- Dengue Fever Fact Sheet
- What is dengue hemorrhagic fever?
- Who gets dengue?
- How is dengue spread?
- What are the signs and symptoms of dengue fever?
- How is dengue fever diagnosed?
- What is the treatment for dengue fever?
- Does past infection with dengue virus make a person immune?
- What can be done to prevent the spread of dengue fever?
- ACLS Guide to Dengue Fever
- Transmission of the Dengue Virus
- Presentation of Dengue
- Symptoms of Dengue
- Undifferentiated Fever
- Dengue Fever With or Without Hemorrhage
- Dengue Hemorrhagic Fever (DHF) or Dengue Shock Syndrome (DSS)
- Are you Planning to Travel to Central or South America? Asia? Africa?
- What Happens if I get Sick with Dengue During my Trip?
- After Your Trip
- Dengue Fever
- What Causes Dengue Fever?
- What Are the Signs & Symptoms of Dengue Fever?
- How Long Does Dengue Fever Last?
- How Is Dengue Fever Diagnosed?
- How Is Dengue Fever Treated?
- Can Dengue Fever Be Prevented?
- How Do People Get Dengue Fever?
- When Should I Call a Doctor?
- How Can I Prevent Dengue Fever?
- Dengue: Practice Essentials, Background, Pathophysiology
Dengue Fever Fact Sheet
Dengue is a disease caused by the bite of a mosquito infected with any one of four specific Dengue viruses. It causes high fever, severe headache, pain behind the eye, joint pain, and muscle pain.
The mosquitos that carry this disease are mainly in tropical areas so travelers may arrive in the United States with dengue fever.
Although most cases occurring in the United States are associated with travel to areas where dengue is endemic, there have been occasional outbreaks of local dengue virus transmission, particularly in southern states.
What is dengue hemorrhagic fever?
Dengue hemorrhagic fever is a more severe form of dengue. Dengue hemorrhagic fever needs to be treated in a timely manner by your health care provider.
Who gets dengue?
People of all ages can get dengue fever if they are exposed to infected mosquitoes. The disease occurs mainly in tropical Asia and the Caribbean, usually during the rainy seasons in areas with high numbers of infected Aedes mosquito. For the latest travel advisory, visit CDC Travel Notice.
How is dengue spread?
Dengue fever is mainly spread by the bite of infected Aedes mosquitoes, which includes A. aegypti and A. albopictus mosquitoes. A mosquito becomes infected when it bites a person who has dengue in his or her blood.
After about a week, the mosquito is able to spread the disease to another person when it bites. Direct spread of dengue from one person to another does not occur.
Aedes aegypti mosquitoes are not found naturally in New York State.
What are the signs and symptoms of dengue fever?
Dengue fever symptoms include sudden onset of a fever that may last from 2 to 7 days with intense headache, joint and muscle pain, and a rash. Mild bleeding of the nose or gums may occur.
The hemorrhagic form of dengue fever is more severe and symptoms may include loss of appetite, persistent vomiting, high fever, headache, difficulty breathing, and abdominal pain.
This may lead to shock and circulatory failure.
Dengue fever may occur from 3 to 14 days after being bitten by an infected mosquito, but usually within 4 to 7 days.
How is dengue fever diagnosed?
Symptoms and travel history can cause a health care provider to suspect dengue fever. Laboratory tests will be needed to confirm diagnosis by seeing if the virus or antibodies against the virus are present in the person's blood.
What is the treatment for dengue fever?
There is no specific treatment available. Intravenous fluids and oxygen therapy are often used for patients who become very ill. Access to proper medical care reduces the lihood that the disease will become more serious.
Does past infection with dengue virus make a person immune?
Infection with one of the four strains of dengue virus usually produces immunity to that strain but does not provide protection against the other strains.
What can be done to prevent the spread of dengue fever?
There are not yet any approved vaccines to prevent infection with dengue virus.
