Abstract
BackgroundAvian Metapneumovirus (aMPV) infections are a huge economical issue for the poultry industry worldwide. Although maternal antibodies do not protect turkey poults against turkey rhinotracheitis (TRT), almost no studies have been conducted so far regarding the impact of these antibodies on vaccine induced immunity development against aMPV infection. We conducted four experiments on commercial turkeys aimed at comparing local humoral and cell mediated immune response of maternally delivered anti-aMPV antibody positive (MDA+; Experiment I and II) and negative (MDA-; Experiment III and IV) turkeys following vaccination with an attenuated live aMPV subtype A vaccine at the day of hatch (Experiment I and III) or at two weeks of age (Experiment II and IV).ResultsRegardless of the birds’ age, vaccination of MDA- turkeys resulted in strong stimulation of CD8+ T lymphocytes in the Harderian gland and tracheal mucosa, whereas vaccination of MDA+ birds stimulated mainly CD4+ T cells in those structures. An increase in the level of anti-aMPV IgY antibodies was noted in the serum (but not in tracheal washings) as early as 7 days after vaccination, but only in birds possessing low levels (MDA+ birds vaccinated at 2 weeks of age) or no maternal anti-aMPV antibodies at the time of vaccination. In MDA+ turkeys vaccinated at hatch, the decrease in serum levels of maternal anti-aMPV antibodies proceeded faster (in comparison to control group), which, together with faster viral clearance, indicates that maternal antibodies can inhibit vaccine virus replication and influence the development of vaccine-induced immunity.ConclusionThis study provides the first documented evidence that the frequency of TRT outbreaks in the field and/or failure of TRT vaccination could be correlated with differences in the immunological status and/or age of vaccinated turkeys.
Highlights
Avian Metapneumovirus infections are a huge economical issue for the poultry industry worldwide
Humoral immunity is strongly stimulated by vaccination or Avian Metapneumovirus (aMPV) infection [7,10,11,12,13], but antibodies do not play a key role in protection against turkey rhinotracheitis (TRT) and should not be considered as indicators of immunity against aMPV infections [7,9,11,12,14,15,16]
The Maternally derived antibodies (MDA)+ group comprised 284 turkeys that were positive for maternally derived antibodies and were obtained from a parent flock vaccinated against TRT (3 times with live aMPV/A vaccine and twice with inactivated vaccine)
Summary
Avian Metapneumovirus (aMPV) infections are a huge economical issue for the poultry industry worldwide. Maternal antibodies do not protect turkey poults against turkey rhinotracheitis (TRT), almost no studies have been conducted so far regarding the impact of these antibodies on vaccine induced immunity development against aMPV infection. One-day-old turkey poults are administered live attenuated vaccines against TRT by coarse spray to provide the earliest possible protection of the upper respiratory tract against aMPV infections [6]. In one-day-old turkey poults, most of which originate from parent flocks vaccinated against TRT, the possible influence of maternal antibodies on the development of vaccine-induced immunity against aMPV is questionable
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