By Amruta Indapurkar
The Zika virus disease, a serious health concern, continues to spread all around the world and for 10 months in 2016 was declared a public health emergency by the World Health Organization (WHO). WHO reported that between 2007 and 2014, 14 countries were affected; whereas, since 2015, 47 countries have reported Zika virus outbreak. However, according to WHO, as of November 2016, Zika is no longer classified as a Public Health Emergency of International Concern but still a long lasting public health challenge. The Center for Disease Control (CDC) has reported 5,234 cases of Zika virus disease in the U.S. and 36,526 cases in U.S. territories from January 2015 to April 2017. Since summer in the northern hemisphere is fast approaching, and with summer comes mosquitos, it is very important that we have a plan to treat, diagnose, and prevent more outbreaks.
Currently, Zika virus can only be detected in a symptomatic person who is in the acute phase of infection. The CDC performs molecular tests to diagnose Zika virus RNA in serum and urine and serological tests to detect immunoglobulin M antibodies against the virus. In case one method fails, another test should be performed to confirm the results. The Food and Drug Administration (FDA) has authorized several diagnostic tests to detect Zika for emergency situations. However, these methods have cross-reactivity for other flavivirus that causes dengue, yellow fever, and chikungunya, and therefore these tests are not specific for Zika. They may give a false positive result for Zika, so they are only authorized for emergency purposes. FDA encourages laboratories to report all the results and problems associated with these methods for developing accurate prognosis. The National Institute of Allergy and Infectious Disease (NIAID) is supporting scientists to develop more rapid, accurate, and specific diagnostic methods that include production of specific antibodies against Zika, development of a novel Zika virus recombinant protein that reduces cross-reactivity, and identification of biosignatures that are unique to Zika.
There are no vaccines available against Zika yet. According to the NIAID, six vaccines are undergoing clinical or pre-clinical review. A DNA-based Zika vaccine moved through two phase 1 clinical trials in 2016 and has recently entered phase 2 clinical trial due to its capability of producing Zika-virus-neutralizing antibodies. This phase 2 clinical trial will evaluate safety, immunogenicity, dose, and efficacy of the vaccine. Separately, a purified inactivated Zika vaccine is undergoing phase 1 clinical trial and the results will decide whether it can enter phase 2. NIAID is planning to test this vaccine as a booster for the DNA-based Zika vaccine. Further, the live attenuated vaccine, in which the virus has been weakened, was developed for Zika and Dengue infections and is currently in phase 3 clinical trial in Brazil. A monovalent vaccine has been discovered specifically for Zika and will enter phase 1 clinical trials at John Hopkins University. The same vaccine against Zika and all four types of Dengue infection entered clinical testing in May 2017. An mRNA vaccine for Zika will enter clinical testing in late 2017, and a genetically engineered vesicular stomatitis virus (VSV) for Zika is in early stages of development and will be tested in tissue culture and animal models. An AGS-v vaccine is undergoing phase 1 clinical trial and was developed for prevention from multiple mosquito-borne diseases. Its mechanism of action involves development of an immune response against salivary proteins of disease-carrying mosquitoes in a vaccinated person.
In near future, we might have a vaccine that can prevent Zika, but until then, it is very important to prevent its exposure using methods such as using mosquito repellents, emptying standing water, and using netting. In addition, a paper published in Frontiers in Microbiology describes some interesting prevention techniques that have not only been successful for controlling Dengue, but can also be used to control Zika. Outbreaks may be controlled by using Integrated Vector Management (IVM), a decision-making process to optimize the use of resources for vector control for Dengue that can be modified to address Zika. Another technique involves introduction of Wolbachia bacteria in mosquitoes. Wolbachia is a reproductive parasitic bacterium that reduces mosquito-to-human transmission of disease. It does this by genetically altering mosquitoes to produce offspring that are weak and can’t survive. This will decrease the overall number of mosquitoes and reduce the incidence of mosquito-borne diseases.
The most important step is to encourage and speed up the research programs that can give us specific diagnostic tests, treatment, and prevention for this disease. Zika virus has been around for years, and with time the severity of its exposure has increased. It is important to act now and stay safe.