Where Has Zika Gone?
Although Zika virus (ZIKV) was isolated in 1947 in Uganda, the first major outbreak of ZIKV did not occur until 2007. This outbreak occurred outside of Africa, and it was reported that 73% of the residents of the Yap Islands were infected with ZIKV. In 2013 the virus spread throughout Cambodia, Thailand and French Polynesia and it was here that unique congenital neurological symptoms were first observed. By 2014, infections were reported in Northeastern Brazil and through Central, South and North America with the number of cases peaking in 2016.
From 2014 to 2015, previously "symptomless" individuals infected with the virus began to show specific symptoms including rash, fever, and conjunctivitis. These symptoms were later correlated to a positive ZIKV infection. Additionally, babies from infected mothers were being born with smaller than normal heads (microcephaly). Although the infants never tested positive for ZIKV, their mothers reported rashes that were consistent with ZIKV infection. The virus was eventually detected in the amniotic fluid of pregnant woman confirming that the virus could be transmitted from mother to fetus and was linked to newborn microcephaly.
Due to the fast-spreading nature of the virus in the southern states of the United States, a travel advisory was released by the Centers of Disease Control (CDC) warning pregnant women and women planning on becoming pregnant to avoid areas were virus infection was prominent, including Miami-Dade county in Florida. It was still unknown, however, why this virus spread so rapidly to the Americas. One plausible reason provided by Dr. Michael Diamond from the Washington University School of Medicine is that the virus found a niche where the population was completely immunologically naive. This allowed the virus to infect and rapidly spread in individuals whose immune systems had never seen the virus before. During this process the virus also became more virulent, which explains why symptoms began to manifest during cases in 2014 and 2015.
So where did the virus go? In 2018 only 34 cases of ZIKV were reported by the CDC in the U.S. compared to 5,168 that were reported in 2016. Dr. Diamond suggests that herd immunity may be protecting the population against new infection, i.e. after the peak in infections, enough people have become immunologically protected against the virus. Once a critical threshold of immunity in the population is reached and dependent on the reproductive rate of the virus, a partially immunized population is protected from outbreaks, similar to the protective effects of childhood vaccinations. This makes it very difficult for the disease to spread. However, Dr. Scott Weaver at the University of Texas would advise to not discount future infections yet. The virus is constantly mutating and limiting the impact of herd immunity. Questions regarding the long-term effects of those individuals infected and babies born to infected mothers still exist. ZIKV can affect infected adults well after the infection and symptoms subside and has been linked to Guillain Barre syndrome, a rare autoimmune nervous system disorder.
While the immediate ZIKV outbreak is over, additional research to better understand ZIKV replication and the development of novel, broadly acting compounds and vaccines to prevent future outbreaks is critical. ZIKA and other flaviviruses, still have no preventative or therapeutic product available, and additionally work is required to prevent future outbreaks of mosquito borne infections. With our robust suite of customizable in vitro and ex vivo assays, we are well positioned to support and provide services for academic, non-profit and commercial organizations looking to develop their novel technologies against a variety of viral targets. These services include both the development of direct acting, and host targeted antivirals, as well as services to support neutralizing and therapeutic antibodies, biologics and vaccine development operations. Contact us to learn more about our antiviral discovery, development and commercialization services, and to schedule an introductory teleconference with our technical team.