Playground equipment and dirt have germs that can  help strengthen a child’s immune system, but sandboxes are full of parasitic germs that can cause severe infections.

Dr. Philip M. Tierno, Jr., a professor of microbiology and pathology at NYU School of Medicine, told CBS News, “You don’t want parasites to be included with the germs that you interface with. It’s not any germ — come one, come all. You have to be selective.”

Feral cats, raccoons, and other animals sometimes make sandboxes their litter boxes. Since diseases like Baylisascariasis (raccoon roundworm), toxocariasis and toxoplasmosis are transmitted through the fecal-oral route, children can become infected while playing in animals bathroom.

Here is a list of some infections caused by parasites that can be found in sandboxes.

Roundworm from Raccoons

Baylisascaris procyonis is a parasitic roundworm that is found in raccoons. Tierno told CBS News that the worm lives in the intestinal tract of raccoons and produces thousands of hardy eggs that are shed in the feces.

study from 2009 found that more than 50% of backyards surveyed in the Chicago suburbs contained raccoon poop. Another study  from the same year discussed Canada’s first case of raccoon roundworm encephalitis, a serious brain infection, in a 7-year-old boy. The study documented, “The child often played in an open sandbox in the backyard and had a habit of putting his hands in his mouth… soil from the sandbox contained B. procyonis eggs.”

Human infected with the worm get Baylisascariasis, which can affect the brain and spinal cord, the eye or other organs, depending on where the larvae migrate. According to the U.S. Centers for Disease Control and Prevention (CDC), symptoms of infection usually take a week or so to develop and may include nausea, fatigue, loss of muscle control or blindness.

Toxocariasis

Toxocariasis is caused by a roundworm found in dogs and cats called Toxocara cani and T. cati respectively. Researchers consider it the “most common human parasitic worm infection in the United States.”

A 2013 study in the journal of the Pediatric Infectious Diseases Society stated that the eggs are found in sandboxes because they are visited by stray cats and dogs. Studies have found toxocara eggs in sandboxes ranging from 0.3% in New Jersey to 39% in Kansas.

According to CDC, many people who are infected are asymptomatic. When symptoms develop in children, they may have coughs, abdominal pain, headaches and behavioral or psychiatric problems.

A JAMA Psychiatry 2014 editorial suggested that toxocariasis may be partially responsible for the achievement gap in U.S. neighborhoods in extreme poverty where rates of roundworm are high.

Toxoplasmosis

Toxoplasmosis is transmitted through cat feces. Young and outdoor felines are most likely to carry the parasite toxoplasma gondii, also known as T. gondii.

T. gondii produces the parasite inside of the cat, which are left in litter boxes, gardens and sandboxes. The parasite can then be picked up by children.

Toxoplasmosis causes flu-like symptoms in children and can cause birth defects is a pregnant woman is infected.

Some research also links the parasite to a higher risk of mental disorders such as schizophrenia and outbursts of anger.

Tips on Healthy Sandbox Play

  1. Cover the sandbox when not in use.
  2. Seal the bottom of the sandbox.
  3. Make sure public sandboxes you use are covered at night and cleaned out regularly.
  4. Examine your  backyard sandbox weekly by sifting through the sand.