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Evaluation of Anaplasma marginale from tick cell culture as an immunogen for cattle
E F Blouin1, J T Saliki, K M Kocan
1Department of Anatomy, Pathology and Pharmacology, College of Veterinary Medicine, Oklahoma State University, Stillwater 74078-2007, USA. blouin@okway,okstate.edu
Abstract:
Anaplasma marginale has been propagated and continuously passaged in an Ixodes scapularis cell line. Anaplasma development was characterized and cultures with a high density of rickettsiae were harvested at a predictable rate. Culture-derived A. marginale (CAM) remained infective for cattle and was used effectively as antigen in diagnostic tests with the sensitivity to identify bovine carriers of A. marginale. This study presents results of an initial trial using the CAM as an immunogen for cattle. CAM was mechanically disrupted, frozen at -70 degrees C, and inactivated with beta-propiolactone. Two intact yearling cattle were immunized with CAM and Freund's adjuvant, receiving 4 subcutaneous injections at 3-4 week intervals. Two control yearling cattle received adjuvant and PBS. Serum samples were evaluated by competitive ELISA (C-ELISA) using CAM as antigen and the standard complement fixation test (CFT). All cattle were subsequently challenged with A. marginale-infected blood from a carrier cow. An additional intact calf was inoculated with live CAM from the same passage and screened by C-ELISA and CFT. Sera collected from immunized cattle were negative or suspicious by CFT throughout the immunization study. The same sera were strongly positive by C-ELISA two weeks after the first injection and throughout the study. All cattle became infected following challenge-exposure with blood, but immunized cattle exhibited longer prepatent periods as well as lower parasitemias and percent reduction of packed cell volumes as compared with the controls. The calf receiving live CAM became infected and underwent a mild clinical reaction with positive C-ELISA and CFT results and did not become clinically ill following blood challenge. This preliminary study suggests that the CAM antigen is highly immunogenic in cattle. Furthermore, the CFT did not identify immunized animals whereas the C-ELISA (using CAM) was highly sensitive for detection of both immunized and infected animals.
Insights
Culture-derived Anaplasma marginale (CAM) proved infective and immunogenic in cattle. CAM antigen shows promise for diagnosing and potentially preventing bovine anaplasmosis, with competitive ELISA being a sensitive diagnostic tool.
Area of Science:
- Veterinary Immunology
- Parasitology
- Cell Biology
Background:
- Anaplasma marginale is a significant cattle pathogen.
- Propagation in Ixodes scapularis cell lines offers a consistent source of Anaplasma marginale.
- Culture-derived A. marginale (CAM) has shown potential as a diagnostic antigen.
Purpose of the Study:
- To evaluate the immunogenicity of CAM as a potential vaccine candidate in cattle.
- To compare the diagnostic sensitivity of competitive ELISA (C-ELISA) and complement fixation test (CFT) for detecting immune responses to CAM.
Main Methods:
- Anaplasma marginale was cultured in an Ixodes scapularis cell line and processed into CAM antigen.
- Cattle were immunized with inactivated CAM and adjuvant, with controls receiving adjuvant and PBS.
- Serum samples were tested using C-ELISA and CFT, followed by challenge with live A. marginale.
Main Results:
- Immunized cattle developed strong positive C-ELISA responses, while CFT results were largely negative or suspicious.
- Following challenge, immunized cattle showed delayed prepatent periods, reduced parasitemia, and less severe packed cell volume reduction compared to controls.
- A calf inoculated with live CAM developed a mild infection and was detectable by both C-ELISA and CFT.
Conclusions:
- Culture-derived A. marginale (CAM) is immunogenic in cattle and may offer protection against clinical disease.
- C-ELISA using CAM antigen is a highly sensitive method for detecting immune responses in both immunized and infected cattle.
- CAM holds potential as a valuable tool for both vaccination and diagnostics in bovine anaplasmosis control.