Dengue spreads in Africa

5 Mar 2010

Paul Chinnock

Source: TropIKA.net

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Mosquito control is at present the only way of preventing dengue. Here a Cuban health worker sprays insecticide in a tyre depot. [Credit: WH/TDR.]

News reports from South America, the Caribbean, southern Asia and the Pacific confirm that cases of dengue fever are becoming more common every year. In the first two months of 2010, Sri Lanka for example reported 8000 cases. Puerto Rico has, meanwhile, declared an epidemic, and Malaysia has announced stricter enforcement measures on mosquito control after rapid rises in case numbers in recent weeks. But the situation in Africa remains unclear. The mosquito Aedes aegypti, the most common vector of dengue, occurs across Africa but most cases of dengue there go undiagnosed.

Now, however, an article in the journal Eurosurveillance [1] says there is ample evidence to conclude that one of the four strains of dengue is spreading in West Africa. The situation first received attention in October last year when a major dengue epidemic began in the Cape Verde islands off the West African coast (see TropIK.net News). According to the US Centers for Disease Control, over 21,000 suspected cases and six deaths were recorded in this outbreak. Approximately 60 cases were also reported in nearby Senegal. Countries such as Senegal, however, lack diagnostic facilities and it is likely that only a fraction of cases would have been detected.

The Eurosurveillance article argues that serological and virological data obtained from returning European travellers can make a major contribution to what is known about the occurrence of dengue in Africa. It goes on to provide a brief review of historic reports of dengue virus in Africa, and summarises the recent outbreaks and the links to imported cases of dengue virus infection in Europe.

The Cape Verde outbreak was caused by dengue virus serotype 3 (DENV-3), which was first recorded in Africa in 1984 in Mozambique. It has since appeared in several parts of the continent, reaching West Africa in 2008.The first evidence of its presence there came from Europe, when the virus was detected in travellers returning from the area with signs of illness.

All four dengue serotypes have now been reported in Africa since the mid-1960s. Historical reports suggest the first African dengue epidemic occurred even earlier, in 1927 in South Africa but is not possible to say which serotype was responsible.

The lack of information on the incidence of dengue in Africa is of great concern and this situation seems likely to continue. Even laboratories which can diagnose infections such as HIV and yellow fever lack the facilities to identify dengue.

Why it matters

Most cases of dengue are unpleasant while they last but patients do recover. Only a small minority (usually less than 3%) develop life-threatening dengue haemorrhagic fever (DHF). While there is no specific treatment for dengue, patients with DHF can be given treatment for their symptoms in hospital but in Africa many people lack good access to such treatment. It is important therefore that we should know how common dengue and DHF are in Africa and whether the disease is spreading.

An evaluation [2] of commercially available rapid diagnostic tests for dengue was published last year showing that some do perform well, although there is still need for improvement. (Another new test has been announced only this week.) Cost considerations, however, will be crucial if such tests are to be used widely in Africa.

Other hopeful signs on dengue fever include the 11 potential vaccines that are now under development, according to a recent review featured on TropIKA.net. The recent breeding of genetically-altered male mosquitoes that carry a fatal gene and could be released into the wild may also offer a way forward.

References

1. Franco L, Di Caro A, Carletti F, Vapalahti O, Renaudat C, Zeller H, Tenori A (2010). Recent expansion of dengue virus serotype 3 in West Africa. Euro Surveill; 15(7):2. Available from: http://www.ncbi.nlm.nih.gov/pubmed/20184854

2. Hunsperger EA, Yoksan S, Buchy P, Nguyen VC, Sekaran SD, Enria DA, Pelegrino JL, Vázquez S, Artsob H, Drebot M, Gubler DJ, Halstead SB, Guzmán MG, Margolis HS, Nathanson CM, Rizzo Lic NR, Bessoff KE, Kliks S, Peeling RW (2010). Evaluation of commercially available anti-dengue virus immunoglobulin M tests. Emerg Infect Dis; 15(3):436-40. Available from: http://www.ncbi.nlm.nih.gov/pubmed/19239758