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Comparing the regional epidemiology of the cassava mosaic and cassava brown streak virus pandemics in Africa

Comparing the regional epidemiology of the cassava mosaic and cassava brown streak virus pandemics in Africa

Legg, J.P., Jeremiah, S.C., Obiero, H.M., Maruthi, M.N. ORCID: 0000-0002-8060-866X, Ndyetabula, I., Okao-Okuja, G., Bouwmeester, H., Bigirimana, S., Tata-Hangy, W., Gashaka, G., Mkamilo, G., Alicai, T. and Lava Kumar, P. (2011) Comparing the regional epidemiology of the cassava mosaic and cassava brown streak virus pandemics in Africa. Virus Research, 159 (2). pp. 161-170. ISSN 0168-1702 (doi:

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The rapid geographical expansion of the cassava mosaic disease (CMD) pandemic, caused by cassava mosaic geminiviruses, has devastated cassava crops in twelve countries of East and Central Africa and is well documented. Region-level epidemiological studies continue to reveal a more-or-less regular pattern of annual spread along a contiguous ‘front’. More recently, outbreaks of cassava brown streak disease (CBSD) were reported from Uganda and other parts of East Africa that had been hitherto unaffected. Recent survey data reveal several significant contrasts between the regional epidemiology of the two pandemics: i) severe CMD spreads in an ‘expanding concentric rings’-like manner, whilst CBSD seems to be spreading from independent hot-spots; ii) the severe CMD pandemic has arisen from virus recombination and inter-species synergy, whilst current knowledge suggests that the CBSD pandemic is a ‘new encounter’ situation; iii) CMD pandemic spread has been tightly linked with the appearance of super-abundant B. tabaci whitefly populations, in contrast to CBSD, where outbreaks have occurred 3-12 years after whitefly population increases; iv) the cassava mosaic geminiviruses (CMGs) causing CMD are transmitted in a persistent manner, whilst cassava brown streak viruses (CBSVs) appear to be semi-persistently transmitted; and v) different patterns of symptom expression mean that phytosanitary measures are easy to implement for CMD but have limited effectiveness whilst the same measures are hard to do for CBSD but potentially very effective. One important similarity between these two cassava virus pandemics is that the viruses occurring in pandemic-affected areas are also found elsewhere, indicating that contrary to earlier published information, the viruses per se are unlikely to be the key factors driving the two pandemics. A model is proposed for the temporal relationship between B. tabaci abundance and changing incidences of both CMD and CBSD in the Great Lakes region. This emphasizes the pivotal role played by the vector in both pandemics and highlights the urgent need to identify effective and sustainable strategies for controlling whiteflies on cassava.

Item Type: Article
Additional Information: [1] Published in: Virus Research, Volume 159, Issue 2, August 2011 - Plant Viruses and Virus Vectors: Exploiting Agricultural and Natural Ecosystems.
Uncontrolled Keywords: cassava mosaic geminiviruses, cassava brown streak viruses, Bemisia tabaci, whitefly, East Africa, epidemic
Subjects: S Agriculture > SB Plant culture
Faculty / School / Research Centre / Research Group: Faculty of Engineering & Science > Natural Resources Institute
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Last Modified: 18 Oct 2016 09:13

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