JUL 04, 2019 11:03 AM PDT

Emerging Arbovirus Infections in the Americas

WRITTEN BY: Dena Aruta

Arboviruses are arthropod-borne pathogens with more than 130 strains known to cause human infections. The majority of these strains belong to three genera: Flavivirus, Alphavirus, and Orthobunyavirus. Due to the increased prevalence and rapid spread of arbovirus infections, they have emerged as one of the most significant health concerns today in the Americas. Espinal et al. along with The Global Arbovirus Group of Experts examine the progress, challenges, and recommendations for prevention and control of arbovirus infections in North, Central, and South America.

The reemergence of dengue and yellow fever viruses and the spread of Zika and chikungunya viruses to new areas have led to global pandemics with a significant mortality rate. Dengue, a flavivirus, is spread by the Aedes (A. aegypti and A. albopictus) mosquito and is second only to malaria as a cause of a vector-borne infection with high mortality and morbidity rates. There were 1,7 million cases of dengue reported to the Pan American Health Organization (PAHO) in 2010; the number increased to 2.2 million by 2016. In addition, the incident rates have risen from 174.6 to 220/100,000 individuals. The total number of cases each year is probably greatly underreported with disease modeling estimates around 58 million in just Latin American and the Caribbean islands in 2010. 

During this same time, yellow fever made its appearance in urban areas emerging from mostly sylvatic-restricted (a disease in wild animals) infections. Since 2007, 13 countries have experienced extensive circulation of the yellow fever virus resulting in epizootic diseases that have spread to humans, especially in urban areas. It remains an enormous public health concern for most countries in Central and South America.

Chikungunya and Zika had not previously been found in the Western Hemisphere before 2013. The island of Comoros and India experienced an epidemic outbreak in 2005 that infected more than 1 million people and resulted in significant musculoskeletal complications. By 2013, chikungunya had spread pandemically to more than 43 countries, including the Americas. Zika was first identified in the Americas in 2014 in Chile and Brazil, which spread quickly becoming one of the worst global health crises for these countries in many years. It can be transmitted sexually, unlike yellow fever, dengue, and chikungunya, and causes microcephaly, Guillain-Barré syndrome, and other neurologic disorders. 

When Zika and chikungunya re-emerged in 2016, a situation developed that had not yet been seen: "the cocirculation of four important human arboviruses transmitted by the same mosquito, primarily Aedes aegypti, in the same time and place." Deforestation, change in temperature by two degrees Celsius, and migration of unvaccinated populations have been blamed for this unprecedented situation.

Unfortunately, there is inadequate surveillance in these areas as well as a lack of serologic testing that can consistently differentiate between these flaviviruses that are closely related. As a result, there are significant challenges for medical and healthcare personnel to respond adequately to these devastating infections.

Most infections are either asymptomatic or mild, but some result in "high fever, hemorrhage, meningitis, encephalitis, hepatitis, and even death. Clinical diagnosis can be a challenge since initial symptoms are similar, and the sensitivity and specificity of serologic tests are poor with cross-reactivity among related viruses. The lack of specific antiviral drugs to treat these infections has led to case management of arboviral diseases with symptomatic and supportive care the only options.

Vector control is a challenge for many countries, and vaccines may be the most effective way to control and prevent arboviral infections. However, there are only two licensed vaccines available: "the live attenuated yellow fever 17D vaccine and a recently licensed live attenuated chimeric yellow fever–derived tetravalent dengue vaccine (CYD-TVD)." There are no current vaccines for Zika, dengue, or chikungunya, but there are several candidates currently being tested in clinical trials. 

The Global Arbovirus Group of Experts made the following recommendations: 

Cases need to be detected earlier so essential clinical and public health interventions can be implemented in a more timely fashion. Efforts to improve the following will be critical: laboratory capacity and diagnostics, case reporting and management, integrated surveillance system with an emphasis on data quality, and community communication to minimize exposures. Research, including that for vaccine development, improved diagnostics, and operational research for best practices such as vector control within an integrated approach and vaccination achieving high coverage rates among communities most at risk will also be essential. 

About the Author
  • After earning my Bachelor of Science degree in biology/chemistry from Virginia Polytechnic Institute and State University (aka Va. Tech), I went on to complete clinical rotations in laboratory medicine at Roanoke Memorial Hospital. I spent the next 21 years working in healthcare as a clinical microbiologist. In 2015, I combined my fascination with medicine and passion for writing into a freelance career, and I haven't looked back. Even though my expertise is in microbiology and infectious diseases, I'm adept at writing about any medical topic. Being a freelance writer allows me to pursue a career where I can work at home with my two feline assistants, Luke and Grace. I'm a firm supporter of animal rights and volunteer for a local rescue during my free time. 
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