New ‘dipstick’ test for Zika, dengue

October 11, 2017

A fast and cost-effective new dipstick test for Zika virus can distinguish between it and dengue viruses without cross-reactivity, according to a report in Science Translational Medicine. Also, results of a new randomized controlled trial-the largest of its kind to date-suggest that text messaging may help some pregnant women quit smoking.

A fast and cost-effective new dipstick test for Zika virus (ZKV) can distinguish between it and dengue viruses (DENV) without cross-reactivity, according to a report in Science Translational Medicine. The diagnostic also is an advance, said the developers, because it can detect viral proteins at far lower concentrations than commercially available assays (4 to 21 ng/mL versus 75 to 150 ng/mL).

Because ZKV and DENV have homologous proteins and nucleic acids, molecular, antigenic and serologic diagnostic tests for them can be associated with cross-reactions and false-positive results. The developers of the new test, Bosch and colleagues, report that the strips showed serotype-specific signals that were statistically distinct (P < 0.001). Images of the strips were captured with a mobile phone camera and automated image recognition and processing was used to objectively quantify the authors’ data.

To develop the dipstick, the researchers characterized monoclonal antibody pairs and translated them into rapid immunochromatography tests that would specifically detect the viral nonstructural 1 (NS1) protein antigen and distinguish the 4 DENV serotypes (DENV1-4) and ZIKV without cross-reaction. The immunochromatography tests were validated in de-identified serum samples of patients from Brazil, Mexico, Colombia, Panama, Guatemala, and India. The samples had been drawn from febrile patients during routine care and frozen. Before the new tests were used on the samples, the sera were validated with reverse transcriptase polymerase chain reaction (RT-PCR), and ELISA was also used on positive tests.

Using a 30-µL serum sample, the sensitivity and specificity of the DENV1-4and the pan-DENV test, which detects all 4 dengue serotypes, ranged from 0.76 to 1.00. Sensitivity and specificity of the ZIKV rapid test were 0.81 and 0.86, respectively, using a 150-µL serum input. Serum ZIKV NS-1 protein concentrations were about 10-fold lower than corresponding DENV NS1 concentrations in infected patients; moreover, ZIKV NS1 protein was not detected in PCR-positive patient urine samples. The rapid tests detected DENV NS1 at 2 to 5 days after onset of symptoms and the ZIKV NS1 rapid test detected ZIKV NS1 at days 2 to 8.

The researchers said the current cost for each test strip is $5, largely because they involve use of commercial gold nanoparticles and small-scale antibody production. They believe the cost of the nanoparticles can be “decreased by 1000-fold by using laboratory-made nanoparticles that have excellent performance” and say that cost will be lowered further by scale-up of antibody production.

The authors noted that the testing they have described is effective only for analysis of samples collected during the acute phase of virus infection, before the virus is cleared by the immune system. Their approach and reagents, they said, “have immediate application in differential clinical diagnosis of acute ZIKV and DENV cases, and the platform can be applied toward developing rapid antigen diagnostics for emerging viruses.”

NEXT: Text messages and smoking cessation in pregnancy

 

Text messages and smoking cessation in pregnancy

Results of a new randomized controlled trial (RCT)-the largest of its kind to date-suggest that text messaging may help some pregnant women quit smoking. The findings point to the best outcomes in the second and third trimesters and in women at least 26 years old.

Published in the American Journal of Preventive Medicine , the data are from an RCT designed to determine whether Quit4baby, an interactive and intensive text messaging program, would promote smoking cessation in pregnant women already enrolled in the Text4baby health text messaging program.

Recruitment for the study was done by sending nearly 40,000 text messages between July 2015 and February 2016 to Text4baby subscribers. A total of 497 women were randomized, 250 to the Text4baby and Quit4baby messages and 247 to only Text4baby as controls.

Quit4baby was adapted from a program for adult smokers call Text2Quit and its messages describe expected outcomes of quitting smoking for mother and baby and getting support from an ex-smoker “quitpal.” Text4baby sends 3 weekly health texts timed to a woman’s due date, and 6 of its standard messages are on smoking cessation. Text4baby has more than 1 million enrollees and is endorsed by a network of partners including the Centers for Disease Control and Prevention and the American College of Obstetrician and Gynecologists.

The primary outcome of the RCT was 7-day biochemically confirmed point prevalence abstinence at 3-month follow-up, defined as a self-report of no smoking in the past 7 days on the 3-month survey and a cotinine level ≤ 13 ng/mL from a saliva sample.

At 1 month, not smoking in the past 7 days was reported by 28.8% of the intervention group and 15.79% of the control group (P < 0.01); at 3 months, the percentages were 35.20% and 22.67%, respectively (P < 0.01). Biochemical verification of smoking status at 3 months showed no significant differences (P = 0.13) but significant differences favoring use of the intervention in older smokers and in the second or third trimester were seen (both P < 0.05).  Self-report of late pregnancy 7- and 30-day point prevalence abstinence favored the intervention group (P < 0.001, P < 0.01). At 6-month follow-up and postpartum, no significant differences were observed.   

The authors believe the study’s findings “could have clinical importance in large samples” because they point to “the program’s ability to replicate some of the elements of intensive in-person counseling previously found to be effective with pregnant smokers.” Timing of the invitation to quit smoking, they said, is important and they recommend future research on “understanding the optimal timing of the smoking cessation offer, the value of repeated offers throughout pregnancy, and how to assist smokers of all ages.”