Immunization For Dengue Fever May Be Coming Soon

Dengue fever has been one of the most notorious of all tropical diseases for 200 years. With the reality of climate change, it's no longer only tropical.

What Is Dengue Fever?

Dengue (pronounced den-gee with a hard g) fever is the most common mosquito-born illness in the world. More people get dengue fever than get malaria. More people get dengue fever than get yellow fever. Every year, over 400 million people are infected with the virus that causes dengue fever after mosquito bites, although most do not come down with symptoms.

How dengue infection expresses itself depends a lot on the age of the victim. In children under 15, the virus usually causes vague symptoms including a mild fever and maybe a mottled rash, or maybe not. In adults, symptoms show up two or three days after the mosquito bite and may include:

• Headache.

• Pain behind the eyes.

• Severe muscle pain, especially in the lower back, arms, and legs.

• Painful joints, usually in the knees and shoulders

• Nausea and vomiting (diarrhea is rare).

• Rash, consisting of a bumpy maculopapular or macular confluent rash over the face, torso, and the folds of the elbows and knees, with islands of skin unaffected.

• Muscle weakness, sometimes severe.

• Muscle pain, sometimes so severe that the illness used to be known as "breakbone fever."

• Altered taste sensation

• Loss of appetite.

• Sore throat.

• Swollen lymph glands.

• Mild hemorrhagic (bleeding) manifestations (petechiae of the eyes, bleeding gums, nosebleed, blood in the urine, and, in women who have not reached menopause, unusually heavy periods).

As the disease progresses, it may cause bleeding symptoms that are more severe. About the same time as the initial fever breaks, it's as if the patient springs leaks. There can be oozing of blood plasma from the eyes, nose, mouth, anus, and genital organs, and there can also be serious internal bleeding in the digestive tract. Any cuts or scrapes will start to bleed. Loss of blood can lead to seizures and loss of consciousness. There can be destruction of heart tissue (cardiomyopathy), inflammation of testes (orchitis) or ovaries (oophoritis), depression, liver damage, and severe inflammation of the eyes. When dengue fever progresses to its second stage, 50 percent of people will die without treatment.

Dengue Fever is Spreading

Textbooks used to say that dengue fever was unknown in Europe. In recent years, there have been cases in France, Italy, and Croatia. In January of 2016, there were 240 cases of dengue on the Big Island of Hawaii. Dengue has appeared in Florida, and caused death in Texas. It is one of several threats to opening the Olympics in Brazil. Nearly three billion people in at least 112 countries are exposed to the disease, and the number is only increasing. Biologists predict that by the year 2100 there will be cases in Norway, Russia, Germany, the United Kingdom, most of the United States, and Canada.

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Part of the problem has been the re-emergence of species of mosquito known as Aedes aegypti, the only insect that transmits it. This mosquito was wiped out 50 years ago with DDT in much of the tropical world, but new strains resistant to pesticides have emerged. Aedes aegypti was never wiped out the in the southern United States. Since it is now impossible to get rid of the mosquito, attention has turned to finding a vaccine.

Dengue Fever Vaccine, And What To Do Until It is Available

Dr. Anna Durban and colleagues at the Johns Hopkins Bloomberg School of Public Health in Baltimore in the United States have developed a vaccine covering four strains of dengue fever they have dubbed TV003. This is an attenuated live vaccine, that is, it is a vaccine that contains live virus modified to cause a less serious reaction in the recipient. Last year they tested the vaccine and a placebo on groups of volunteers. Six months after giving the shots, volunteers were exposed to the virus. In the placebo group, everyone developed viremia, with detectable levels of virus in their blood. Of the volunteers given the placebo, 80 percent developed a rash and 20 percent developed neutropenia, the destruction of white blood cells. None of the volunteers given the attenuated live virus developed viremia; the virus could not be detected in their blood. None of the volunteers given the actual vaccine developed a rash or symptoms of blood cell destruction.

The test at Johns Hopkins was just a phase II trial, and a broader phase III clinical trial is underway in Brazil. However, Dr. Durban's vaccine is not the first for dengue fever. Another vaccine with a serious problem was actually approved in Mexico earlier this year (2016) in Mexico, the Philippines, and Peru.

The Problem with Trivalent Vaccine for Dengue Fever

The vaccine approved earlier this year was a trivalent vaccine, effective against three of the four strains of dengue fever. Clinical testing confirmed that the vaccine was effective against those three strains of the virus.

The problem with a trivalent vaccine turned out to be that if you are vaccinated for three strains of the dengue virus and then you are exposed to the fourth, not only do you not have protection against that strain, it is more virulent. It causes far worse symptoms than if you had not been vaccinated at all. As long as mosquitoes in your location do not become infected with the fourth strain, you don't have a problem, but if someone who has been infected with the fourth strain outside your area moves to your location and then is bitten by a mosquito that in turn bites you, you can become extremely sick. A trivalent vaccine can be better than no vaccine in a dengue fever outbreak, but at some point you may need a second immunization with the tetravalent vaccine, covering all four strains.

What to Do If You Can't Get Dengue Fever Vaccine

Most people who come down with dengue don't develop life-threatening symptoms. If you get some of the symptoms of the first stage of dengue after you have been bitten by mosquitoes, then be on the lookout for symptoms of dehydration (dizziness, dry skin, dark urine). Treating dehydration, by drinking water with at least a small amount of electrolytes (juice or even sugar and salt), will reduce some of the other symptoms, especially headache.

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Better yet, don't get bitten by mosquitoes in the first place. Wear long sleeves and long pants. Use mosquito repellant. Stay indoors when mosquitoes are especially active, at sunup and sunrise. Don't let water pool around your home. Dengue fever isn't treatable. Do what you can to avoid it.