Efficacy of a new tetravalent coryza vaccine against emerging variant type B strains

Veterinary Autogenous Vaccines for Poultry in Europe-Many Ways to Crack an Egg

In the past decade, European animal farming has increasingly used autogenous vaccines for the prevention of nonnotifiable diseases. In Europe, these vaccines are exclusively inactivated bacterial and viral vaccines, with a set of specific regulations that differentiate them from conventional vaccines. The highest number of applications most likely occurs in poultry, as these animal species are farmed in the highest numbers compared with other types of food-producing animals. In 2019, autogenous vaccines came within the scope of harmonized European regulation for the first time, although many important aspects are still missing and need to be further developed. Consequently, several important legal provisions remain in national legislations and can vary tremendously between different member states of the European Union. The inclusion of autogenous vaccines in the management of certain diseases of poultry is justified by the nonavailability of licensed vaccines and the evolution and diversity of antigens in the field that are not covered by licensed vaccines. In addition, these vaccines aid in reducing the use of antibiotics. The methods for isolating and typing pathogenic isolates to obtain relevant antigens are pathogen specific and require a careful approach based on clinical evidence. Manufacturing processes are optimized according to regulatory standards, and they represent the most critical factor influencing the quality of autogenous vaccines and their placement on the market. This review presents the important requirements for manufacturing autogenous vaccines for poultry in addition to the relevant regulatory considerations. The results from a survey of several European Union member states regarding specific provisions within their national legislations are also presented.

Common viral and bacterial avian respiratory infections: an updated review

Many pathogens that cause chronic diseases in birds use the respiratory tract as a primary route of infection, and respiratory disorders are the main leading source of financial losses in the poultry business. Respiratory infections are a serious problem facing the poultry sector, causing severe economic losses. Avian influenza virus, Newcastle disease virus, infectious bronchitis virus, and avian pneumovirus are particularly serious viral respiratory pathogens. Mycoplasma gallisepticum, Staphylococcus, Bordetella avium, Pasteurella multocida, Riemerella anatipestifer, Chlamydophila psittaci, and Escherichia coli have been identified as the most serious bacterial respiratory pathogens in poultry. This review gives an updated summary, incorporating the latest data, about the evidence for the circulation of widespread, economically important poultry respiratory pathogens, with special reference to possible methods for the control and prevention of these pathogens.

Characterization of a highly virulent Avibacterium paragallinarum isolate

Infectious coryza (IC) is an important respiratory infectious disease in chickens. In this study, an Avibacterium paragallinarum Page serovar C strain, named ZJ-C, was isolated from a local layer flock that was routinely vaccinated with an inactivated trivalent vaccine, using reference strain Modesto as the serovar C immunogen. The pathogenicity, immunogenicity, and genetic characteristics of ZJ-C were studied. The minimum pathogenic dose of the isolate was 100 CFU, which was 1/1,000 of the dose of the serovar C reference strain Modesto. The vaccination-challenge trial in specific pathogen-free (SPF) chickens showed that the ZJ-C bacterin could provide 100% protection against challenge from both ZJ-C and Modesto strains, whereas Modesto provided 100% protection against challenge from itself, but only 70% protection against ZJ-C. Sequence analysis of the HMTp210 hypervariable region (region 2) showed that the homology of region 2 between ZJ-C and Modesto was 96.14%, whereas the homology between ZJ-C and the Kume serovar C-4 reference strain HP60 was 99.83%. Phylogenetic analysis of region 2 showed that ZJ-C was most closely related to cluster C-4, represented by HP60. The experimental data obtained in this study will help the selection of optimal vaccine strains and assist serotyping studies of Av. paragallinarum.

The Protective Efficacy of an Inactivated Vaccine against Avibacterium paragallinarum Field Isolates

Infectious coryza (IC) is an acute respiratory disease caused by Avibacterium paragallinarum (Av. paragallinarum). In recent years, there have been frequent outbreaks of IC in chickens vaccinated with an inactivated vaccine, causing huge losses to the poultry industry. In this study, the protective efficacy of the trivalent inactivated IC vaccine (PT Medion Farma Jaya) against the field isolates of three serovars of Av. paragallinarum was verified. After vaccination, the hemagglutination inhibition antibody titers in double-vaccinated groups (A2, B2, and C2) were higher than those in single-vaccinated groups (A1, B1, and C1). The highest antibody titer was 213.1 at 3 weeks after the booster vaccination in group A2. Consistent with the trend in hemagglutination inhibition antibody titers, the protective efficacy of double vaccination was better than that of single vaccination. The clinical symptoms and pathological changes were alleviated, or the bacterial shedding was significantly reduced with double vaccination after challenge with field isolates of three serovars (p < 0.05). In particular, the chickens with double vaccination showed no clinical symptoms, pathological changes, or bacterial shedding after challenge by the serovar C strain. There was no significant difference in body weight and egg production between the double-vaccinated groups and the negative control group (p > 0.05). Therefore, we recommend that the commercial IC vaccine should be double-vaccinated in clinical applications.

