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Control of CAV from the Hens through the Progeny:
Chicken infectious anemia virus (CAV) can affect the progeny in
three forms:
- Vertical transmission from the hen through the egg/chick.
- Horizontal transmission in the first two weeks of age.
- Co-infection with other immunosuppressive agents such as IBD,
after three weeks of age.
Until now, one type of CAV virus (CAV-1) has been found as the
predominant isolate around the world. But more investigation is
needed to continue searching for different strains of the virus that
may be prevalent in the field, such as CAV-7 (Spackman E, Cloud SS
and Rosenberger JK. Avian Diseases. 2002:46(4):956963.). CAV
is highly resistant to disinfectants and seems to be prevalent in
long-established broiler breeder farms. One of the initial
approaches to controlling the disease was to move the litter from
older flocks and place it in the pullet houses, ensuring that the
pullets were getting the infection and developing antibodies before
the onset of laying fertile eggs. Because the horizontal
dissemination of the CAV was slow within the flock, the objective
was to reduce the vertical transmission of the CAV, without knowing
the level of immunity needed to meet that objective.
Initially, homogenous CAV isolates from tissues were used to
formulate autogenous vaccines. Later commercial vaccines became
available, bringing a clearer concept of the level of immunity
needed in order to reduce and/or eliminate vertical transmission. In
an experiment presented by Malo, et al (Intervet. VSD Newsletter.
November 1995), 70-week-old birds possessing different levels of
antibodies against CAV were challenged with a high dose of a field
isolate by the intramuscular route. Their results demonstrated that
vertical transmission took place in birds with virus neutralization
(VN) less than 8 or IDEXX CAV ELISA titers less than 1000. However,
in birds with VN greater than or equal to 8 (or IDEXX CAV ELISA
titers greater than or equal to 1000), excretion of the challenge
virus was not observed. Therefore, the objective for vaccination
programs in pullets is to achieve titers of at least 1000 before the
onset of laying fertile eggs. Titers can easily be determined by
using the IDEXX CAV ELISA test kit with the 1:100 dilution option.
The first serologic testing for CAV is recommended at 6–7
weeks post-vaccination, and repeated 30 weeks later, each time using
23 serum samples per flock. By using this program, broiler-breeder
companies can monitor the vaccination technique, the vaccination
crews and the persistence of the immune response based on different
vaccination programs (e.g., wing-web or water vaccine application)
and different vaccines, and then build their own expected baselines.
Pullets or broiler breeder flocks with mean titer groups of 1, 2, 3
or 4 are considered to be protected against vertical transmission of
CAV. After generating these baseline data, they can recognize an
expected condition and/or prevent any unexpected results in the
broiler-breeders based on vertical transmission of CAV.
By using serology as a monitoring program, you can cover the
first two steps in the control of the dissemination and pathology of
the CAV virus—the vertical transmission and the effect of CAV
in the first two weeks of age. However, CAV field challenge after
three weeks at the broiler houses in combination with IBD may
continue to be a threat because the objective of the broiler-breeder
or light breeder vaccination was to reduce vertical transmission and
give some protection during the first two weeks of age only.
If broiler companies want to monitor and build data from
two-week-old broilers or younger, we suggest using the IDEXX CAV
ELISA at the 1:10 dilution. It is relevant for the bleeding crew to
mention the sample size and the quality of the chicks sampled. An
example of the chick quality would be: 30 chicks, three-days old,
40–45 grams, good physical appearance, not dehydrated, and with
healthy umbilical zones (no yolk sac retention or infection
suspected).
IDEXX CAV Ab ELISA Titers/Titer Groups: 1:100 Sample Dilution
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VISIT US AT THE FOLLOWING EVENTS
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Guatemala City, Guatemala—May 7–9, 2003
VI Congreso Centroamericano y Del Caribe De Porticultura, Centro
de Convenciones del Hotel Westin Camino Real. Booth 11.
Campinas, Sao Paulo, Brazil—May 7–9, 2003
APINCO
Foundation for Poultry Science & Technology World Poultry Science
Association Brazilian Branch Meeting, Centro de
Convenções do Hotel The Royal Palm Plaza em Campinas,
SP, Brazil. Dr. Ricardo Muñoz of IDEXX will present
Strategies to Control the Main Diseases in Poultry at the Ermitage
Hotel on May 8, at 7:00 p.m.
Florianópolis Brazil—May 14–16, 2003
AveSui,
being held at the Centro de Convenções de
Florianópolis. Dr. Ricardo Munoz of IDEXX will present
Strategic Control and Importance of Salmonella sp in Swine
Herds and Serological Monitoring of Mycoplasma hyopneumoniae
on May 13th at the II International Seminar on Production, Market
and Pork Quality.
Des Moines, Iowa, United States—June 5–7, 2003
World
Pork Expo, at the Iowa State Fair Grounds, Booth #2463.
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In Poultry Testing
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