Page 260 - Avian Virology: Current Research and Future Trends

Chicken Infectious Anaemia Virus | 253

PTA. In an earlier publication using 4% ammonium molybdate, (Fig. 9.3B), indicating a T=1 lattice containing 60 viral protein
the same authors reported a mean size of 23.5 ± 0.8 nm (Todd (VP) 1 subunits.
et al., 1990). In addition to the virus particles, smaller particles The buoyant density of CAV in caesium chloride gradients is
of 11 nm (Imai et al., 1991) or ring-like structures of 15 nm reported to be between 1.33 to 1.37 g/ml (Goryo et al., 1987b;
(McNulty et al., 1990a) were detected in MSB1-propagated CAV Gelderblom et al., 1989; Todd et al., 1990). The Cornell CIA-1
preparations. However, similar structures were also seen in prepa- isolate has a density of 1.36 g/ml (Lucio et al., 1990). The
rations from non-infected MSB1 cells and seem to be unrelated sedimentation coefficient for CAV is estimated to be 91S using
to CAV. isokinetic sucrose gradients (Allan et al., 1994).
Gelderblom et al. (1989) and McNulty et al. (1990a) origi-
nally described the virus particles as a regular T=3 icosahedron Resistance to heat and chemical treatment
with 32 subunits. However, using unstained, cryopreserved CAV CAV is resistant to heating at 80ºC for 15 minutes (Yuasa et al.,
particles (Fig. 9.3A), Crowther et al. (2003) developed a three- 1979) and only partially inactivated after 30 minutes at 80ºC
dimensional map of CAV. This map indicates that CAV has a and completely after 15 minutes at 100ºC (Goryo et al., 1985).
capsid structure of 12 pentagonal trumpet-shaped capsomeres However, for minced viraemic chicken meat the core tempera-
ture needs to be 95ºC for 10 to 30 minutes to achieve complete
inactivation (Urlings et al., 1993). This suggests that undercooked
chicken meat could be the source of CAV DNA in humans
detected by PCR assays.
CAV is highly resistant to treatment with chloroform and
ether (Yuasa et al., 1979; Goryo et al., 1985) as can be expected
for non-enveloped viruses. Yuasa (1992) tested the effectiveness
of chemicals for inactivation of CAV. Treatment with orthodi-
clorobenzene, inverted or amphoteric soap were ineffective when
used for 2 hours at 37ºC. Iodine and sodium hypochlorite were
effective only when used at 10% for 2 hours at 37ºC but not or
less effective when CAV was present in 20% liver homogenates.
Prolonging the treatment to 24 hours at room temperature did
not increase the effectivity of 5% sodium hypochlorite. Treatment
A with 1% glutaraldehyde at room temperature for 10 minutes inac-
tivated CAV even in 20% liver homogenate. Beta-propiolactone at
0.4%, which is often used to prepare inactivated vaccines, requires
24 hours at 4ºC to inactivate CAV. Treatment with 5% formalde-
hyde requires 24 hours at room temperature to inactivate CAV
in liver suspensions. Formaldehyde fumigation was ineffective
in completely inactivating CAV. Organic solvents were also inef-
fective, while 0.1 N NaOH at 37ºC for 2 hours or at 15ºC for 24
hours reduced titres in 20% liver suspensions 10-fold. Under the
same conditions, 0.1 N HCl had only a minor effect.
Taylor (1992) found that treatment of CAV-infected cells with
90% acetone for 2 hours at room temperature had no effect on
virus viability. This has some important consequences because
acetone is often used to fix MSB1-infected cells for immuno-
fluorescence studies. In view of this finding it will be prudent to
consider acetone fixed CAV positive samples as medical waste.

Propagation

Introduction
B CAV can be isolated and propagated in 1-day-old SPF chicks,
chicken embryos and cell culture. The latter is preferred but may
result in false negative results in which case the other two meth-
Figure 9.3 Micrographs of chicken anaemia virus. (A)
Cryomicrograph of CAV. Scale bar, 50 nm. (B) Three-dimensional ods may be needed.
maps of CAV computed from cryomicrographs. The capsid is formed
from 12 pentagonal trumpet-shaped capsomeres, indicating a T=1 Cell culture
surface lattice containing 60 subunits. From Crowther et al., Journal
of Virology. Vol. 77, No. 24 Dec. 2003, pp. 13036–13041. Copyright Thus far, CAV is the only gyrovirus, and probably the only member
@ 2003, with permission of the American Society for Microbiology. of the Anelloviridae, that has been propagated successfully in vitro,