Pathogenicity of Avibacterium paragallinarum Strains from Peru and the Selection of Candidate Strains for an Inactivated Vaccine

Worldwide, Avibacterium paragallinarum is the aetiological agent of infectious coryza in poultry. Vaccines are the best means of control, helping reduce clinical signs and colonization of this bacterium. Most vaccines are based on international reference strains, or, lately, regional strains, but, generally, without any information regarding their virulence. The characterization of the pathogenicity of 24 Av. paragallinarum strains of the three Page serogroups, including four variant strains of serogroup B, all isolated from infectious coryza outbreaks in Peru, was performed. After experimental inoculation into the infraorbital sinuses, information regarding their capacity to induce infectious coryza typical clinical signs, spreading, and colonization was recorded. Furthermore, after intraperitoneal inoculation, septicaemia and death were registered. Differences among strains in these parameters were observed, even within strains from the same serogroup. Finally, the four most pathogenic strains, one from each serogroup, were chosen to formulate an experimental vaccine that was tested successfully against homologous challenges in reducing clinical signs and colonization in vaccinated birds compared to unvaccinated ones. This is the first time that Av. paragallinarum strains from Peru were studied thoroughly for their virulence in a search for improving vaccine formulation.

Isolation, Serovar Identification, and Antimicrobial Susceptibility of Avibacteriumparagallinarum from Chickens in China from 2019 to 2020

Infectious coryza is an acute infectious respiratory disease in chickens that is caused by Avibacterium paragallinarum (A. paragallinarum). Infectious coryza has major economic effects due to decreased egg production in growing birds and slowed growth in broilers. In this study, we isolated and identified 40 strains of A. paragallinarum from chickens that showed typical clinical signs of coryza in part of China from 2019 to 2020. Using a hemagglutination-inhibition test, 11 isolates were identified as serovar A, 10 isolates were identified as serovar B, and 19 isolates were identified as serovar C. Antimicrobial sensitivity tests showed that high minimum inhibitory concentration (MIC) values were encountered for compounds sulfamethoxine sodium and oxytetracycline hydrochloride. Especially, of the 40 A. paragallinarum isolates, 30% had an MIC value of compound sulfamethoxine sodium of 64 μg/mL, 10% of 128 μg/mL, and 15% of 256 μg/mL. For oxytetracycline hydrochloride, 85% of isolates showed MIC values of 64 μg/mL or more. Excitingly, the MIC values of β-lactamase (amoxicillin, ampicillin, and ceftiofur) were low, with 77.5%, 70%, and 92.5% of isolates having an MIC value of ≤1 μg/mL, respectively. Our results may provide a reference for the treatment of infectious coryza.

Concurrent infection of Avibacterium paragallinarum and fowl adenovirus in layer chickens

The diagnosis of a concurrent infection of Avibacterium paragallinarum and fowl adenovirus (FAdV) in an infectious coryza–like outbreak in the outskirt of Beijing is reported. The primary signs of the infection were acute respiratory signs, a drop in egg production, and the presence of hydropericardium–hepatitis syndrome–like gross lesions. Laboratory examination confirmed the presence of A. paragallinarum by bacterial isolation and a species-specific PCR test. In addition, conventional serotyping identified the isolates as Page serovar A. Fowl adenovirus was isolated from chicken liver specimen and identified by hexon gene amplification. In addition, histopathologic analysis and transmission electron microscopy examination further confirmed the presence of the virus. Both hexon gene sequencing and phylogenetic analysis defined the viral isolate as FAdV-4. The pathogenic role of A. paragallinarum and FAdV was evaluated by experimental infection of specific-pathogen-free chickens. The challenge trial showed that combined A. paragallinarum and FAdV infection resulted in more severe clinical signs than that by FAdV infection alone. The concurrent infection caused 50% mortality compared with 40% mortality by FAdV infection alone and zero mortality by A. paragallinarum infection alone. To our knowledge, this is the first report of A. paragallinarum coinfection with FAdV. The case implies that concurrent infections with these 2 agents do occur and more attention should be given to the potential of multiple agents during disease diagnosis and treatment.

