Whether previous exposure to West Nile virus affects the intensity of subsequent Zika virus infection is a possibility that is currently under investigation by researchers at the Texas Tech University Health Sciences Center El Paso (TTUHSC El Paso), El Paso, TX.
"For those who already have been infected with West Nile, there are two possible outcomes," said Anjali Joshi, PhD, infectious disease researcher, TTUHSC El Paso. "The exposure could either help inhibit Zika infection, or make it much worse."
Dr. Joshi and colleague Himanshu Gard, PhD, received a 2-year grant from the National Institute of Allergy and Infectious Diseases (NIAID). They plan to collect blood samples from 500 residents of El Paso and test them for the presence of West Nile antibodies.
They will use these samples to explore antibody-dependent enhancement (ADE), in which the presence of certain antibodies can either fuel or fight a subsequent infection.
ADE occurs in individuals with Dengue, another mosquito-borne virus. First infections of Dengue are usually mild, but subsequent mosquito bites carrying another of the four different strains of Dengue usually lead to more severe symptomatology.
"In Dengue, these preexisting antibodies enhance the uptake of the virus, making the infection more severe and the symptoms worse," explained Dr. Joshi.
The same is not true, however, for tick-borne encephalitis, another viral illness. Initial infection with tick-borne encephalitis actually protects against the Japanese encephalitis virus.
Zika virus is a relative of West Nile virus, and is slowly spreading in the United States. Once enough blood samples are collected, Dr. Joshi and colleagues will assess whether the West Nile antibodies enhance or inhibit subsequent Zika virus infection.
In the case of an enhancing effect, special precautions need to be taken by affected individuals against mosquito bites. If the effects are inhibitory, that is, if West Nile inhibits Zika, vaccine developers may have a particularly good avenue to pursue in developing a vaccine for West Nile virus, because such a vaccine may protect against Zika, and vice versa, said Dr. Joshi.
In a previous study, Dr. Joshi and colleagues found that serum from mice infected with West Nile inhibited cellular infection with Zika virus. These results, however, may not translate to humans, and much study is needed before Zika becomes widespread.
"The El Paso area is endemic to West Nile Virus infection and 80% of people who have been infected are not even aware of the infection. The question is 'How are we going to react to Zika when it arrives? Will Zika follow the same track as West Nile?'" concluded Dr. Garg.