Zika and pesticides - innocent until proven guilty

Up until a few months ago it is unlikely that you had ever heard of Zika virus before, or microcephaly for that matter; but today both of these topics are splattered across the news. Microcephaly can cause babies to be born with smaller heads than normal, which can eventually lead to smaller brain size and slower development. With headlines pointing in all different directions, some blaming pesticide usage for the poor birth outcomes, it can be hard to discern what is true. So what do you need to know about the Zika virus and how can you protect yourself?

Zika was first discovered in the Zika forest in Uganda in 1947. The virus is transmitted by the Aedes egypti mosquito, a species of mosquito that is very closely associated with human beings and is known to transmit yellow fever, dengue, and chikungunya as well. This mosquito is common in many places around the world, and can be difficult to control as their eggs stay viable for up to a year after being completely dried out. Once the eggs are back in a wet environment they will hatch.

This is a huge problem in tropical countries, where mosquitoes have access to ample water sources all year round. In order to solve this problem pesticides are applied to pools of standing water where mosquitoes may breed; this may even include drinking water. In Brazil, the pesticide used to eradicate the Aedes aegypti mosquito is called pyriproxyfen. Pyriproxyfen acts by mimicking a hormone found in invertebrates that is not seen in mammalian animals, and thus, even at extremely high doses, it usually does not affect the animals. But still many people are wondering if it is this pesticide that is causing the recent surge in microcephaly in infants. It is here that we must remember: correlation does not imply causation.

While pyriproxyfen, the pesticide currently being blamed for the outbreak, is used in many places across Brazil, it is not used in three of the cities which have reported the majority of the cases of both Zika and microcephaly - Recife, Jaboatao and Paulista. Pyriproxyfen has been approved for use for 20 years and in 40 countries around the world; it is currently used as a pesticide on citrus fruits in Israel, South Africa, Spain and Italy, places where there is no current outbreak of microcephaly. In South America, it has been used for over a decade. Additionally, the WHO cites animal studies which have shown that the larvicide is filtered out through the urine within 48 hours of ingestion.

Scientific tests have found presence of the Zika virus in the blood, tissues, and amniotic fluid of infants with microcephaly which lends a significant amount of evidence to it being the source of these birth defects. Microcephaly is also not exclusive to Zika, and has been associated with the transmission of other viruses from the mother to the child during pregnancy. Microcephaly can also be caused by a wide variety of factors including genetics, malnutrition, prenatal infection, and exposure to toxic substances - drugs, alcohol, and chemicals. It is not unreasonable for individuals to question potential environmental exposures in the occurrence of an outbreak; yet, in this case, it seems that pyriproxyfen is not the culprit.

There is, as always, more research to be done, but all current evidence points to Zika virus as the cause of microcephaly in prenatally infected infants. To protect yourself the CDC advises that women who are pregnant or trying to get pregnant do not travel to areas where there are currently Zika outbreaks. Additionally, using bug spray, wearing clothes that do not leave your skin exposed, and being sure to clean up any pools of standing water near your house and/or work can help decrease your risk of mosquito bites.

Margo Henkhaus