A Fecal egg count is a snap shot of a specific moment in time. The test detects eggs of mature parasites that live inside the body and pass their eggs to the outside by shedding them into the dogs stool’s. It is possible that at the time of testing the parasites are too young to produce eggs, if no eggs are being shed the infection cannot be detected.
There is also a possibility the eggs are In such small numbers at the time of testing they would be undetectable Thus showing a negative result. The above is extremely rare but we would like to point out the possibilities.