Dengue outbreaks in Tanzania: recent trends and importance of research data in disease surveillance

September 10, 2019

About 40% of the world’s population today lives in an area endemic with dengue in more than 100 countries. Globally, there are about 390 million dengue infections per year; of which only a quarter manifest clinically. In Africa, Dengue has been reported in 34 countries, mostly from the eastern part of the continent. The incidence of dengue has increased 30-fold over the past 50 years. The global expansion of dengue has been related to increased international travel, unplanned urbanization, changes in environmental factors, host–pathogen interactions and population immunological factors. Inadequate vector control measures have also created favourable conditions for dengue virus transmission and its mosquito vectors.

On March 19, 2019, the World Health Organization was notified of Dengue fever outbreak in Dar es Salaam, Tanzania. As of 11th August 2019, the total confirmed cases reported since the beginning of the outbreak was 6,873 cases including 13 deaths. Majority of the cases were reported from Dar es Salaam followed by Tanga. Dengue cases have also been reported from Pwani, Arusha, Kagera, Singida and Morogoro Regions.

Before 2019, Tanzania has reported Dengue epidemics in 2010, 2012, 2013-2014 and 2018. In 2013 and 2014, Tanzania experienced the first worst dengue outbreak. During this epidemic a total of 1,969 and 961 cases of suspected and confirmed dengue cases, respectively were reported. Of these, the majority (99.4%) were cases reported in Dar es Salaam. Other affected regions were Arusha, Dodoma, Kagera, Kigoma, Kilimanjaro, Lindi, Mbeya, Morogoro, Mwanza, Njombe and Ruvuma. Again, in March 2018, 11 cases dengue were reported in the coastal cities of Dar es Salaam and Tanga.

Dengue was first described in Tanzania by Spanish sailors visiting the southern coast of Tanzania during the 15th Century. The name dengue is believed to be a corruption of Kiswahili words “Ki denga Pepo”, meaning cramp-like seizure caused by an evil spirit.

In Tanzania, several studies have reported presence of Dengue virus in both clinical samples and mosquitoes in different parts of the country (Table 1). Baseline surveillance data on febrile out-patients on Pemba island and Tosamaganga in Iringa region in February-March 2007 reported a dengue prevalence of 7.7% and 1.8%, respectively. In 2011 seroprevalence survey among 500 health adult blood donors in Zanzibar showed a Dengue virus infection prevalence of 50.6%. Higher prevalence rates of Dengue infections have been reported among febrile patients in Kilosa (38.2%) and Moshi (10%). Such seroprevalence findings are important source of evidence of the circulating pathogens in the country. They could easily be incorporated into the national surveillance systems and provide basis for preparedness and response. Studies have revealed that patients with acute dengue infections are often misdiagnosed and treated with either anti-malarial or antibiotics.

 

Dengue prevalence in Tanzania, 2010-2018

District/Region Percent of infected persons (%)
Kilosa 38.2
Moshi 9.7-10.7
Pemba 7.7
Babati 1.54
Iringa 1.8
Zanzibar 50.6
Dar es Salaam 20.9

 

Dengue virus is transmitted to human by mosquitoes, mainly Aedes aegypti. Aedes aegyptiis highly domestic and a day-biting species that prefers to feed on humans, most often for two hours after sunrise and several hours before sunset. Ae. aegypti usually bites indoors, in shady areas, or when the weather is cloudy. The mosquito prefers to breed in small and inconspicuous containers of water, both natural and artificial, such as discarded cans and cups, uncovered barrels, buckets, roof gutters, barrels, flower pots, tree holes, water tanks, toilet tanks, or tires.

 

The disease is under-recognized and under-reported in Tanzania because of low awareness by health care providers, other prevalent febrile illnesses, and lack of diagnostic testing and systematic surveillance. While efforts are made to strengthen the diagnostic capacity of the health facilities, it is critical for an effective surveillance system to incorporate other data sources such as research. Surveillance, reporting, and diagnosis of dengue in the country remain largely passive. Active community-based epidemiological studies with intensive vector control and engagement of community in event-based surveillance could contribute to prevention and control of dengue. A strong surveillance system coupled with research are essential tools to detect, understand, prevent, control, and respond to existing, new and re-emerging infectious diseases. Research evidences may complement government efforts and create/strengthen awareness by providing current, credible information about magnitude of epidemic-prone diseases, most often not captured by the traditional surveillance programmes. Such data hold tremendous potential to initiate epidemiological follow-up studies, big data mining and provide complementary epidemic intelligence context to traditional surveillance sources. Realising the importance of evidence from epidemiological studies, it is critical to consider the promotion of uptake of research findings to consolidate the national disease surveillance and response strategies.

 

Share on FacebookTweet about this on TwitterShare on LinkedInShare on Google+Email this to someone