Spring snowmelt often reveals the unwelcome and unpleasant sight of dog feces on city streets. However, the problem goes beyond this: The meltwater can spread parasite eggs from the feculence and into the soil.

Veterinary parasitologist Liina Laaneoja told "Vikerhommik" that this can happen even when the dog feces have been washed away or are no longer visible on the ground. "Melting snow can wash parasite eggs from the piles into the soil and onto surfaces. This means the real situation may be worse than it seems at first glance," she explained.

The effects depend on the parasite species. Some may cause diarrhea, while others migrate through different organs in the body. Parasites also live at the expense of their host and can weaken the host's system.

They can include both single-celled organisms and worms, and studies in Estonia have identified both roundworm and tapeworm varieties. Some, if contracted, can cause gastrointestinal problems, while others undergo a more complex developmental cycle in the body.

For example, after entering the body, roundworm larvae may begin migrating through tissues. While they do not develop into adult worms in humans, their migration can still damage tissues. In some cases they can even end up in the eye or other organs.

Often owners may not notice the presence of parasites. "The fact that no worms have been seen in an animal does not mean they are not there," Laaneoja noted.

Feces left in the environment can also be a source of infection for animals — including, ironically, dogs themselves — which can pick up parasites through contaminated soil or by coming into contact with the feces of other animals.

The eggs of many parasites are not immediately infectious. It may take several days or even weeks for them to develop to that stage. For this reason, promptly cleaning up feces can significantly reduce the risk of infection. "If feces are removed immediately, parasite eggs often do not yet have time to become infectious," Laaneoja explained. The same principle applies to cats, which is why litter boxes should be cleaned regularly.

Parasites can also be inadvertently brought into the home via shoes or clothing. Some parasite eggs are very resilient and can spread via soil or dust. For this reason, even indoor pets should receive deworming treatment from time to time.

As a general recommendation, indoor pets should be dewormed once or twice a year. For dogs that go outside, the classic recommendation is more frequent treatment, at around four times a year, although the exact schedule depends on the animal's lifestyle. If an animal roams freely, hunts, or eats raw food, deworming may be needed even more often.

Laaneoja stressed that cleaning up after a dog is not only a matter of courtesy toward others, but also an important public health measure. "If we leave feces uncollected, we put other animals, people and even our own pet at risk," she noted.