Zika virus hasn’t been on the front page much lately, but case numbers continue to rise in many countries. The World Health Organization stated recently that Zika infection has been documented in 75 countries throughout the globe.
One of the many unusual aspects of Zika virus is that Brazil has, far and away, the most cases of babies born with birth defects. The most prominent of these is microcephaly, a condition where the brain fails to grow normally, causing a striking appearance where the head is much smaller than normal. Brazil has about 2000 cases of this abnormality, while Colombia has the second highest with only 57; the U.S. is third with 31 cases, including miscarriages. Within Brazil itself, the Northeastern part of the country has the highest number of infants affected by the debilitating effects of the virus.
The American Society of Tropical Medicine, in its annual meeting in Atlanta, discussed this disparity, which has fueled a hotbed of speculation about the disparity.
A Brazilian health official, Pedro Fernando da Costa Vasconcelos, suggests that vaccination against Yellow Fever, a virus in the same family as Zika, may be a factor. In Northeastern Brazil, few receive this vaccine compared to other parts of the country. It’s possible, he says, that the vaccine may give some cross-protection against Zika.
A number of other theories exist, including effects on humans by certain pesticides used in the epidemic zone and, perhaps, contaminated lots of vaccines. However, no hard data has, as yet, implicated these and other possibilities as part of the equation.
Another factor may be the growing tendency of women to terminate their pregnancies in the face of a diagnosis of Zika infection. Still another, according to Albert Ko, a Yale professor, relates to the difficulty tracking numbers of abortions for this reason and the fact that many never know they had the infection at all. Zika has no symptoms whatsoever in 80% of patients. The rest experience fever, joint aches, rashes, and eye redness.
What is obvious, however, is that there are wide variations in the percentage of Zika infections to birth defects. Puerto Rico recently reported its first case of microcephaly in a newborn, but has catalogued more than 30,000 people infected with Zika.
Professor Ko says that a new large-scale study will follow thousands of pregnant women with Zika diagnoses. Genetics, prior viral infections, and even the mosquitoes that transmit the virus will be evaluated. It’s possible that, with this information, a more definitive picture of factor involved in Zika-related birth abnormalities will emerge.
An issue not commonly considered is what effect Zika infection may have long-term in apparently unaffected infants. Will they reach normal milestones like walking and talking at the appropriate time? Down the road, will they perform adequately in school? It will take years to find out.
Meanwhile, cases continue to accumulate, mostly travel related. A total of close to 36,000 cases have been documented by the Centers for Disease Control and Prevention (CDC) in the United States and the U.S. territory of Puerto Rico. New cases are still being reported in Florida by the Department of Health, which says that 1,165 total cases (153 in pregnant women) exist in the state as of November 11, 2016. Of these, 225 were transmitted by local mosquitoes.
Some good news: A vaccine called Zika Purified Inactivated Virus, or ZPIV, seems to be showing promise in research conducted, and human trials have begun at the Walter Reed Army Institute of Research. In addition, Dr. Michael Diamond of the University of Washington has identified an antibody that might protect the unborn fetus against the effects of the Zika virus on nervous tissue. Research is ongoing on these and other fronts in the battle against what has become a worldwide epidemic.
Joe Alton, MD
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