Effect of essential oils on the immune response to some viral vaccines in broiler chickens, with special reference to Newcastle disease virus

Abstract

This trial assessed the efficacy of a commercial essential oil (EO) product on the immune response to vaccination against Newcastle disease (ND) and subsequent challenge with virulent ND virus genotype VII (vNDv genotype VII) by using the following experimental groups of broiler chickens (Each group had 21 birds with 3 replicates in each, n = 7): NC (negative control), PC (positive control), VC (vaccinated), and VTC (vaccinated and treated with EOs). Moreover, in a trial to study the effect of EOs on vNDv genotype VII in vivo as a preventive or therapeutic measure, 2 additional ND-vaccinated groups were used (PRV: medicated 1 D before vNDv challenge for 5 D; and TTT: medicated 2 D after vNDv challenge for 5 D). In addition, the immune-modulatory effect of EOs on the avian influenza (AI), infectious bronchitis (IB), and infectious bursal disease (IBD) vaccines was assessed through the serological response. The use of EOs along with administration of ND vaccines (VTC) revealed a lower mortality rate (42.86%), clinical signs, and postmortem lesion score (11) than ND vaccines alone (VC) (52.28% mortality and score 15), in addition to lower hemagglutination inhibition (P < 0.05) (6.5 ± 0.46) and viral shedding (10 log 2.28 ± 0.24) titres 1 wk after challenge in comparison with VC (8.63 ± 0.65 and 10 log 3.29 ± 0.72, respectively). Nevertheless, the EOs mixture (VTC) (1952 ± 28.82) did not significantly (P > 0.05) improve growth performance compared with the nontreated birds (NC and VC) (1970 ± 19.56 and 1904 ± 38.66). EOs showed an antiviral effect on vNDv in vivo (in chickens) as a preventive measure (PRV) as well as some therapeutic effect (TTT) through decreasing the viral shedding titres (loNC₀), mortality rate, and severity of clinical signs and postmortem lesions, in addition to serum malondialdhyde level. Regarding the other viruses, the EOs mixture did not improve the immune response to the AI and IB vaccines but significantly (P < 0.05) increased the ELISA antibody titre for IBD virus at the 28th D of age (2,108 ± 341.05). The studied EOs mixture showed an immune-stimulating response to ND and IBD vaccines, antiviral effect against ND virus, especially if administered before the challenge; however, it did not have a growth-promoting effect.

Keywords: Newcastle; avian influenza; essential oils; immune response; infectious bronchitis.

Figure 1

Hemagglutination inhibition (HI) titre (log 2) of Newcastle disease antibodies throughout the experimental period. Geometric mean of 12 serum samples per group (four/replicate) at each observation time. Different letters at each observation time indicate to significant difference (P < 0.05). NC, negative control; PC, positive control; PRV, preventive; TTT, therapeutic group; VC, vaccinated and challenged; VTC, vaccinated, treated, and challenged.

Figure 2

Clinical signs and postmortem lesions in experimental groups challenged with vNDv. A: depression, B: swollen head and closed eye lids, C: greenish diarrhoea, D: proventricular haemorrhage, E: congested trachea, F: button-like ulcers on the intestine, G: enlarged mottled spleen.

Figure 3

Viral shedding (loNC₀) in the oropharyngeal swabs at 2, 4, and 7 D after challenge in 6 experimental chicken groups. Data are the average of 3 replicates per group (two pooled samples/replicate). NC, negative control; PC, positive control; PRV, preventive; TTT, therapeutic group; VC, vaccinated and challenged; VTC, vaccinated, treated, and challenged.

Figure 4

(A) Malondialdehyde (MDA) level (nmol/mL) in the serum and (B) superoxide dismutase (SOD) level (U/mL) in the serum of experimental groups (pre- and post-vNDv challenge). Data are means of 6 birds per group (two birds/replicate). Different letters at each observation time indicate to significant difference (P < 0.05). CV% of experimental groups for both parameters was in range of 0.4 to 18.9%. CV%, coefficient of variation percentage; NC, negative control; PC, positive control; PRV, preventive; TTT, therapeutic group; VC, vaccinated and challenged; VTC, vaccinated, treated, and challenged.

Figure 5

Hemagglutination inhibition (HI) titre (log 2) of avian influenza H5 antibodies. Geometric mean of 12 serum samples per group (four/replicate) at each observation time. Different letters at each observation time indicate to significant difference (P < 0.05). CV% range was 7.2 to 19%. CV%, coefficient of variation percentage; EO, essential oil; NC, negative control; VC, vaccinated and challenge; VTC, vaccinated, EOs treated, and challenged.

Figure 6

ELISA antibody titres for infectious bronchitis (IB) virus (A) and infectious bursal disease (IBD) virus (B). The ELISA titre was obtained from 12 serum samples per group (four/replicate) at each observation time. Different letters at each observation time indicate to a significant difference (P < 0.05). CV% range among experimental groups for both parameters was 4.6 to 19.7%. NC, negative control; VC, vaccinated and challenged; VTC, vaccinated, EOs treated, and challenged.