Characterization of emergent Avibacterium paragallinarum strains and the protection conferred by infectious coryza vaccines against them in China

Infectious coryza (IC), an acute respiratory disease of chickens, is caused by Avibacterium paragallinarum. Here, the current epidemiological status of IC was investigated in China over 5 yr (2013 to 2018). A total of 28 Av. paragallinarum field isolates were identified by PCR tests and by sequence analysis of the hemagglutinin gene. The pathogenicities of 4 field isolates, the efficacy of 2 commercial inactivated oil-emulsion IC vaccines and vaccines containing different Av. paragallinarum isolates were also evaluated. The PCRs revealed a high rate (51.5%) of sample positivity for Av. paragallinarum during 2013 to 2018. Phylogenetic analysis showed that most field strains fell into the same cluster and had a farther genetic relationship with the early isolates from China. Pathogenicity testing revealed that the Chinese Av. paragallinarum isolates were able to induce the typical clinical signs of IC; hence, they were clearly pathogenic to chickens. Vaccine efficacy tests revealed that the 2 commercial inactivated oil-emulsion IC vaccines we tested had low protection rates against 2 selected Av. paragallinarum isolates after a single immunization, whereas the inactivated vaccine containing the Av. paragallinarum BJ26 isolate generated a relatively high protection rate against the field isolates compared with other three tested vaccines. The results indicate that IC is currently prevalent in China, and that commercial vaccines have not counteracted its presence in this country.

Bacterial vaccines in poultry

BACKGROUND

Poultry bacterial pathogens are mainly controlled by using high-cost sanitary measures and medical treatment. However, the drug-resistant strains of pathogens continuously emerge, and medical treatments are often ineffective. Moreover, there is increasing public objections to drug residues in poultry products. The other important type of control is the vaccination which depends on immunity. This immunological control is the major practical alternative to chemotherapy. Success of vaccines in combating poultry diseases depends mainly on the choice of the proper type of vaccines, correct time of its usage, and method of administration.The types of vaccines include attenuated live vaccines, and these vaccines were shown to be effective in inducing protection. The second type is killed vaccine or whole bacteria extracts which is less successful in providing protection compared to live vaccines. The metabolic product vaccine (toxoids) is the third type of vaccine. The recombinant DNA technique was adopted to produce the protective antigens in a sufficient amount and in cost-effective ways.

CONCLUSIONS

Protection studies against bacterial diseases were performed by using several trials: living vaccines (live attenuated vaccines; live, non-pathogenic microorganisms; live, low virulence microorganism), inactivated (killed) vaccines (heat-inactivated, chemical inactivates, radiation), metabolic product vaccines (toxoids), subunit vaccines (whole cell proteins, outer membrane proteins, purified flagellar proteins (flagellin), fimbrial proteins, pilus proteins, lipopolysaccharides), vaccines produced by recombinant deoxyribonucleic acid (DNA) technology, and DNA vaccines.

Identification and characterization of Dutch Avibacterium paragallinarum isolates and the implications for diagnostics

This study reports the results of diagnostic and molecular typing methods for 18 Avibacterium paragallinarum isolates obtained from outbreaks of infectious coryza in commercial layer flocks in the Netherlands. Isolation, biochemical identification, species-specific PCR tests and classical serotyping were performed. In addition, molecular typing by Enterobacterial Repetitive Intergenic Consensus-Based Polymerase Chain Reaction (ERIC-PCR) and sequence analysis of the partial HPG2 region of A. paragallinarum were applied and results of both techniques were compared. Moreover, the pathogenicity of an isolate of the most common genotype detected in the Netherlands was determined in an animal experiment. All 18 Avibacterium isolates were nicotinamide adenine dinucleotide-dependent. All isolates were detected by the species-specific conventional PCR while 33% of the isolates were missed by the species-specific real-time PCR. Sequence analysis showed a probe mismatch as a result of a single nucleotide polymorphism (G1516A). Modification of the probe of the real-time PCR was necessary to overcome false negative results. Molecular typing showed that sequence analysis of the partial HPG2 region was in concordance with ERIC-PCR results and indicated the presence of two major genotypes. Serotyping showed the presence of serovars A-1, A-2 and B-1. There was no correlation between genotyping results and serotyping results. Inoculation of an isolate of the most prevalent genotype, and belonging to serovar A-1, into brown layer hens demonstrated the pathogenicity of this isolate.

