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TRT diagnosis & vaccination scheduling in Turkeys

21 October 2021, at 8:00am

The results of vaccination with live Pneumovirus vaccines are sometimes very difficult to understand. In fattening turkeys, this is the most important viral respiratory disease and it only can be fought by preventing the pathology with live vaccines. In this article we will discuss how to understand the results of serologies in order to create the best vaccination schedules and to evaluate the administration and protection.

Quick review of administration

To achieve good administration, it is important that the medical device can reach a droplet size of 170-200 microns and can achieve a projection distance of two metres.

Also, the vaccination should be carried out within 30 minutes, so that the temperature of the poultry house does not increase too much.

Administration must be carried out with the aim of not leaving blind spots. To achieve this, the idea would be to divide the house into “streets”, depending on the number of pipelines and feeders.

Then each operator will always start at the edges, to make sure that the animals in the corners and against the walls are vaccinated correctly. Each operator will cover the poultry house completely.

Since they start at the wall, they will change positions when they meet each other in the centre and go in the opposite direction, so the last run they make is once more against the corners and the walls. In this way, each operator can walk slowly, making two complete passes through the house, directing the spray nozzle 0.3-0.5m above the heads of the birds.

How to make a good diagnosis of TRT?

To determine an outbreak of TRT the flock must have shown clinical signs, a decrease in production performance and it must be confirmed by laboratory diagnosis.

It is very important to differentiate between contact and infection. When there is contact, we will find positive seroconversion without clinical signs whilst infection means positive seroconversion signs.

For the laboratory diagnosis there are two options: PCR and ELISA. Both are very useful for detecting an outbreak, vaccination scheduling and monitoring. In the case of PCR, this shows if the flock is positive or negative and in the case of ELISA it is more important to evaluate seropositivity than the antibody level.

Laboratory diagnosis: What, When and Why?

In the case of a suspected outbreak, take swabs or tissue imprints on FTA cards from the nasal turbinate, tracheal tissue from healthy birds at the beginning of clinical signs. In addition, also take 15-20 serum samples from each poultry house two or three weeks after the beginning of clinical signs.

For vaccination scheduling and monitoring it is good to check if the vaccine virus is replicating by doing a PCR 5 to 7 days after vaccination and to take 15-20 serum samples two to three weeks after each vaccination.

In any of these cases, it would be interesting to check how the animals are by the end of the production cycle by taking another 15-20 samples of serum.

How long are birds protected after vaccination?

Protection starts 7 days after the vaccination. The duration of protection depends on the field pressure, under normal conditions it can last 6-9 weeks.

It is a local immunity that produces respiratory protection by competitive exclusion, cellular immunity and IgA.

Regarding the fact that the level of serological response induced by live aMPV vaccines is not a good indicator of the degree of protection, in accordance with Ganapathy et al. (2007), the best-case scenario after administration of a live pneumovirus vaccine is to have low titers.

In turkeys, ELISA titres below 2,000 indicate that the field virus is being displaced. Although in a high field challenge situation the titres could be between 2,000 and 10,000 but the animals could still be protected, it all depends if there are clinical signs and low performance. On the other hand, if there are titres from 10,000 to 30,000 it is because there is a severe infection in the flock.

In the case of a low field challenge situation this would be an example of the results of:

20 days old turkeys 2 weeks after one live vaccine.
20 days old turkeys 2 weeks after one live vaccine.
12 weeks old after three live vaccines at day 1, week 2 and week 9.
12 weeks old after three live vaccines at day 1, week 2 and week 9.

In both cases there are even negative animals which is not a reason to worry or think of vaccine failure.

In the case of a high challenge situation this would be another example of the results:

8 weeks old after two live vaccines at day 1 and week 2.
8 weeks old after two live vaccines at day 1 and week 2.
14 weeks old after three live vaccines at day 1, week 2 and week 6.
14 weeks old after three live vaccines at day 1, week 2 and week 6.

Conclusions

In order to use diagnostic techniques as useful tools to control turkey rhinotracheitis, the timing for taking samples is crucial. Secondly, it is important to collect data from different flocks to be able to compare the results and to correctly interpret them over time. In this way we can make a personal classification of our farms and achieve better and faster prevention.

Lastly with that information we need to differentiate between contact and infection, so it is always important to confirm clinical signs and low performance to determine an outbreak.

References
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Gough RE; Jones RC, 2008. Avian Metapneumovirus. In: Diseases of Poultry, 12th edition [ed. by Saif, Y. M. \Fadly, A. M. \Glisson, J. R. \McDougald, L. R. \Nolan, L. K. \Swayne, D. E.]. Ames, Iowa, USA: Blackwell Publishing, 100-110.
LI., J., Cook J.K.A., Brown T.D.K., Shaw K., Cavanagh D., (1993). Detection of turkey rhinotracheitis virus in turkeys using the polymerase chain reaction. Avian Pathology. 22, 771-783.
Buys, S.B., DU Preez J. H., (1980). A preliminary report on the isolation of a virus causing sinusitis in turkeys in South Africa and attempts to attenuate the virus. Turkeys. 28, 36.
American Association of Avian Pathologists, Inc, (2013). Avian Metapneumovirus Infection. In: Avian Disease Manual, 7th edition [ed. by Boulianne, M. \Brash, M.L. \Charlton, B.R. \Fitz-Coy, S. H. \Fulton, R. M. \Julian, R. J. \Jackwood, M.W. \ Ojkic, D. \Newman, L. J. \Sander, J. E. \Shivaprasad, H. L. \ Wallner-Pendleton, E\ Woolcock, P. R.]. 26-28

Product Manager at Hipra
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