Don’t Let Parasites Hide in a Negative Exam

    Not long ago, Emily, our exam assistant, adopted a dog named Cocoa from the Humane Society of West Michigan. While at the shelter, Cocoa had been diagnosed with Giardia, a zoonotic parasite—meaning it’s transferable from animals to humans.

    Once she was home, Cocoa received prescriptions for Panacur and Metronidazole and was treated with antibiotics. To keep the Giardia from spreading to humans, Emily did sanitation at home—washing everything and making sure to pick up and dispose of Cocoa’s stool immediately.

    When they went into the vet for a reevaluation of Cocoa’s stool, Emily was surprised to find that the stool had tested positive for Coccidia, another zoonotic parasite completely unrelated to the Giardia. With this knowledge, Emily was able to start Cocoa’s treatment for Coccidia.

    This story shows the importance of reevaluation when it comes to parasites. After a positive fecal test (meaning the stool contains some sort of parasite), it’s recommended to test stool again every 3–4 weeks until two concurrent samples have been shown to not contain parasites.

    One negative fecal exam does not guarantee the pet is parasite-free. Parasite life cycles have several stages, including one where eggs are visibly shed into the intestines. Testing stool during a stage when the parasite is not shedding eggs can lead to a false negative. Waiting the 3–4 weeks before testing again allows young parasites to mature and shed eggs so that they may be detected in the sample.

    For Cocoa’s health and for the health of her humans, they will continue to test Cocoa’s stool until they get two negatives in a row and can have confidence that she is free from parasites!