Since cases of dengue appearing in New York are imported, preventive measures are advised for travelers going to affected areas to minimize exposure to mosquitoes. The most effective protective measures are those that avoid mosquito bites.
Use of insect repellents may be helpful in minimizing exposure. More information on repellents can be found at Environmental Protection Agency – insect-repellents.
- Be sure to follow label directions.
- Try to reduce the use of repellents by dressing in long sleeves and pants tucked into socks or boots.
- Children should only handle repellents with adult supervision. Adults should apply repellents to their own hands first and then gently spread on the child's exposed skin. Avoid applying directly to children's hands. After returning indoors, wash your child's treated skin and clothing with soap and water or give the child a bath.
- Do not apply near eyes, nose or mouth and use sparingly around ears.
- After returning indoors, wash treated skin with soap and water.
ACLS Guide to Dengue Fever
Dengue is a re-emerging public health concern with two-fifths of the world population being at risk of infection. It is a mosquito-borne viral infection primarily transmitted by the bite of an infected female of the species Aedes aegypti (figure 1) and the specie_s Aedes albopictus_.
There are five serotypes of the dengue virus: DENV-1, DENV-2, DENV-3, DENV-4, and DENV-5. A person infected by one of the serotypes is immune for life against that specific strain, but is not protected against the other four serotypes.
Figure 1. Aedes aegypti is the vector that carries the virus.
Transmission of the Dengue Virus
Mosquitoes are necessary for the transmission of the virus—it cannot be spread directly from person to person. A mosquito that transmits the virus is known as a vector, or carrier, of the disease.
However, not all mosquitoes spread dengue, only those who have previously bitten an infected person (figure 2). Once a mosquito becomes infected, it remains infected and can continue to spread the virus throughout the entirety of it’s life, which is roughly 3-4 weeks.
In humans, there are two periods of interest when it comes to transmission: the incubation period, which marks the onset of symptoms; and the latency period, the period between infection and the onset of when the person can spread the disease.
The incubation period (4-10 days) provides a rough estimate of the latency period, as most individuals have been noted to become infectious within 24 hours pre or post the onset of symptoms. Once infectious, a person can transmit the infection, via the Aedes mosquitoes, for 4-5 days (with a maximum of up to 12 days).
Figure 2. Dengue transmission cycle: A healthy mosquito bites a dengue-infected human whereby the mosquito becomes infected with the virus. The dengue-infected mosquito then bites a healthy human and transmits the virus through the bite and into the blood. The cycle then starts over again.
Presentation of Dengue
After the initial incubation period, those who have become infected by the dengue virus may either be asymptomatic or go through three forms of the disease:
- Undifferentiated Fever
- Dengue Fever with or without hemorrhage
- Dengue Hemorrhagic Fever or Dengue Shock Syndrome
The Centers for Disease Control and Prevention (CDC) (2016), noted that up to 75 % of all DENV infections are asymptomatic, that is, they have no clinical signs or symptoms of disease.
Symptomatic dengue commonly presents as a non-specific, mild to moderate, acute, febrile illness; however, as many as 5 % of dengue infections progress to a severe, life-threatening disease—dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS).
Severe forms typically manifest after a 2-7 day febrile phase and are often preceded by warning signs.
Symptoms of Dengue
Because early clinical findings are non-specific, knowing how to recognize the warning signs of severe infection can reduce the risk of death among patients with severe dengue.
Undifferentiated fever can mimic any number of other acute illnesses with fever—it does not meet case definition criteria for dengue fever. It’s difficult to diagnose physical exam and routine tests alone. Unless a specfic dengue diagnostic test is performed, the diagnosis remains unknown.
