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Interactions between avian phagocytic leukocytes and microbiological agents associated with avian tenosynovitis

Mills, Jennifer Noreen (1990) Interactions between avian phagocytic leukocytes and microbiological agents associated with avian tenosynovitis. PhD thesis, Murdoch University.

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Tenosynovitis in commercial poultry in Australia was previously hypothesised to be due to a primary subclinical or mild clinical infection with avian reovirus which predisposed to a secondary staphylococcal infection, particularly by Staphylococcus aureus, resulting in severe clinical disease. The principle objectives of the studies reported in this thesis were to determine if one possible mechanism whereby avian reovirus infection could predispose to a secondary bacterial infection was by suppression of the phagocytic or bactericidal activity of leukocytes, and if there was any correlation between the virulence of staphylococci isolated from chickens with tenosynovitis and the phagocytic or bactericidal activity of leukocytes for these staphylococci.

The investigation included a study of two pathogenic and two non-pathogenic strains of staphylococci and four strains of avian reovirus representing the four antigenic types of avian reovirus detected in Australia.

Techniques were developed to separate heterophils from the peripheral blood of chickens, and to assess the functional activity of these cells. A simple and reproducible procedure using a Percell density gradient was developed which provided fractions containing 96.9% and 99.8% heterophils of 96% to 98% viability with some contaminating erythrocytes. The heterophil function tests which were developed were the phagocytosis of staphylococci and latex beads, the bactericidal activity against staphylococci, and heterophil adherence to nylon fibres: the heterophils purified by Percell density gradient centrifugation were found to be capable of these functions.

A method was also developed for the culture of adherent mononuclear cells {MN) from both peripheral blood and bone marrow. The function of these cultured adherent MN was assessed by the phagocytosis of S. aureus and latex beads.

A comparison was made of the bactericidal activity of heterophils against two pathogenic and two non-pathogenic strains of staphylococci which had been isolated from chickens with tenosynovitis. All strains were killed by heterophils but one of the two non-pathogenic strains, S. aureus strain 1333, was killed at a faster rate than the other strains. Rapid destruction of this strain was also detected when it was added to whole blood and occurred. in a dose-dependent manner when it was added to lysed heterophils, indicating that the bactericidal activity was due to exposure to a component of the heterophils and did not require viable heterophils. The rapid killing of strain 1333 by heterophils was considered to be a probable cause of the lack of pathogenicity of this strain in normal chickens. In contrast, the other non-pathogenic strain, S. hyicus strain 1609, was the most resistant to heterophil-mediated killing. Compared to the results obtained with heterophils, both the non-pathogenic bacterial strains were found to be phagocytosed by cultured adherent MN to a lesser extent than the pathogenic strains, indicating that in normal chickens these cells were not responsible for the lack of pathogenicity of the two non-pathogenic strains of staphylococci examined. It was concluded that the lack of pathogenicity of S. hyicus strain 1609 in normal chickens was not related to its comparative destruction by either heterophils or adherent MN in vitro, and was likely to be due to other intrinsic properties of this strain.

The replication of avian reovirus was investigated in various types of peripheral blood and lymphoid tissue cells. Replication of avian reovirus was not detected in heterophils, thrombocytes or Band T lymphocytes. The phagocytic and bactericidal activity of heterophils and the adherence of heterophils to nylon fibres also were not affected by reovirus infection. It was concluded that avian reoviruses were unlikely to modify the bactericidal activity of heterophils for staphylococci. However, replication of all four strains of avian reovirus was detected in cultured MN of bone marrow and peripheral blood origin and resulted in lysis and fusion of the infected cells. The avian reovirus strain of antigenic type A and the RAM-1 strain replicated in a higher percentage of these cells than the strains of antigenic type Band C, indicating the existence of strain variation in the capacity of avian reoviruses to replicate in MN. Reovirus infection of cultured MN impeded their phagocytic function, but no indirect suppression of phagocytosis by uninfected cultured MN was caused by cytokines released from the infected cells. Assuming the behaviour of cultured adherent MN is analogous to MN in vitro, these results indicate that reovirus infection would reduce the phagocytosis of both pathogenic and non-pathogenic strains of staphylococci by MN and could predispose chickens to infection by staphylococci.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Veterinary Studies
Supervisor(s): Wilcox, Graham
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