On 13 May 2022, So Tomé and Principe’s MoH alerted WHO of a dengue epidemic. 103 dengue fever cases and no fatalities were recorded from 15 April to 17 May. The country’s first dengue epidemic.

Case summary

Five health districts in So Tomé and Principe reported 103 dengue fever illnesses and no fatalities from 15 April to 17 May 2022. (figure 1). The Rio Grande health district reported the most cases (90, 87%), followed by Mézochi (7, 7%), Lobata (4, 4%), Cantagalo (1, 1%), Principe (1, 1%) (figure 2). 10-19 (5.9 instances per 10 000), 30-39 (7.3), 40-49 (5.1), and 50-59 were the most affected age groups (6.1 cases per 10 000). Fever (97, 94%), headache (78, 76%), and myalgia were most common (64, 62 percent ).

30 RDT-confirmed samples were forwarded to an international reference laboratory in Lisbon, Portugal, on April 29. Further lab findings revealed early acute dengue illness and dengue virus serotype 3. (DENV-3). Preliminary data reveal additional serotypes in the samples.

On 11 April, a hospital in So Tomé and Principe reported a possible dengue case. This patient had a travel history and was diagnosed with a prior dengue illness.


Dengue is a mosquito-borne virus. Dengue is distributed globally, particularly in urban and semi-urban regions. Aedes aegypti and Ae. albopictus mosquitoes carry the illness. Dengue virus causes dengue (DENV). Four DENV serotypes may cause infection. Over 80% of DENV patients are symptomless (asymptomatic). DENV causes flu-like symptoms. Sometimes severe dengue develops.

There is no particular therapy for dengue, but quick identification, detection of warning symptoms of severe dengue, and good case management is crucial to preventing patient fatalities. Dengue fatalities are commonly linked to delayed medical attention.

Occasional cases acquired outside have been documented among persons returning from a dengue-transmitting locale, but there is no solid proof that So Tomé and Principe have imported dengue. So Tomé and Principe have never recorded a dengue epidemic despite being in the dengue belt and having favorable circumstances for transmission.

Government reaction

The epidemic has prompted the following actions from national health authorities:

• Holding weekly meetings between MoH and WHO to discuss technical aspects of the outbreak. • Developing, validating, and disseminating a dengue response plan. • Conducting multidisciplinary epidemiological investigations and active case detections in several health districts. • Conducting entomological investigations to identify breeding sites and fogging and source reduction measures in some affected localities.

• Organizing deployments of foreign specialists to boost So Tomé and Principe’s laboratory capability, as well as case management, risk communication, entomology, and vector control expertise.

WHO: risks

The risk at the national level is high due to the presence of the mosquito vectors Aedes aegypti and Aedes albopictus; (ii) favorable environment for mosquito breeding grounds after heavy rains and floods since December 2021; (iii) concurrent outbreaks of diarrheal disease, malaria, COVID-19, and other health challenges; and (iv) decreased functionality of sanitation and water management systems in health facilities due to structural damage. High proportions of dengue cases are asymptomatic, and monitoring and diagnosis are limited. Dengue is similarly difficult to treat clinically. Community awareness and risk communication are minimal.

Regional and global risk is minimal. Hence Tomé and Principe is an island without land boundaries, so future expansion would need vectors.

WHO: Diagnosis

• Health facilities should have access to dengue diagnostic testing.

• So Tomé and Principe’s outlying islands should be informed about the epidemic and given RDTs to identify instances.

Integrated Vector Management (IVM) should be improved to eliminate breeding places, decrease vector populations, and limit individual exposure. This includes larval and adult vector control tactics such as environmental management, source reduction, and chemical control.

• Vector control measures should be adopted in homes, workplaces, schools, and healthcare institutions to avoid vector-person interaction.

 • Community-supported source reduction measures and vector monitoring should be implemented.

• Wear clothing that reduces skin exposure and apply repellents to exposed skin or garments. Use repellents as directed.

• Window and door screens and insecticide-treated mosquito nets may limit vector-person interaction in closed areas.

• Based on current knowledge, WHO does not propose travel or trade restrictions to So Tomé and Principe.

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