Dengue Fever With or Without Hemorrhage
Dengue fever is the most common and less severe form of the virus. It begins with a sudden onset of high fever that usually lasts between 3-5 days, and is accompanied by the following symptoms:
- High fever, possibly as high as 106 °F (41 °C)
- Severe headache
- Possible bleeding from the mouth and nose
- Retro-orbital pain (pain behind the eyes) that is exacerbated by eye movements
- Muscle and joint pain, usually in the knees and shoulders
- Loss of appetite and difficulties in the sense of taste
- Rash, macules, or papules on the chest and lower limbs
- Nausea and vomiting
Dengue Hemorrhagic Fever (DHF) or Dengue Shock Syndrome (DSS)
The third clinical presentation is DHF, which may progress to DSS. Early symptoms of dengue hemorrhagic fever are similar to those of dengue fever, but 5-7 days after initial onset, the symptoms worsen and may include:
- Acute epigastralgia (pain in the upper abdomen)
- Bleeding of the nose, mouth or gums
- Bleeding or bruising under the skin
- Hematemesis (vomiting blood) and vomiting without blood
- Dry skin and mucous membranes
- Excessive thirst
- Insomnia and restlessness
- Tachycardia (high heart rate)
- Tachypnea (high respiratory rate)
The most severe progression of dengue is dengue hemorrhagic shock, also known as dengue shock syndrome. It is characterized by severe low blood pressure caused by hypovolemia, or low blood volume, in relation to severe dehydration and circulatory failure.
This phase is also characterized by a significant drop in temperature, which may fool some into believing that the person is recovering, when, in fact, this is the most critical period when caregivers should be most vigilant. Without immediate and appropriate supportive care, its fatality rate is above 20 %; however, this is not the most common scenario.
The CDC illustrates the three phases of the DHF infection in figure 3, which include:
- Febrile phase: high fever from viremia, virus in the blood.
- Critical/plasma leak phase: sudden onset of varying degrees of plasma leak into the pleural and abdominal cavities. When plasma shifts from the circulatory system to the spaces between organs the person becomes rapidly dehydrated, resulting in hypovolemia.
- Convalescence or reabsorption phase: sudden arrest of plasma leak with a naturally occuring reabsorption of plasma.
Figure 3. Phases of infection resulting in DHF (CDC, 2014).
Dengue is a disease that has spread over time. Currently, it is present in 128 countries and found in mostly tropical and subtropical areas around the world (figure 4). In the last 4-5 decades, the incidence of dengue in the world has increased significantly.
Dengue cases are underreported and many cases are misclassified.
It is estimated that 390 million dengue infections occur every year, of which 96 million have clinically manifested. Each year, about 500,000 people clinically progress to severe dengue; a large proportion of these cases are children.
About 2.5 % of all cases result in fatality.
Figure 4. Risk of dengue infection worldwide. Red indicates the highest risk of becoming infected.
Are you Planning to Travel to Central or South America? Asia? Africa?
Before traveling to areas where dengue is endemic, it is important to take certain precautions:
- Research the risk of dengue in the destination you are planning to travel to on the web or in tourist offices, health agencies, etc.
- Avoid mosquito-infested places within the area of your destination.
- If at all possible, avoid going out during times of high mosquito activity, such as sunrise and sunset.
- Wear long sleeves and pants.
- Try wearing clothing that has insect shield technology built into it.
- Use mosquito repellents.
- Make sure doors and windows have mosquito nets and leave them closed to prevent entry of mosquitoes.
- Avoid areas where there is standing water, especially during hours of high mosquito activity.
Between late 2015 and early 2016, the use of the first vaccine against dengue, Dengvaxia (CYD-TDV), or Chimerivax, was approved in several countries for people aged 9-45 years living in endemic areas. Discovery of DENV-5 and other similar strains in the future may further impede the Dengue Vaccine Initiative.
There are other live-attenuated vaccines that are currently in developmental phases and clinical trials. At present, the WHO is only recommending the dengue vaccine in areas where data signals a high burden of disease.
What Happens if I get Sick with Dengue During my Trip?
If dengue is suspected, it is very important that you visit a doctor within the region you are visiting as soon as possible.
Currently, there is no specific treatment for dengue, but early detection and medical care lowers fatality rates below 1 %.
Liquids, oral and intravenous, are supplied to prevent dehydration, and acetaminophen is used to treat high fever. It is important to avoid taking aspirin, ibuprofen, or naproxen as these can increase bleeding problems.
