Preventing a Pandemic – How Zika was Stopped
“In the April 2016, we described the rapid spread of Zika virus from East Africa, through Southeast Asia, and into South and Central America. At that time, the virus had not made significant inroads in the United States. Unfortunately, that is no longer the case. Short on funds and with no therapeutics or vaccines in sight, U.S. health officials are scrambling to prepare for a protracted fight with a tenacious foe.”
Chris Fellner, Pharmacy and Therapeutics, December 2016
Before the current coronavirus pandemic, there was another infectious disease threat to the United States (U.S.) in 2016. Although it had been previously identified decades before, the Zika virus had not been considered a public health concern until it began to spread through the Americas in 2015. Graphic photographs of deformed newborns from infected women flooded the mass media and sparked fears that the United States was facing a devastating pandemic. With little known regarding transmission, prevention, or treatment, public health officials prepared for the worst. Fortunately, due to aggressive public health interventions, the Zika virus pandemic was rapidly extinguished in the United States and the response provides multiple lessons for the study and treatment of communicable diseases.
Surprisingly, the Zika virus (ZIKV) was first isolated in the Zika Forest in Uganda in 1947. At that time, the virus was strictly enzootic, meaning confined to nonhuman animals, and transmitted via mosquitoes. When the virus migrated to Asia, a new lineage of the virus emerged in a type of mosquito, Aedes aegypti, which was capable of transmitting the virus to humans. Nevertheless, fewer than 20 mild cases had been reported before 2007. Subsequently, there were outbreaks in small Pacific islands in 2007 and 2013. In 2015, a pandemic was identified with cases in Africa, the Caribbean and the Americas. “The ZIKV pandemic was an example of a “perfect storm,” in which a new American subclade (strains isolated in the Americas) emerged from the Asian lineage of the virus and was introduced into a uniformly susceptible population that had not been previously exposed to ZIKV. The pandemic underscores the ability of the virus to be efficiently transmitted in Aedes-infested settings and to spread across regions through human mobility and travel (Musso 2019).”
In addition to non-vector borne transmission via blood transfusion and maternal-fetal transmission, Zika was found to be unique from other arboviruses in that it may be transmitted through sexual contact. Clinically, 50-80% of infections are asymptomatic. “Maternal–fetal transmission of ZIKV may occur in all trimesters of pregnancy, whether infection in the mother is symptomatic or asymptomatic. Vertical transmission has been estimated to occur in 26% of fetuses of ZIKV-infected mothers in French Guiana, a percentage similar to transmission percentages that have been observed for other congenital infections (Musso 2019).” For symptomatic cases, illnesses are generally mild after a 3 to 14-day incubation period. Symptoms include rash, fever, arthralgia, myalgia, and conjunctivitis. Rarely, illness can be severe and fatal. The more severe manifestations include the following: Guillain-Barre syndrome, an autoimmune polyneuropathy (2-3/10,000 cases); thrombocytopenic purpura, a bleeding disorder with low platelets; and congenital zika, with microcephaly and devastating neurologic damage. As many as 5-14% of newborns born to infected women will be afflicted, with mortality as high as 4-7% in the first week of life. This high risk for often lethal congenital defects mobilized the response to this illness.
The first step in the response to this pandemic was to develop adequate testing to identify infected individuals. The testing involves paired urine and blood samples which are checked initially for nucleic acid testing early in the illness and then for the presence of antibodies two weeks later. There can be some cross reactivity with other flaviviruses. Because testing may be less reliable during pregnancy, ultrasound can be used to look for the congenital neurologic deformities. Because no anti-viral treatments have been approved for the illness, clinical care is mainly supportive and makes prevention even more important. Much of the preventative strategies revolve around vector-control strategies already associated with the Aedes mosquito. As per the EPA, in addition to individuals wearing appropriately protective clothing and repellants, the scientifically proven strategy to limit mosquito requires an integrated approach involving removing mosquito habitats, using structural barriers, controlling mosquitoes at the larval stage, and controlling adult mosquitoes (EPA 2020).” Tracing contacts and education were also especially in preventing the sexual transmission of the disease. Currently, clinical trials are underway in the development of a vaccine.
With the World Health Organization officially declaring that Zika was a pandemic, resources were mobilized to quickly identify the causal link with birth defects. Within 3 years, over 6000 scientific publications have led to improved testing, tracking, and future vaccines. “The pandemic is illustrative of the universal failure of vector-control programs in regions where rapid urbanization and interconnectivity promote epidemic spread. However, new vector-control approaches, such as those that involve genetically modified mosquitoes, wolbachia-transfected mosquitoes, and pyriproxyfen-based larvicide, are under evaluation (Musso 2019).” The response allowed the U.S. to rapidly control the disease. According to the CDC, in 2016, there 5,168 symptomatic Zika disease cases in the U.S., the majority of which were from returning travelers. Nevertheless, 224 cases were identified to be due to local mosquito-borne transmission in Florida and Texas. By 2017, the local mosquito and sexually transmitted cases were down to a total of 15 in the U.S. In 2019, there have been no cases reported of transmission in the U.S., and only 19 cases in returning travelers. The combination of testing, reporting, and educating, both the public and providers, stopped the spread of Zika in the United States. Although the novel coronavirus has been more difficulty to stem, the response to the Zika pandemic demonstrated that a focused response, using a well-established scientific approach, may eradicate a public health threat.
Works Cited
“For Healthcare Providers.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 12 Oct. 2018, www.cdc.gov/zika/hc-providers/index.html.
Fellner, Chris. “Zika in America: The Year in Review.” P & T : a peer-reviewed journal for formulary management vol. 41,12 (2016): 778-791.
Musso, Didier, et al. “Zika Virus Infection — After the Pandemic.” New England Journal of Medicine, vol. 381, no. 15, 2019, pp. 1444–1457., doi:10.1056/nejmra1808246.
“Success in Mosquito Control: An Integrated Approach.” EPA, Environmental Protection Agency, 11 Oct. 2016, www.epa.gov/mosquitocontrol/success-mosquito-control-integrated-approach.