Investigation 007
What the Slide Cannot Say
Three parasites cause cancer. Nobody is checking for a fourth.
Cancer, found and missed
Iodine in the specimen
Iodine reaches tissue three ways before a pathologist ever sees it, and it kills organisms on contact. Whether that is why parasites go unreported is a different question.
What we are reading
Gathered for the investigation and not yet written up. Each note says what the paper does and does not show.
- Heaselgrave W, Hamad A, Coles S, Hau S. In Vitro Evaluation of the Inhibitory Effect of Topical Ophthalmic Agents on Acanthamoeba Viability.10.1167/tvst.8.5.17 · PMID 31588380
THE central citation for this node, and it says the thing out loud. Testing topical agents against Acanthamoeba cysts and trophozoites, povidone iodine's antiamoebic effect was 'superior to the current diamidines' — and then the clinical warning, verbatim: 'Ophthalmologists should be aware that certain topical anesthetics and ophthalmic preparations containing BAC PRIOR TO SPECIMEN SAMPLING may affect the viability of Acanthamoeba spp. IN VIVO, resulting in FALSE-NEGATIVE RESULTS IN DIAGNOSTIC TESTS.' So the mechanism is documented, in print, in a specialty that looked. NOW THE PART THAT MUST BE SAID IN THE SAME BREATH: the false negative here is in a VIABILITY test — culture. A dead organism does not grow. It is still visible under a microscope. Applying this to histopathology requires an extra step nobody has taken, which is exactly why it is worth naming as an open question rather than a finding.
- Muthukumar V, Shi L, Chai N, Langenbucher A, Becker SL, Seitz B, Orosz E, Stachon T, Kiderlen AF, Bischoff M, Szentmáry N. Efficacy of Off-Label Anti-Amoebic Agents to Suppress Trophozoite Formation of Acanthamoeba spp. on Non-Nutrient Agar Escherichia coli Plates.10.3390/microorganisms10081642 · PMID 36014060
How good an antiparasitic iodine actually is. Eight off-label anti-amoebic drugs tested against four Acanthamoeba isolates in five biological replicates. Only ONE — povidone iodine at 1% — completely suppressed trophozoite formation from drug-challenged cysts, in every isolate, every replicate. Chlorhexidine, miltefosine and dibromopropamidine mostly failed. Iodine is not a mild antiseptic that happens to be near parasites; on this evidence it is the most reliably cysticidal agent on the shelf. Surgical skin prep is 7.5-10% povidone iodine — roughly ten times the concentration tested here.
- Padzik M, Baltaza W, Conn DB, Szaflik JP, Chomicz L. Effect of povidone iodine, chlorhexidine digluconate and toyocamycin on amphizoic amoebic strains, infectious agents of Acanthamoeba keratitis.10.26444/aaem/99683 · PMID 30586959
Corroborates the effect against both a clinical corneal isolate and a laboratory strain, with povidone iodine 'promising' against reference chlorhexidine. Note the co-author: David Bruce Conn of Harvard's Museum of Comparative Zoology, the same parasitologist who wrote the Hymenolepis correspondence in the New England Journal. A small field.
- Mewara A, Khurana S, Gupta S, Munda VS, Singh S, Sehgal R. Diagnostic performance of mini parasep solvent-free faecal parasite concentrator for the diagnosis of intestinal parasitic infections.10.4103/ijmm.IJMM_19_44 · PMID 32003337
The necessary correction to the iodine story, kept on this node so it cannot be quoted without it. Iodine mount is a ROUTINE parasitology stain. Killing an organism and hiding an organism are different operations, and iodine performs the first while assisting the second's opposite.
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