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

Abstract and Introduction

Abstract

The increasing geographical spread and disease incidence of arboviral infections are among the greatest public health concerns in the Americas. The region has observed an increasing trend in dengue incidence in the last decades, evolving from low to hyperendemicity. Yellow fever incidence has also intensified in this period, expanding from sylvatic-restricted activity to urban outbreaks. Chikungunya started spreading pandemically in 2005 at an unprecedented pace, reaching the Americas in 2013. The following year, Zika also emerged in the region with an explosive outbreak, carrying devastating congenital abnormalities and neurologic disorders and becoming one of the greatest global health crises in years.

The inadequate arbovirus surveillance in the region and the lack of serologic tests to differentiate among viruses poses substantial challenges. The evidence for vector control interventions remains weak. Clinical management remains the mainstay of arboviral disease control. Currently, only yellow fever and dengue vaccines are licensed in the Americas, with several candidate vaccines in clinical trials.

The Global Arbovirus Group of Experts provides in this article an overview of progress, challenges, and recommendations on arboviral prevention and control for countries of the Americas.

Introduction

The ever-increasing geographical spread and rising disease incidence of arboviral (arthropod-borne virus) infections are among the most significant public health concerns in the Americas.[1,2] In addition to the reemergence of dengue virus (DENV) and yellow fever virus (YFV), new arboviral pathogens once confined to specific regions of the world, such as chikungunya virus (CHIKV) and Zika virus (ZIKV), recently resulted in pandemics associated with significant morbidity.[3–6]

Dengue infection is an Aedes-borne disease caused by flaviviruses and is second only to malaria as a cause of vector-borne disease mortality and morbidity. For several decades, the Americas have observed an increasing trend in dengue incidence, evolving from low to hyperendemicity, with epidemics recurring approximately every 3 to 5 years.[3] In 2010, 1.7 million dengue cases were reported to the Pan American Health Organization (PAHO), an incidence rate of 174.6 cases per 100 000 population.[7] In 2016, 2.2 million cases were reported (220.0 cases per 100 000 population),[8] though rates were trending lower in 2017.[8] These rates are likely a significant underestimate; modeling studies estimate as many as 53.8 million DENV infections in Latin America and the Caribbean in 2010, including 13.3 million symptomatic infections—way above the numbers reported to PAHO.[9]

In 2005, CHIKV caused an outbreak on the island of Comoros, followed by a large outbreak in India, resulting in more than 1 million cases and significant postinfectious musculoskeletal sequelae. Subsequently, CHIKV spread pandemically at an unprecedented pace, reaching the Americas in 2013, rapidly resulting in more than 1.3 million infections reported in more than 43 countries.[2,10] Incidence rates climbed as high as 137.1 infections per 1000 person-years among Nicaraguan children during the peak of the epidemic.[11]

ZIKV, like CHIKV, had not previously circulated within the Western Hemisphere, and resulted in an explosive outbreak in the Americas, with its identification first on Easter Island, Chile, in 2014, followed by northeast Brazil in 2015, and then spreading throughout the Americas. By late 2015, Zika had become one of the greatest global health crises in years and was associated with devastating congenital abnormalities including microcephaly (Figure 1), Guillain-Barré syndrome, and other neurologic disorders, and with the ability to spread by sexual contact.[6,12–16] By late 2016, ZIKV transmission had extended to 48 countries and territories in the Americas, with a total of 707 133 reported cases. These estimates are also likely a significant underestimate as reporting is passive and, therefore, they do not capture asymptomatic cases.[17,18]

Figure 1.

Brazilian Mother With Her Baby With Microcephaly, a Consequence of an Intrauterine Zika Virus Infection: Recife, Brazil, 2016 Source. Photo courtesy of the Pan American Health Organization. Printed with permission.

For decades, YFV persisted in the Americas as sylvatic cycles of transmission. Beginning in 1997, YFV circulation in Brazil and neighboring countries intensified. In 2008, Asunción, Paraguay, experienced its first urban yellow fever outbreak, which accounted for almost 50% of all yellow fever cases reported that year in the Americas.[19] Over the past 30 years, YFV activity had been restricted to an enzootic area shared by Bolivia, Brazil, Colombia, Ecuador, French Guyana, Guyana, Panama, Peru, Suriname, Trinidad and Tobago, and Venezuela. Since late 2007, the region has experienced intense circulation of YFV, with extensive epizootics and spillover outbreaks in humans. The endemic area has extended to include Paraguay and northern Argentina, with human cases and epizootics detected in 2008.[4] Yellow fever continues to be a significant public health concern for these 13 countries of the Americas.[19]

The recent emergences of ZIKV and CHIKV in 2016 created an unprecedented situation: the cocirculation of 4 important human arboviruses transmitted by the same mosquito, primarily Aedes aegypti, in the same time and place. Intense and prolonged rainy seasons and an increase of 2 degrees centigrade in average temperature probably also contributed to an abundance of vectors.[4,20] Deforestation has been associated with yellow fever and Zika outbreaks. Migration of unvaccinated populations to endemic areas has also been a key factor in yellow fever occurrence in South America.[4,20]

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