Biomarkers, immune responses and cellular changes in vaccinated and non-vaccinated goats during experimental infection of M. haemolytica A2 under tropical conditions

Stimulating immunoglobulin response by intramuscular delivery of exopolysaccharides-adjuvanted mannheimiosis vaccine in goats

Background and Aim

Pneumonic mannheimiosis (PM) is a common respiratory bacterial disease among small ruminants. Despite numerous management methods, vaccination remains a suitable strategy to combat or reduce PM in goats and sheep. Thus, a study was conducted in Malaysia to evaluate the immunogenicity of exopolysaccharide-adjuvanted Mannheimia haemolytica A2 vaccine (EPS-MHA2) under laboratory and field conditions for its potential use as an efficient vaccine against PM.

Materials and Methods

This study induced immunoglobulin (Ig) responses following intramuscular (IM) delivery of the EPS-MHA2 vaccine on 12 goats for about 7 months. Goats were divided into three groups, with three goats per group, and they were vaccinated intramuscularly as follows: Group 1 was vaccinated with an adjuvanted vaccine prepared from formalin-killed M. haemolytica serotypes A2 and EPS excipient; Group 2 was vaccinated with formalin-killed M. haemolytica seed only, whereas Group 3 was injected with phosphate-buffered saline (PBS) as the negative control. Measures of specific immunity included serum IgM, IgG, and IgA as well as bronchoalveolar lavage fluid secretory IgA and the size and number of the bronchus-associated lymphoid tissue (BALT).

Results

From the 1^st day of vaccination, Groups 1 and 2 showed a significant (p < 0.05) increase in serum IgM, IgG, and IgA levels. However, the antibodies started to decline 5-week post-vaccination, indicating that the booster dose was necessary. On the second exposure to the same vaccine (booster), the level of antibodies showed a significant increase (p < 0.05), particularly IgG. All groups were challenged intratracheally by virulent MHA2 2 weeks after the decline of second antibodies on the administration of booster. All goats were euthanatized and necropsied 4-week post-challenge. The number and size of the BALT in Group 1 goats significantly increased compared with those in Group 2 and the unvaccinated control. Bacteriological parameters were evaluated, in which MHA2 was reisolated successfully from lung samples in Group 3. The IgA level produced by the group vaccinated with EPS-MHA2 was significantly (p < 0.001) higher than that the MHA2 vaccine and PBS groups. All data obtained were analyzed statistically using a one-way analysis of variance. The results indicate that IM injection of EPS-MHA2 vaccine significantly enhanced the immune response against MHA2.

Conclusion

Therefore, the addition of EPS to MHA2 (EPS-MHA2 vaccine) can effectively protect goats from lethal mannheimiosis infection. Factors such as the ideal concentration of EPS should be further studied to verify its application potential as a vaccine adjuvant, and the extraction of EPS from different microalgae species should be further investigated. This study showed a novel and exciting set of data and a vaccination system, in which the suppressive effects of mannheimiosis may be further investigated.

Seminal and histopathological alterations in bucks challenged with Mannheimia haemolytica serotype a2 and its LPS endotoxin

