Zika may be a step away from dangerous outbreak

US researchers have found that Zika virus can mutate to become more infective - and potentially break through pre-existing immunity.

The finding is in line with the warning issued by the World Health Organisation (WHO), earlier this month. The global health agency warned that the next pandemic could be triggered by insect-borne pathogens, including Zika and dengue.

Researchers from La Jolla Institute for Immunology (LJI) in the US, identified new mutation -- called NS2B I39V/I39T mutation.

It was found to boost the virus's ability to replicate in both mice and mosquitoes. This Zika variant also showed increased replication in human cells.

"The world should monitor the emergence of this Zika virus variant," said Professor Sujan Shresta from La Jolla Institute for Immunology (LJI) in the US, who showed how Zika virus naturally evolves as it encounters more hosts.

Zika virus, which is carried by mosquitoes, caused a global medical emergency in 2016, with thousands of babies born with birth defects such as microcephaly after their mothers became infected while pregnant.

In the study published in the journal Cell Reports, the team recreated infection cycles that repeatedly switched back and forth between mosquito cells and mice.

The researchers found it is relatively easy for Zika virus to acquire a single amino acid change that allows the virus to make more copies of itself - and help infections take hold more easily.

"This single mutation is sufficient to enhance Zika virus virulence," said Jose Angel Regla-Nava, Associate Professor at the University of Guadalajara in Mexico.

"A high replication rate in either a mosquito or human host could increase viral transmission or pathogenicity - and cause a new outbreak."

Zika virus and dengue virus tend to overlap in many countries worldwide. Like Zika, dengue virus is a mosquito-borne flavivirus, and thus shares many biological properties.

Further, Shresta noted that in areas where Zika is prevalent, a vast majority of people have already been exposed to dengue virus and have both T cells and antibodies that cross-react.

According to the WHO, dengue fever infects 390 million people in the 130 countries annually where it is endemic, while Zika virus has been detected in at least 89 countries.

In fact, the viruses are similar enough that the immune response sparked by prior dengue exposure can offer protection against Zika.

But unfortunately, "the Zika variant that we identified had evolved to the point where the cross-protective immunity afforded by prior dengue infection was no longer effective in mice", Shresta said.

Thus "if this variant becomes prevalent, we may have the same issues in real life", she warned.