OE, or Ophryocystis elektroscirrha, is a single celled parasite that can infect monarchs. The microscopic spores can transfer from adult monarchs to eggs or milkweed leaves. This condition can be quite debilitating and it is important to make sure that any supplier of larval monarchs tests each adult monarch for OE
Here at Monarch Watch we test each adult for the parasite prior to releasing them into our breeding cages. There is no test for caterpillars, but we are confident that testing the adults prior to introducing them into the cages, in addition to washing all of our milkweed and regularly sterilizing all surfaces eliminates OE from our breeding population. Some breeders also wash the eggs in a bleach solution, but we do not do that because we maintain our adult monarchs to be OE-free.
If you want to learn more about how to test wild caught monarchs for OE, contact Monarch Health at the University of Georgia: http://www.monarchparasites.org/
If you would like to know more about how to rear monarchs in a way that reduces disease, Monarch Joint Venture has a great info sheet: https://monarchjointventure.org/images/uploads/documents/Monarch_Rearing_Instructions.pdf