For each individual, blood samples were also taken from the heart or the thoracic cavity on a 1-cm2 Whatman blotting paper. All listed animal procedures were pre-approved by the Direction des Services Vétérinaires of the Herault Department (B 34-169-1 Agreement). PUUV serological screening and viral load quantification In the laboratory, each piece of Whatman blotting paper was placed in 1 ml phosphate-buffered saline. These diluted blood samples were screened for IgG antibodies to Puumala virus (PUUV) using immunofluorescence antibody test (IFAT)
as described in Lundkvist et al. . PUUV load was measured in PUUV seropositive voles using real-time quantitative RT-PCR. Total RNA was extracted from lung tissue samples as PUUV concentration SP600125 in vitro is high compared to other organs . We used TriPure Isolation Reagent (Roche) according to the manufacturer’s PND-1186 nmr instructions. One μg of RNA was used for first-strand cDNA synthesis using RevertAid™ H Minus Kit (Fermentas) with random hexamers. Real-time quantitative PCR was done using a DyNAmo Capillary SYBR Green Quantitative PCR kit (Finnzymes)
with a LightCycler instrument (Roche). The following primers (Oligomer) were used: PUUV-forward 5′-GAG GAT ATA ACC CGC CAT GA-3′, PUUV-reverse 5′-CTG GCT TGC AGT GTG TTT TT-3′. Samples were first normalized against variation in vole lung sample quality and quantity to GAPDH expression with the following primers: GAPDH-forward 5′-ATG GGG AAG GTG AAG GTC G-3′ and GAPDH-reverse Carnitine palmitoyltransferase II 5′-TAA AAG CAG CCC TGG TGA CC-3′. We then provide an absolute quantification for PUUV RNA: PUUV copy numbers (copies per 1 μg of total RNA) were calculated from a standard curve created using 10-fold dilutions of in vitro transcribed PUUV S segment RNA (T7 transcription kit, Fermentas). Melting curve analysis was performed according to recommendations of the DyNAmo kit to confirm the specificity of positive samples. Samples were considered PUUV RNA positive when the C T (cycle threshold) value was lower than 40 cycles and
the melting curve showed a specific product. Statistical analyses A logistic regression was first applied to determine vole individual characteristics that best explained PUUV infection. The dependent variable was the presence/absence of anti-PUUV antibodies in voles. Sex, sexual maturity, mass, body condition, Silmitasertib purchase landscape and site nested within landscape were included as independent variables. All possible two way interactions were considered. Model selection was performed using the Akaike’s Information Criterion [AIC, [36, 37]]. The model with the lowest AIC value was viewed as the most parsimonious one, i.e. the one explaining most of the variance with the fewest parameters . Nested models with difference of AIC <2 compared to the model with the lowest AIC were selected.