Second round of an interlaboratory comparison of SARS-CoV2 molecular detection assays used by 45 veterinary diagnostic laboratories in the United States

The COVID-19 pandemic presents a continued public health challenge. Veterinary diagnostic laboratories in the United States use RT-rtPCR for animal testing, and many laboratories are certified for testing human samples; hence, ensuring that laboratories have sensitive and specific SARS-CoV2 testing methods is a critical component of the pandemic response. In 2020, the FDA Veterinary Laboratory Investigation and Response Network (Vet-LIRN) led an interlaboratory comparison (ILC1) to help laboratories evaluate their existing RT-rtPCR methods for detecting SARS-CoV2. All participating laboratories were able to detect the viral RNA spiked in buffer and PrimeStore molecular transport medium (MTM). With ILC2, Vet-LIRN extended ILC1 by evaluating analytical sensitivity and specificity of the methods used by participating laboratories to detect 3 SARS-CoV2 variants (B.1; B.1.1.7 [Alpha]; B.1.351 [Beta]) at various copy levels. We analyzed 57 sets of results from 45 laboratories qualitatively and quantitatively according to the principles of ISO 16140-2:2016. More than 95% of analysts detected the SARS-CoV2 RNA in MTM at ≥500 copies for all 3 variants. In addition, for nucleocapsid markers N1 and N2, 81% and 92% of the analysts detected ≤20 copies in the assays, respectively. The analytical specificity of the evaluated methods was >99%. Participating laboratories were able to assess their current method performance, identify possible limitations, and recognize method strengths as part of a continuous learning environment to support the critical need for the reliable diagnosis of COVID-19 in potentially infected animals and humans.     

Generalized marker regression and interval QTL mapping methods for binary traits in half-sib family designs

A Generalized Marker Regression Mapping (GMR) approach was developed for mapping Quantitative Trait Loci (QTL) affecting binary polygenic traits in a single-family half-sib design. The GMR is based on threshold-liability model theory and regression of offspring phenotype on expected marker genotypes at flanking marker loci. Using simulation, statistical power and bias of QTL mapping for binary traits by GMR was compared with full QTL interval mapping based on a threshold model (GIM) and with a linear marker regression mapping method (LMR). Empirical significance threshold values, power and estimates of QTL location and effect were identical for GIM and GMR when QTL mapping was restricted to within the marker interval. These results show that the theory of the marker regression method for QTL mapping is also applicable to binary traits and possibly for traits with other non-normal distributions. The linear and threshold models based on marker regression (LMR and GMR) also resulted in similar estimates and power for large progeny group sizes, indicating that LMR can be used for binary data for balanced designs with large families, as this method is computationally simpler than GMR. GMR may have a greater potential than LMR for QTL mapping for binary traits in complex situations such as QTL mapping with complex pedigrees, random models and models with interactions.     

Effects of recombinant porcine somatotropin on metabolic rate in growing pigs

Effects of recombinant porcine somatotropin (rpST) on metabolic rate were studied in two trials with 24 crossbred barrows (Yorkshire x Landrace) in each. The barrows weighed about 80 kg (SE within trials 2.2 kg) at the start of the measurements and in each trial 12 pigs received 4 mg of rpST and 12 received a placebo. The diet contained 2.57 Mcal NE/kg and 20% CP (about 1% lysine). Animals were fed approximately 2.8 times maintenance (280 kcal ME.kg-.75.d-1). Heat production (gaseous exchange of CO2 and O2) and activity were measured continuously. Heat production associated with activity was calculated from the regression of heat production on activity. Animals treated with rpST exceeded controls in rate of gain by 252 g/d (P less than .001) and in metabolic rate by 14.5 kcal.kg-.75.d-1 (P less than .01). The rpST treatment increased rectal (+ .2 degrees C) and surface (+ .8 degrees C) temperatures. Activity-related heat production in treated pigs was increased, but this was only partly related to the increase in metabolic rate with rpST. The daily patterns of total and activity-related heat production were similar between pigs in both experimental treatments.     

Plasma levels of prostaglandin F2 alpha metabolite and progesterone in repeat breeder heifers.

A detailed clinical-endocrine investigation was performed in 6 repeat breeder heifers (RBH) with the aim being to ascertain whether endocrine asynchronism exists at luteal regression and during early pregnancy. The heifers were first studied during an open cycle and then after insemination when 3 heifers became pregnant. Circulating plasma levels of PGF2 alpha metabolite were measured every 2nd h, while progesterone (P4) levels were measured every 6th h. The oestrous period and intervals between the onset of oestrus and ovulation were relatively longer, compared with what is normally seen in heifers. Plasma levels of P4 at the onset of oestrus were higher than normal, but it was concluded that the plasma levels of PGF2 alpha metabolite and P4 in RBH at luteal regression and early pregnancy were normal.     

