The effects of dexamethasone on the response of bronchus-associated lymphoid tissue to intranasal administration of formalin-killed Pasteurella haemolytica A2 in goats

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

BACKGROUND

We investigated the biomarkers, immune responses and cellular changes in vaccinated and non-vaccinated goats experimentally challenged with M. haemolytica serotype A2 under rainy and hot tropical conditions. A total of twenty-four clinically healthy, non-pregnant, female goats randomly allocated to 2 groups of 12 goats each were used for the study. The 12 goats in each season were subdivided into three groups (n = 4), which served as the control (G-NEG), non-vaccinated (G-POS), and vaccinated (G-VACC). In week-1, the G-VACC received 2 mL of alum-precipitated pasteurellosis vaccine while G-POS and G-NEG received 2 ml of sterile PBS. In week 2, the G-POS and G-VACC received 1 mL intranasal spray containing 10⁵ CFU of M. haemolytica serotype A2. Inoculation was followed by daily monitoring and weekly bleeding for eight weeks to collect data and serum for biomarkers and immune responses using commercial ELISA test kits. The goats were humanely euthanised at the end of the experiments to collect lungs and the submandibular lymph nodes tissue samples for gross and histopathological examinations.

RESULTS

Regardless of the season, we have observed a significant (p < 0.05) increase in serum concentrations of acute-phase proteins (haptoglobin, serum amyloid A), proinflammatory cytokines (interleukine-1β, interleukin-6), antibodies (immunoglobulin M, immunoglobulin G), and stress markers (cortisol and heat shock protein 70) in the G-POS goats compared to G-VACC and G-NEG. With regards to seasons, there was a significantly (p < 0.05) higher serum concentration with 1.5, 2 and 1-folds increase in the serum interleukin (IL)-1β, cortisol, and heat shock protein (HSP)-70 in the G-POS during rainy compared to the hot season. Histopathology of the lungs in G-POS goats revealed inflammatory cell infiltration, degeneration, haemorrhage/congestion, and pulmonary oedema in the alveoli spaces; thickening of the interstitium, and desquamation of bronchiolar epithelium. Cellular changes in the lymph node were characterized by a marked hypercellularity in G-POS goats.

CONCLUSION

Host responses to pneumonic mannheimiosis based on increased serum levels of biomarkers (cortisol, HSP70, IL-1β and IL-6) and severe cellular changes seen in the lungs and lymph nodes of G-POS goats compared to vaccinated goats and control group are influenced by the high environmental humidity recorded in the rainy season. Increased relative humidity in the rainy season is a significant stress factor for the higher susceptibility and severity of pneumonic mannheimiosis of goats in the tropics. Vaccination of goats using the alum precipitated Pasteurella multocida vaccine before the onset of the rainy season is recommended to minimise mortality due to potential outbreaks of pneumonia during the rainy season.

Experimental infection of Peste des Petit Ruminant virus and Mannheimia haemolytica A2 in goats: immunolocalisation of Mannheimia haemolytica antigens

Nigerian strain of Peste des Petit Ruminant (PPR) virus and Mannheimia haemolytica (MH) biotype A serotype 2, was used successfully to reproduce a concurrent disease in West African Dwarf goats. The development of the various pathological features were studied at regular intervals following infection. The acute inflammatory reaction which had developed by day 3 after initial infection was characterised by flooding of the alveoli by neutrophils, oedema, hemorrhage and syncytial cells together with a moderate bronchial and bronchiolar epithelial necrosis. This progressed to a milder acute broncho interstitial pneumonia with giant cells. At this stage, the mucosal immunity were well developed especially the aggregate form of NALT and more of nodular forms of BALT. The organisms were demonstrated with strong immunostaining in the necrotic center, necrotic alveolar wall, fibrin, serous exudate, and degenerated leukocyte in the alveoli and respiratory airways. The bacterial antigens were observed as a strong immunostaining in the blood vessels of the nasal septum, sinusoid in the liver and interstium of the kidney, cytoplasm of alveolar macrophages, pneumocytes, bronchial and bronchiolar epithelium, in the monocytes in the blood vessels. These findings confirmed the enhancement of MH tropism especially in the respiratory tract, liver and kidney. It also showed that West african dwarf goats are highly susceptible to the intratracheal combined infection of PPR virus and MH. The fact that the infection induces strong mucosal responses, this phenomenon can be explored in Africa with the use of combined PPR virus and MH intranasal vaccines to curtail the menace of pneumonia associated with the combined infection on field.