Pneumonic mannheimiosis is a widespread respiratory bacterial disease of small ruminants caused by Mannheimia haemolytica serotype A2. The disease is known to affect the respiratory organs of infected animals, but its effect on other vital and reproductive organs has not been fully explored. Previous studies have demonstrated increased serum pro-inflammatory cytokine concentration post-challenge with M. haemolytica A2 and its LPS, indicating systemic inflammation in the host. This study determined the potential tissue changes and alterations of sperm parameters due to infection of M. haemolytica A2 and its LPS endotoxin. In this study, twelve experimental bucks were randomly assigned to three groups of four bucks each: group 1 (control group) were intranasally inoculated with 2 mL of PBS pH 7.0, group 2 received 2 mL of 1.2 × 10⁹ CFU/mL M. haemolytica A2 intranasally, and group 3 received 2 mL of LPS extracted from 1.2 × 10⁹ CFU/mL of M. haemolytica A2 intravenously. Semen samples were collected at pre-determined intervals using an electro-ejaculator and analysed immediately after collection. All experimental bucks were slaughtered via exsanguination on day 60 to collect their vital and reproductive organs at necropsy, and the samples were processed and analysed for histopathological changes. The current study has revealed that bucks challenged with M. haemolytica A2 and its LPS exhibited alterations in semen parameters such as motility, wave pattern, viability, and morphological abnormalities. Mild to moderate histopathological changes of the lung, liver, testis, epididymis, vas deferens, prostate, and lymph nodes were also observed in both challenged groups. Therefore, this study revealed the potential harmful effects of respiratory mannheimiosis on the reproductive organs of the infected bucks and sheds light on the expanse of systemic effects of this disease.

Responses of selected biomarkers, female reproductive hormones and tissue changes in non-pregnant does challenged with Mannheimia haemolytica serotype A2 and its outer membrane protein (OMP) immunogen

BACKGROUND

Mannheimia haemolytica causative agent of pneumonic mannheimiosis, a common respiratory disease of goat and sheep, which cause huge economic losses to farmers worldwide. Pneumonic mannheimiosis caused by M. haemolytica serotype A2 has been reported among small ruminants in Malaysia. The lipopolysaccharide (LPS) and outer membrane protein (OMP) are major virulence determinants for M. haemolytica serotype A2. Although pneumonic mannheimiosis is known to cause poor reproductive performance in small ruminants under field conditions, there is a dearth of published information on the specific effects of M. haemolytica serotype A2 infection on the female reproductive physiology. In this experiment, we explored the impact of M. haemolytica serotype A2 and its OMP immunogen on selected pro-inflammatory cytokines, acute phase proteins, female reproductive hormones, and cellular changes in visceral and female reproductive organs of non-pregnant does.

METHODOLOGY

Twelve healthy, non-pregnant, Boer crossbreds does were divided equally into three groups (n = 4); Group 1 served as the negative control and was challenged with 2 ml of sterile PBS intranasally. Group 2 served as the positive control and was challenged with 2 ml of 10⁹ colonies forming unit (CFU) of M. haemolytica serotype A2 suspension intranasally. Group 3 was challenged with 2 ml of OMP extracted from 10⁹ CFU of M. haemolytica A2 intramuscularly. The experimental does were monitored for clinical signs and responses periodically. Blood samples were collected at 0, 1, 2, 4, 6, 12 and 24 h and 3, 7, 21, 35 and 56 days post treatment for serological analyses. All does were euthanised using the halal slaughter method on day 60 post challenge/treatment. Tissues from the uterus, liver, lung and associated bronchial lymph nodes were collected and fixed in 10% formalin for 14 days for histopathological study.

RESULTS

Compared to the control group, the challenged/treated groups showed significant (p < 0.05) increase in the rectal temperature, respiratory rate, heart rate, and rumen motility. Serum analyses revealed that the concentrations of progesterone and estrogen hormones were significantly (p < 0.05) decreased in groups 2 & 3. In contrast, the concentrations of pro-inflammatory cytokines (IL-1β and IL-6) and acute phase proteins (Hp and SAA) were significantly increased (p < 0.05) in the challenged/treated groups compared to the control group. Histopathological lesion scoring revealed mild to moderate cellular changes characterised by congestion, haemorrhage, degeneration, leucocytic cellular infiltration, and cellular necrosis in the tissues of does from the OMP treatment and bacterial challenge groups compared to the control group.

CONCLUSION

The findings from this study suggests that M. haemolytica serotype A2 and its OMP immunogen induced mild to moderate inflammatory and degenerative changes which may potentially interfere with fertilization through hormonal imbalances and cause temporary loss of fertility in infected does.