Increased level of protection of respiratory tract and kidney by combining different infectious bronchitis virus vaccines against challenge with nephropathogenic Brazilian genotype subcluster 4 strains

Figures & data

Table 1. Origin and identification of the seven Brazilian genotype IBV strains used in this study.

Flock	Organ from which isolation	Strain identification	Code used in this study	Genbank accession number
A	Enteric tract	IBV/BRAZIL/2012/Brazil Ae	Brazil Ae	KP202366
A	Respiratory tract	IBV/BRAZIL/2012/Brazil Ar^a	Brazil Ar	KP202371
B	Enteric tract	IBV/BRAZIL/2012/Brazil Be^a	Brazil Be	KP202367
B	Kidney	IBV/BRAZIL/2012/Brazil Bk^a	Brazil Bk	KP202372
C	Enteric tract	IBV/BRAZIL/2012/Brazil Ce^a	Brazil Ce	KP202369
C	Kidney	IBV/BRAZIL/2012/Brazil Ck	Brazil Ck	KP202368
D	Enteric tract	IBV/BRAZIL/2012/Brazil De	Brazil De	KP202370

^aStrains used for the pathotyping and in a vaccination/challenge experiment.

Figure 1. Amino-acids maximum likelihood tree (JTT matrix-based model, 100 bootstrap replicates) for the partial S1 subunit of the IBV spike protein (amino acid 231–346), showing the strains used in the present study (in bold) and the IBV D274, Massachusetts, 793B (4/91) and Arkansas types. The Brazilian strains used for the pathotyping and a vaccination/challenge experiment are identified with¹. Numbers at each node are bootstrap values. The bar represents the number of amino-acids substitutions per site.

Table 2. Pathogenicity for 1-day-old SPF chickens of the Brazilian IBV strains compared to M41

Inoculum	Ciliostasis protection score at 5 and 8 d.p.c.^a		Percentage of birds with IHC^b IBV positive kidneys at 5 and 8 d.p.c.
	5 d.p.c.	8 d.p.c.	5 d.p.c.	8 d.p.c.
Negative control	100	100	0	0
M41	1	53	0	0
Brazil Ar	0	54	73	53
Brazil Be	20	72	15	53
Brazil Bk	22	56	38	43
Brazil Ce	19	59	10	40

^aDays post challenge.

^bImmunohistochemistry.

Table 3. Overview of the results of the vaccination/challenge experiment in which the four Brazilian IBV strains and M41 were tested using Mass and 793B vaccines.

Vaccination programme	Challenge strain at 32 days of age						Mean score for Brazilian strains
	None	M41	Brazil Ar	Brazil Be	Brazil Bk	Brazil Ce
Ciliostasis protection score at 5 days post challenge
None	98	2	47	21	31	3	26
1x Mass (A or B)^a		91	85	88	94	100	92
2x Mass (A or B)^b			94	85	91	90	90
Mass (A or B) + 793B^c			99	100	100	98	99
% of IBV-positive kidneys at 5 and 8 days post challenge
None	0–0	0–0	30; 40^d	15; 23	8; 10	5; 35	27
1x Mass (A or B)		ND	0; 3	3; 13	0; 0	13; 40	14
2x Mass (A or B)			3; 10	5; 20	0; 3	5; 20	13
Mass (A or B) + 793B^c			0; 0	0; 3	0; 0	0; 3	2

^aVaccination at day 1.

^bFirst vaccination at day 1, second at day 14.

^cMass vaccination at day 1, 793B vaccination at day 14.

^dPercentage of positive kidneys at 5 and 8 d.p.c. respectively.