The condition usually lasts a week or more and is normally not deadly.
If you become sick during your trip, you should consider extending your stay until you recovered completely.
After Your Trip
If you develop dengue-related symptoms, it is important that you visit your doctor to rule out an infection by dengue.
You can confuse the symptoms with an acute illness or the flu, but remember that if you are coming from an area where dengue is endemic, it is possible that these symptoms may indicate the presence of dengue.
However, do not to worry, with appropriate care, rest and hydration, you can recover within a matter of a few days.
© 2007 Nature Publishing Group Adapted from Whitehead, S. S. et al. Prospects for a dengue virus vaccine. Nature Reviews Microbiology 5, 518–528 (2007). All rights reserved.
Was this article helpful?
Thanks for your feedback!
Share it Tweet
Dengue (DEN-gee) fever is a tropical disease caused by a virus carried by mosquitoes. The virus can cause fever, headaches, rashes, and pain throughout the body. Most cases of dengue fever are mild and go away on their own after about a week.
Dengue fever rarely strikes in the United States — the last reported outbreak was in Texas in 2005.
But if you plan to travel to a foreign country, especially one in the tropics, it's wise to guard against dengue fever.
Wearing insect repellent, covering sleep areas with netting, and avoiding the outdoors at dusk and dawn (when mosquitoes are most active) can help lower the chances of infection.
What Causes Dengue Fever?
Dengue fever is caused by four similar viruses spread by mosquitoes of the genus Aedes, which are common in tropical and subtropical areas worldwide.
When an Aedes mosquito bites a person who has been infected with a dengue virus, the mosquito can become a carrier of the virus. If this mosquito bites someone else, that person can be infected with dengue fever. The virus can't spread directly from person to person.
In rare cases, dengue fever can lead to a more serious form of the disease called dengue hemorrhagic fever (DHF). DHF can be life-threatening and needs to be treated right away.
What Are the Signs & Symptoms of Dengue Fever?
Symptoms of dengue fever are generally mild in younger children and those who have the disease for the first time. Older kids, adults, and those who have had a previous infection may have moderate to severe symptoms.
Common signs and symptoms of dengue fever include:
- high fever, possibly as high as 105°F (40°C)
- pain behind the eyes and in the joints, muscles and/or bones
- severe headache
- rash over most of the body
- mild bleeding from the nose or gums
- bruising easily
Dengue fever used to be called “breakbone fever,” which might give you an idea of the severe bone and muscle pain it sometimes can cause. The fever isn't actually breaking any bones, but it can sometimes feel it is.
How Long Does Dengue Fever Last?
Symptoms can start anywhere from 4 days to 2 weeks after being bitten by an infected mosquito, and typically last for 2 to 7 days.
After the fever eases, other symptoms can get worse and may cause more severe bleeding; gastrointestinal problems nausea, vomiting, or severe abdominal (belly) pain; and respiratory problems difficulty breathing. Dehydration, heavy bleeding, and a rapid drop in blood pressure (shock) can follow if DHF goes untreated. These symptoms are life-threatening and need immediate medical care.
Someone who's had the illness becomes immune to that particular type of the virus (but can still be infected by any of the other three types).
How Is Dengue Fever Diagnosed?
If you think your child might have dengue fever, call a doctor right away. You should also call a doctor if your child has recently been to a region that has dengue fever and has a fever or severe headache.
To make a diagnosis, the doctor will examine your child and evaluate the symptoms. The doctor will ask about your child's medical history and recent travels, and send a blood sample for testing.
How Is Dengue Fever Treated?
No specific treatment is available for dengue fever. Mild cases are managed with lots of fluids to prevent dehydration and getting plenty of rest. Pain relievers with acetaminophen can ease the headaches and pain associated with dengue fever. Pain relievers with aspirin or ibuprofen should be avoided, as they can make bleeding more ly.
