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With the report from Florida Gov. Rick Scott on Monday that 14 people in the state have been infected with the Zika virus most likely through mosquito transmission, the concern about outbreaks in the U.S. has intensified. The news comes on the heels of new research by Northeastern professor Alessandro Vespignani that can help countries in the Americas plan a response.
A team led by Northeastern professor Alessandro Vespignani responded to a "call to arms " to model the spread of the Zika virus, revealing the disparity between the number of reported cases and the number of projected cases of this largely asymptomatic disease. The results will help countries in the Americas plan a response. Image by YoungHee Jang/Northeastern University
With the report from Florida Gov. Rick Scott on Monday that 14 people in the state have been infected with the Zika virus most likely through mosquito transmission, the concern about outÂbreaks in the U.S. has intensified. The news comes on the heels of new research by Northeastern proÂfessor Alessandro VespigÂnani that can help counÂtries in the Americas plan a response.
The new study, along with interactive maps, provides current numbers as well projections for the number of Zika cases in the Americas through January 2017. It also provides projections for the number of microcephaly cases associated with the disease through October 2017, a date chosen to allow for the nine months of pregÂnancy. Microcephaly is a serious neurological birth defect characterized by a smaller than normal head.
The research is a collaboration overseen by the Center for Inference and Dynamics of Infectious Diseases, a Models of Infectious Disease Agent Study Center of Excellence funded by the National Institutes of Health.
Tackling Zika has been "a call to arms," says Vespignani. "We've been working on the modeling around the clock since January," adds Matteo Chinazzi a postdoctoral research associate in Vespignani's laboratory for the Modeling of BioÂlogÂical and SocioTechnical Systems, or MOBS, and a coauthor of the study.
The team of 14 researchers uses large- scale comÂpuÂtaÂtional epiÂdemic models that inteÂgrate socio- demographic and travel data of target popÂuÂlaÂtions along with simÂuÂlaÂtions of infecÂtion transÂmisÂsion among milÂlions of indiÂvidÂuals to reconstruct disease spread in the past and project it into the future.
Under- reporting is rife in affected counÂtries because up to 80 percent of people with the disÂease are asymptomatic, says Vespignani, the Sternberg Distinguished Professor of Physics and director of the Network Science Institute at Northeastern. "Even of those with sympÂtoms, probÂably only one- third will go to the doctor and get diagÂnosed," he says.
Indeed, the number of travel- associated cases of Zika in the U.S. reported by the CenÂters for DisÂease ConÂtrol and PreÂvenÂtion (CDC) may be just the tip of the iceÂberg, according to the research.
The team, half of which is at NorthÂeastern, projected that as of June 15 there were close to 30,000 cases of travel- related Zika in the U.S., a number 25 times greater than that reported by the CDC on the same date.
The discrepancy results from the difference between reported cases of the mosquito- borne virus--those actually diagnosed and reported to the CDC's surÂveilÂlance system--and those that fly under the radar but that the researchers' modeling algorithms can project.
"We don't project very large outÂbreaks in the continental U.S.," says VespigÂnani, whose lab has been running the simulations of infection transmission--a job that requires using some 30,000 procesÂsors at once. "But there is a cerÂtain set of countries in the Americas that has the right mosquitoes, the right weather, and the right socioeconomic conÂdiÂtions for major outÂbreaks." Those conÂdiÂtions include lack of air conÂdiÂtioning, poor sanitation, and little access to education, for example, instrucÂtion on preventative measures such as removal of standing water, which attracts mosquitoes.
Among those counÂtries are Brazil, with 15 percent of the popÂuÂlaÂtion affected by the virus; Colombia, with 8 percent, and Puerto Rico with 10 percent. Puerto Rico is being parÂticÂuÂlarly hard hit right now. "That's because Puerto Rico is entering mosÂquito season," says Qian Zhang, a postdoctoral research assoÂciate in MOBS and a coauÂthor of the study. "The weather conditions, including temperature and humidity, are now favorÂable for the Zika spread."
Still, the risk of conÂtracting Zika as a result of the 2016 Olympics in Rio de Janeiro is extremely small, says VespigÂnani. That's because the increase in air travel from Zika- affected areas will be minimal--less than 1 perÂcent. The number of cases in Brazil, where the virus surÂfaced between August 2013 and April 2014, reached its peak in the first half of 2015 and has been declining since, affecting close to 10 to 15 perÂcent of the population.
"The number of people traveling with Zika all over the world has already been huge," says Vespignani. "And Rio is not very much affected at the moment. So the half- million people who will travel there for the Games are just a small perÂturÂbaÂtion in the entire picÂture of the virus' spread."
Projecting the spread of Zika has been much more difÂfiÂcult than doing so for Ebola or the flu, says VespigÂnani, who has mapped both. That's because the disÂease is primarily transmitted not from person to person but from mosquitoes to people, most often the species Aedes aegypti but also Aedes albopictus,both of which carry the dengue and yellow fever viruses as well.
Thus data on human mobility, socio- demographics, and temperature changes--the bread and butter of epidemic modeling--must be comÂpounded with data on the mosquitoes, much of which is uncerÂtain, such as their travel patÂterns, abunÂdance, and lifeÂcycle depending on temperaÂure. "Unfortunately, mosquitoes do not have a GPS attached to them," says Ana Pastore- Piontti, also a postÂdocÂtoral research assoÂciate on the MOBS team who has also worked with VespigÂnani on past disÂease threats such as the Ebola epidemic.
In addition, reÂatively little is known about Zika itself, for example, preÂcisely when and where the virus arrived in Brazil, the length of the incuÂbaÂtion period in humans and mosÂquiÂtoes, and whether humans can develop immunity to the virus.
Indeed, with no data available specifically on the relationship between Zika and its host mosÂquiÂtoes, the researchers had to rely on the historical literature on other mosquito- borne disÂeases including dengue, malaria, and chikunÂgunya. "But that means that we are making a lot of assumpÂtions that Zika is close to dengue, for example," says Kaiyuan Sun, PhD'19. He and Dina Mistry, PhD'18, are also coauÂthors of the Zika study.
Given all the uncertainties, the researchers cauÂtion that their findÂings are "projections," rather than "foreÂcasts." "We use 'foreÂcast' when we have a level of conÂfiÂdence in past data--such as the origin of the disÂease and the proÂgresÂsion of outbreaks--that allows us, even with some flucÂtuÂaÂtions, to project into the future," says VespigÂnani. "With Zika we are saying, 'These are the sceÂnarios based on a number of assumpÂtions and an attempt to get some plausible path for the future.'"
Source: Northeastern University