In a study in the New England Journal of Medicine, Zika virus has been linked to microcephaly, a condition where infants are born with abnormally small heads often due to abnormal brain development.
Researchers cited an investigation in French Polynesia. French Polynesia is an overseas collectivity of France, comprising 118 dispersed islands in the South Pacific. The risk of microcephaly due to Zika virus infection was .95 percent, which was based on eight microcephaly cases in a population of about 270,000 people with an estimated rate of Zika infection of 66 percent.
Currently in Brazil, thousands of cases have been identified of infants with suspected microcephaly due to Zika virus. Researchers analyzed data from Bahia, a state in Brazil.
From the study in French Polynesia and a study in Yap Island, located in the western Pacific Ocean, it is evident that the number of reported Zika cases are only a fraction of the actual number of Zika cases that occur.
Therefore, when doing the study in Brazil, the researchers couldn’t rely on the available data. So, they assumed a 10 to 80 percent infection of Zika virus rate. This number was based on estimates from Yap Island, which was 73 percent, French Polynesia, which was 66 to 86 percent, and reports from surveys not attributed to a specific outbreak, which sat around 6 to 40 percent.
The researchers apportioned the risk of 10 to 80 percent across 2015 with the highest point in May 2015. They also assumed all pregnant women were equally susceptible to infection, no one person at more risk than another. In addition, they estimated the number of actual microcephaly cases compared to reported microcephaly cases, with the highest number in December 2015. Finally, they assessed the association between risk of infection with microcephaly cases reported in the Brazilian Live Births Information System between July 2015 and February 2016.
Researchers had to consider different risk rates, from 10 to 80 percent, possible overreporting, and an uncertain baseline rate, two to 12 cases per 10,000 births. Considering these factors, researchers found a significant association between the risk of microcephaly and the risk of infection in the first trimester of pregnancy. Researchers came up with a range of estimated risk due to infection in the first trimester of pregnancy 0.88 percent to 13.2 percent.
The lower end of the range was similar to the study in French Polynesia, which was .95 percent risk of microcephaly due to infection of Zika.
There are limitations with estimates of microcephaly due to Zika infection. There is limited available data. The data in Bahia, Brazil is still being collected. Carefully designed surveys could help with the estimates.
Managing editor of The New England Journal of Medicine also conducted an interview with Dr. Eric Rubin, a professor of immunology and infectious diseases at the Harvard T.H. Chan School of Public Health and an associate editor at the Journal, on the state of the Zika virus and directions for research and prevention.
A growing number of recommendations say that women avoid pregnancy and practice safe sex in areas where the mosquito-borne Zika virus is present, which is 60 countries or territories. Eleven countries or territories have reported cases of microcephaly. Microcephaly is not the only risk associated with Zika virus, too. Not only the brain, but the eye and the spinal cord could also be affected.
As for the summer Olympics in Brazil, there is no consensus among health professionals as to whether or not they should be cancelled. A group of medical professionals do want the games to be cancelled. Many also think it’s an individual choice to go or not, but it is not risk free. So, people must take precautions. Since it’s a mosquito borne illness, avoiding mosquito bites is critical. Dr. Rubin predicted that insecticides sales will rise. It is also documented that the infection can be sexually transmitted, so safe sex is recommended.
Microcephaly is often a mild infection. The most severe manifestations, like microcephaly, weren’t recognized until there was a big outbreak in Yap Island, and then, it was only recognized after the fact. It is still unclear what manifestations will show up as the affected children grow older.