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The loop-mediated isothermal amplification (LAMP) assay Prevention and control
(Huang et al., 2010) may be a cheap alternative to qPCR assays. It is very difficult to prevent infection with CAV in commercial
The sensitivity of LAMP assays was reported to be superior to the flocks due to its ubiquitous presence in poultry houses, extreme
conventional PCR assay, but this test lacks the ability to quantify resistance to disinfectants, and the transmission of viral DNA
the amount of viral DNA in a sample in contrast with the qPCR from breeders even in the presence of high VN titres. Once birds
assay. are infected there is no treatment to eliminate CAV. The only way
Detailed information on serological tests, isolation of CAV and to reduce the clinical or subclinical impact of infection is vaccina-
molecular assays has recently been published (Smyth and Schat, tion against CAV in pullets to provide maternal immunity against
2016). Several commercial ELISA kits are available using differ- CAV. In addition, control of other pathogens such as IBDV and
ent approaches. These kits are useful to provide a flock profile reovirus is important. The use of CAV-contaminated litter to
for breeder flocks. Based on the seroconversion rates and anti- expose pullets is never acceptable.
body titres, companies can then decide if vaccination of breeder
flocks is needed to provide maternal immunity to the chicks. It Current vaccines
is important to properly collect the serum samples; especially Currently there are three international vaccine companies pro-
haemolysis can negatively influence the results of ELISA tests ducing live attenuated vaccines for CAV. Lohmann Animal Health
for CAV (Kurian et al., 2012). The use of the ELISA kits by SPF (Elanco) produces the Cux-1 vaccine which was originally devel-
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producers is not always straight-forward because non-specific oped by Vielitz et al. (1987). It is sold as AviPro Thymovac and
reactions can occur (Michalski et al., 1996). For that reason, SPF administered in drinking water. Merck Animal Health produces
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producers often use several kits to confirm positive results and CAV-VAC , which was derived from the 26P4 isolate originally
follow up with PCR assays or VN assays. Several VN assays have described and sequenced by Claessens et al. (1991). The third
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been published including a microplate test (Jørgensen, 1990) vaccine, Circomune from CEVA, uses the Del-Ros isolate
and a test using a qPCR assay to demonstrate the absence of viral described by Rosenberger and Cloud (1989b). These two vac-
replication (van Santen et al., 2004b). The microplate test relies cines are administered by wing-web inoculation. Not all vaccines
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on the reading of CPE in the suspension cultures, which may be are available in all countries. For example, AviPro Thymovac is
subjective when there is a low level of virus replication. The use of not licensed in the USA.
the qPCR-based assay avoids this problem. The three vaccines are recommended for use in pullets
Virus isolation is rarely done unless virus is needed for experi- between 9 to 15 weeks of age and may cause lesions in chickens
mental purposes and can be done by inoculation of MSB1 cells younger than 3 weeks of age. Vielitz and colleagues (Vielitz et al.,
as discussed in the section on Propagation. Detailed protocols 1991; Vielitz and Voss, 1994) published the results of field trials
for virus isolation and identification are provided by Smyth and showing that vaccination provided protection in the offspring
Schat (2013). through maternal antibodies. In a few instances when the vac-
cine was administered at or after 17 weeks of age parent flock
seroconversion was incomplete and the offspring were not fully
Economic importance protected. Recently, Chansiripornchai (2016) conducted a field
The economic impact of clinical disease can be directly correlated study comparing seroconversion rates and titres after vaccination
with the increase in mortality and subsequent increase in con- of Ross 308 broiler breeders using the three vaccines. Sera were
demnations (Engström and Luthman, 1984; Vielitz and Landgraf, tested using the BioChek Elisa kits with the following cut-off
1988; Chettle et al., 1989; Davidson et al., 2004). The economic values: no protection with titres < 724, moderate protection with
impact of subclinical CAV infections is more difficult to estimate, titres between 724 and 2295, and protection with titres > 2296.
and subclinical infection often may have been a trigger for other At 23 weeks of age only the Cux-1 vaccine had an average titre
diseases leading to increased condemnations (e.g. Hagood et > 2296, while the other two vaccines were just below this value.
al., 2000; De Herdt et al., 2001; Sommer and Cardona, 2003). However, the SD was high for all three vaccines, so independently
McNulty et al. (1991) reported that flocks without CAV antibod- of the vaccine used many birds would have been in the protected
ies had a significantly better feed-conversion ratio and greater range. At 27 and 32 weeks of age titres had dropped for all three
weight/bird than flocks with CAV antibodies at processing but vaccines and were below < 2296. Additional comparative studies
there was no difference in mortality or dermatitis incidence are needed to determine if there are indeed differences between
between the two types of flocks. The same group did not find the vaccines in reaching the threshold level of protection and for
an impact on feed conversion rates when they analysed flocks how long the titres remain above the cut-off value for protection
derived from breeders without CAV antibodies. These flocks as suggested by BioChek.
did experience an increase in mortality and significantly lower
weights than birds from unaffected flocks. There were no appar- Potential new vaccines
ent negative effects on mortality or general performance in the Development of new vaccines is important to protect broilers
breeder flock during seroconversion between 20 and 31 weeks of against subclinical immunosuppression. Several problems will
age (McIlroy et al., 1992). Jørgensen et al. (1995) and Goodwin et need to be addressed to produce safe vaccines for broilers. The
al. (1993) did not find a correlation between seroconversion for first problem is that any live vaccine will need to replicate in the
CAV and performance. host to produce an immune response without causing subclinical