As it was with the introduction of West Nile and Chikungunya to the western hemisphere, we are seeing yet another mosquito-transmitted virus escape its endemic boundaries and spread to a new hemisphere. This time it’s Zika virus. And with these introductions, you often see enough people infected in a period of high scrutiny that “unusual” case presentations are noted. As we have seen with our experience with many other pathogens, the “first wave” of transmission of an exotic pathogen in an immunologically naive, “new” population yields concerning reports of disease considered more severe than is typically seen in that pathogen’s native environment.
CNN is currently reporting on concern that microcephaly, a birth defect, is possibly associated with the ongoing Zika epidemic in Brazil. We note this is a late media report, as this has been an issue we’ve been monitoring for quite some time now. Below is what we published for our clients almost two weeks ago:
Disease: Zika Virus/Microcephaly
Recap/Description of Hazard: As of December 5th, 1761 cases of microcephaly have been reported in Brazil, a major spike in cases compared to previous year averages (~150 to 200 cases). The introduction of Zika virus into the country is a suspected reason for this spike, though the associations drawn between Zika infection during pregnancy and congenital microcephaly have not been confirmed. Zika virus infection and Chikungunya infection have both been associated with neurological disorders, including Guillain-Barre syndrome (GBS) and microcephaly in infants, in past outbreaks. Of the 1761 cases of microcephaly reported in Brazil in 2015, a majority have occurred in Pernambuco, Paraiba, Bahia, Rio Grande do Norte, Sergipe, and Alagoas. The outbreak of Zika during the first half of 2015 represents the first introduction of Zika into Brazil, and occurred during simultaneous transmission of Chikungunya and dengue fever.
French Polynesia Zika Outbreak 2013-14
In 2013, French Polynesia and New Caledonia experienced the first ever reported outbreak of Zika virus with 8,000+ suspected cases. A report from the European Centers for Disease Control (ECDC) following the outbreak in 2014 noted that 70 suspected cases of Zika infection presented with neurological complications, including 38 cases of Guillain-Barre syndrome (GBS). The ECDC report states: “The clustering in time of GBS cases is considered unusual as the annual number of GBS cases in French Polynesia are 5, 10, 3 and 3 in 2009, 2010, 2011 and 2012, respectively.” Only one of the 38 cases was confirmed to have Zika virus, while others had antibodies to Zika. It is important to note that similarities in clinical and epidemiological characteristics with other viruses, including dengue and Chikungunya, can make a definitive Zika diagnosis difficult without appropriate laboratory measures.
The fact that Zika is an “emerging” virus, in the sense that little is known about its epidemiological characteristics and only one major outbreak had been reported prior to 2015, makes it difficult to determine its potential for severity. The outbreak in French Polynesia was the first to raise the possibility that Zika could be associated with GBS. Previous connections with microcephaly had not been drawn prior to the outbreak in Brazil, though a past outbreak of Chikungunya on the island of Reunion had led to cases of microcephaly. The French Polynesia outbreak illustrated the potential for Zika to spread rapidly and lead to damaging neurological consequences. The strain found in Brazil is closely aligned with a strain from French Polynesia, and the introduction of Zika into Brazil is considered to have occurred during an international canoe race held in Rio de Janeiro in August 2014, featuring competitors from French Polynesia, New Caledonia, Cook Islands, and Easter Island.
IDIS Level: The spike in microcephaly patients in the northeast of Brazil is an IDIS Category 3 outbreak; confirmed associations with Zika virus or Chikungunya may lead to Cat 4 or Cat 5 levels.
Relevance: Brazil’s annual dengue incidence is one of the highest in the world, due in part to a welcome climate for the Aedes spp. vector. This same vector can transmit Chikungunya and Zika virus, two diseases that have recently been introduced into the country. The potential for concurrent outbreaks of dengue, Chikungunya, and Zika in Brazil in 2016 is concerning, especially given the close associations being made between Zika, Chikungunya, and neurological complications. Public health countermeasures need to ensure that laboratory tests are run to confirm the presence of a specific virus in order to properly distinguish the threat of neurological symptoms.
Current vs. Forecast: No forecast for Zika exists in the country. However, Zika is spread by the Aedes spp. mosquito, as are dengue and chikungunya. Ascel Bio’s forecast for dengue fever in Brazil indicates a significant increase in disease activity in the first half of the year, starting in January. Disease surveillance and laboratory diagnostics will be very important to understanding the epidemiological characteristics of Chikungunya, Zika, and dengue concurrently in Brazil.
Guidance: Wear mosquito repellent and empty mosquito breeding spots (stagnant water) around the house and workplace. Caution is advised when traveling to affected areas, especially for pregnant women.
Final Observation: A spike in Zika infections in the beginning of 2015 is being associated with some concerning side effects at the end of the year. With Zika and Chikungunya now spreading in the region in addition to dengue, public health efforts to eliminate the mosquito vector and confirm diagnoses through laboratory measures are critical. The potential for disruption due to a confirmed relationship between Zika and GBS/microcephaly is CAT 4/5 in Brazil, based on current reporting trends.