Most cases of dengue fever go away within a week or two and won't cause any lasting problems. If someone has severe symptoms of the disease, or if symptoms get worse in the first day or two after the fever goes away, seek immediate medical care. This could be an indication of DHF, which is a medical emergency.
To treat severe cases of dengue fever at a hospital, doctors will give intravenous (IV) fluids and electrolytes (salts) to replace those lost through vomiting or diarrhea. When started early, this is usually enough to effectively treat the disease. In more advanced cases, doctors may have to do a blood transfusion.
In all cases of dengue infection, efforts should be made to keep the infected person from being bitten by mosquitoes. This will help prevent the illness from spreading to others.
Can Dengue Fever Be Prevented?
There's no vaccine to prevent dengue fever. The best protection is to prevent bites by an infected mosquito. Be sure to:
- Use screens on doors and windows, and promptly repair broken or damaged screens. Keep unscreened doors and windows shut.
- Have kids wear long-sleeved shirts, long pants, shoes, and socks when they go outside, and use mosquito netting over their beds at night.
- Use insect repellent as directed on kids. Choose one with DEET or oil of lemon eucalyptus.
- Limit the amount of time kids spend outside during the day, especially in the hours around dawn and dusk, when mosquitoes are most active.
- Don't give mosquitoes places to breed. They lay their eggs in water, so get rid of standing water in things containers and discarded tires, and be sure to change the water in birdbaths, dog bowls, and flower vases at least once a week.
By taking these precautions and keeping your kids away from areas that have a dengue fever epidemic, the risk of contracting dengue fever is small for international travelers.
Reviewed by: Steven Dowshen, MD
Date reviewed: November 2017
How Do People Get Dengue Fever?
When a mosquito bites a person who has dengue fever, the mosquito becomes infected with the virus that causes the disease. It can then spread the virus to other people by biting them.
Dengue fever is not contagious, so it can't spread directly from person to person. Since different viruses can cause dengue fever, someone can get the disease more than once.
When Should I Call a Doctor?
If you think you might have dengue fever, call a doctor right away. You also should call a doctor if you develop symptoms of the infection after going to a region that has dengue fever.
A doctor (or nurse practitioner) will examine you. He or she will ask you questions about how you're feeling, your medical history, and recent travels. Your doctor might want you to give a blood sample to test for the disease.
If you've been diagnosed with dengue, call your doctor or get to a hospital emergency room right away if your symptoms get worse or if new symptoms appear, especially in the day or two after the fever goes down.
How Can I Prevent Dengue Fever?
You can help keep yourself free of dengue fever by avoiding mosquito bites. If you live in or will be visiting an area where there's dengue fever:
- Use screens on doors and windows. Repair broken or damaged screens quickly. Keep unscreened doors and windows shut.
- Wear long-sleeved shirts, long pants, shoes, and socks when you go outside.
- Use mosquito netting over your bed at night.
- Use an insect repellent as directed. Choose one with DEET or oil of lemon eucalyptus.
- Limit the amount of time you spend outside during the day, especially in the hours around dawn and dusk, when mosquitoes are most active.
- Don't give mosquitoes places to breed. They lay their eggs in water. So get rid of standing water in things wading pools and gutters. Change the water in birdbaths, dog bowls, and flower vases every few days.
There is no vaccine against dengue fever yet. Because the infection is common in tropical and subtropical areas, take precautions when visiting those regions.
Reviewed by: Steven Dowshen, MD
Date reviewed: November 2017
Dengue: Practice Essentials, Background, Pathophysiology
Dengue is the most common and important arthropod-borne viral (arboviral) illness in humans. Globally, 2.5-3 billion individuals live in approximately 112 countries that experience dengue transmission.
While the annual incidence is unclear owing to incomplete global reporting and misclassification of illness, approximately 3.2 million individuals were infected globally in 2015.
It is caused by infection with 1 of the 4 serotypes of dengue virus, which is a Flavivirus (a genus of single-stranded nonsegmented RNA viruses).
