OUTBREAK AND UPDATE
Dengue Outbreak in Kenya: Sign of a Larger Issue?
By Michele Barry, MD, FACP, and Brian Blackburn, MD. Dr. Barry is Senior Associate Dean for Global Health at Stanford University; Dr. Blackburn is a Clinical Assistant Professor in the Division of Infectious Diseases and Geographic Medicine at Stanford University. Dr. Barry is a retained consultant for the Ford Foundation and has received research or grant support from Johnson & Johnson Corporate Foundation, the Doris Duke Foundation, and the National Institutes of Health. Dr. Blackburn reports no financial relationship to this field of study.
This article originally appeared in the December 2011 issue of Travel Medicine Advisor. It was edited by Frank Bia, MD, PHD, and peer reviewed by Lin Chen, MD. Dr. Bia is Professor (Emeritus) of Internal Medicine (Infectious Disease and Clinical Microbiology); Yale University School of Medicine, and Dr. Chen is Assistant Clinical Professor, Harvard Medical School; Director, Travel Medicine Center, Mt. Auburn Hospital, Cambridge, Mass. Drs. Bia and Chen report no financial relationships relevant to this field of study.
Synopsis: An outbreak of dengue fever in northeastern Kenya has recently sickened at least 5,000 people.
Source: ProMed Archive Number 20111004.2985; Oct. 4, 2011.
An outbreak of dengue fever in northeastern Kenya was first reported in September 2011, and is believed to be spreading rapidly, with at least 5,000 people infected within the first weeks of this outbreak. The Kenyan Ministry of Public Health reported four confirmed deaths, but with only one public hospital and a few private clinics in the epicenter (Mandera, near the border with Ethiopia and Somalia), the toll was likely higher.
Another recent, large epidemic of dengue occurred on the Cape Verde Islands off the West African coast in March 2010, with more than 21,000 suspected cases and 6 deaths reported by the U.S. Centers for Disease Control and Prevention; almost 60 cases were also reported by ProMed in nearby Senegal. Unfortunately, poor diagnostic capabilities in these West African countries likely adversely affected the accuracy of the surveillance data obtained during that outbreak.
Commentary
Dengue fever, an arboviral disease with a typical incubation period of 4-7 days, is caused by four circulating serotypes of dengue virus. This disease is not usually considered a major threat to travelers to Africa. Although this outbreak in remote northeastern Kenya did not occur near areas frequented by tourists, dengue fever does pose a threat to travelers and relief works in Africa. Of 24,920 returned travelers seen at GeoSentinal clinics from March 1997 to March 2006, 28% cited fever as a chief reason for seeking care. Dengue was the cause of fever for 6%, although this diagnosis was made less frequently than malaria (21% of febrile travelers) and diarrheal illness (15% of febrile travelers).1 Although dengue was diagnosed in only 1% of the febrile travelers who had been to sub-Saharan Africa in this study, the poor surveillance for dengue in the region undoubtedly contributed to the low reported numbers. In a large review of ill returned travelers, dengue fever was primarily found in travelers returning from southeast Asia (especially in June and September), south Central Asia (especially in October), South America (especially in March), and the Caribbean (especially in August and October).2 One study estimated the incidence of dengue fever to be nearly 3% in Dutch travelers who spent a median of 1 month traveling in Asia (where travel-related dengue is a more frequent diagnosis) in the early 1990s.3
A 1956 retrospective serosurvey suggested that dengue has existed in Africa at least as far back as 1926-1927, when it caused a major epidemic in Durban, South Africa. Despite poor surveillance for dengue in most of Africa, it is clear that fever caused by all four serotypes has increased dramatically since 1980, as multiple outbreaks of dengue have occurred in most regions of Africa over the past three decades.4 It has been presumed that these outbreaks have most likely been transmitted by Aedes aegypti, which is widely distributed in the region.
Because most dengue infections are subclinical or manifest as undifferentiated fever, they are often undiagnosed or are treated as malaria or other febrile illnesses endemic to a given area, such as typhoid or leptospirosis. Chikungunya is another viral infection that mimics dengue and also circulates in sub-Saharan Africa. Given the recently documented outbreaks of dengue in sub-Saharan Africa, this infection may be more of an issue there than currently appreciated, and the relatively low case numbers a product more of poor surveillance rather than low disease burden. Thus, dengue should not be discounted as a possible cause of fever in travelers returning from Africa, and hopefully epidemiological studies will better define the distribution of dengue in Africa in the coming years.5
References
1. Wilson M, et al. Fever in returned travelers: Results from the GeoSentinel Surveillance Network. Clin Infect Dis 2007;44:1560-1568.
2. Schwartz E, et al. Seasonality, annual trends, and characteristics of dengue among ill returned travelers, 1997-2006. Emerg Infec Dis 2008;14:1081-1088.
3. Cobelens F, et al. Incidence and risk factors of prob- able dengue virus infection amongst Dutch travellers to Asia. Trop Med Int Health 2002;7:331-338.
4. Sang R. Dengue in Africa. Available at: www.tropika.net/review/061001-Dengue_in_Africa/article.pdf. Accessed Nov. 6, 2011.
5. Centers for Disease Control and Prevention. CDC Health Information for International Travel 2012. Oxford, UK: Oxford University Press; 2012.
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