Cassava cultivation is associated with a wide range of diseases that seriously undermine the food and economic security in African countries. The most notable of these is CMD, caused by a complex of cassava mosaic geminiviruses (CMGs; Geminiviridae, Begomovirus). To better understand the epidemiology of CMD as a major constraint of cassava production, we investigated a large-scale plant epidemiological survey in Central African Republic (CAR) and Madagascar, as part of two PhDs with a CAR student, Innocent Zinga (2010-2012), and a Malagasy student, Mireille Harimalala (2010-2012). CMD was shown to be the most serious constraint to cassava in both countries (Harimalala et al., 2014; Zinga et al., 2013). CMD is distributed throughout the two countries, with an average incidence of 85% in CAR. Importantly, 94% and 95% of diseased plants collected in CAR and Madagascar, respectively, had cutting-derived CMD infection, suggesting that farmers mostly use virus-infected cuttings for planting. Molecular diagnosis revealed that the causal agents of CMD in CAR, Chad (Zinga et al., 2012), and Burkina Faso (Tiendrébéogo et al., 2009) are ACMV and/or EACMV-UG. We also demonstrated that 58% of CMD samples of CAR present mixed infections (ACMV and EACMV-UG) and that the severity of symptoms was significantly higher in these samples (Zinga et al., 2013). Molecular diagnosis of CMGs in Madagascar revealed an unprecedented diversity of six species: ACM, EACMC, EACMK, EACMV, SACMV, and CMMGV (Harimalala et al., 2014; Harimalala et al., 2012). Distinct geographical distributions were observed for the six species in Madagascar. While ACMV was more prevalent in the central highlands, EACMV and EACMKV were prevalent in lowlands and coastal regions. Molecular diagnosis revealed that mixed infection (up to four co-infected viruses) occurred in 21% of the samples and was associated with higher symptom severity scores. All our results suggest that mixed infection and synergism between CMGs co