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situations seems to have developed beyond the
local level.
The epidemics of severe CMD that occurred
in the 1990s in Uganda (Gibson et al. 1996;
Otim-Nape et al. 1997) spread subsequently to
Kenya and Tanzania by the late 1990s (Legg and
Thresh 2000). The epidemic of severe CMD in
Uganda devastated the country's cassava produc-
tion, causing losses valued in excess of US$60
million annually between 1992 and 1997 (Otim-
Nape 1993; Thresh et al. 1994; Otim-Nape et al.
1997; Legg 1999). Farmers literally abandoned
the crop in large parts of the country, and in east-
ern districts widespread food shortages led to
some famine-related deaths (Thresh and Otim-
Nape 1994). During the second half of the 1990s,
the epidemic spread to the neighboring coun-
tries of Sudan and eastern Democratic Republic
of Congo (DRC), with a similar impact on cas-
sava cultivation (Legg 1999). Key characteristics
of what was by this stage known as the CMD
pandemic were high incidences of severe CMD
(Gibson et al. 1996), association with a syner-
gistic interaction between ACMV and EACMV
(Harrison et al. 1997b; Pita et al. 2001), pres-
ence of an EACMV recombinant strain (Deng
et al. 1997; Zhou et al. 1997), rapid vector-
borne spread (Otim-Nape et al. 1997), and super-
abundant
B. tabaci
populations (Legg and Ogwal
1998). Although it is not possible to attribute
a single causal element for this pandemic, it is
possible that the conjunction of these different
elements worked together to promote the viral
pandemic (Legg and Fauquet 2004).
The first deployed resistance came from
M.
glaziovii,
a source that was used to develop culti-
vars, providing effective control of the disease for
many years. However, the emergence in Uganda
in the late twentieth century of a new and highly
virulent strain further threatened cassava pro-
duction in that country and spread quickly to
other parts of East and Central Africa (Legg and
Fauquet 2004). First it was discovered that the
pandemic was associated with a novel recombi-
nant virus, the EACMV Uganda strain (EACMV-
UG2) (Patil and Fauquet 2009). This novel gem-
inivirus strain has been found to be associated
with the CMD pandemic in Uganda and Kenya
(Harrison et al. 1997a; Harrison et al. 1997b;
Deng et al. 1997; Zhou et al. 1997). EACMV-
UG2 was identified as the dominant virus in
pandemic-affected areas of Kenya and Tanza-
nia (Legg 1999), Rwanda (Legg et al. 2001), and
Burundi (Bigirimana et al. 2003). The EACMV-
UG2 is reported as expanding further in Rwanda-
Burundi and in the entire Congo basin, extending
up to Gabon and Cameroon (Neuenschwander
et al. 2002; Legg et al. 2006). The virus has also
been found in what is now South Sudan (Har-
rison et al. 1997a). EACMV-UG2 has the sero-
logical properties of ACMV but from nucleotide
sequencing data, it has been shown to have most
of the features of the EACMV genome. Sequence
analyses confirmed the presence of a recombi-
nant fragment in the coat protein gene, a feature
later found to be common for begomoviruses
(Padidiam et al. 1999).
Synergism between cassava mosaic gemi-
niviruses - that is, mixed ACMV and EACMV
infections - have also been implicated in the
widespread epidemic reported in Uganda and
subsequently in neighboring countries (Harrison
et al. 1997b; Legg 1999; Pita et al. 2001). Studies
of the relationship between CMGs and the pan-
demic, with the specific primer PCR diagnos-
tics developed by Zhou and colleagues (1997),
revealed a consistent association of the recombi-
nant EACMV-UG with ACMV (Harrison et al.
1997; Pita et al. 2001; Deng et al. 1997; Zhou
et al. 1997). Significantly this biological phe-
nomenon has been attributed to the emergence of
new geminivirus diseases and has been hypothe-
sized to be a key factor in the genesis and spread
of the CMD pandemic in East and Central Africa
(Harrison et al. 1997; Legg 1999; Fondong et al.
2000; Pita et al. 2001). Plants infected with
EACMV-UG and ACMV expressed more severe
symptoms than those infected with EACMV or
ACMV alone (Harrison et al. 1997b; Pita et al.
2001). In Uganda, it has been demonstrated that
while plants infected with mild (less aggressive)
strains of EACMV-UG yielded only 12% less
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