Efficacy of tetravalent coryza vaccine against the challenge of Avibacterium paragallinarum serovars A and B isolates from Indonesia in chickens

Aim:

Infectious coryza is caused by Avibacterium paragallinarum. In Indonesia, this infection results in a 10%-40% decrease in egg production by laying hens. This study was conducted to determine the effectiveness of tetravalent coryza vaccine contained A. paragallinarum bacterin serovars A, B, C2, and C3; strain A-221, B-Spross, C2-Modesto, and C-3-Akko in layers based on antibody titer and clinical signs using a post-challenge test.

Materials and Methods:

Forty four-week-old Lohmanns strain chickens were used in this study. Forty chickens were divided into four groups for serological and challenge test: Group 1 (unvaccinated and challenged by A. paragallinarum serovar A), Group 2 (unvaccinated and challenged by A. paragallinarum serovar B), Group 3 (vaccinated and challenged by A. paragallinarum serovar A), and Group 4 (vaccinated and challenged by A. paragallinarum serovar B). Vaccination was done using the tetravalent vaccine in oil-emulsion adjuvant contained A. paragallinarum bacterin serovars A, B, C2, and C3; strain A-221, B-Spross, C2-Modesto, and C-3-Akko. Vaccination was performed at day 1 and booster was done at day 14. Blood serum was collected on days 0, 14, and 28 for the hemagglutination-hemagglutination inhibition (HI) test. The challenge test was given at day 29 through intranasal administration using A. paragallinarum serovars A-L2447 and B-L1710 approximately 6×10⁸ CFU/mL. Clinical signs were observed for 14 days post-infection. At the end of the study, chickens were euthanized, and pathological features of the infraorbital sinus, facial skin, and trachea were recorded.

Results:

Data analysis of antibody titers and pathological changes was performed descriptively, while clinical symptom scores were analyzed non-parametrically with the Mann–Whitney U-test using SPSS version 21. At days 14 and 28 post-vaccination, the antibody titer in Group 3 was 5 HI and 20 HI, respectively. However, the antibody titers in Group 4 at 28 days post-vaccination were 0 HI. Clinical observations, the vaccinated groups that were challenged with A. paragallinarum serovars A and B showed clinical symptoms on days 4 and 6 post-infection, namely mild unilateral facial edema and severe bilateral facial edema, respectively. Clinical signs in Groups 3 and 4 were less severe than in Groups 1 and 2 (p<0.05). Pathological examination findings supported clinical observations and serological testing.

Conclusion:

Tetravalent coryza vaccine in chickens has efficacy to protect against the challenge test of A. paragallinarum serovars A and B isolated from Indonesia.

Early migration pattern of Avibacterium paragallinarum in the nasal passage of experimentally infected chicken and Japanese quail by immunohistochemistry

Infectious coryza (IC) is often a curse for poultry farmers when it occurs concurrently with several pathogens causing swollen head syndrome. The disease is caused by Avibacterium paragallinarum, which inflicts initial damage to the nasal and respiratory epithelium. This facilitates the progression of disease pathology across the nasal cavity, thereby providing a platform for multiplication of opportunistic microbes. In this study, we attempted to investigate the early entrance and migration pattern of A. paragallinarum in chicken and Japanese quail following experimental infection, by employing an in-house developed polyclonal antiserum against this pathogen. Antigenic-specificity of the raised antiserum was subsequently evaluated through immune-dot blot techniques and counter-current immunoelectrophoresis (CIE). The resultant antiserum characterized the antigen localization within formalin-fixed and partially decalcified nasal tissue sections though immunohistochemistry (IHC). Japanese quail showed prominent localization of the bacterial antigen at 12 h post-infection in anterior turbinates. However, the chicken exhibited a higher level of the bacterial pathogen with intense immuno-reactivity at 24 and 48 h post-inoculation. The decline in immunostaining intensity in the nasal tissue of chicken as well as Japanese quail by 72 h post-infection signifies either an attempt to resolve the infection by the resident immune cells across the nasal passage of the host, or its dissipation by certain inherent innate immune factors present across the nasal passage that are still unknown to us. In the present study, we used a moderately virulent pathogen (A. paragallinarum) that inflicted a mild to moderate degree of damage to histo-architecture of the nasal passage and provided a discernible migratory pattern with fewer alterations, along with provision toward unravelling basics of the immuno-pathogenetic mechanism. This knowledge will support efforts towards the development of a future mucosal nasal vaccine in birds affected with IC.

