The history of severe dengue in Cuba seems to favor this pathogenic interpretation, at least in part. Here the first epidemic of dengue hemorrhagic fever and dengue shock occurred in the Region of the Americas caused by serotype 2 in 1981. During this period, the patients who most frequently presented severe dengue were children under 15 years of age, and of these, the majority were schoolchildren and adolescents (78.1%) who could have previously been infected by the serotype 1 virus that circulated in 1977, while preschool children (18.4%) and infants (3.5%) constituted the minority, whose minor age prevented them from having contact with it [10]. Later, in our country there was no circulation of dengue virus for sixteen years, demonstrated by the epidemiological and serological surveillance of febrile cases and in 1997, during an outbreak located in Santiago de Cuba, only adults, who supposedly maintained antibodies against the virus, aggravated serotype 1 acquired in 1977 [10].

The WHO reports that in recent decades the incidence of dengue in the world has increased enormously, with severe dengue being a life-threatening complication because it involves extravasation of plasma, fluid accumulation, respiratory distress, severe bleeding or organ failure. That is why the importance of investigating and describing the most frequent sonographic findings to detect early the severity and progression of the disease. The number of reported cases rose from 2.2 million in 2010 to 3.2 million in 2015. Europe is faced with the possibility of dengue outbreaks, local transmission was first reported in France and Croatia in 2010, and detected imported cases in three other European countries (WHO, 2017) [12].

In a study conducted in India and published in The British Journal of Radiology, an ultrasound scan was performed on 88 patients between 2 to 9 years of age, 32 between the second or third day of fever, all showing thickening of the gallbladder wall and pericholecystic fluid., 21% had hepatomegaly, 6.25% had splenomegaly and minimal right pleural effusion. Follow-up ultrasound on day 5 to 7 revealed ascites in 53%, left pleural effusion in 22%, and pericardial effusion in 28%. Of 56 patients who underwent fever from the fifth to the seventh day for the first time, all had gallbladder wall thickening, 21% had hepatomegaly, 7% had splenomegaly, 96% had ascites, 87.5% had right pleural effusion, 66% had left pleural effusion and 28 .5% had pericardial fluid. Concluding that the ultrasound findings of thickening of the gallbladder wall with or without polyserositis in a febrile patient should suggest the possibility of dengue fever and dengue hemorrhagic fever (Sai Venkata et al. 2005) [13-14].

In a study developed in Indonesia by H.S. Pramuljo et al. and published in the journal Pediatric Radiology, volume 21. (February 1991), p.100-102, performed abdominal ultrasound in 29 children with dengue hemorrhagic fever and they were correlated with the findings described in the literature, finding that the distribution by age it showed a predominance between 2 and 10 years. Most of the patients were hospitalized on days 3 and 4 of the illness. All cases had pleural effusions, 20 bilateral cases and 9 cases only on the right side, 20 of 29 cases presented ascites, 8 cases had an abnormal wall of the gallbladder and one case, an abnormal liver parenchyma [15].

In the imaging unit of Rawson Hospital. Down Pucará Córdoba, Argentina (2009). Ultrasound examinations were performed on 29 patients with dengue, 18 females and 11 male, with a mean age of 35.6 years. Finding thickening of the gallbladder wall (n = 7) (24%); free abdominal / pelvic fluid (n = 9) (31%); hepatomegaly (n = 5) (17%); splenomegaly (n = 4) (14%); pericholecystic fluid and pleural effusion (n = 2) (7%). Concluding that ultrasound is a useful tool to confirm suspected cases of dengue and to detect early the severity and progression of the disease (Castrillón et al. 2009) [16]. In another prospective, cross-sectional, descriptive study carried out at the Mexican Institute of Social Security in Veracruz, (2006) published in Mediagraphic, where of 132 patients, 21 had classic dengue and 111 with hemorrhagic dengue. Χ² was used for the statistical significance of the sonographic and laboratory findings. Gallbladder wall thickening was observed in 86%, pleural effusion in 66%, ascites in 60%, and acute alithiatic cholecystitis in 36%. Thickening> 3 mm had a sensitivity of 87%, specificity of 48%, concluding that a thickening of the gallbladder wall> 3 mm is a sonographic finding suggestive of dengue hemorrhagic fever (Quiroz et al. 2006) [17]. In 2009, at the Roosevelt Hospital, 97 cases of patients with suspected severe dengue were detected, who underwent abdominal ultrasound, of which 72% were diagnosed with free fluid in the abdominal cavity, pleural effusion in 25% of cases and without findings compatible with dengue hemorrhagic fever in 5%. Given the sensitivity of 87% for gallbladder wall thickening> 3 mm in dengue hemorrhagic fever, this data can be used as a criterion to confirm the disease. A positive predictive value of 90% can serve as indicative criteria for immediate hospitalization and monitoring (Merck, 2016) [18].