Live ND vaccines inadequate for low ND challenge countries

Since it was first officially described in 1926, Newcastle disease (ND) has established as a major disease threat for commercial poultry including chickens, turkeys, quails, pheasants, as well as for hobby and zoo birds.

In low ND challenged countries, industrial chickens are often facing the uncontrolled circulation of lentogenic (vaccine) strains, especially in high densely populated poultry areas. As a result, they may show subtle to overt respiratory signs, because of the inflammation of the trachea. It may worsen in case of suboptimal husbandry conditions (too high stocking density, high ammonia level, wet litter, poor ventilation). As a result, flock uniformity will decrease, and secondary opportunistic respiratory infections (eg, E.coli) may arise with the need to apply antibiotic medication. Ultimately, slaughterhouse condemnations may increase due to excessive airsacculitis.

Economical advantage

Production parameters differences measured in large scale field trials have demonstrated the consistency in ND protection with distinctive benefits of Vectormune ND over the live ND conventional vaccination programmes and to translate them into economic advantages.

Here, we present an example of a comparative field performance study involving 29 commercial broiler flocks from a country in Europe with low ND field virus challenge. Production performance parameters are presented in Table 1 indicating the statistical significance for the main parameters measured with the consequent economic benefits. Vaccination programme in the live vaccine group was B1 at day old age with spray and La Sota at 14 days of age with drinking water. In Vectormune ND group the only the reference rHVT-ND vaccine was at the hatchery.

The economical benefits were calculated based on the production differences considering additional 250 g/ bird in slaughter body weight and 7 points lower in the feed conversion ratio with the Vectormune ND vaccination programme which translates into € 142 per 1,000 birds in this study (Figure 1).

Figure 1 – Slaughter and mortality rate per vaccination.

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Why live ND vaccines are unsuitable for low ND challenged areas

Vaccination is an important part of the prevention programme against ND. The essential required characteristic from an ideal vaccine is well balanced safety and efficacy.

Indeed, safety is the first priority for low ND pressure conditions. In the image below reveals the key performance indicators of an ideal vaccine in terms of safety characteristics. Live ND vaccines are not meeting those expectations.

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Silent spread of lentogenic strains

An example of a silent spread of lentogenic strains in ND-free regions such as Brazil is presented here. A broiler Integration in Brazil producing 7.7 million day-old chicks/month, with no history of ND vaccination conducted in the last 20 years was evaluated for the presence of a viral respiratory infection. Condemnations at this company, including airsacculitis were reaching around 0.5% monthly representing 38,500 chickens / month. A standard ND vaccination practice in layer and breeder farms in the same area is to regularly vaccinate their flocks with Hitchner B1 live conventional vaccine.

Serological evaluation of broiler flocks showed high end-point serology at processing age at 42 days (ND Idexx ELISA). Results of the evaluation of the condemnations rate and medication costs for 2 consecutive broiler cycles without ND vaccination (298,000 chickens/ cycle; 8 houses) and after the administration of the reference rHVT-ND vaccine for one broiler cycle are shown in Figure 2. (A total of 285,000 chickens/cycle; same 8 houses).

Figure 2 – Comparative serological results and economic benefits before and after the inclusion of Vectormune ND in a commercial broiler company located in an ND-free region.

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The reference rHVT-ND vaccine prevented the uncontrolled circulation of lentogenic strains in ND-free areas, as evidenced by the lower Idexx serological titers; furthermore, it increased significantly the production performance of the flocks by improving respiratory health and by reducing the therapeutic use of antibiotics.

No side effects from using the rHVT-ND vaccine

In regions free of Newcastle disease like European countries, there are losses in broiler flocks’ performance due to the post-vaccination reactions caused by live attenuated ND vaccines. Spleen samples from 139 broiler flocks were collected at 4 weeks of age to verify the detection of the HVT vector of Vectormune ND. Additionally, the production performance parameters from broiler flocks vaccinated with live ND vaccines has been compared with the production data from broiler flocks vaccinated with the reference rHVT-ND vaccine (Figure 3).

Figure 3 – Differences in performance results with the use of the reference rHVT-ND vaccine.

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Blood samples were also collected at slaughter from a total of 339 broiler flocks before and after the use of Vectormune ND vaccine and tested for antibody response to NDV using 2 commercial Elisa kits (IDVet specific for the rHVT-F insert and a conventional ND Elisa from Idexx) Figure 4.

Figure 4 – Different ND Elisa results using two Elisa kits: A conventional ND Elisa (Idexx) vs. Vector specific F Elisa kit.

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Control and prevention of Newcastle Disease outbreaks

Vectormune ND is a strong tool to break the uncontrolled transmission of NDV among chickens in a house, in between houses in a farm, and ultimately among farms in a high densely populated poultry area. These graphs (Figure 5) demonstrate that the reference rHVT-ND vaccine controls and prevents Newcastle Disease outbreaks despite of a different genotype between challenge strain and vaccine insert. Seeder subgroups were challenged with 5.0 log₁₀ELD₅₀ of velogenic NDV intra-nasally. Contacts were co-mingled with seeders from 8 hours post-challenge. Oro-nasal swabs and cloacal swabs were collected daily for 14 days post-challenge; vNDV amount was quantified by RT-qPCR. Individual results and mean & STD of Ct values are shown.

Figure 5 – Kinetics of velogenic NDV shedding in vaccinated and unvaccinated birds after direct infection (seeder subgroups) or contact infection (contact subgroups).

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Protection against lentogenic strains

Newcastle disease continues to challenge poultry production operations even in low ND challenged countries. With live ND vaccines it is not possible to keep the balance between safety and efficacy. There is a need to protect against lentogenic strains; however, on the other hand there is also a need to be safe! One option was live mild vaccines but there is a risk of virus circulation in the field and some post vaccination reactions, hence the therapeutic use of antibiotics. Other option was not to vaccinate but then welcome all the risk of ND!

The reference rHVT-ND vaccine prevents the uncontrolled circulation of lentogenic NDV strains in ND-free areas, increasing significantly the performance of the flocks by improving respiratory health and by reducing the use of antibiotics as a direct consequence.

References available upon request