Selection of Avibacterium paragallinarum Page serovar B strains for an infectious coryza vaccine

Infectious coryza is an important respiratory disease of chickens around the world and is caused by Avibacterium paragallinarum. Among the three Page serovars currently recognized for this bacterium, serovar B is a major circulating serovar in China nowadays. The cross-protection ability of the Page serovar B reference strain (0222) and five local isolates was evaluated by a vaccination-challenge trial in SPF chickens. The clinical signs seen in control birds challenged by strain 0222 and isolate HB 01 were significantly different, with isolate HB 01 giving more severe clinical signs. In terms of cross-protection, the protection in the groups vaccinated with isolate HB 01 and BJ 02 was significantly higher than that in the groups vaccinated with 0222 and the other three isolates. In addition, an experimental oil adjuvant trivalent vaccine, containing field isolate HB 01 antigen, was compared for immune efficacy with two commercial trivalent infectious coryza vaccines containing internationally recognized serovar B strains. The experimental oil adjuvant trivalent vaccine elicited best protection (80%) among the three trivalent vaccines. In conclusion, the oil adjuvant vaccine, containing field isolate HB 01 may be a better choice in control of current serovar B Av. paragallinarum outbreaks in China under current circumstances.

Naturally Occurring β-Nicotinamide Adenine Dinucleotide-Independent Avibacterium paragallinarum Isolate in Peru

The β-nicotinamide adenine dinucleotide (NAD) requirement has been considered to be essential for the isolation of the causal agent of infectious coryza, Avibacterium paragallinarum. Nevertheless, NAD-independent reports from South Africa and Mexico dismissed this paradigm. It is now accepted that both NAD-dependent and NAD-independent agents are able to cause infectious coryza and thus belong to the species A. paragallinarum. Here, we report for the first time in Peru a NAD-independent isolate from broiler chickens with typical signs of infectious coryza that have received a trivalent inactivated vaccine against infectious coryza. The isolate was identified based on its morphology, biochemical and serologic tests, and PCR results. Partial 16S rRNA gene sequence analysis confirmed the isolate as A. paragallinarum. There have been no cases of NAD-independent A. paragallinarum isolates reported in South America. Increasing reports around the world highlight not only the need to reconsider the in vitro nutritional requirements of this species for its correct isolation but also the cross-protection conferred by commercial infectious coryza vaccines against NAD-independent isolates.

Genotyping, pathogenicity, and immunogenicity of Avibacterium paragallinarum serovar B-1 isolates from the Americas

The bacterium Avibacterium paragallinarum is the etiologic agent of infectious coryza of chickens. Among the nine Kume serovars currently recognized in this bacterium, serovar B-1 is a common serovar in the Americas. In the current study, serovar B-1 isolates from Ecuador (seven isolates), Mexico (seven isolates) and Panama (two isolates) were genotyped. In addition one Panamanian, one Ecuadorian, and two Mexican isolates were used in a vaccination-challenge trial in which the vaccine was based on the 2671 serovar B-1 reference strain. Genotyping by enterobacterial repetitive intergenic consensus-based PCR (ERIC-PCR) resulted in ten distinguishable ERIC patterns for the 16 isolates and the two reference strains of Av. paragallinarum included in the study. No ERIC patterns were shared among isolates of the three different countries. In the vaccination-challenge trial, one isolate from Panama showed a significantly lower virulence than did the three other isolates. In terms of cross-protection, chickens vaccinated with reference strain 2671 and challenged with an Ecuadorian strain showed 40% protection, a significantly lower protection than the homologous protection level. The other three field isolates gave a similar protection level to the homologous challenge.

