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A Detailed Look at the Zika Virus Epidemic in Brazil

MAR 01, 2017 | KRISTI ROSA
One of the most interesting aspects of The First International Conference on Zika Virus was the fact that attendees were provided with additional insight into how Zika, which continues to spread around the world via Aedes aegypti mosquitoes, has impacted a number of different countries.
In his presentation during the first session on Zika epidemiology on February 23, 2017, Pedro Fernando de Costa Vasconcelos, MD, PhD, director of the World Health Organization (WHO) Collaborating Center for Arbovirus and Research, Evandro Chagas Institute, took a closer look at the Zika virus in Brazil, a country that was unexpectedly hit by the virus during 2015 and 2016.
Dr. Vasconcelos opened the session by touching on the fact that genetic studies have revealed that Zika has evolved into three different genotypes, or strains: West African, East African, and Asian. He continued on to highlight a study that was published in 2007 by Edward B. Hayes that discussed the first time that Zika was detected outside of Africa and Asia.
“The emergence of Zika virus outside of its previously known geographic range should prompt awareness of the potential for Zika virus to spread to other Pacific islands and the Americas,” quoted Dr. Vasconcelos.
Zika was first recognized in early 2015 in the “metropolitan area of Maranhão” by a polymerase chain reaction (PCR) test, but, in his newest research, Dr. Vasconcelos shows that “the virus arrived several months before the outbreak.” So, what prevented Zika from being recognized as soon as it should have been for what it was?
“It was difficult to define if it was Zika virus, or Dengue, or chikungunya, three arboviruses that are circulating together in Brazil. Perhaps this explains why Zika virus [recognition was delayed] in Brazil, because the clinical symptoms when these occurred for Zika, [were] Dengue fever-like, or chikungunya-like fever; it’s very difficult,” Dr. Vasconcelos explained. He then showed a table of laboratory-confirmed cases of Zika virus from 2015, and for Brazil, “it was estimated that half a million to 1.5 million infections” were confirmed. Nevertheless, these numbers could potentially underestimate the true prevalence of Zika at that time due to the issues faced when it came to differentiating between the three vector-borne diseases.
When Zika first hit Brazil, the threat that it posed to unborn fetuses was not yet known. However, in September 2015, there was a notable increase in the cases of microcephaly that were reported to the Ministry of Health (MoH). By the following month, “it was clear that an epidemic of microcephaly and other central nervous system (CNS) malformations was occurring in Brazil, particularly in the northeast region, with an increased incidence in the states of Pernambuco, Paraiba, Alagoas, Rio Grande do Norte, Ceará, and others, but not in states of other geographical regions.” At this point, a potential link between “the temporal association of the microcephaly cases” and the Zika epidemic occurring in the northeast was suggested, but no evidence had confirmed it yet.
On November 28, 2015, the MoH ultimately established the relationship “between the increase in occurrence of microcephaly and Zika virus infection through the detection of Zika virus genome in the blood and tissue samples of a baby from the state of Pará,” as was reported in an epidemiological alert released by the Pan American Health Organization (PAHO) and WHO. Dr. Vasconcelos explained that the aforementioned newborn died within five minutes of being born and presented with other “congenital anomalies” in addition to microcephaly, such as arthrogryposis and atresia of esophagus and trachea among others. Researchers from the Instituto Evandro Chagas (IEC) were able to demonstrate Zika virus RNA within the “blood, brain, and viscera fragments” of the newborn and they passed this information along to the MoH. This case marked the first “documented finding” of Zika virus found in a patient with microcephaly.
The MoH report also detailed two additional Zika-related deaths of patients “with respectively systemic lupus erythematosus under long-term use of steroids and Evans syndrome” These deaths were also the first documented Zika-related adult deaths.
This was just the beginning; when it comes to an epidemiological estimation of Zika virus cases, the MoH estimates the range was between 500,000 to 1.5 million cases in 2015 in Brazil, and about 200,000 cases in 2016. Dr. Vasconcelos stressed, however, that when it comes to cases of microcephaly associated with Zika virus, the average microcephaly birth rate per 100,000 live births in Brazil has increased markedly since the time span of 2010 to 2014. For example, in the northeast region of Brazil, the average microcephaly birth rate per 100,000 live births in Paraíba between 2010 and 2014 was 7.4; the average in 2015 was 436.2!
Dr. Vasconcelos demonstrated this increase in microcephaly rates for a number of other states as well, with most of occurring in the northeast region states of: Pernambuco, Rio Grande do Norte, Alagoas, and Sergipe. He stated, “more than 80% of all ZIKV infections and 90% of microcephaly cases proceed from states in the northeast region of the country.” According to Dr. Vasconcelos, the reason for this remains to be determined.
“ZIKV is the causal etiologic agent of the microcephaly and other CNS malformations; ZIKV in persons with immunologic or autoimmune disorders can result in severe disease and deaths due to severe encephalitis; the high levels of ZIKV antigens/RNAs are found in the brain of both babies with microcephaly and adult patients suggest an intense neurotropism. The immunologic mechanisms of this phenomenon remains to be determined, but suggest a prominent Th2 response,” remarked Dr. Vasconcelos.

First International Conference on Zika Virus

Session 1: Zika Epidemiology
Zika Virus Epidemic in Brazil: State of the Art
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