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Dengue and severe dengue

* Dengue is a mosquito-borne viral infection.
* The infection causes flu-like illness, and occasionally develops into a potentially lethal complication called severe dengue.
* The global incidence of dengue has grown dramatically in recent decades.
* About half of the world’s population is now at risk.
* Dengue is found in tropical and sub-tropical climates worldwide, mostly in urban and semi-urban areas.
* Severe dengue is a leading cause of serious illness and death among children in some Asian and Latin American countries.
* There is no specific treatment for dengue/ severe dengue, but early detection and access to proper medical care lowers fatality rates below 1%.
* Dengue prevention and control solely depends on effective vector control measures.

Dengue is a mosquito-borne infection found in tropical and sub-tropical regions around the world. In recent years, transmission has increased predominantly in urban and semi-urban areas and has become a major international public health concern.

Severe dengue (previously known as Dengue Haemorrhagic Fever) was first recognized in the 1950s during dengue epidemics in the Philippines and Thailand. Today, severe dengue affects most Asian and Latin American countries and has become a leading cause of hospitalization and death among children in these regions.

There are four distinct, but closely related, serotypes of the virus that cause dengue (DEN-1, DEN-2, DEN-3 and DEN-4). Recovery from infection by one provides lifelong immunity against that particular serotype. However, cross-immunity to the other serotypes after recovery is only partial and temporary. Subsequent infections by other serotypes increase the risk of developing severe dengue.

Global burden of dengue

The incidence of dengue has grown dramatically around the world in recent decades. Over 2.5 billion people – over 40% of the world’s population – are now at risk from dengue. WHO currently estimates there may be 50–100 million dengue infections worldwide every year.

Before 1970, only nine countries had experienced severe dengue epidemics. The disease is now endemic in more than 100 countries in Africa, the Americas, the Eastern Mediterranean, South-east Asia and the Western Pacific. The American, South-east Asia and the Western Pacific regions are the most seriously affected.

Cases across the Americas, South-east Asia and Western Pacific have exceeded 1.2 million cases in 2008 and over 2.3 million in 2010 (based on official data submitted by Member States). Recently the number of reported cases has continued to increase. In 2010, 1.6 million cases of dengue were reported in the Americas alone, of which 49 000 cases were severe dengue.

Not only is the number of cases increasing as the disease spreads to new areas, but explosive outbreaks are occurring. The threat of a possible outbreak of dengue fever now exists in Europe and local transmission of dengue was reported for the first time in France and Croatia in 2010 and imported cases were detected in three other European countries. A recent (2012) outbreak of dengue on Madeira islands of Portugal has resulted in over 1800 cases and imported cases were detected in five other countries in Europe apart from mainland Portugal.

An estimated 500 000 people with severe dengue require hospitalization each year, a large proportion of whom are children. About 2.5% of those affected die.

Transmission
Aedes aegypti; adult female mosquito taking a blood meal on human skin.
WHO/TDR/Stammers

The Aedes aegypti mosquito is the primary vector of dengue. The virus is transmitted to humans through the bites of infected female mosquitoes. After virus incubation for 4–10 days, an infected mosquito is capable of transmitting the virus for the rest of its life.

Infected humans are the main carriers and multipliers of the virus, serving as a source of the virus for uninfected mosquitoes. Patients who are already infected with the dengue virus can transmit the infection (for 4–5 days; maximum 12) via Aedes mosquitoes after their first symptoms appear.

The Aedes aegypti mosquito lives in urban habitats and breeds mostly in man-made containers. Unlike other mosquitoes Ae. aegypti is a daytime feeder; its peak biting periods are early in the morning and in the evening before dusk. Female Ae. aegypti bites multiple people during each feeding period.

Aedes albopictus, a secondary dengue vector in Asia, has spread to North America and Europe largely due to the international trade in used tyres (a breeding habitat) and other goods (e.g. lucky bamboo). Ae. albopictus is highly adaptive and therefore can survive in cooler temperate regions of Europe. Its spread is due to its tolerance to temperatures below freezing, hibernation, and ability to shelter in microhabitats.
Characteristics

Dengue fever is a severe, flu-like illness that affects infants, young children and adults, but seldom causes death.