Infection with one dengue serotype confers lifelong homotypic immunity to that serotype and a brief period (approximately 2 years) of partial heterotypic immunity to other serotypes, but an individual can eventually be infected by all 4 serotypes. Several serotypes can be in circulation during an epidemic.
Dengue is transmitted by mosquitoes of the genus Aedes, which are widely distributed in subtropical and tropical areas of the world (see the image below). An individual with dengue is capable of transmitting the virus for 4-5 days (maximum, 12 days) to a capable vector.
After an incubation period of 5-10 days, the infected mosquito can transmit virus for the rest of its life span (2 weeks to 1 month).
Aedes albopictus is more cold tolerant than Aedes aegypti, so it can survive and transmit virus in the more temperate regions of the United States and Europe.
The global incidence of dengue has increased dramatically in the last several decades, with an estimated 40%-50% of the world’s population in 128 countries at risk.
[2, 3, 4] Today, severe dengue largely affects Asian and Latin American countries, where it is a leading cause of hospitalization and death.
The World Health Organization (WHO) ranked dengue as one of the top ten threats to global health in 2019. 
Initial dengue infection may be asymptomatic (50%-90%),  may result in a nonspecific febrile illness, or may produce the symptom complex of classic dengue fever (DF).
Classic dengue fever is marked by rapid onset of high fever, headache, retro-orbital pain, diffuse body pain (both muscle and bone), weakness, vomiting, sore throat, altered taste sensation, and a centrifugal maculopapular rash, among other manifestations. The severity of the pain led to the term breakbone fever to describe dengue.
A small percentage of persons who have previously been infected by one dengue serotype develop bleeding and endothelial leak upon infection with another dengue serotype. This syndrome is termed severe dengue (reclassified in 2009 by the WHO, previously referred to as dengue hemorrhagic fever and dengue shock syndrome).
Severe dengue has also been termed dengue vasculopathy. Vascular leakage in these patients results in hemoconcentration and serous effusions and can lead to circulatory collapse. This, in conjunction with severe hemorrhagic complications, can lead to a shock syndrome, which poses a greater fatality risk than bleeding per se. 
Dengue virus transmission follows 2 general patterns: epidemic dengue and hyperendemic dengue. Epidemic dengue transmission occurs when dengue virus is introduced into a region as an isolated event that involves a single viral strain.
If the number of vectors and susceptible pediatric and adult hosts is sufficient, explosive transmission can occur, with an infection incidence of 25-50%. Mosquito-control efforts, changes in weather, and herd immunity contribute to the control of these epidemics.
Transmission appears to begin in urban centers and then spreads to the rest of the country.  This is the current pattern of transmission in parts of Africa and South America, areas of Asia where the virus has reemerged, and small island nations.
Travelers to these areas are at increased risk of acquiring dengue during these periods of epidemic transmission.
Hyperendemic dengue transmission is characterized by the continuous circulation of multiple viral serotypes in an area where a large pool of susceptible hosts and a competent vector (with or without seasonal variation) are constantly present. This is the predominant pattern of global transmission.
In areas of hyperendemic dengue, antibody prevalence increases with age, and most adults are immune. Hyperendemic transmission appears to be a major risk for dengue hemorrhagic fever. Travelers to these areas are more ly to be infected than are travelers to areas that experience only epidemic transmission.
Because the signs and symptoms of dengue fever are nonspecific, attempting laboratory confirmation of dengue infection by serodiagnosis, reverse-transcriptase polymerase chain reaction (RT-PCR), or culture is important.
Serodiagnosis is made on the basis of a rise in antibody titer in paired IgG or IgM specimens. Results vary depending on whether the infection is primary or secondary (see Presentation and Workup).
Dengue is a reportable disease in the United States; known or suspected cases should be reported to public health authorities.
Dengue fever is usually a self-limited illness. Supportive care with analgesics, judicious fluid replacement, and bed rest is usually sufficient.
Successful management of severe dengue requires intravascular volume replacement, with careful attention to fluid management and proactive treatment of hemorrhage.
