Magnetic iron-nickel sulphides in the Pliocene and Pleistocene marine marls from the Vrica section (Calabria, Italy)

The rock magnetic properties of the late Pliocene and early Pleistocene open-marine marls from the Vrica section in Calabria (Italy) point to magnetic sulphide as the main magnetic mineral and remanence carrier. The maximum blocking temperatures, however, are between 340 and 360°C, which is too high for stoichiometric monoclinic pyrrhotite. Magnetic concentrates of the sediment are rich in iron sulphide grains and iron-nickel sulphide grains. Microprobe observations show that most of the grains are of the order of 1 ~m in size and attached to iron-bearing clay flakes. Microprobe analyses of the sulphides yield a large range of compositions, ranging from pyrite through greigite-pyrrhotite to sulphur-deficient monosulphides, and with Ni contents varying from zero to a few atom percent in the pyrite grains and from zero to as much as 35 atm% in the monosulphides. The high Ni content of many of the grains is extraordinary and has not been reported before in marine sediments. Most of the compositions cannot be directly connected with a known mineral phase. The marine depositional environment of the marls imposes an authigenic origin for the sulphides, and this is supported by several observations. The great number of sulphide grains in the magnetic concentrates suggests that at least one of the sulphide compositions must have a ferrimagnetic structure, possibly the sulphides with a metal to sulphur ratio close to that of monoclinic pyrrhotite, and between 25 and 35% of the Fe replaced by Ni. The Ni substitution could possibly be the cause of the high blocking temperatures

Evaluation of two commercial, rapid, ELISA kits testing or scrapie in retro-pharyngeal lymph nodes in sheep

AIMS: To estimate the number of cases of scrapie that would occur in sheep of different prion protein (PrP) genotypes if scrapie was to become established in New Zealand, and to compare the performance of two commercially available, rapid ELISA kits using ovine retro-pharyngeal lymph nodes (RLN) from non-infected and infected sheep of different PrP genotypes. METHODS: Using published data on the distribution of PrP genotypes within the New Zealand sheep flock and the prevalence of cases of scrapie in these genotypes in the United Kingdom, the annual expected number of cases of scrapie per genotype was estimated, should scrapie become established in New Zealand, assuming a total population of 28 million sheep. A non-infected panel of RLN was collected from 737 sheep from New Zealand that had been culled, found in extremis or died. Brain stem samples were also collected from 131 of these sheep. A second panel of infected samples comprised 218 and 117 RLN from confirmed scrapie cases that had originated in Europe and the United States of America, respectively. All samples were screened using two commercial, rapid, transmissible spongiform encephalopathy ELISA kits: Bio-Rad TeSeE ELISA (ELISA-BR), and IDEXX HerdChek BSE-Scrapie AG Test (ELISA-ID). RESULTS: If scrapie became established in New Zealand, an estimated 596 cases would occur per year; of these 234 (39%) and 271 (46%) would be in sheep carrying ARQ/ARQ and ARQ/VRQ PrP genotypes, respectively. For the non-infected samples from New Zealand the diagnostic specificity of both ELISA kits was 100%. When considering all infected samples, the diagnostic sensitivity was 70.4 (95% CI=65.3-75.3)% for ELISA-BR and 91.6 (95% CI=88.2-94.4)% for ELISA-ID. For the ARQ/ARQ genotype (n=195), sensitivity was 66.2% for ELISA-BR and 90.8% for ELISA-ID, and for the ARQ/VRQ genotype (n=107), sensitivity was 81.3% for ELISA-BR and 98.1% for ELISA-ID. CONCLUSIONS: In this study, the ELISA-ID kit demonstrated a higher diagnostic sensitivity for detecting scrapie in samples of RLN from sheep carrying scrapie-susceptible PrP genotypes than the ELISA-BR kit at comparable diagnostic specificity