The mosquito-borne viruses, Zika and dengue fever, plague developing countries around the world. Dengue can cause hemorrhagic fever, and Zika can lead to devastating congenital neurological defects. Properly diagnosing a patient with one of these infections is challenging, however, because the viruses are closely related.
Flavivirus nonstructural 1 (NS1) protein, the viral protein commonly targeted by antibody-based diagnostic tests, has approximately 70% sequence similarity between Zika and dengue viruses, says Kimberly Hamad-Schifferli, an engineer at University of Massachusetts, Boston. “It’s very hard to make antibodies that can distinguish between them.”
To tackle this problem, Hamad-Schifferli and Lee Gehrke, an immunobiologist at MIT and Harvard University, led a 53-person international team to develop a simple dipstick test that uses pairs of antibodies to sandwich NS1, allowing the scientists to distinguish between the two viruses (Sci. Transl. Med. 2017, DOI: 10.1126/scitranslmed.aan1589).
The team generated hundreds of antibodies against the NS1 protein using animal and cell models and then tested hundreds of antibody pairs to determine which combinations would be most sensitive and specific to the dengue and Zika viral proteins. The top pairs were used in the dipstick tests.
In the assay, gold nanoparticles tagged with one antibody bind to viral proteins in patient serum. The dipstick, coated with a second virus-specific antibody, wicks up the serum. In roughly 15 minutes, the virus protein is “sandwiched” between the two antibodies and the tagged gold nanoparticles accumulate on a test area on the dipstick, creating a red spot. The team confirmed the accuracy of these tests using serum samples from dengue and Zika patients from North and South America and India.
“This is an excellent piece of work,” comments Shamala Devi Sekaran, an immunologist at the University of Malaysia. “It certainly is very impressive, and they managed to evaluate a number of samples from different geographical areas, albeit not all.”
In addition to expanding the pool of clinical Zika and dengue samples, the team hopes to use the new method to develop rapid tests for other mosquito-borne diseases.