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Loyal Parasite: 41-Year-Old Infection

1:00:07 recording · AUTO · 3 speakers

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Brief overview

TWiP 268 covers a 41-year schistosomiasis case and CRISPR screens that pin Cryptosporidium survival on CP23.

  1. Schistosoma mansoni stayed viable for 41 yearsOne swim in Lake Kivu, found by chance on colonoscopy decades later, with worms still producing eggs.
  2. Haploid life cycle makes Cryptosporidium ideal for CRISPROnly one gene copy to disrupt, and repair happens by homologous recombination, so deletions are precise with few off-target effects.
  3. CP23 is essential but not on the surfaceKnockout blocked growth in mice, yet the antigen localises to the pellicle, not the micronemes or sporozoite trails.
Executive Summary AI
  • This is This Week in Parasitism episode 268, recorded on october 24th 2025, with Vincent Racaniello hosting Daniel Griffin from New York and Christina Nowla from Glasgow, plus a reminder about the listener survey on how the show shapes scientific literacy and trust in science.0:00
  • Christina's snippet is a Stalin et al. case report, an uncorrected proof for the Journal of Travel Medicine, titled viable schistosoma mancini infection 41 years after last exposure, found incidentally in a Swiss woman during a routine screening colonoscopy in 2024 that showed granulomas with calcified and non-calcified viable Schistosoma mansoni eggs.6:07
  • Her only exposure was a single swim in Lake Kivu in Rwanda 41 years earlier, she was positive for circulating cathodic and anodic antigen in urine but not blood, consistent with a low worm burden, she tolerated treatment well, and the authors call it the longest documented S. mansoni infection, beating the previous record by three years.9:00
  • The main paper, Targeted CRISPR Screens Reveal Genes Essential for Cryptosporidium Survival in the Host Intestine, published open access in Nature Communications by Watson, Sala and colleagues from the Francis Crick Institute and the Chan Zuckerberg Biohub, improved transfection and vector design, settled on 50 base pairs of homology for recombination, and screened 11 pyrimidine salvage genes, eig15:07
  • A second CRISPR screen of 11 reported vaccine candidates found nine affected fitness, and inducible knockout of immune-dominant antigen 23, CP23, cut growth in culture by 24 hours and completely blocked parasite growth in mice, while imaging placed CP23 in the pellicle rather than the micronemes or sporozoite trails, pointing at gliding motility and reinfection rather than a simple surface antibod47:53
Key Quote
“Oh, my gosh, decades later, you're still not out of the woods.”
— Daniel Griffin13:40
Key Quote
“You can do inducible excision because if you simply cut out a gene with CRISPR, if it's needed, it's going to be lethal and you can't grow them.”
— Vincent Racaniello41:21
Key Quote
“So I think what they demonstrated here is despite previous work showing that this might be a surface antigen, it's actually not localized on the surface at all”
— Christina Nowla51:52