Overview of Emerging Arboviruses

Ann M. Powers

Disclosures

Future Virology. 2009;4(4):391-401. 

In This Article

Identification of an Arboviral Epidemic Pathogen

The purest form of arboviral emergence is probably the epidemic activity of a pathogen in an area where it has never before been identified without any prior evidence that the pathogen was circulating or causing disease. One such example of this form of arboviral emergence occurred in 2007 when physicians on Yap Island in the Federated States of Micronesia reported an outbreak of illness characterized by rash, conjunctivitis and arthralgia. Since the CHIKV epidemic was ongoing in Southeast Asia and areas of the Indian Ocean at that time, one possible and logical etiology for this febrile outbreak in the Western Pacific was CHIKV. However, three serum samples were found to be positive in a commercially available dengue virus IgM antibody test, implicating a dengue virus as the likely infecting agent. Given that local physicians believed the clinical presentation was unlike that of dengue viruses that had twice before affected the island, additional testing was performed at the CDC Arbovirus Diagnostic and Reference Laboratory in Fort Collins, CO, USA. While no CHIKV or dengue virus-specific nucleic acid was found in any acute samples, RNA from another arbovirus, ZIKV, was detected in 15 samples collected within 10 days of illness.[84]

Zika virus is a little-studied flavivirus that was first isolated from a rhesus monkey in the Zika Forest, Uganda, in 1947.[85,86] ZIKV has been isolated from humans in Uganda and Nigeria, and there is serologic evidence of human ZIKV infection in several countries in Africa and Asia.[86–88] However, no previous outbreaks of the virus have been reported; only 18 cases of human ZIKV illness have ever been documented[89–92] and, significantly, ZIKV transmission has not been reported outside of Africa and Asia. Curiously, without any indication of ZIKV activity in other geographic areas with temporal overlap, this virtually unknown pathogen emerged in an island population, causing an estimated 871 cases of febrile illness. Furthermore, a serosurvey revealed that 73% of participants had ZIKV IgM antibody, suggesting that almost 5000 of the island's inhabitants had been infected.[84] Unfortunately, no ZIKV was detected in any mosquito samples and, therefore, the transmission vector could not be determined with certainty. However, the most abundant mosquito, Aedes hensilli, had previously been suggested to bethe most likely vector of previous dengue virus transmission on Yap.[93] Furthermore, Ae. hensilli is closely related to Ae. aegypti,from which ZIKV has been isolated in nature.[94] These reports, combined with laboratory infection of Ae. hensilli with ZIKV [Ledermann, Powers, Unpublished Data], indicated that this species may have been a vector of ZIKV transmission in this outbreak.

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