Dengue should be suspected when a high fever (40°C/ 104°F) is accompanied by two of the following symptoms: severe headache, pain behind the eyes, muscle and joint pains, nausea, vomiting, swollen glands or rash. Symptoms usually last for 2–7 days, after an incubation period of 4–10 days after the bite from an infected mosquito.

Severe dengue is a potentially deadly complication due to plasma leaking, fluid accumulation, respiratory distress, severe bleeding, or organ impairment. Warning signs occur 3–7 days after the first symptoms in conjunction with a decrease in temperature (below 38°C/ 100°F) and include: severe abdominal pain, persistent vomiting, rapid breathing, bleeding gums, fatigue, restlessness, blood in vomit. The next 24–48 hours of the critical stage can be lethal; proper medical care is needed to avoid complications and risk of death.

Treatment

There is no specific treatment for dengue fever.

For severe dengue, medical care by physicians and nurses experienced with the effects and progression of the disease can save lives – decreasing mortality rates from more than 20% to less than 1%. Maintenance of the patient’s body fluid volume is critical to severe dengue care.

Immunization

There is no vaccine to protect against dengue.

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Dengue fever is the world’s fastest growing mosquito-borne disease. Over 50 million people suffer from dengue fever each year, and 40% of the world’s population may be at risk. It is quickly becoming even more widespread, and is growing in severity.

Dengue symptoms range from mild and flu-like to high fever, rash, severe headache, pain behind the eyes, muscle and joint pain. The joint pain can be so severe that dengue has been given the name ‘breakbone fever’. Nausea, vomiting, and loss of appetite are also common. In the more severe form, sometimes called dengue haemorrhagic fever (DHF), blood vessels start to leak and cause bleeding from the nose, mouth, and gums. Without prompt treatment, the blood vessels can collapse, causing shock (dengue shock syndrome) and ultimately fatality.

Around 25,000 people die from Dengue Fever each year. Severe cases require hospitalization and constant monitoring. Dengue is also an extremely expensive disease, estimated to cost the global economy over US$5 billion per year.

Dengue fever occurs in most tropical areas of the world. It is common in Asia, the Pacific, Australia, Latin America and the Caribbean and is continuing to spread having now reached North America. A recent Natural Defence Resource Council report shows that 28 US states are now at risk.
Current control methods aren’t working

There is neither specific medication nor vaccine for dengue. The only way currently to control the disease is to control the mosquito which spreads it: the dengue mosquito, Aedes aegypti.

Existing methods of controlling the dengue mosquito, which include spraying or fogging using chemical pesticides, have failed to stop the spread of the disease. That’s partly because the mosquitoes have developed resistance, but also because the Aedes aegypti mosquito lives in and around human habitation – even breeding happily in vases, water jars and other vessels in people’s houses – so it can be very difficult to reach.

The Oxitec approach

Using advanced genetics and molecular biology Oxitec has developed a new and innovative solution to controlling the dengue mosquito, Aedes aegypti.

The Oxitec solution harnesses the natural instincts of male mosquitoes to find females in the wild. Oxitec has used genetic modification to create ‘sterile’ male insects which seek out and mate with females. After an Oxitec mosquito has successfully mated with a wild female, any offspring that result will not survive to adulthood, so the mosquito population declines.

The Oxitec Control Programme is the system through which Oxitec mosquitoes are released and monitored in a dengue-hit area over a predetermined and sustained period of time. By applying the Oxitec Control Programme to an area, the mosquito population in that area can be dramatically reduced or eliminated.

The Oxitec approach is targeted at a single species, unlike conventional insecticides or pesticides which kill insects indiscriminately. This means that, as well as being more effective, it is much better for the environment than conventional tools.

The benefits

The personal cost of dengue fever for the individual is high. But dengue also places a strangle-hold on entire communities. The economic cost of dengue is phenomenal and is estimated to cost the global economy US$5 billion annually. In addition to the high cost of current control methods, and the even higher cost of caring for dengue patients, dengue outbreaks can devastate tourism in countries which often rely on the income which overseas visitors can bring.

