There are indications that Zika may have contributed by surpressing the immune system.
Yes, generally speaking , the sick, the elderly, and the very young , who have an undeveloped immune system are at risk.
Indications? Well, that 's what diseases DO.
The human immune system has gotten weaker, I read. It doesn't seem to be "survival of the fittest" anymore, since modern medicine seems to have a cure for almost everything.
From Google: The Zika virus is a mosquito-transmitted infection related to dengue, yellow fever and West Nile virus.
Although it was discovered in the Zika forest in Uganda in 1947 and is common in Africa and Asia, it did not begin spreading widely in the Western Hemisphere until last May, when an outbreak occurred in Brazil.
Note the "related to" part. Viruses seem to mutate and come up with yet another life of illness for humans.
I also read that we can't kill viruses yet and we simply must allow our immune systems to keep us alive while the virus lives out its short life in our bodies.
Don't you think that newer and still ugly viruses will continue to appear? I do. It seems a part of nature's cycle of life and death.