Admission to an intensive care unit is indicated for patients with severe dengue (see Treatment).
The earliest known documentation of dengue fever– illness was in the Chinese Encyclopedia of Symptoms during the Chin Dynasty (CE 265-420). The illness was called “the water poison” and was associated with flying insects near water.
Earliest recorded outbreaks
Outbreaks of febrile illnesses compatible with dengue fever have been recorded throughout history, with the first epidemic described in 1635 in the West Indies.
In 1779-1780, the first confirmed, reported outbreak of dengue fever occurred almost simultaneously in Asia, North America, and Africa. In 1789, the American physician Benjamin Rush published an account of a probable dengue fever epidemic that had occurred in Philadelphia in 1780. Rush coined the term breakbone fever to describe the intense symptoms reported by one of his patients.
A dengue epidemic in East Africa in the early 1820s was called, in Swahili, ki denga pepo (“it is a sudden overtaking by a spirit”). The English version of this term, “Dandy fever,” was applied to an 1827-28 Caribbean outbreak, and in the Spanish Caribbean colonies, that term was altered to “dengue.”
Increased distribution after World War II
Probable outbreaks of dengue fever occurred sporadically every 10-30 years until after World War II. The socioeconomic disruptions caused by World War II resulted in increased worldwide spread of dengue viruses and capable vectors. The first epidemic of dengue hemorrhagic fever in the modern era was described in Manila in 1953. After that, outbreaks of dengue fever became more common.
A pattern developed in which dengue fever epidemics occurred with increasing frequency and were associated with occasional dengue hemorrhagic fever cases.
Subsequently, dengue hemorrhagic fever epidemics occurred every few years. Eventually, dengue hemorrhagic fever epidemics occurred yearly, with major outbreaks occurring approximately every 3 years.
This pattern has repeated itself as dengue fever has spread to new regions.
Although initial epidemics were located in urban areas, increased dengue spread has involved suburban and rural locales in Asia and Latin America. The only continents that do not experience dengue transmission are Europe and Antarctica.
In the 1950s, 9 countries reported dengue outbreaks; currently, the geographic distribution includes more than 100 countries worldwide.
Several of these countries had not previously reported dengue, and many had not reported dengue in 20 years.
Dengue transmission spread from Southeast Asia into surrounding subtropical and tropical Asian countries, southern China and southern Taiwan, the Indian subcontinent and Sri Lanka, and down the island nations of Malaysia, the Philippines, New Guinea, northeastern Australia, and several Pacific islands, including Tahiti, Palau, Tonga, and the Cook Islands. Hyperendemic transmission is reported in Vietnam, Thailand, Indonesia, Pakistan, India, Malaysia, and the Philippines. Dengue continues to extend its range.
In the Americas, dengue epidemics were rare post war because Aedes mosquitoes had been eradicated from most of the region through coordinated vector-control efforts. Systematic spraying was halted in the early 1970s because of environmental concerns. By the 1990s, A aegypti mosquitoes repopulated most of the countries in which they had been eliminated.
In 2014, increased cases of dengue were reported to the WHO in the Peoples Republic of China, Cook Island, Fiji, Malaysia, and Vanuatu, which experienced an outbreak of dengue serotype 3 (DENV-3) after a 10-year hiatus. In 2015, large outbreaks of dengue were reported in the Philippines (>169,000 cases), Malaysia (>111,000 suspected cases), and Brazil (>1.5 million cases). Delhi, India, experienced its worse outbreak since 2006.
DENV-1 and DENV-2
Serotype 1 dengue (DENV-1) was first reported in French Polynesia and Japan in 1943, followed by Hawaii.  DENV-1 was introduced into a largely susceptible population in Cuba in 1977. Serosurveys indicated that more than 44% of the population was infected, with only mild disease reported.
The first dengue hemorrhagic fever epidemic in the Americas occurred in Cuba in 1981 and involved serotype 2 dengue (DENV-2), with hundreds of thousands of cases of dengue in both children and adults, 24,000 cases of dengue hemorrhagic fever, 10,000 cases of dengue shock syndrome, and 158 reported deaths.
