Once a person gets the dengue virus from a mosquito, the virus attaches to and enters the person's white blood cells. (The white blood cells are part of the immune system, which defends the body by fighting off threats, like infections.) As the white blood cells move around the body, the virus makes copies of itself. The white blood cells react by making many special proteins, like interferon, which tell the immune system to work harder because there is a threat in the body. These proteins cause the fever, flu-like symptoms, and severe pains that happen with dengue.
If a person has a bad infection, the virus makes copies of itself much more quickly inside the body. Because there is a lot more of the virus, it can affect many more organs (like the liver and the bone marrow). The virus can stop the bone marrow from making platelets normally. This makes very bad bleeding much more likely to happen.
Babies and young children with dengue are more likely than adults to become very sick. Women are more likely than men to get very sick. Dengue can be life-threatening in people with chronic (long-lasting) diseases, like diabetes and asthma.
There are four different types of the dengue virus. Once a person has had one type of the virus, he usually is protected from that type for the rest of his life. However, he will only be protected against the other three types of the virus for a short time. If he later gets one of those three types of the virus, he will be more likely to have serious problems, like dengue shock syndrome or dengue hemorrhagic fever.
Usually, doctors diagnose dengue by examining the infected person and realizing that their symptoms match dengue. However, when dengue is in its early stages, it can be difficult to tell the difference between this disease and other infections caused by viruses.
The World Health Organization says that a person probably has dengue if:
The World Health Organization also says that in areas where dengue is common, any warning signs, plus a fever, usually signal that a person has dengue fever.
Some blood tests show changes when a person has dengue fever. The earliest change is a low number of white blood cells in the blood. A low number of platelets can also signal dengue. Special blood tests can look for the dengue virus itself; the virus's nucleic acids; or the antibodies that the immune system makes to fight off the virus. However, these special tests are expensive. Also, in many areas where dengue is common, most doctors and clinics do not have laboratories for blood tests or special machines.
It can be difficult to tell the difference between dengue fever and chikungunya. Chikungunya is a similar viral infection that has many of the same symptoms of dengue, and happens in the same parts of the world. Dengue can also have some of the same symptoms as other diseases, like malaria, leptospirosis, typhoid fever, and meningococcal disease. Often, before a person is diagnosed with dengue, their doctor will do tests to make sure they do not actually have one of these diseases instead.
In 1997, the World Health Organization (WHO) created a system for describing the different types of dengue fever. Eventually, the WHO decided that this old way of dividing dengue needed to be simpler. It also decided that not everyone with dengue fever fit into the old categories.
In 2009, the WHO changed its system for classifying (dividing) dengue fever. However, the older system often is still used.
The WHO's old system divided dengue into three categories:
In 2009, the WHO created a simpler system which divided dengue fever into two types:
There are no vaccines that can keep people from getting the dengue virus. The best ways to prevent dengue are to protect people from mosquito bites and to control the mosquito population.
The best way to control the mosquito is to get rid of its (the places it lives) The best way to do this is to get rid of areas with standing water (water that does not move). Mosquitoes like standing water and often lay its eggs, to prevent getting bitten by mosquitoes, people can:
The WHO suggests a program for preventing dengue (called an "Integrated Vector Control" program) that includes five different parts:
There are no specific treatments for dengue fever. No known anti-viral medications (medicines which kill viruses) will kill the dengue virus. Health workers can give "supportive treatment" - treat dengue's symptoms to try to make patients feel better.
Different people need different treatments, depending on their symptoms. Some people can get better just by drinking fluids at home, and checking with their doctor to make sure they are getting better.
Treating dehydration is very important. Sometimes, people are so dehydrated that they need intravenous fluids - fluids given through a needle placed into a vein. Usually, people only need intravenous fluids for a day or two.
Doctors can give medicines like acetaminophen (paracetamol) for fever and pain. Non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen and aspirin should not be used because they make bleeding more likely.
People with bad dengue may need blood transfusions. Having extra blood will help a person if their blood pressure is getting very low (like it does in dengue shock syndrome) or if they do not have enough red blood cells in their blood (because they are bleeding from dengue hemorrhagic fever).
When people reach the recovery stage of dengue, doctors usually stop giving intravenous fluids to prevent fluid overload (having too much fluid in the body). If a person gets fluid overload, doctors can give a type of medication called a diuretic, which will make the patient urinate out the extra fluid.
Most people with dengue recover and don't have any problems afterward.
Without treatment, 1% to 5% of infected people (1 to 5 out of every 100) die from dengue. With good treatment, less than 1% die. However, 26% of people with severe dengue die.
Dengue is common in more than 110 countries. Every year, it infects 50 to 100 million people around the world. It also causes half a million hospitalizations and about 12,500 to 25,000 deaths around the world each year. However, the World Health Organization says that dengue fever is not taken as seriously as it should be. It calls dengue one of 16 "neglected tropical diseases" - diseases which do not get enough attention. In every million people, dengue causes about 1600 years of life to be lost. This is about the same as other tropical and deadly diseases, like tuberculosis. However, the WHO says the neglected tropical diseases, like dengue, do not get the attention and money that is needed to find treatments and cures.
Dengue is becoming much more common around the world. It is the most common viral disease that is spread by arthropods. In 2010, dengue was 30 times more common than it was in 1960. Scientists think dengue may be getting more common because:
Dengue happens most around the equator. 2.5 billion people live in areas where dengue happens. 70% of these people live in Asia and the Pacific. In the United States, 2.9% to 8% of people who come back from traveling in areas where dengue happens, and have a fever, were infected while traveling. In this group of people, dengue is the second most common infection to be diagnosed, after malaria.
Dengue fever is probably a very old disease. An ancient Chinese medical encyclopedia from the Jin Dynasty (which existed from 265 to 420 AD) talked about a person who probably had dengue. The book talked about a "water poison" that had to do with flying insects.
Written records from the 17th century talk about what may have been epidemics of dengue (where the disease spread very quickly in a short time). The most likely early reports of dengue epidemics are from 1779 and 1780. These reports talk about an epidemic that spread across Asia, Africa, and North America. From that time until 1940, there were not many more epidemics.