Study finds heavy rainfall a time indicator of mosquito-borne Zika, Chikungunya outbreaks

A new study found that outbreaks of mosquito-borne viruses Zika and Chikungunya typically occur approximately three weeks after heavy rainfall.

The researchers also discovered that Chikungunya will predominate over Zika when they circulate simultaneously because of Chikungunya’s shorter incubation period. Chikungunya has an incubation period of two days, compared to 10 days for Zika. This finding explains why a late-2015 Zika epidemic in Rio de Janeiro ended while the number of Chikungunya cases increased in February 2016.

For the study, the researchers screened 10,459 blood and urine samples from residents of 48 municipalities in the state of Rio de Janeiro for Chikungunya, dengue, and Zika. They evaluated dates of major rainfalls, the geographic distribution of mosquito-borne virus incidence in cities and neighborhoods and the timing of epidemics.

They confirmed 1,717 cases of Zika infection, 2,170 cases of Chikungunya and 29 cases of dengue. They identified Zika more frequently in neighborhoods with little access to municipal water infrastructure. The occurrence of Chikungunya was weakly correlated with urbanization.

Rains began in October 2015 and the largest wave of Zika occurred approximately one month later. Zika cases significantly decreased in February 2016, coinciding with the beginning of a Chikungunya outbreak.

UCLA researchers Trevon Fuller, Umme-Aiman Halai, Ryan Harrigan, Thomas B. Smith, and Dr. Karin Nielsen-Saines along with collaborators at the Oswaldo Cruz Foundation in Brazil wrote the paper, which was published in the peer-reviewed journal PLOS ONE.