In 1997, Asian genotype DENV-2 was reintroduced, and dengue shock syndrome and dengue hemorrhagic fever were seen only in adults who had previously been infected with DENV-1 in 1977. Disease and case-fatality rates were higher in those who had been infected with DENV-2 20 years after their initial DENV-1 infection than those who were infected 4 years apart.
Data from other countries supports the finding that the severity of secondary dengue infections appears to intensify with longer intervals between infections. [11, 12] Since then, dengue fever and dengue hemorrhagic fever cases have progressively increased.
In 1986, the first clearly identified local transmission of dengue in the United States occurred in Texas. Carriers of the virus were believed to have crossed the border from Mexico; the local vector population was then infected. Since then, seasonal autochthonous infection has been reported in both Texas and Hawaii.
In 2001-2002, Hawaii experienced its first outbreak of dengue since World War II ended. The outbreak involved 2 variants of DENV-1 that were transmitted by A albopictus.
Predominantly affecting young adults and adults, 122 cases of dengue fever spread slowly on Maui, Oahu, and Kauai. The epidemic was traced to viremic visitors from Tahiti, which was then experiencing a severe outbreak of the infection.
In 2015, Hawaii reported more than 65,000 cases, with ongoing transmission reported in 2016.
Two competent vectors, A aegypti and A albopictus, are currently seasonally abundant in some areas of the southwestern and southeastern United States, including Texas, Arizona, New Mexico, Louisiana, Mississippi, Alabama, Georgia, and mid to south Florida. A aegypti has also been reported sporadically in portions of North Carolina, South Carolina, Tennessee, Arkansas, Maryland, and New Jersey. The range of A albopictus extends almost as far north as the Great Lakes.
As suggested by a reported case of a woman aged 63 years who died from complications of dengue acquired in New Mexico or Texas in 2012, the disease may not be adequately recognized in the United States as a source of potentially fatal acute febrile illness. The patient had initially been diagnosed with West Nile virus, but a postmortem bone marrow biopsy revealed the presence of dengue virus. [13, 14]
In addition, the patient’s records revealed that she met the clinical case definition for hemophagocytic lymphohistiocytosis, a hyperinflammatory syndrome that is sometimes associated with dengue and that, in this instance, was the cause of death.
Dengue fever did not naturally occur in the European Union and in continental Europe because these areas did not have an appropriate vector population to allow further spread of dengue from viremic individuals returning from other countries. However, dengue does occur in several overseas territories of European Union members.
In recent decades, reports of dengue infections in long-term expatriates, aid workers, military personnel, immigrants, and travelers returning from the tropics and subtropics have been increasing. In 2010, local transmission was reported in France and Croatia. Another outbreak with more than 2000 cases occurred in Madeira in 2012.
Factors believed to be responsible for the spread of dengue include the following:
- Explosive population growth
- Unplanned urban overpopulation with inadequate public health systems
- Poor control of standing water and vectors
- Viral evolution
- Increased international recreational, business, and military travel to endemic areas
All of these factors must be addressed to control the spread of dengue and other mosquito-borne infections. Unplanned urbanization is believed to have had the largest impact on disease amplification in individual countries, whereas travel is believed to have had the largest impact on global spread. [6, 8, 9, 12, 15]
Liu-Helmersson et al (2016) found that, over time, the duration and intensity of dengue transmission in Europe have increased. With increasing levels of greenhouse gas emissions, the authors predict that changes in intensity and duration will occur more rapidly. 
Over the past decades, the GeoSentinel Network of Travel Medicine providers has demonstrated that dengue has become more frequently diagnosed than malaria in travelers returning from tropical areas other than Africa.
Such sentinel travel surveillance can augment global and national public health surveillance. More recent studies have not supported an earlier suggestion that climate change is also directly responsible for increased transmission.
[11, 9, 12]