Vaccination of one-day-old broiler chicks against infectious coryza

In order to evaluate the protection conferred by an experimental inactivated vaccine against infectious coryza, three challenge trials were undertaken using 112 1-day-old broilers. The vaccine "Hepa Inmuno NC" included bacterial antigens of Avibacterium paragallinarum (serogroups A, B, variant B, and C) as well as antigens of Newcastle virus and hepatitis virus. Fifty-six broiler chicks were vaccinated at the first day of life at the hatchery while another 56 chicks were left unvaccinated. Three infection trials were conducted simultaneously using each of the three serogroups A, B, or C of Av. paragallinarum. In each trial, 17 vaccinated and 17 unvaccinated broilers were used. Challenge was performed at day 31 of life by injection, into the left infraorbital sinus, of approximately 1 x 10(5) colony forming units of the corresponding Av. paragallinarum strain. Clinical signs were recorded on day 2 postchallenge. All broilers were euthanatized and both infraorbital sinuses were bacteriologically examined for the presence of Av. paragallinarum on day 5 postchallenge. In comparison with the unvaccinated broilers, the vaccine significantly reduced the number of broilers with clinical signs after challenge with serogroup B, and significantly fewer vaccinated broilers were positive for the presence of Av. paragallinarum after challenge with serogroup C. On the other hand, no significant protection was observed when broilers were challenged with Av. paragallinarum from serogroup A. Despite the high infection rates in vaccinated chicks after an experimental infection with Av. paragallinarum, it was possible to reduce colonization of Av. paragallinarum (serogroup B) and clinical signs (serogroup C) in broiler chicks by vaccination at the first day of life. Further cross-protection trials should be done, including other Av. paragallinarum strains in the vaccine, especially those from serogroup A.

The vaccination-challenge trial: the gold standard test to evaluate the protective efficacy of infectious coryza vaccines

Infectious coryza is an upper respiratory tract disease of chickens with the major impact occurring in multi-age flocks. We investigated the relationship between the level of antibodies, as detected by a haemagglutination-inhibition (HI) assay, in infectious coryza-vaccinated chickens and the protection against challenge in those chickens. In one experiment, chickens given a single dose of either of two infectious coryza vaccines lacked a detectable HI response to vaccination but showed significant levels of protection 11 weeks after vaccination. In contrast, in chickens given two doses of an infectious coryza vaccine and challenged 3 weeks after the second vaccine dose, there was a strong serological response with 36/40 birds having a HI titre of 1/20 or greater. In this trial there was an apparent relationship between titre and subsequent protection, with none of the 32 chickens with a titre of 1/40 or 1/80 showing any clinical signs and only one of the same group yielding the challenge organism on culture. In contrast, three of the four vaccinated chickens with a HI titre less than 1/5 developed the typical clinical signs of coryza and yielded the challenge organism on culture. Overall, our results suggest that HI titres cannot be regarded as a definitive predictor of vaccine efficacy. We suggest that the vaccination-challenge trial is the gold standard for the evaluation of the immune response to infectious coryza vaccines.

Evaluation of the Protection Conferred by a Disinfectant Against Clinical Disease Caused by Avibacterium paragallinarum Serovars A, B, and C from Argentina

This work evaluates the efficiency of the administration of the disinfectant N-alkyl dimethyl benzyl ammonium chloride (TIMSEN) in the prevention of the horizontal transmission of serovars A, B, and C of Avibacterium paragallinarum, the causative agent of avian infectious coryza. This disinfectant was administered in drinking water (50 ppm) and once or twice per day by coarse spray (800 ppm, 8 ml per m3 during 3 seconds). In three trials conducted with vaccinated birds, the disinfectant reduced the clinical signs of infectious coryza significantly (P < 0.05). There was no significant effect when the product was used in a fourth trial with unvaccinated birds. Furthermore, the application of only one daily environmental spraying was sufficient to significantly reduce clinical signs. According to these results, in order to diminish the clinical signs of infectious coryza in birds vaccinated against A. paragallinarum, it is recommended to administer this disinfectant in drinking water and by environmental spraying.

Cross-protection study of the nine serovars of Haemophilus paragallinarum in the Kume haemagglutinin scheme

The cross-protection and haemagglutination-inhibition antibodies present in chickens vaccinated with one of the nine currently recognized Kume haemagglutinin serovars of Haemophilus paragallinarum were investigated. The results confirmed the widely accepted dogma that serogroups A, B, and C represent three distinct immunovars. Within Kume serogroup A, there was generally good cross-protection among all four serovars. However, within Kume serogroup C, there was evidence of a reduced level of cross-protection between some of the four serovars. The haemagglutination-inhibition antibody levels generally showed the same trend as with the cross-protection results. This study suggests that some apparent field failures of infectious coryza vaccines may be due to a lack of cross-protection between the vaccine strains and the field strains. Our results will help guide the selection of strains for inclusion in infectious coryza vaccines.