Dengue fever is a mosquito-borne viral disease that typically occurs in various areas of sub-Saharan Africa [
1‐
5]. Dengue fever is caused by Dengue virus (DENV), which exists in four serologically distinct serotypes designated as (DENV-1), (DENV-2), (DENV-3) and DENV-4). The severity of DENV infection varies from mild fever to complicated clinical hemorrhagic disease leading to shock and subsequent death [
6‐
8]. In the recent years, DENV has spread significantly to different States of Sudan [
9‐
12]. Currently, DENV infection constitutes one of the major unresolved public health problems in the country. The major economic losses occur in areas of endemicity in the eastern part of Sudan particularly, Kassala and the Red Sea States [
13‐
15]. In Sudan, most dengue fever cases are asymptomatic or probably accompanied by a mild febrile illness. However, severe cases are usually observed when more than one DENV serotypes are coexisting in a particular area of endemicity in the country [
7,
8]. The first documented outbreak of DENV in Sudan occurred in 1986 among residents of the Red Sea State [
16]. Shortly thereafter, several epidemic cycles of dengue have been recorded among residents of the neighboring Kassala State based on clinical presentation. Subsequently, serological evidence of DENV in Kassala State was demonstrated by detection of DENV immunoglobulin G (IgG) antibodies using ELISA assay [
9,
11,
12]. Confirmation of active circulation of DENV in this State was made possible by direct detection of DENV immunoglobulin M (IgM) antibodies and reverse transcription RT-PCR [
14,
17]. DENV serotypes 1 and 2 were reported in the Red Sea State whereas DENV-2 was reported as the prevalent serotype circulating in Kassala State [
16,
17]. However, DENV serotype 3 (DENV-3) has never been reported in Kassala State, eastern Sudan. A recent sero-epidemiologic survey reported an exceptionally high prevalence (47.6%) of DENV-specific IgG antibodies in El-Gadarif State, eastern Sudan, suggesting considerable circulation of DENV in the area at some time in the past [
18]. However, active circulation of DENV in El-Gadarif State is yet to be confirmed by conventional virus isolation attempts and molecular characterization studies. It is, therefore, becoming obvious that DENV has spread to different part of the country and that the disease becomes endemic in the eastern region of Sudan. It is possible that DENV spreads to other areas, including northward into Egypt and eastward to Ethiopia, Eretria, and probably across the Red Sea into Saudi Arabia. How DENV travels is unclear but probably involves movement of infected patients and mosquito vectors as well as intercontinental transfer of commercial products [
19‐
24]. Recently, high incidence of dengue fever has been reported in eastern Sudan as witnessed by frequent sporadic cases and multiple outbreaks in 2010, 2013, 2017 and 2018 [
17,
25]. The highest incidence of infections occurs between the months of September and November, which coincides with the high rainy season. A previous report has described the molecular characterization of DENV-2 in Kassala State, eastern Sudan [
17]. With the exception of this report, no information is currently available in regard to the serotypes and associated genotypes of DENV circulating in Sudan. In this context, further study on molecular characterization of DENV isolates would be necessary to better understand the biology, ecology and the molecular epidemiology of the disease. In the present study, an outbreak of DENV serotype 3 (DENV-3) characterized by acute febrile illness occurred in Kassala State, eastern Sudan, 2019. ELISA NS1 assay was used to detect early infection in acute phase sera of infected patients. The detection of DENV and identification of the virus serotype was determined by serogroup-specific and serotype-specific DENV RT-PCR assays, respectively. The partial genome sequences generated from the amplified is Capsid/premembrane (CprM) protein gene were purifies and employed for subsequent phylogenetic analysis. Phylogenetic tree was constructed to determine the genotypes of the DENV serotype associated with the disease outbreak. The results of this study would be expected to provide invaluable clues for improved surveillance and control of the disease in Sudan.