Leptospirosis: pathogenesis and red cell destruction : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Palmerston North, New Zealand
A study was made of the morphological changes in red blood cells (RBC's) from hamsters and calves during the development of haemoglobinaemia following infection with Leptospira interrogans serovars ballum and pomona respectively. The major changes seen by scanning electron microscopy of RBC's from the haemoglobinaemic animals were spherocytosis and surface pitting. The major change seen by transmission electron microscopy was vacuolation of abnormally shaped RBC's with some vacuoles containing a small amount of a fine granular material. Few RBC's showed evidence of haemoglobin loss even though the animals from which the RBC's came were severely haemoglobinaemic. Those RBC's which did show haemoglobin loss contained membrane-bound dense granular inclusions in addition to the vacuoles observed in the fully haemoglobinated RBC's. The spherocytes from the haemoglobinaemic animals probably arose from echinocytes which were seen in prehaemoglobinaemic hamsters. Echinocytes seen in calves injected with 'toxin' can probably be considered as equivalent to echinocytes seen in the prehaemoglobinaemic hamsters. These echinocytes had membrane-bound portions of cytoplasm segregated from the remainder of the cytoplasm. It is thought that these portions of cytoplasm are defective and subsequently become digested in autophagocytic vacuoles with complete digestion resulting in the empty vacuoles or those containing a small amount of fine granular material as seen in the fully haemoglobinated RBC's. Inability of the cell to either fully digest or expel material within autophagocytic vacuoles may explain dense granular inclusions seen within partially haemoglobinated RBC's which are considered the most severely affected RBC's. Present studies support other work that a 'toxin' elaborated by the organisms rather than mechanical damage is responsible for the lesions observed. The original lesion is thought to be biochemical although biochemical studies were beyond the scope of the present work. This biochemical lesion is likely to be similar in all affected tissues. Sufficient biochemical and physiological differences exist between adults and neonates and between individuals of similar age of the same species, and between different animal species to explain the differences in susceptibility of RBC's to leptospiral 'toxins'. RBC's from cattle, hamsters and humans suspended in non-immune plasma and incubated with ballum and pomona were never haemolysed while those suspended in saline were always haemolysed. Normal plasma thus has a protective effect. The protective action of plasma demonstrated in vitro required reconciliation with some conflicting findings of parallel studies in vivo in which RBC's were destroyed resulting in haemoglobinaemia. It therefore appears that another mechanism may be responsible for RBC destruction in vivo. Because RBC sequestration resulting in lowering of the PCV and haemoglobin occurred in the prehaemoglobinaemic animals, involvement of the reticulomacrophage system appeared likely. Other workers have suggested that RBC's which already have an abnormality may be further damaged or lysed within the splenic circulation. Thus in leptospiral infections, leptospiral 'toxins' may induce changes in RBC's leading to their sequestration within the spleen resulting in further damage and ultimately lysis and haemoglobinaemia. The ground is now set for further studies to identify the putative biochemical lesions which would pave the way for development of new therapeutic regimes to prevent the more severe clinical features of the disease.
Content removed due to copyright restriction:
Thompson, J. C., & Pauli, J. V. (1981). Colostral transfer of gamma glutamyl transpeptidase in calves. New Zealand Veterinary Journal, 29(12), 223-226.
Mackintosh, C. G., & Thompson, J. C. (1979). A rapid method for the detection of leptospiraemia. New Zealand Veterinary Journal, 27(10), 224-225.
Mackintosh, C. G., Marshall, R. B., & Thompson, J. C. (1981). Experimental infection of sheep and cattle with leptospira interrogans serovar balcanica. New Zealand Veterinary Journal, 29(1-2), 15-19.