Scientists tried to understand how the Zika virus caused microcephaly in Brazil, and at a higher rate than in other countries which also had the Zika virus. The investigators failed to first consider the overall infectious burden in Brazil, in humans and pets, and only tested mothers and infants for the Zika virus. Immortal pathogens and parasites in pets can attach to and hide other pathogens, and co-infections can work synergistically to reach new areas in the body and worsen the damage caused by the pathogens.
The most likely co-infection was toxoplasmosis, because fifty to eighty percent of women of child bearing age in Brazil have toxoplasmosis, toxoplasmosis alone can get into the brain of a fetus and cause microcephaly, Zika could have become a bacteriophage of toxoplasmosis, and the co-infections could cause microcephaly at a higher rate.
https://www.youtube.com/watch?v=WbG6mzYUnyU&feature=youtu.be&fbclid=IwAR07cSRiUzBpr1LyW6_XXDtifWuQI9z0N3RTdP37Hv9HXv6oyu1qvRAe1gg