The Oxitec solution provides a proven means of protecting people from dengue fever. It will enable individuals and whole communities to go back to work and get on with their lives free from this dangerous and debilitating disease. It will alleviate a major economic burden for governments around the world, and free up resources within communities to allow increased spending on other healthcare problems.

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The Tiger mosquito or forest day mosquito, Aedes albopictus (Stegomyia albopicta), from the mosquito (Culicidae) family, is characterized by its black and white striped legs, and small black and white striped body. It is native to the tropical and subtropical areas of Southeast Asia; however, in the past couple of decades this species has invaded many countries throughout the world through the transport of goods and increasing international travel. This mosquito has become a significant pest in many communities because it closely associates with humans (rather than living in wetlands), and typically flies and feeds in the daytime in addition to at dusk and dawn. The insect is called a tiger mosquito because its striped appearance is similar to a tiger. Aedes albopictus is an epidemiologically important vector for the transmission of many viral pathogens, including the West Nile virus, Yellow fever virus, St. Louis encephalitis, dengue fever, and Chikungunya fever, as well as several filarial nematodes such as Dirofilaria immitis.

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Oxitec Wants To Release Genetically Modified Mosquitoes Into Florida Keys

Mosquitoes aren’t just a pesky nuisance causing Floridians to claw at swollen welts on their limbs; they can also transmit deadly disease. Back in 2009, the Florida Keys suffered an outbreak of Dengue Fever, a fatal condition with flu-like symptoms, the first there since 1934.

Now a British biotech company Oxitec thinks they have the solution to avoiding future outbreaks: genetically modified mosquitoes. Their mutant skeeters not only glow red when placed under a microscope, they also carry a gene that causes new offspring to self-destruct.

In theory, Oxitec wants to release their GM male mosquitoes into the Keys so that they will mate with existing females and hatch larvae that won’t live long enough to bite people.

Many Key Westers are alarmed that a British biotech company wants to use their backyard for a genetic experiment. Resident Mila de Mier went as far as setting up an online change.org petition in April, which now has over 100,000 signatures of support.

“Nearly all experiments with genetically-modified crops have eventually resulted in unintended consequences…Why would we not expect GM (genetically modified) insects, especially those that bite humans, to have similar unintended negative consequences? Will the more virulent Asian tiger mosquito that also carries dengue fill the void left by reductions in A. aegypti? Will the dengue virus mutate (think antibiotic resistant MRSA) and become even more dangerous?”

In order to avoid a repeat of the 2009 outbreak, which lasted for 15 months and made 93 people sick, the Florida Keys Mosquito Control District spends upwards of a million dollars to blanket the chain of islands with pesticides.

As a Broward New Times cover story pointed out, Floridians may take current mosquito control measures for granted. In the days before the state’s extensive mosquito control programs, skeeter swarms in some areas were so dense “it was impossible to breathe without inhaling mouthfuls of mosquitoes.”

This isn’t the first time genetic engineering could be used to combat Dengue Fever. In 2010, Oxitec released 3 million mutant male mosquitoes into the Cayman Islands and report that within a year, the local population was cut by 80 percent.

If the Food and Drug Administration approves their “animal bug patent,” Oxitec will likewise release upwards of 10,000 GM mosquitoes at an undisclosed 36-square-acre block near the Key West Cemetery.

Oxitec admits their system isn’t foolproof. About one female is accidentally released for every 1,500 male mosquitoes, according to New Times, and it’s the females that bite and suck blood.

In April, the Florida Keys Environmental Coalition wrote to Gov. Rick Scott, asking him to stop Oxitec, pointing to the unknown consequences of being bit by one these rogue GM female mosquitos: “… biting female mosquitoes could inject an engineered protein into humans along with other proteins from the mosquitos’ salivary gland. Oxitec has yet to conduct or publish any study showing that this protein is not expressed in the salivary gland and therefore cannot be passed on to humans.”

As there haven’t been any reported cases of Dengue Fever in the Keys since 2009, residents are calling for more research to be done before introducing a brand new species into the local environment.

“We need more data. If something goes wrong the consequences could be catastrophic not only for humans but also the whole ecosystem, and I don’t want my family being used as laboratory rats for this.”