Laboratory Diagnosis of Tick-Borne Infections

Advantages/Uses of PCR

July 2010

So, I thought that this case nicely highlights some of the advantages and potential uses of PCR in this setting. First, it allowed for confirmation of the morphologic identification which was made on the conventional blood smear. And this allowed for differentiation between similar appearing organisms, given that Plasmodium falciparum was in the differential diagnosis. Another potential advantage to PCR is that it may allow for detection of low parasitemia that could be missed on a peripheral blood smear. And in general, PCR is more sensitive than peripheral blood smear for detection of intra-erythrocytic parasites.

The use of PCR also fits into the IDSA guidelines that I had mentioned previously, which state that active babesiosis should be diagnosed by the clinical presentation – in this case, viral -like symptoms AND identification of parasites in the blood by either smear or PCR. Now, because patients may have persistent antibodies to babesia from prior exposure, serology alone does not warrant treatment for babesiosis.

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Jump to section:

• Introduction
• Presentation Outline
• Tick-Borne Diseases
• Advantages and Limitations of Conventional Tests
• Molecular Diagnostic Methods Potential Advantages
• Molecular Diagnostic Methods Potential Disadvantages
• Treatment and Diagnostic Recommendations
• Case 1
• Diagnostic Workup
• Representative Image Giemsa-stained Peripheral Blood Smear
• Differential Diagnosis
• Which one is Plasmodium falciparum?
• Main Morphologic Features Table
• Classic Maltese Cross
• Extracellular Forms of Babesiosis
• Side-by-Side Comparison
• Further Workup
• Malaria PCR
• Babesia microti PCR
• Advantages/Uses of PCR
• Potential Disadvantages
• Potential Disadvantages
• Case 2
• Lyme Disease: Diagnostic Approach
• Reported Cases of Lyme Disease, 2008
• Serologic Assay: Test of Choice for Diagnosis of Lyme Disease
• Case 2, Further Workup
• Potential Roles for PCR
• Which Specimens Should be Tested by PCR?
• PCR for Detection of Borrelia burgdorferi DNA in Blood
• Case 3
• Live Tick Image
• Tick Image Close Up
• IDSA Guidelines
• IDSA Guidelines, continued
• Testing of Ticks by PCR
• Case 4
• Tick-Borne PCR Panel
• Diagnostic Tests for HME and HGA
• PCR for Diagnosis of Ehrlichiosis/Anaplasmosis
• Ehrlichia and Anaplasma PCR Assay Graph
• Phylogenetic Tree
• Ehrlichia muris-like Organism
• All Patients with EML had Tick Exposure
• Prevention of Tick-Borne Diseases
• Conclusions
• Conclusions, continued
• Questions?