Cats in the U.S. deposit about 1.2 million metric tons of poop each year. The kitty litter contains an infectious parasite called Toxoplasma gondii, making it a huge public health problem.

About a third of the world's population carries the parasite without showing any symptoms of the infections. Infections caused by the parasite made headlines last year after a Danish study reported that women who are exposed to the parasite are suicidal.

NHS Choices then published a study review of the Danish study saying that although cat-owners are at no risk of developing health complications after handling cat feces, pregnant women should limit their exposure to the parasite.

Later, in Dec 2012, another study from Sweden published in the journal PLOS One showed that the parasite alters the way the brain works by hijacking a key neurotransmitter called gamma-Aminobutyric acid or GABA.

According to CDC, more than 60 million men, women and children in the U.S. carry the Toxoplasma parasite, but only few show any symptoms as the immune system is capable of keeping the parasite from causing any harm.

A recent study from University of Auckland had earlier found that some people who get acute toxoplasmosis show chronic symptoms such as fever, fatigue and muscle aches.

"The accumulation of Toxoplasma gondii oocysts, found in cat feces, may be a much bigger problem than we realize because of their apparent long life and their association with some diseases," said E. Fuller Torrey, who directs the Stanley Medical Research Institute, according to a news release.

Torrey said that more research and better control of cats are required to lower the risk associated with the parasite.

Places where cats deposit their waste have about 400 oocysts per square foot or more and these oocystes can cause an infection.

Dirt gathered under fingernails can harbor about 100 T. gondii oocytes, according to estimates by earlier studies.

Simple measures such as keeping cat litter boxes covered and wearing gloves while gardening can limit exposure to the parasite.