Ten thousand New Zealanders may have lost vision - sometimes permanently - due to toxoplasmosis, an infection triggered by a parasite spread by cats.

Otago University researchers estimate 40,000 people are affected by ocular toxoplasmosis - one in four seriously - but their efforts to develop new treatments are being hampered by a lack of funding.

"When there is inflammation in the retina, the vision becomes blurry, and sometimes we can see when the inflammation goes away, it leaves a scar, and the vision is never going to recover."

World-wide, up to one in three people are infected - but rates could be even higher in New Zealand: 43 percent according to one study in Waikato.

The parasite, Toxoplasma gondii, reproduces in cat guts and is spread through eggs in their faeces.

It was not just a problem for people, Russell said.

"Toxoplasmosis is a killer of some of our precious native wildlife, including birds like kiwi and kākā, and our unique Hector's and Māui dolphins. It also causes big problems for sheep farmers, leading to the loss of lambs."