Arch Virol (2006) 151: 2161–2180
Ultrastructural study of myxoma virus morphogenesis
J.-L. Duteyrat, J. Gelﬁ, and S. Bertagnoli
UMR 1225 Interactions Hˆotes-Agents pathog`enes, INRA/ENVT, Ecole Nationale
V´et´erinaire de Toulouse, Toulouse, France
Received September 26, 2005; accepted April 26, 2006
Published online June 9, 2006
Summary. Poxviruses are among the largest and most complex viruses known.
Vaccinia virus, the prototype of the family Poxviridae, has been studied much
more than myxoma virus.
The aim of this work was to have a better knowledge about myxoma virus
The characterization of the main stages of MV morphogenesis was achieved
by ultrastructural and immunological analysis. Speciﬁc antibodies were raised
against M022L and M071L, two envelope proteins of extracellular enveloped
virus and intracellular mature virus, respectively. The main stages of assembly
were similar to those seen with other poxviruses, and the duration of the whole
replication cycle was estimated to be around 16 h, longer than what was described
for vaccinia virus. Morphological changes of infected cells were associated with
the development of long cellular projections and enlarged microvilli. Intracellular
enveloped viruses are associated with the cytoskeleton to move through the cell.
Unlike earlier studies, as many cell-associated enveloped viruses as intracellular
enveloped viruses were observed in relation with specialized microvilli, although
these structures were rarely noticed. Finally, an unusual spreading process was
observed, which uses cytoplasmic corridors.
The Poxviridae are a large family of complex DNA viruses that replicate in
vertebrate and invertebrate hosts. Their genome is composed of a single linear
double-stranded DNA molecule and encodes its own machinery required for both
replication and transcription. Thereby, they are able to replicate and assemble in
the cytoplasm of host cells. The most notorious member, variola virus, caused
smallpox and consequently had a profound impact on human history. More-
over, vaccinia virus (VACV) was the ﬁrst animal virus seen microscopically,
grown in tissue culture, accurately titered, physically puriﬁed and chemically