Development of an indirect enzyme-linked immunosorbent assay test for detecting antibodies to chicken astrovirus in chicken sera

Figures & data

Table 1. Summary of chicken serum samples used.

Serum group	Bird type	Age	Number of serum samples	Number of sets/houses	Table no.
(1a) SPFa	Non-infected controls	14–42 days	40	3	2
(1b) SPFb	Non-infected controls	12 weeks	27	1	2
(2) SPFc	CAstV experimentally infected birds	36 days	15	1	3
(3a) GP org A	Grandparents	12–14 weeks	168	10	2, 4
(3b) GP org B	Grandparents	1 day–52 weeks	150	4	2
(4) P org C	Broiler parents	Various	1864	68	5, 6
(5) P org D (Middle East)	Problem flocks	18.5–36.4 weeks	72	4	4

Note: All sera are derived from UK sources unless otherwise specified.

Table 2. Summary of ELISA results obtained with negative serum samples.

Serum group	Age	Number of samples	Number of sets/houses	Mean ratio	Standard deviation
1. SPF (1a)	14–42 days	40	3	0.00	0.01
2. SPF (1b)	12 weeks	27	1	0.01	0.01
3. GP organization A (3)	12–14 weeks^a	138	7	0.04	0.03
4. GP organization B (3)	1 day–52 weeks	150	4	0.12	0.06

Note: Numbers in parentheses denote serum sample source as summarized in Table 1.

^aConfirmed as negative by indirect IF (see Table 4).

Table 3. ELISA ratio values obtained with serum samples obtained from SPF chickens experimentally infected with 3 CAstV isolates.

Sera group SPF (2c)	11672	VF08-29	612
1	0.06	0.37	0.07
2	1.27	1.21	0.45
3	0.01	0.84	0.03
4	1.59	0.06	0.00
5	1.71	1.66	0.00

Note: Number in parenthesis denotes serum sample source as summarized in Table 1.

Table 4. Serum sets compared by ELISA and indirect IF.

Serum group	Age	Number of samples (submissions)	No positive by indirect IF	No positive by ELISA	S/P ratio range of positive samples
1 (3a)	12–14 week	138 (7)	0	0	<0.30
2 (3a)	12–14 week	30 (3)	28	26	0.31–1.96
3^a (5)	18.5 week	21 (1)	1	0	<0.30
4^a (5)	34 week	21 (1)	21	21	0.56–2.06
5^b (5)	31.5 week	15 (1)	0	1	0.32
6^b (5)	36.4 week	15 (1)	14	14	0.33–1.55

Note: Numbers in parentheses under Serum group denote serum sample source as summarized in Table 1.

^aGroups 3 and 4 are from same parent flock.

^bGroups 5 and 6 are from the same parent flock.

Table 5. Seropositivity results obtained for serum sets.

Serum group (4)	No. sets	No. sera	No. sets seronegative	No. sets with low seropositivity	No. sets with medium seropositivity	No. sets with high seropositivity
1	6	320	2	0	2	2
2	2	92	0	0	0	2
3	4	440	0	0	1	3
4	11	289	2	5	1	3
5	12	120	5	1	1	5
6	1	22	1	0	0	0
7	14	280	0	0	9	5
8	6	120	1	0	1	4
9	6	61	3	2	1	0
10	2	40	1	0	1	0
11	4	80	1	1	2	0
Totals	68	1864	16 (23.5%)	9 (13.2%)	19 (27.9%)	24 (35.3%)

Notes: Variability in ELISA S/P ratios.

Number in parenthesis after Serum group indicates the serum source in Table 1.

Table 6. Comparison of S/P ratios for serum sets with high and low seropositivities.

Serum group (4)	No. sets	No. sera	No. negatives	No. weak S/P ratios	No. moderate S/P ratios	No. strong S/P ratios
Overall	68	1864	774 (41.5%)	294 (15.8%)	562 (30.2%)	234 (12.5%)
Sets/flocks with high seropositivity	24	840	90 (10.7%)	160 (19.1%)	407 (48.5%)	183 (21.8%)
Sets/flocks with low seropositivity	9	190	168 (88.4%)	16 (8.4%)	5 (2.6%)	1 (0.6%)

Note: Number in parenthesis after Serum group indicates the serum source in Table 1.