Anthrax other diagnostic studies: Difference between revisions
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==Overview== | ==Overview== | ||
==Diagnostic Studies== | ==Diagnostic Studies== |
Revision as of 00:28, 17 July 2014
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Overview
Diagnostic Studies
Other studies to diagnose Anthrax infection include:
Test | Initial Findings | Serial Monitoring |
---|---|---|
EKG | Atrial fibrillation with rapid ventricular response | |
Lumbar puncture | At admission unless contraindicated | Headache Confusion Other neurologic symptom If meningitis, meningeal signs will only be present at a later stage |
Other imaging | As relevant to site of exposure Evaluate edema Evaluate inflammation Evaluate necrosis |
For headache, confusion or other neurologic symptom If meningitis, meningeal signs will only be present at a later stage |
Echocardiogram | Evaluate for pericardial effusion Evaluate for myocardial dysfunction |
Hemolysis
B. anthracis was shown to be haemolytic on blood agar made with sheep red cells that had been washed with buffered saline containing calcium and magnesium. Similarly, the anthrolysin is presumably haemolytic. Reports are also occasionally encountered of haemolysis in blood or on agar containing blood of certain species, including human.[1]
Lecithinase
B. anthracis either produces lecithinase to a lesser extent than its close relatives, B. cereus and B. thuringiensis, or produces a lecithinase with a lower activity. In the lecithinase test on egg yolk agar, the zone of opalescence or “halo” almost always seen around colonies or areas of growth of B. cereus and B. thuringiensis is only sometimes visible around B. anthracis, probably only becoming apparent at 48 hours (35-37 °C) and usually in a narrow band when present. Opalescence should be looked for under the colony/area of growth by scraping away some of the colony material. It can be seen here after 24 hours incubation at 35–37 °C. While B. anthracis grows well on conventional egg yolk agar, it grows less well than B. cereus on Kendall’s BC egg yolk-mannitol agar; the growth of B. anthracis on this medium (24–48 hours) is greyish as compared to the deep purple of B. cereus and, in contrast to B. cereus, a zone of opalescence does not form around the growth of B. anthracis. once again, colony material must be scraped away to see the underlying LV (lecithovitellin) reaction.[1]
Motility
Although examination for motility is always listed as one of the primary identification tests for B. anthracis, it is doubtful that the test is often done on new isolates or checked more than rudimentarily and occasionally on culture collection cultures. Certainly, the first obvious appearance for diagnostic test purposes is lack of motility, but in view of the existence of genes associated with motility, and even one recent report that includes electron micrographs showing flagella, perhaps the “absoluteness” of non-motility in B. anthracis should be revisited.[1]
PCR
PCR is becoming more widely available as a means of confirming the presence of the virulence factor (capsule and toxin) genes, and hence that an isolate is, or is not, virulent B. anthracis. For routine purposes, primers to one of the toxin genes (usually the Protective Antigen gene) and to one of the enzymes mediating capsule formation are adequate. In laboratories not equipped for PCR tests, if doubt remains to the definitive identity of a suspect B. anthracis isolate, inoculation into a mouse or guinea-pig may be the only way remaining to determine conclusively if it is virulent B. anthracis. However this should be a last resort procedure and confined to situations where a definitive identification is essential.
References
- ↑ 1.0 1.1 1.2 "Anthrax in Humans and Animals" (PDF).