Dengue

Dengue fever is an ancient disease of viral origin: the first case is mentioned in a Chinese medical encyclopaedia compiled between the 3rd and 5th centuries. Descriptions of several epidemics emerged in the 17th century, with the first outbreak documented in 1779, in North America, Asia and Africa. The disease has been widespread since World War II, which encouraged its spread to other areas of the world where it had previously been absent.

Today, 40 percent of the world's population (corresponding to approx. 3 billion people) live in areas at risk of dengue transmission. In fact, the disease is endemic in more than 100 countries and affects more than 400 million people each year, causing approximately 22,000 deaths.

CAUSES

Dengue is caused by the virus of the same name, from the Flaviviridae family. Four different serotypes of dengue virus have been isolated, and are classified as DENV-1, DENV-2, DENV-3 and DENV-4. A person can develop the disease from any of these serotypes, even if they have been infected in the past by one of the others. Primary infection, usually caused by a single serotype, is believed to result in permanent immunity to that serotype, while immunity with other serotypes is only partial and temporary.

Subsequent infections (secondary infections) caused by a different serotype to the previous one may consequently increase the risk of developing severe dengue, due to a highly complex immune mechanism that alters the body’s response to the infection.

TRANSMISSION

Dengue transmission occurs through the bites of infected female mosquitoes, primarily the genus Aedes, that have fed on the blood of infected individuals.

Characterised by their black bodies with white stripes and the fact that they are active both day and night, these two species are also involved in the spread of other dangerous diseases, such as yellow fever and dengue. Aedes aegypti is the main vector and is usually found in tropical and sub-tropical regions. Aedes albopictus is known as the "tiger mosquito”, which is found in the more temperate regions of Europe, Asia, and Africa.

Whereas, direct human-to-human transmission is extremely rare and only possible through direct contact with infected blood.

GEOGRAPHICAL DISTRIBUTION

Dengue is endemic in over 100 countries, from Africa, the Americas, and the eastern Mediterranean, to south-east Asia, the western Pacific and all tropical regions, with local variations in risk that depend on rainfall, temperature and relative humidity levels, and rapid urbanisation with no urban planning procedures.

There is an increasing epidemic trend, with 1.2 million cases reported in the Americas, Southeast Asia, and Western Pacific in 2008, and over 3.34 million cases in 2016.

The increase in new cases of dengue can also be attributed to the spread of the virus to new areas. Urbanisation and climate change are all factors that enable the vector mosquito to find new habitats in which to breed. Whereas, intercontinental travel can facilitate the migration of the mosquito or the virus, causing dengue outbreaks even in areas that had never experienced the disease before.

The first outbreak in Europe occurred in 2012, on the island of Madeira, in Portugal, where the virus infected over 2,000 people. In 2015, an indigenous transmission of dengue virus (DENV-1) occurred in the south of France, in Nimes, causing 7 cases of infection. Like many others in Europe, the country is home to the tiger mosquito, which has allowed the disease to spread. The identified primary case was imported from French Polynesia.

In 2017, only imported cases occurred in Europe: 23 European countries reported 2,026 cases of Dengue virus. Germany reported the highest rate (31.3%), followed by the United Kingdom (23%), France, Spain and Sweden. In August 2020, there was a case of dengue contracted on Italian soil, in Veneto.

SYMPTOMS

The incubation period of dengue varies between 5-6 days. This is followed by a broad spectrum of clinical symptoms, from subclinical or asymptomatic forms (in which people do not even realise they have been infected), to symptomatic forms, characterised by fever (sometimes very high) that can persist for more than ten days; muscle and joint pain, and a pinkish rash that commonly presents on the torso.

In more severe cases, symptoms can include severe flu-like symptoms and encephalitic or liver disorders. Some individuals develop a severe form of dengue, characterised by severe bleeding, multi-organ failure (MOF), and plasma leakage. In this form, first identified in the 1950s and now prevalent in most Asian and Latin American countries, there is a real risk of death if the disease is not managed appropriately.

DIAGNOSIS

Suspicion of dengue may arise during clinical examination of the patient, through observation of the symptoms, or from their medical history (e.g., recent travel to an endemic area).

Usually, diagnosis of the virus is based on laboratory tests that look for specific antigens, identification of the virus using PCR tests, or analysis of the patient’s blood parameters.

TREATMENT

There is no specific treatment for dengue. Treatment is based on treating the symptoms and supporting vital functions.

In classic cases of dengue, rest and frequent hydration is usually sufficient, with treatment of specific symptoms with fever reducers and pain killers. Aspirin (acetylsalicylic acid) drugs should be avoided, as they can cause or aggravate bleeding.

The haemorrhagic form of dengue must be followed carefully, with intravenous replenishment of fluids and mineral salts; blood and plasma transfusions may be necessary in very severe cases.

PREVENTION

Prevention of dengue transmission starts with appropriate preventive behavioural measures, especially during the day, when mosquitoes are most active.

• Use an effective mosquito repellent
  The Centers for Disease Control and Prevention (CDC) recommend repellents with the following active ingredients: DEET (>25%); Picaridin; IR3535; Oil of Lemon Eucalyptus (OLE); Para-menthane-diol; 2- undecanone.
• Keep covered
  Wear clothes that cover the legs and arms; light-coloured clothing is best.
• Check the surrounding environment
  Stagnant water is the perfect habitat for mosquitoes to breed. Make sure there is no stagnant water in discarded tyres or industrial containers, swimming pools, storm drains, plant pot saucers, etc. To reduce the risk of transmission, systematic pest control campaigns to fight the Aedes mosquito population appear to be an essential intervention.

A new vaccine against Dengue is available

Qdenga (the commercial name of the drug) is a live attenuated vaccine, capable of protecting against the 4 serotypes.

It is administered subcutaneously in the upper part of the arm (deltoid muscle) starting from 4 years of age, and involves the administration of two doses, spaced three months apart. At the moment there are no data on when to administer a possible booster dose, probably in the future a booster dose will be recommended after 3-5 years.

The vaccine is well tolerated and the side effects are those common to other vaccines: pain at the injection site, headache, muscle pain. It is the only vaccine capable of also protecting subjects who have contracted Dengue in the past (limitation of the previous vaccine), it is therefore a recommended vaccine for all international travelers.

 

 

Source: CDC, WHO

The information presented is general in nature, is published for informational purposes for a general public and does not replace the relationship between patient and doctor.