Passive immunization against Histomonas meleagridis does not protect turkeys from an experimental infection

Figures & data

Table 1.  Experiment 1: mortality and mean lesion scores of groups of turkeys after active immunization and challenge with H. meleagridis

					Mean lesion scores^e
Group^a	Total^b	Immunization	Challenge^c	Mortality (%)^d	Caeca	Liver
UNC	4	−	−	0^A	0.0^A	0.0^A
INC	10	–	+	60^B	2.8^B	2.9^B
IC	8	Infection/treatment	+	0^A	1.1^C	0.1^A
IM	10	intramuscular	+	10^A	2.2^B	2.2^B
Different uppercase superscript letters (within a column) indicate a statistical difference (P≤0.05). ^aUNC, uninfected, non-immunized control; INC, infected, non-immunized control; IC, immunized by infection and treatment; IM, immunized by intramuscular injection with H. meleagridis antigens. ^bNumber of turkeys in each group on the day of challenge. ^cEach group, except for the UNC group, was challenged with 10^5 H. meleagridis. ^dMortality by 10 days post challenge: three INC birds died 9 days post challenge, three died 10 days post challenge; one IM bird died 8 days post challenge. ^eMean lesion scores on the day of autopsy. Birds that died of histomonosis were given a lesion score of 4 per organ.

Figure 1.  Experiment 2: serum antibody responses of groups of turkeys after active immunization with H. meleagridis. Turkeys immunized at 0 d.p.i., with a booster at 20 d.p.i. (indicated by the asterisk). HIC, immunized by intracloacal infection with H. meleagridis; HIM, immunized intramuscularly with H. meleagridis antigens; PIC, immunized by intracloacal injection with H. meleagridis-negative liver and caecal homogenate; PIM, immunized as PIC but intramuscularly; CON, non-immunized control. Titres measured by indirect immunofluorescence. Different lowercase letters indicate significant differences between treatments at each time point.

Table 2.   Lytic activity of anti-H. meleagridis antibodies after different incubation times

	Reduction in growth of H. meleagridis by serum antibodies after incubation (%)^a
Sample^b	1 h	3 h	Overnight
HIC
Undiluted	88	100	100
1/10	75	50	50
1/100	75	0	−50
1/1000	33	−67	−67
HIM
Undiluted	67	100	100
1/10	50	38	−25
1/100	50	50	50
1/1000	−50	−50	−100
CON
Undiluted	0	0	−100
1/10	−43	−43	−186
1/100	−43	−43	−114
1/1000	0	0	−150
Controls
PC^c	−71	−71	−186
PP^d	−40	−100	−200
^a% reduction=[(concentrationstart – concentration x hours after incubation)/concentrationstart]×100. A negative value indicates growth, a positive value indicates reduction. ^bReaction containing parasites, complement and (un)diluted test sera from HIC, HIM or CON groups. HIC, immunized by intracloacal infection with H. meleagridis; HIM, immunized intramuscularly with H. meleagridis antigens; CON, non-immunized control group. ^cControl reaction containing parasites and complement. ^dControl reaction containing only parasites.

Figure 2.  Experiment 3: serum antibody responses of groups of turkeys after passive immunization and challenge with H. meleagridis. *Transfer of immune serum and challenge (4 h later) with H. meleagridis at 0 days post transfer (dpt). PASHIC, passively immunized with HIC antibodies; PASHIM, passively immunized with HIM antibodies; PASPIC, received antibodies from PIC; PASPIM, received antibodies from PIM; POS, non-immunized challenged group; NEG, non-immunized non-challenged group. Titres measured by indirect immunofluorescence. Different lowercase letters indicate significant differences between treatments at each time point.

Table 3.  Experiment 3: passive immunization and challenge against H. meleagridis

					Mean lesion scores^e
Group	Total^a	Antibodies^b	Challenge^c	Deaths^d	Caeca	Liver
PASHIC	5	HIC	+	0	3.0^A	2.8^A
PASHIM	6	HIM	+	1	3.0^A	2.3^A
PASPIC	5	PIC	+	0	2.7^A	2.2^A
PASPIM	6	PIM	+	0	2.8^A	2.3^A
POS	5	/	+	0	3.0^A	2.5^A
NEG	8	/	−	0	0.0^B	0.0^B
Different uppercase superscript letters (within a column) indicate a statistical difference (P≤0.05). ^aNumber of turkeys in each group. ^bGroup from Experiment 2 providing the antibodies. ^cEach group, except for NEG, was challenged with 3×10^5 H. meleagridis. ^dNumber of deaths. ^eMean lesion scores. Animals that died from histomonosis were given a lesion score of 4 per organ.