Agent Of Tick-borne Fever Research Articles

Studies of Anaplasma phagocytophilum in sheep experimentally infected with the human NY-18 isolate: Characterization of tick feeding sites

Anaplasma phagocytophilum, transmitted by ticks of the genus Ixodes, was first described in Scotland as the agent of tick-borne fever in sheep and more recently as the cause of human granulocytic anaplasmosis in the U.S. and Europe. We previously reported sheep as an experimental host for the human NY-18 isolate of A. phagocytophilum. While clinical signs were not observed and infected granulocytes were not seen in stained blood smears, these sheep served as a good host for infection of ticks. In this research we characterized tick feeding sites to better understand tick/host/pathogen interactions. Ixodes scapularis adults were allowed to feed for 2 and 4 days on experimentally infected sheep, after which biopsies were taken beneath tick feeding sites for histopathology, PCR and immunohistochemistry (IHC) studies. In addition, the expression of selected immune response genes was studied in blood and feeding site biopsies. While necrosis was too advanced in 4-day biopsies for accurate cell counts, higher numbers of eosinophils and neutrophils were found in 2-day biopsies from infected sheep as compared with the uninfected controls. An unexpected result was the documentation of higher dermal inflammation in infected sheep at sites without ticks. A. phagocytophilum infected granulocytes were localized by immunohistochemistry (IHC) in skin biopsies using rabbit antibodies against the recombinant A. phagocytophilum major surface protein 4 as the primary antibody for indirect peroxidase-anti-peroxidase and fluorescent antibody IHC. These infected cells are likely to be the source of infection for ticks. Sheep therefore served as good hosts for studying host/pathogen/tick interactions of this human strain of A. phagocytophilum, and provided a means of producing infected ticks for future studies on tick/pathogen developmental and transmission cycles.

Intrauterine infection with Ehrlichia phagocytophila in a cow

An infection with Ehrlichia phagocytophila, the agent of tickborne fever, can cause abortion or stillbirth in cows in late pregnancy but, to the authors' knowledge, there have been no reports...

Purification of Cytoecetes phagocytophila, the causative agent of tick-borne fever, from Infected ovine blood

Cytoecetes phagocytophila, the causative agent of tick-borne fever, was successfully separated by Percoll and Renografin density gradient centrifugation and by cellular affinity chromatography, from the peripheral blood leucocytes of experimentally infected sheep. After centrifugation on Renografin or Percoll density gradients, infectious particles of C. phagocytophila banded at buoyant densities which ranged between 1.063 to 1.140. Rickettsiae separated by wheat germ lectin cellular affinity chromatography retained their morphology but often lost their infectivity. Cell-free C. phagocytophila remained infective to susceptible sheep for 6 months when kept at -114 degrees C in sucrose phosphate buffer with 10 per cent dimethylsulphoxide as a cryopreservative.

Aegyptianella pullorumCarpano 1928—fine structure and taxonomy

Intraerythrocytic granules in the blood of Sudanese fowls first seen by Balfour (1908) were namedAegyptianella pullorumby Carpano (1928).Electron microscopy of a Rhodesian strain ofA. pullorumindicated the similarity between these organisms and theRickettsia-PLT group of organisms, also their dissimilarity to Sporozoa which we have studied. The organism was coccoid or coccobacillary, measuring up to 0·6 μm in diameter, and in longitudinal sections 1·5–3 μm. Pleomorphic and dividing forms were observed. Each organism was surrounded by two unit membranes with short internal invaginations from the inner membrane only. A layer of ribosome-like particles varying in density and depth gave the impression of an outer cortex. Irregular extensions of this layer towards the centre of the organism followed the lines of fine DNA-like filaments forming a web lattice throughout the substance of the organism. There was no well-defined nucleus as seen in Protozoa. Single as well as groups of organisms were situated in vacuoles lined by a membrane similar to the erythrocytes' own outer membrane. No intranuclear organisms were seen.The similarity of these organisms to symbionts studied by Roshdy and Bird in both adult and immature stages ofA. persicusis illustrated. From this evidence, and its apparent likeness to the tick-borne fever agent, there is good reason for includingA. pullorumamong the Rickettsiaceae. The position suggested for it is between theRickettsiaand PLT group of organisms, closely allied toWolbachia, the agent of tick-borne fever (Cytoecetessp.) and the agent of bovine heart water disease (Cowdria ruminantium).We thank Mr R. Jacobson, F.I.M.L.T. for his willing assistance in conducting the sensitivity test, also Miss L. Lanigan and Mr D. Day for their technical and photographic assistance.