A double-molecular beacons (DMB) based assay was developed for porcine circovirus 2(PCV2) detection. Two single-stranded DNA molecular beacons which could specifically hybridize with PCV2 genome DNA respectively in different sequence were designed according to the characteristics of the PCV2 genome sequences. The fluorescence signal was amplified 80 times by DMB, which was 2-4 times higher than that of single molecular beacon. Under the optimal conditions of 10 mmol/L MgCl2 , 20 mmol/L Tris-HCl (pH=8. 0), 40 ℃ and 30 min incubation time of DNA with DMB, the enlargement factor was increased linearly with DNA concentration over the range from 2 nmol/L to 200 nmol/L, with a detection limit of 1 nmol/L. The method was applied to detect PCV2 in genome of 18 swine fever samples and 8 PCV2 positive cases were found, which were confirmed by PCR method.

Objective:To investigate the clinical characteristics of elderly patients with coronavirus disease 2019(COVID-19), in order to provide scientific evidence for the diagnosis and treatment of COVID-19 in elderly patients.Methods:Clinical data of 102 patients with COVID-19 admitted to the B11 East Ward of the Zhongfaxincheng campus and the E1-3 ward of the Guanggu Campus of Tongji Hospital affiliated to Huazhong University of Science and Technology in Wuhan from 1 February 2020 to 28 February 2020 were retrospectively collected and analyzed.Patients were categorized into 2 groups: the elderly group(≥60 years old)and the young and middle-aged group(<60 years old). Differences in epidemiological features, demographics, clinical symptoms, laboratory results and imaging findings between the two groups were retrospectively analyzed.Results:Among 102 patients with COVID-19, 58 were in the elderly group(≥60 years old), with a median age of 67.0(63.8, 71.0)years old, and 44 in the young and middle-aged group(<60 years old), with a median age of 47.5(38.0, 51.8)years old.There was no significant difference in gender ratio between the two groups( χ2=0.033, P=0.855). Of 102 patients, 42.0%(21/50)had close contact with an infected person, 14.0%(7/50)were from infection clusters, and 18.0%(9/50)had suspected hospital-acquired infections.Fever and cough remained the most common symptoms, but gastrointestinal symptoms such as nausea, poor appetite, diarrhea and muscle cramps were also warning signs.Fatigue and cough were the most common presenting symptoms in elderly male patients.Bilateral patchy infiltrates(57.9%, 22/38)and ground-glass opacities(42.1%, 16/38)were the main imaging features and 42.1%(16/38)patients had multiple areas of the lungs involved.Over 50% patients had increased levels of blood glucose, D-dimer, fibrinogen, C-reactive protein, procalcitonin, multiple cytokines and neutrophil-to-lymphocyte ratio, as well as decreased levels of albumin, hemoglobin, hematocrit, lymphocytes and serum calcium.Compared with the young and middle-aged group, the elderly group had higher rates of abnormality in levels of D-dimer and serum calcium( χ2=7.067 and 4.166, P=0.008 and 0.041). Conclusions:Fever and cough are the most common symptoms in elderly patients with COVID-19.Elderly patients with COVID-19 have multiple abnormalities in clinical laboratory test results, which show a certain level of specificity compared with young and middle-aged patients.