Dengue Fever: controlling and preventing possible outbreaks

It is news in recent days that nearly 2 million "probable cases" of Dengue Fever have been reported in Brazil since the beginning of 2024. The number of possible infections is the highest since 2000 and 4 times the total number of infections reported during the same period in 2023. Ten Brazilian states have already declared a state of emergency, with São Paulo among the many cities.

Of all the diseases caused by Arboviruses, the one caused by Dengue virus (belonging to the Flavivirus genus like West Nile viruses, Zika virus, and Hepatitis C virus) is currently causing the greatest concern.

The virus has 4 serotypes (i.e., "subgroups," referred to as DEN-1, DEN-2, DEN-3, DEN-4), each of which can cause the disease. The first infection usually does not generate particular concerns; however, if later infection with a different serotype occurs, a phenomenon known as "Antibody-Dependent Enhancement (ADE)" may occur, i.e., antibodies generated by the first infection may promote, rather than prevent, infection and aggravation of disease that can lead to death, a kind of immune paradox, which is rare (e.g., has not occurred with either infection or anti-COVID-19 vaccination), but demonstrated precisely in the case of Dengue virus infection.

Currently, the situation in Italy is under control, although the risk of contracting the virus is still potentially present. We cannot determine with certainty whether the situation is worrying, as there is a lack of seroprevalence studies that provide a complete picture of the presence of anti-Dengue antibodies in the Italian population, from North to South.

In general, however, people who acquire the infection while travelling, if they do not prevent mosquito bites, put other people at risk as they can themselves become a source of infection. Therefore, it is critical to understand how this disease is transmitted so that the correct measures can be implemented to prevent and contain its spread.

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Dengue disease

Dengue is a viral disease transmitted mainly by mosquitoes of the genus Aedes, particularly Aedes aegypti. This disease is a major cause of fever in tropical and subtropical areas such as Africa, Southeast Asia and China, India, the Middle East, Latin and Central America, Australia, and several parts of the Pacific, affecting millions of people each year.

Transmission

Dengue transmission occurs primarily through the bite of infected female mosquitoes of the genus Aedes, which feed on the blood of an infected person and then transmit the virus by biting a healthy person.

These mosquitoes are particularly active during the day, especially in the early morning hours and before sunset. In rare cases, Dengue can be transmitted through contact with infected blood or blood products and, very rarely, from mother to child during pregnancy or at childbirth.

Symptoms

Dengue symptoms vary from the mild, flu-like form to more severe forms, such as hemorrhagic Dengue or Dengue shock syndrome. Symptoms generally appear 4 to 10 days after the mosquito bite and may include high fever, severe headache, pain behind the eyes, muscle and joint pain, fatigue, nausea, vomiting, and sometimes rashes.

In more severe forms, symptoms can progress to hemorrhage, drop in blood pressure to shock, and, in extreme cases, death.

Prevention, treatment, cure

Currently, the most effective strategy to prevent Dengue is to avoid contact with mosquitoes carrying the virus. This includes eliminating mosquito breeding sites near inhabited areas, such as collections of standing water in pots, tires, and other objects that can collect rainwater. The use of insect repellents, clothes that cover most of the body, bed nets, and mosquito nets on windows can also reduce the risk of bites. Since Aedes mosquitoes are most active in the early morning hours, it is especially important to use protection during this part of the day.

There is no specific therapy for Dengue. Clinical management focuses on treatment of symptoms and supportive care. Hydration is critical, and in mild cases, the disease can be managed with rest, fluid intake, and the use of antipyretics to control fever and relieve pain.

However, aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs) should be avoided because of the risk of bleeding. In severe cases, treatment may require hospitalization for intravenous fluid administration and close monitoring of vital signs and blood pressure.

Vaccines

Recently, Dengue vaccines have been developed, offering hope in preventing the disease. However, the use of these vaccines is complex, as their efficacy may vary depending on the viral serotype and the individual's previous exposure to the virus (to precisely avoid the possibility of ADE). Therefore, decisions regarding vaccination require careful evaluation by health professionals, considering the benefits and risks based on geographic area and prevalence of the disease.

Dengue is therefore a significant global public health challenge, especially because of its increasing geographic spread and increasing outbreaks. Research continues to focus on new prevention methods, more effective treatments, and optimization of vaccination strategies.

Combating Dengue requires an integrated approach that includes disease surveillance, improving public awareness, and implementing more effective vector control strategies. With these measures, it is hoped to reduce the impact of Dengue on vulnerable populations worldwide.

Article written in collaboration witth Guido Poli, Full Professor of General Pathology at UniSR, and Elisa Vicenzi, Group Leader Viral pathogens and biosafety Unit at IRCSS San Raffaele Hospital.

References

• https://www.ansa.it/sito/notizie/mondo/americalatina/2024/03/19/in-brasile-verso-2-milioni-casi-dengue-record-in-24-anni_6368f635-9280-4f2a-a2e2-e532e5d3415d.html
• https://www.epicentro.iss.it/febbre-dengue/
• https://www.salute.gov.it/portale/malattieInfettive/dettaglioSchedeMalattieInfettive.jsp?lingua=italiano&id=215&area=Malattie%20infettive&menu=indiceAZ&tab=7
• https://www.who.int/news-room/fact-sheets/detail/dengue-and-severe-dengue