Pharmacokinetics of chloramphenicol in calves during the first weeks of life

The pharmacokinetics of chloramphenicol, either administered as the monosuccinate ester or as a veterinary formulation, were studied in calves from the first day of life to the age of 10–12 weeks and compared with the results obtained in adult cattle. (1) After intravenous injection of 0.15 mmol/kg chloramphenicol monosuccinate, the plasma elimination half life of intact ester fell from a value of 33 min on the first day of life to 15 min at the age of 10–12 weeks (value in cows = 14 min). Free chloramphenicol reached maximal plasma concentrations after 2–3 h on the first day of life, but in less than 15 min in cows. The elimination half-life fell from about 15 h on day 1 to 4.8 h at the age of 10–12 weeks (4.2 h in cows). The bioavailability of the ester was more than 90% on Day 1, but declined to 50–60% from Day 7 on account of rapid renal excretion: 21–28% of the total dose was excreted as intact ester in a 2 h period following injection in calves aged 10–12 weeks. (2) The veterinary formulation of chloramphenicol proved toxic when administered intravenously at a dose of 0.15 mmol/kg, and even a dose of 0.093 mmol/kg was less well tolerated than 0.15 mmol/kg of the monosuccinate ester. (3) The pharmacokinetics of chloramphenicol fitted an open two-compartment model, the half-life of the elimination phase corresponded well to the values determined in the experiments with the monosuccinate ester. (4) The intramuscular injection of 0.15 mmol/kg of the ester or 0.093 mmol/kg of chloramphenicol provided ‘therapeutic’ plasma concentrations (≥ 5 μg/ml) within 15–30 min and for about 24 h in calves aged 7 days. (5) Chloramphenicol crossed the placenta when given to cows shortly before a Caesarian section, but equilibrium was not reached within 50–100 min. (6) The binding of chloramphenicol to serum proteins was dependent both on total protein and drug concentrations. It rose from less than 30% on day 1 to about 40% in adult cattle. (7) Recommendations for a dosage regime for chloramphenicol in calves are made on the basis of the pharmacokinetic data.     

Critical night length for bud set and its variation in two photoperiodic ecotypes of Betula pendula

We studied the variation in critical night length for bud set in two photoperiodic ecotypes (two latitudinally distant stands) of silver birch (Betula pendula Roth) in three phytotron experiments. Seeds from 21 open-pollinated mother trees in a southern (Tuusula, 60 degrees N) and a northern (Kittil?, 67 degrees N) Finnish stand were germinated and grown for 4 weeks in a 24-h photoperiod in a greenhouse and then moved to different night length treatments at 18 degrees C for 4 to 6 weeks. Night lengths from 5 to 8.5 h were used for southern origin seedlings and from 1 to 4.5 h for northern origin seedlings. At the end of the treatments, apical bud set was observed and the percentage of seedlings with bud set calculated for each treatment and tree progeny. The critical night lengths (CNL) for 50% bud set were determined separately for seedlings from each mother tree by regression analysis. In both ecotypes, the mean percentage of seedlings with bud set was lowest for the shortest night lengths and increased rapidly as night lengths increased. Mean CNL with its 95% confidence interval for the southern and northern ecotypes was 6.3 +/- 0.2 and 3.1 +/- 0.3 h, respectively. The CNL of the two ecotypes differed significantly in three experiments. Within-ecotype variance of the CNL was significantly higher in the northern ecotype (0.484) than in the southern ecotype (0.150). Significant differences in CNL were detected between individual mother trees of the southern ecotype, but not between mother trees of the northern ecotype. The ranking of individual mother trees, based on CNL, differed in the three experiments.     

Swinepox--skin disease with sporadic occurrence

Swinepox virus infection results in an acute, mild or subclinical course and is characterised by typical poxvirus skin lesions in affected pigs. Additionally, sporadic vertical swinepox virus transmission leads to congenital generalised infection and subsequent abortion or stillbirth. The present report describes the occurrence of epidermal efflorescences in two piglets after intrauterine natural suipoxvirus infection. No clinical abnormalities of the gilt and littermates as well as in other pigs from this herd were present. One of the affected piglets was stillborn and submitted for necropsy, the other animal was alive at birth, but died 3 days later. Histologically, a proliferative to ulcerative dermatitis with epithelial ballooning degeneration and characteristic intracytoplasmatic inclusion bodies was observed. The pathomorphological and histopathological suspected diagnosis of a poxvirus infection was confirmed by electron microscopy. Furthermore, the agent was identified as suipoxvirus by polymerase chain reaction. As demonstrated here, obvious skin lesions in suipoxvirus infection leads to a suspected diagnosis in newborn piglets on macroscopic examination. However, further post mortem examinations, including electron microscopy as well as molecular techniques are essential for the identification of the aetiology and the exclusion of differential diagnoses. Because the disease only affected two pigs there was only a small economic loss. A valid diagnostic plays an important role in advising farmers and for herd health monitoring.