Dengue – Chad

16 October 2023

On 15 August 2023, a dengue outbreak was declared by the Ministry of Public Health and Prevention in Chad. As of 1 October, there have been 1 342 suspected cases, including 41 confirmed cases reported across eight health districts in four provinces. Among the confirmed cases, one death was reported. Abéché health district in Ouaddaï province, is the current epicentre of the outbreak. The Ministry of Public Health and Prevention has initiated a number of key response activities by implementing, in collaboration with WHO and partners, the national contingency plan for dengue preparedness and response. Dengue is a viral infection transmitted to humans through the bite of infected mosquitoes. Many dengue infections produce only mild flu-like illness and over 80% of cases are asymptomatic. There is no specific treatment for dengue; however, timely detection of cases and appropriate case management are key elements of care to prevent severity and fatality of dengue. This is the first dengue outbreak reported in Chad, and the country has limited surveillance, clinical and laboratory capabilities. Given the favorable environmental conditions for mosquito spread, an ongoing humanitarian crisis due to a massive influx of refugees and returnees from Sudan and limited response capacities, WHO assesses the risk posed by this outbreak as high at the national level.

Description of the Situation

On 15 August 2023, the Ministry of Public Health and Prevention of the Republic of Chad officially declared an outbreak of dengue in Abéché health district, Ouaddaï province, in the east of the country, representing the first dengue outbreak ever reported in Chad.

The declaration was made after the confirmation of dengue infection in eight out of 12 blood samples tested using real-time polymerase chain reaction (real-time PCR) at the national Biosafety and Epidemics Laboratory (LaBiEp) in N’Djamena. Subsequently, the samples were sent to the Institut Pasteur in Cameroon for confirmation, which was completed on 22 August by PCR and ELISA, confirming the presence of dengue.

As of 1 October, there have been 1 342 suspected cases, including 41 confirmed cases reported across eight health districts in four provinces. Among the confirmed cases, one death was reported (Case Fatality Ratio (CFR) among confirmed cases 2.4%).

The dengue serotype responsible for this outbreak remains unknown.

Eight districts in four provinces (NDjamena, Ouaddaï, Sila, and Wadi Fira) have reported confirmed dengue cases. Notably, Ouaddaï, the epicentre of the outbreak, has reported the highest number of confirmed cases, accounting for 31 out of the total 41 confirmed cases (76% of confirmed cases). The age group most affected by this outbreak are those between 15 to 34 years old, representing 27% of the reported confirmed cases. 

Epidemiology

Dengue is a viral infection transmitted to humans through the bite of infected mosquitoes and is found in tropical and sub-tropical climates worldwide, mostly in urban and semi-urban areas. The primary vectors that transmit the disease are Aedes aegypti mosquitoes and, to a lesser extent, Aedes albopictus.

Dengue virus (DENV) has four serotypes (DENV-1, DENV-2, DENV-3, DENV-4). Infection with one serotype provides long-term immunity to the homologous serotype but not to the other serotypes; sequential infections with a different serotype put people at greater risk for severe dengue. Many DENV infections produce only mild flu-like illness and over 80% of cases are asymptomatic.

There is no specific treatment for dengue; however, the timely detection of cases, identifying any warning signs of severe dengue infection, and appropriate case management are key elements of care to lower the CFR during an outbreak to less than 1%.

Although Chad has previously experienced outbreaks of arboviruses such as chikungunya and yellow fever, this is the first dengue outbreak ever reported in the country. Chad, including the Ouaddaï province, experienced a chikungunya outbreak in 2020, with a total of 34 052 cases recorded and one associated death.

Public Health Response

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