -- named partly after the one-eyed maneaters of Greek mythology -- is making inroads by preventing the spread of the disease. ^^

It has enabled scientists in Vietnam to reduce dengue-carrying mosquitoes by 96 percent across 45 villages, completely wiping them out in at least one, Phan Boi. But the tiny creature does not act alone. Villagers ensure the mesocyclops, which occurs naturally in Vietnam and other countries, are put into household water supplies where mosquitoes commonly breed. It is too early to predict the global implications of the experiment's success, but long-time project participant John Aaskov, who works with the WHO in Australia, is optimistic. "This program is going to be of benefit wherever people want to try it, certainly throughout the region,'' said Aaskov, adding it could also be used in Africa and South America. ^^

Image Source: Centers for Disease Control and Prevention

Text Sources: CDC Health Information for International Travel, U.S. Department of Health and Human Services; National Geographic, New York Times, Washington Post, Los Angeles Times, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.

Last updated April 2014

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