Variant CJD: research

What is the case and genotype background?

The CDC describes variant CJD as a separate and much rarer disease than classic CJD, tied to eating beef from cattle with bovine spongiform encephalopathy. It was discovered in the United Kingdom in 1996, and the CDC reports four United States cases, all in people likely exposed outside the United States. The 2026 Viruses review states that nearly all variant CJD patients are methionine homozygous at codon 129, and that acquired forms including variant CJD are now exceedingly rare because of stronger preventive measures.

How well can blood be tested?

Two 2016 papers in the same issue of Science Translational Medicine set the position.

Bougard and colleagues, working from the Etablissement Francais du Sang with the Paris Brain Institute, the AP-HP CJD unit and the Edinburgh unit, combined plasminogen bead capture with protein misfolding cyclic amplification. In a blinded panel of 256 plasma samples the assay identified 18 clinical variant CJD patients, with 100 percent sensitivity and a 95 percent confidence interval of 81.5 to 100 percent, 99.2 percent analytical specificity and 100 percent diagnostic specificity. It also detected silent carriage in two blood donors who later developed variant CJD, 1.3 and 2.6 years before clinical onset.

Concha-Marambio and colleagues, from the Mitchell Center in Houston with the Besta institute in Milan and the Edinburgh surveillance unit, applied amplification to blood from 14 variant CJD cases against 153 controls that included sporadic CJD patients, other neurological patients and healthy subjects. They reported 100 percent sensitivity and specificity, detection in every blood fraction tested, a requirement of only a few microlitres, and an estimated PrPSc concentration near 0.5 pg per ml. The authors state that further studies are needed for full validation.

The animal work that followed extended the lead time. Concha-Marambio, Chacon and Soto studied 3 macaques peripherally infected with macaque-adapted variant CJD prions against 28 uninfected controls. Prions were detected from the first bleed at 65 days after inoculation, and at every later time point, which was 759 days before clinical onset in two animals and 644 days in the third. On 140 blinded buffy coat samples, 72 from infected animals and 68 controls, per-replicate sensitivity was 95.8 percent with a confidence interval of 88.3 to 99.1 percent, per-replicate specificity was 100 percent, and all 68 control replicates were negative. Grouping replicates by collected sample gave 100 percent for both. Buffy coat outperformed plasma at the preclinical stage: three amplification rounds detected all 3 preclinical buffy coat samples, while only 2 of 3 preclinical plasma samples were positive after four rounds.

Lead times of this length in an experimentally infected primate do not establish the same in a naturally infected person. For what this implies for donor policy, see blood and plasma.

Does RT-QuIC work on blood?

Less well than amplification, on the evidence available. Thomas and colleagues developed a whole blood iron oxide magnetic extraction RT-QuIC assay and compared it with magnetic bead amplification. On a reference human variant CJD brain homogenate, the amplification method reached a 10 to the minus 9 dilution while RT-QuIC reached about 10 to the minus 5 or minus 6. In blood from bovine spongiform encephalopathy infected sheep, their assay was positive in 9 of 12 whole blood samples, and of the eleven whole blood samples corresponding to buffy coats previously positive by amplification, 8 were positive by RT-QuIC. No human blood was tested in that study, and the authors list the small preliminary sheep panel and the need for a larger blinded panel among their limitations, noting that human blood testing depends on strict criteria for releasing human samples.

What does infectivity, as opposed to seeding activity, look like?

Douet and colleagues reported infectivity by bioassay in erythrocytes, leukocytes and plasma from one variant CJD patient, and in the plasma of 2 of 4 patients whose tests were positive for sporadic CJD, describing the levels as comparable to those reported in animals with transmissible spongiform encephalopathies. A seeding assay result and an infectivity result answer different questions, and the infectivity evidence in human blood rests on very few patients.

What is the position on cerebrospinal fluid?

The Montpellier group moved their amplification method to cerebrospinal fluid and reported 40 of 41 clinical variant CJD samples positive, a sensitivity of 97.6 percent, and 0 of 57 non-variant samples positive, where the non-variant group comprised 23 sporadic CJD, 1 genetic CJD and 33 non-CJD samples. The single initial negative was a probable case which tested positive on duplicate retesting. The report states that the work requires a biosafety level 3 laboratory and highly experienced personnel, and it is presented as a research result on a panel of 98 samples rather than a validated clinical test.

What does variant CJD material contribute to decontamination work?

It is the reference material for instrument decontamination. Belondrade and colleagues contaminated stainless steel wires with variant CJD brain homogenate, air dried and treated them, then implanted them intracerebrally in tgBov tg110 mice overexpressing bovine prion protein about six times the physiological level, comparing the outcome with Surf-PMCA on the same treatments.

Three treatments gave no transmission with survival beyond 700 days: 2 percent sodium hypochlorite, 1 N sodium hydroxide and steam at 134 degrees. The water control gave 75 percent transmission. Of six commercial products, one gave no transmission and one gave 10 percent, while the other four gave 90 to 100 percent transmission. The authors note that these products had been approved using hamster assays with a different prion strain, and argue that such approval does not reliably predict efficacy against variant CJD prions. They also note that their wires were air dried while clinical devices are usually moist. Their transgenic human prion protein mice, tg650, had survival times beyond 700 days, which made them unsuitable for measuring decontamination. See decontamination.

Which tissue methods are used?

Schulz-Schaeffer and colleagues described the paraffin-embedded tissue blot, which transfers sections to nitrocellulose, digests with high concentration proteinase K and probes with monoclonal antibodies, so that the distribution of prion aggregates is preserved on archival material. Their paper reports that the method detected prion protein in variant CJD without stating how many variant cases were examined, alongside moderate to strong staining in 42 sporadic CJD cases covering all three codon 129 genotypes and no staining in any of 24 control brains. In mice infected with the ME7 strain it detected faint signal at 30 days after inoculation against 120 days for Western blot, with clinical signs at 177 days.

Which bodies set donor and healthcare policy?

In England the Department of Health and Social Care publishes Minimise transmission risk of CJD and vCJD in healthcare settings, produced by the Advisory Committee on Dangerous Pathogens TSE risk management subgroup, formerly the TSE Working Group. It was first published on 27 November 2012 and last updated on 18 November 2021, and its annexes cover the distribution of infectivity in tissues, decontamination and waste disposal, instrument quarantine, endoscopy, handling of bodies after death, presurgical assessment and ophthalmology. See the ACDP TSE subgroup and the Commission on Human Medicines.

In Germany the Arbeitskreis Blut lists three current prion statements: S 27 of 6 December 2024 on exclusion criteria for blood and plasma donation in relation to variant CJD, an undated statement on the risk of variant CJD transmission by plasma derivatives, and a 2005 statement published in Bundesgesundheitsblatt 9/2005 and posted on 13 September 2005. See Arbeitskreis Blut.

Other bodies with a role in this area are described at ANSM, the Etablissement Francais du Sang, the EDQM, the ECDC, the CEA prion unit, the Besta institute, Catalonia public health, D-Gen and Alliance BioSecure.

The disease group as a whole is set out in disease research, and the assay comparisons in diagnostics research.