Zika Virus was first discovered in a rhesus monkey from the Zika Forest, Uganda in 1947. The following year, the virus was found in nearby mosquitoes, and in 1952, the first human cases were reported in Uganda and the United Republic of Tanzania. Since this time, human cases occurred sporadically throughout Africa and southern Asia.
In 2007, approximately 75% of the residents of the Pacific Island of Yap (Micronesia) were infected with Zika virus (estimated to be more than 900 people). Prior to this, only 14 human cases of Zika had been documented, making this the first large Zika outbreak.
In 2013 and 2014, a smattering of small outbreaks and individual cases was officially documented in Africa and the Pacific Islands, including French Polynesia, Easter Island, the Cook Islands, and New Caledonia.
In May 2015, Brazil confirmed that Zika virus was circulating in the country. This was the first report of Zika disease being acquired from local mosquito populations in the Americas. Over the next year, neurological disorders were found to be associated with a history of Zika infection, and there was an unusual increase in the incidence of birth defects among newborns. Meanwhile, Zika virus continued to spread further into the Americas.
Puerto Rico reported its first case of Zika infection in December 2015 and has since documented more than 10,000 cases. On August 12, 2016, the US government declared a public health emergency in Puerto Rico, which will allow access to funds, personnel, and other resources to help combat the epidemic.
Over the last year, the continental US has reported almost 2,000 cases of travel-related Zika infection. In late July 2016, Florida officials announced what appeared to be the first case of locally-transmitted Zika in the continental US, in which the virus was transferred to humans from the local mosquito population. While these locally-transmitted cases appear to be isolated to Miami-Dade county, the news raises questions about whether or not local cases could be found elsewhere, and if this indicates the potential for a local epidemic.
Due to the recent emergence of Zika within the Americas and the limited information about the virus, both the public and experts have questions as to why Zika is currently spreading so quickly. As IEM subject-matter expert Dr. Rashid Chotani, MD, MPH, discusses in his Zika Perspective post, there is a combination of conditions that impact Zika’s ability to spread:
- Presence of Zika-infected mosquitoes
- Climate conditions favorable to breeding grounds
- Transmission of Zika virus between humans and mosquitoes
- Human mobility
Overview of the Virus
Zika virus belongs to a family of viruses known as Flaviviridae \ˌflā-vi-ˈvir-ə-ˌdē\ and is related to the viruses that cause dengue fever, yellow fever, Japanese encephalitis, and West Nile fever. Sequencing analysis of Zika virus shows it has African and Asian lineage, the latter of which is linked to the widespread epidemic activity in the Americas since 2015.
More information can be found regarding specific characteristics of Zika virus below: