Emerging and Reemerging Aedes-Transmitted Arbovirus Infections in the Region of the Americas

Implications for Health Policy

Marcos A. Espinal, MD, DrPH; Jon K. Andrus, MD; Barbara Jauregui, MD, MSc; Stephen Hull Waterman, MD, MPH; David Michael Morens, MD; Jose Ignacio Santos, MD, MSc; Olaf Horstick, PhD (DrMed), FFPH, MPH, MSc, MBBS; Lorraine Ayana Francis, DrPH, MHA; Daniel Olson, MD

Disclosures

Am J Public Health. 2019;109(3):387-392. 

In This Article

Surveillance

Currently, the inconsistent and inadequate surveillance in the region along with the lack of laboratory serologic testing that can consistently differentiate between closely related flaviviruses poses substantial challenges to respond adequately to these diseases.[21]

Limitations of Existing Systems and Rationale

Existing arbovirus surveillance systems have several limitations, including problems intrinsic to passive surveillance, lack of organizational structure and integration within existing systems, and inadequate laboratory capacity.

Triggered by syndromic fever and rash reporting, most countries in the Americas collect clinical and laboratory data for arboviral diseases through voluntary passive case reporting within health care systems. Most national laboratories have access to serologic and molecular diagnostic testing for existing arboviral pathogens, but fewer laboratories have sequencing and genotyping capability for identifying novel emerging pathogens, genotypes, and outbreaks. Regional laboratory networks exist to facilitate logistical support, technical expertise, and data sharing such as PAHO's Arbovirus Diagnosis Laboratories Network of the Americas.[22]

Data analysis, reporting, and data sharing systems also vary. Although many countries require mandatory reporting of all arboviral diseases, case reporting is often not performed, especially within the private sector. Many countries publish routine case counts of suspected and confirmed arboviral disease cases, though the quality and timeliness of reporting varies. The PAHO Health Information Platform for the Americas is a real-time, voluntary, electronic reporting system that facilitates rapid reporting of data in the region.[23]

Existing surveillance systems, including syndromic, laboratory-based, and other (e.g., postmortem, clinician-based, event-based) systems are often not integrated, which limits their ability to link relevant data and leverage existing resources. Given limited resources, surveillance systems may place a large focus on current arboviral diseases and not dedicate sufficient resources to identify new or emerging arboviral pathogens.

Cross-reactivity of serologic testing between flaviviruses (particularly DENV and ZIKV) makes interpretation difficult. Numerous rapid diagnostic tests of varying quality make laboratory interpretation difficult, especially in the context of changing arboviral epidemiology. Inadequate attention to logistics of sample transport and subsequent testing leads to delays in the availability and reporting of results. Many laboratories do not perform postmortem testing. These limitations in the performance of existing laboratory systems became even more evident during the introduction of new pathogens in the region such as ZIKV.

Surveillance Diagnostics

Given the challenge in clinical differential diagnosis among DENV, ZIKV, and CHIKV, in 2016, the PAHO Directing Council proposed to its member states a strategy for comprehensive surveillance of arboviral diseases. This strategy is based on the coordination and strengthening of epidemiological surveillance, integrated vector control, and laboratory diagnosis.[24]

The clinical differential diagnosis of DENV, ZIKV, and CHIKV is challenging and underscores the importance of laboratory diagnostic tests. Antibody detection tests can distinguish among the alphaviruses (e.g., CHIKV, Venezuelan equine encephalitis, Mayaro, and Ross River viruses) and the flaviviruses (e.g., DENV, ZIKV, YFV, West Nile, and Japanese encephalitis viruses). However, because of previous exposure to related flaviviruses and extensive cross-reactions among flaviviruses, serological tests such as immunoglobulin M (IgM) enzyme-linked immunosorbent assay (ELISA) and neutralization assays are not reliable in many situations for distinguishing among flaviviruses.

The most reliable diagnostic tests include nucleic acid tests such as reverse-transcription polymerase chain reaction, and the nonstructural glycoprotein-1 ELISA. The latter detects acute-phase infections. Only the nonstructural glycoprotein-1 ELISA is currently commercially available, and only for DENV.[25]

Until a decade ago, IgM ELISA was the diagnostic method of choice for yellow fever diagnosis. However, the cross-reactivity among flaviviruses again is a major limitation. In endemic areas, immunity to other flaviviruses is very common, and some severe dengue patients present with the clinical manifestations of yellow fever. In addition, IgM may persist for months and is therefore not a reliable marker of a recent YFV infection. The development of molecular diagnostic tools has significantly advanced the diagnosis of yellow fever and the ability to distinguish severe infections caused by wild-type virus versus the 17D vaccine strain.[26]

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