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Aedes albopictus Introduction into Continental Africa, 1991

From April 15 through July 20, 1991, an epidemic of yellow fever (YF) occurred in Delta State, Nigeria. In September 1991, as part of a follow-up investigation, mosquito oviposition cups were deployed in four rural communities with YF, all within a 24-kilometer radius of the principal town of Agbor (Figure 1). Based on findings from the follow-up investigation, this report documents the first record of breeding populations of Ae. albopictus--a competent YF virus vector--in continental Africa.

The cups were deployed approximately 200 meters from human dwellings at the edge of deciduous forest strips that separate villages and farmlands. Cup liners were collected after 48 hours, and those containing eggs of Aedes mosquitoes were sent to CDC for specific identification. Eggs were hatched and larvae mass-reared to the adult stage.

Ae. albopictus were present in collections from three communities (Igbodo, Owa-Alero, and Egbudu-Aka). The combined 271 specimens from Igbodo and Owa-Alero included the following: Ae. aegypti, 74%; Ae. albopictus, 18%; Ae. apicoargenteus, 4%; Ae. lilii, 3%; and Ae. simpsoni subgroup, 2%. The 14 specimens from Egbudu-Aka represented two taxa: Ae. albopictus, 64%; and Ae. africanus, 36%. In addition, eight adults were reared from Mbiri; all were identified as Ae. africanus. Reported by: VI Ezike, ACN Nwankwo, National Arbovirus and Vectors Research Div, Federal Ministry of Health, Enugu; US Agency for International Development, Lagos, Nigeria. Combatting Childhood Communicable Diseases Program, Div of Field Svcs, International Health Program Office; Div of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: The colonization history of Ae. albopictus in other areas suggests a likelihood for further spread of Ae. albopictus in Africa (1,2). Ae. albopictus has colonized both urban and rural forested areas in Delta State, and--with its ability to adapt to a variety of oviposition sites, its biting habits, and its competence as a YF virus vector in the laboratory--Ae. albopictus may link sylvan and urban YF transmission cycles.

Live larvae of Ae. albopictus recently entered South Africa in used tires imported from Japan (3), and Ae. albopictus was previously introduced into the United States and Brazil in used tires imported from Asia (4). This would suggest that importation of used tires was the likely method of introduction into Nigeria. However, in Africa, imported cargo is not routinely inspected for mosquitoes, and other undetected populations of Ae. albopictus may now exist.

Field and laboratory data indicate that Ae. albopictus is an efficient laboratory vector of a number of viruses that cause human disease--including dengue (DEN), YF, chikungunya, Rift Valley fever, and West Nile--in Africa (5,6). Of particular concern to public health officials is its potential role in DEN and YF transmission, two viruses that continue to cause epidemic disease in Africa. Strains of Ae. albopictus from Asia and strains introduced into North America are efficient vectors of DEN and YF (6,7). In addition to the role of Ae. albopictus in epidemic DEN transmission, its ability to transmit DEN viruses vertically as a reservoir host may facilitate endemic transmission (8).

Ae. albopictus may displace Ae. aegypti in parts of Africa, as it has in some areas of the southern United States (9), and alter established arbovirus transmission cycles. Virus transmission studies with African strains of YF virus and Ae. albopictus from Nigeria are in progress. The distribution of Ae. albopictus in Nigeria and throughout continental Africa needs to be further characterized.

References

  1. Hawley WA. The biology of Aedes albopictus. J Am Mosq Control Assoc Suppl 1988;1:1-40.

  2. Moore CG, Francy DB, Eliason DA, Monath TP. Aedes albopictus in the United States: rapid spread of a potential disease vector. J Am Mosq Control Assoc 1988;4:356-61.

  3. Cornel AJ, Hunt RH. Aedes albopictus in Africa?: first records of live specimens in imported tires in Cape Town. J Am Mosq Control Assoc 1991;7:107-8.

  4. Reiter P, Sprenger D. The used tire trade: a mechanism for the worldwide dispersal of container breeding mosquitoes. J Am Mosq Control Assoc 1987;3:494-501.

  5. Shroyer DA. Aedes albopictus and arboviruses: a concise review of the literature. J Am Mosq Control Assoc 1986;2:424-8.

  6. Mitchell CJ. Vector competence of North and South American strains of Aedes albopictus for certain arboviruses: a review. J Am Mosq Control Assoc 1991;7:446-51.

  7. Gubler DJ, Rosen L. Variation among geographic strains of Aedes albopictus in susceptibility to infection with dengue viruses. Am J Trop Med Hyg 1976;25:318-35.

  8. Rosen L, Shroyer DA, Tesh RB, Freier JE, Lien JC. Transovarial transmission of dengue viruses by mosquitoes: Aedes albopictus and Aedes aegypti. Am J Trop Med Hyg 1983;32:1108-19.

  9. Hobbs JH, Hughes EA, Eichold BH II. Replacement of Aedes aegypti by Aedes albopictus in Mobile, Alabama. J Am Mosq Control Assoc 1991;7:488-9.



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