Almost half of the population of Managua, Nicaragua, is infected with Zika virus, according to a study by UC Berkeley School of Public Health researchers. Eva Harris, professor of Infectious Diseases and Vaccinology at the School of Public Health and director of the UC Berkeley Center for Global Public Health, led the research, which was published August 27 in the Proceedings of the National Academy of Sciences.
“Knowing that 50 percent of the population was infected in only a three-month period during the epidemic is important because it means that another epidemic of that size and ferocity in the near future is very unlikely,” says Harris.
Zika virus was first isolated and identified in Uganda in 1947. The virus jumped the Pacific to the Americas over six decades later, eventually leading to the 2015-16 epidemic that spread the disease throughout the Western Hemisphere. Most cases of the virus result in mild symptoms such as fever and rash. But the major concern with Zika virus stems from the fact that it can be passed from a pregnant woman to her fetus, possibly resulting in severe birth defects like microcephaly.
After the epidemic, the seroprevalence of Zika virus—the percentage of a population that was infected by the pathogen—was unknown. “Seroprevalence studies are important for public health officials and the international scientific community to understand the extent of the Zika epidemic in Nicaragua, and by extension, in Latin America,” says Harris.
Harris and her team tested blood samples from 3,740 children and 1,074 adults from a district in Managua, the capital and largest city in the country, with nearly 1.5 million people in the metropolitan area. The researchers also used a specific and sensitive assay to differentiate antibodies against Zika virus from those against dengue virus, which is closely related to Zika virus.
They found that 36 percent of children and 56 percent of adults tested positive for Zika virus antibodies; overall 46 percent of the population had been infected by the virus.
“We were also able to use the seroprevalence information to determine demographic, biological, spatial, and environmental risk factors for infection,” says Harris.
Within these numbers, the researchers recorded a higher seropositivity in females than males, found that seroprevalence increased with age in children and leveled off with adulthood, and discovered a direct relationship between seropositivity and body surface area in children, suggesting that larger children are more likely to be bitten by mosquito vectors. The study also revealed a gradient of seropositivity highest around the general cemetery, implicating it as a potential environmental source for amplification of risk.
Harris’s team consisted of doctoral student Fausto Bustos Carrillo, postdoc Raquel Burger-Calderon PhD, and faculty scientist Josefina Coloma PhD from the School of Public Health; joined by Aubree Gordon PhD, an epidemiologist from the University of Michigan, and a large group of scientists and researchers from the Nicaraguan Ministry of Health and the Sustainable Sciences Institute in Managua, a nonprofit started by Harris in 1998 to improve scientific and technological capability in developing countries.
“This was a large team effort,” says Harris.
By Austin Price