Use of a polymerase chain reaction assay to study response to oxytetracycline treatment in experimental Candidates Mycoplasma haemolamae infection in alpacas

Department of Biomedical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, OR 97331, USA.
American Journal of Veterinary Research (Impact Factor: 1.34). 10/2009; 70(9):1102-7. DOI: 10.2460/ajvr.70.9.1102
Source: PubMed


To develop a PCR assay for Candidatus Mycoplasma haemolamae (CMhl) infection in alpacas and use it to study the efficacy of oxytetracycline treatment and development of a subclinical carrier state.
8 healthy adult alpacas.
Alpacas initially had negative results for CMhl in blood samples via PCR assay and were experimentally infected with CMhl; 4 were treated with oxytetracycline, and 4 were not treated. All were monitored regularly via PCR assay, blood smear examination, PCV, rectal temperature, and physical examination. At 6 months after treatment, all alpacas were immunosuppressed by administration of dexamethasone and tested for CMhl.
7 of 8 alpacas had positive PCR assay results 4 to 6 days after experimental infection. When organisms were detectable on a blood smear, they were seen 2 to 6 days after positive results of PCR assay. Infection was often associated with mild anemia that was usually transient. No alpacas became hypoglycemic. Oxytetracycline treatment was not associated with faster clearance of organisms or resolution of anemia, and 4 of 4 treated alpacas still had positive results of PCR assay when immunosuppressed 6 months later; 0 of 3 nontreated alpacas had positive results of PCR assay following immunosuppression. Transient fever was detected in 3 alpacas during immunosuppression.
The PCR assay was more sensitive than blood smear examination for detection of infection. Clinical signs, anemia, and fever were not necessarily associated with infection. Oxytetracyline administration did not consistently clear CMhl infection. Although treated with oxytetracycline, infected alpacas remained chronic carriers.

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    • "This suggests a component of the dam's immune system is capable of reducing the number of parasites to below the threshold for detection, while producing antibodies specific to this organism. This is also compatible with prior reports (Tornquist et al., 2009, 2011). It is therefore possible that prior infection may provide the immunologic mechanisms necessary to clear infection and protect the newborn that acquires the organism early in life while colostral antibodies are still in circulation. "
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    • "Most recently, a real-time PCR method based on the SYBR Green principle has been published that permits initial screening for suspected hemoplasma infection in a broad range of mammalian species (Willi et al., 2009). The assay described herein allows quantification of bacterial burden with a sensitivity of one copy per 5 ml of blood, which is more sensitive than what had been published for a conventional CMhl PCR assay (Tornquist et al., 2009). The analytical specificity of the CMhl real-time TaqMan 1 PCR assay predicted in silico was confirmed by testing DNA from different hemotropic and non-hemotropic mycoplasma species. "
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