Dengue is an infectious febrile illness of viral origin, first identified in 1789 by Benjamin Rush, who named it "breakbone fever" due to the intensity of myalgia and arthralgia.

In recent decades, the incidence of dengue has increased worldwide. The WHO estimates that between 50 million and 100 million infections occur each year, with more than 2.5 billion people (40% of the world's population) at risk of contracting the disease.

It is caused by an RNA virus of the genus Flavivirus, family Flaviviridae. Currently, four serotypes of this virus are recognized: Denv 1, Denv 2, Denv 3, and Deng 4. These possess immunological and antigenic properties characterized by structural antigens (C, M, E) and seven non-structural antigens (NS1 to NS5).

The vectors of the dengue virus are female hematophagous mosquitoes of the Aedes aegypti and Aedes albopictus species. The transmission cycle begins when a healthy mosquito feeds on the blood of a person infected with dengue, thus becoming a vector. The cycle continues when this mosquito, infected with the dengue virus, feeds on the blood of a healthy person, transmitting the virus to that person.

There are several theories about the pathogenesis of dengue; one of the most widely accepted is the immunoamplification theory. This theory states that in a primary infection, specific antibodies are created for a particular dengue serotype, neutralizing the virus. Subsequently, in a secondary infection, these specific antibodies are thought to bind to the Fc region of target cells (monocytes and lymphocytes), triggering viremia and the subsequent release of inflammatory factors, which in turn causes fluid leakage due to tissue damage.

After an incubation period of 3-10 days, it presents with sudden onset of fever, chills, myalgia, arthralgia, nausea, vomiting, headache, retro-orbital pain, and photophobia.

Several definitions have been established for the prompt identification of the disease. These concepts have evolved over time and based on the results of research conducted on the disease. One classification that remains in use for epidemiological purposes is to consider dengue as classic and hemorrhagic. However, several guidelines establish the following concepts.

Probable case of non-severe dengue (NSD): Any person of any age who resides in or has traveled from a region with dengue transmission within the 14 days prior to the onset of signs and symptoms, and who presents with fever and two or more of the following signs or symptoms: nausea, vomiting, rash, myalgia, arthralgia, headache, retro-orbital pain, petechiae, and/or a positive tourniquet test and/or leukopenia.

Probable case of dengue with warning signs (DSA): Any probable case that, in addition to meeting the criteria for dengue with warning signs (DNG), presents one or more of the following warning signs: severe and continuous abdominal pain, persistent or intractable vomiting, fluid accumulation (ascites, pleural effusion, pericardial effusion), mucosal bleeding (epistaxis, gingival bleeding), lethargy or irritability, postural hypotension, hepatomegaly greater than 2 cm, progressive increase in hematocrit, platelet count less than 100,000 platelets per microliter or progressive decrease in platelets and/or progressive decrease in hemoglobin.

Probable case of severe dengue (DG): Any probable case of dengue that presents one or more of the following findings: Shock due to severe plasma leakage, evidenced by: tachycardia, cold extremities and capillary refill equal to or greater than three seconds, weak or undetectable pulse, convergent pulse pressure ≤ 20 mmHg, late-phase hypotension, and fluid accumulation leading to respiratory failure. Severe bleeding, as assessed by the treating physician (examples: hematemesis, melena, heavy vaginal bleeding, central nervous system bleeding). Severe organ involvement, such as: significant liver damage, kidney involvement, central nervous system involvement (altered mental status), heart involvement (myocarditis), or other organ involvement.

Warning signs to consider in a suspected case of dengue include: severe abdominal pain, persistent and intractable vomiting (>5 times a day), clinical evidence of fluid accumulation, active bleeding in mucous membranes (gastrointestinal tract, hematuria), neurological or mental status changes (lethargy, restlessness), hepatomegaly >2 cm (liver failure), and elevated hematocrit coexisting with a decreased platelet count.

Dengue diagnosis is primarily clinical, based on the characteristic signs and symptoms assessed during the course of the illness. For epidemiological surveillance, laboratory confirmation is performed using virological tests—such as PCR—during the first days of disease (febrile phase), as well as serological tests after day 6 from symptom onset. Serology includes the detection of IgM antibodies, while antigen-based methods detect the non-structural protein 1 (NS1), which is typically detectable during the first five days of clinical symptoms.

The differential diagnosis should primarily include rickettsial diseases, typhoid fever, leptospirosis, viral exanthems, and even various hematological disorders. The Americas, through the Pan American Health Organization, have consistently monitored dengue fever. Since 2014, a steady increase in reported dengue cases has been observed, especially in Brazil and Mexico; however, other tropical countries have also experienced periodic outbreaks.

During 2024, reports from the World Health Organization highlighted the large number of dengue cases in India and the Eastern Pacific countries. However, while Brazil had the highest number of cases, the incidence rate per 100,000 inhabitants was significantly higher in French Guiana, with 5,426.48 cases. Brazil also had the highest number of deaths, although the case fatality rate was higher in Niger (20.69%) and Sudan (2.12%).

Climate change has created favorable conditions for the expansion of the Aedes aegypti and Aedes albopictus mosquitoes. However, the disease's emergence is subtle until explosive outbreaks occur, after which it remains endemic.

In Mexico, an upward trend has been observed since 1985; however, in 2024, the number of cases far exceeded the historical average (271,588). The cases occurred mainly in the Pacific region, led by the state of Jalisco (50,622), while the state of Nayarit had the highest incidence per 100,000 inhabitants (1,650.87).

On the other hand, cases of dengue hemorrhagic fever (dengue with warning signs and severe dengue) decreased compared to historical averages, with an incidence of 3.6 per 100,000 inhabitants. Nayarit also had the highest incidence, with 21.81 per 100,000 inhabitants.

In Mexico, the increase in dengue cases begins in June, peaking in September and October, while in the Southern Hemisphere, specifically in Brazil, the peak occurs in March and April, with cases decreasing in June.

The age group with the highest number of dengue cases was 24 to 44 years old, representing the economically active population, while severe cases are concentrated at the extremes of age.

In conclusion, dengue is a disease that continues to spread intermittently throughout the world, especially in tropical areas; however, climate change is causing cases to appear in places that are not considered endemic.

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