Toxoplasmosis in humans and the role of cats in human infection (particularly pregnant women) have been the subject of much research and argument over the years. The latest results of 20 years of research in the United States of America are summarised below.
CATS are the only known definitive host for toxoplasma. Cats become infected usually early in life, by eating infected rodents, worms, flies, cockroaches or drinking from infected water supplies. They then shed toxoplasma “eggs” (oocysts) in their faeces for between 7-14 days.
IT IS RARE FOR CATS TO SHED THESE OOCYSTS AGAIN WITHIN THEIR LIFETIME! - Even if the cat is sick itself with clinical toxoplasmosis.
Oocysts must sporulate to become infectious; this takes 5-7 days of dry conditions. Contact with fresh faeces cannot cause infection in cats.
Cats are very fastidious and usually don’t allow faeces to remain on their skin/hair long enough for oocysts to sporulate. Therefore it is almost impossible to catch toxoplasmosis from your cat! However, toxoplasmosis oocysts can survive in the environment for up to 2 years.
HUMAN INFECTION therefore is mostly from contaminated sandpits, soil or water and poorly cooked meat.
TOXOPLASMOSIS IS IMPORTANT STILL - especially for pregnant women and immunodeficient human - those receiving treatment for immune mediated diseases, cancer, transplant patients and HIV positive patients. However it was also found in this USA study that all Veterinary personnel and immunosuppressed patients had no greater incidence of toxoplasma than the general population.
RULES FOR PREGNANT WOMEN AND IMMUNOSUPPRESSED PEOPLE:
1. Know your own immune status first. In New Zealand approximately 45% of humans have contacted toxoplasmosis as children and have good immunity to it.
2. Don’t feed your cats under-cooked meat and try to prevent them hunting.
3. Don’t empty the cats litter tray yourself - get someone else to do it! Always clean the cats litter tray daily - flush the faeces and clean the tray with scalding water.
4. Wear gloves in the garden when working with any soil or potting mix and wash your hands well after gardening!
5. Boil water well when camping or using water from the environment for cooking or drinking.
6. Cover children’s sandpits when not in use.
7. Control possible “other” hosts such as cockroaches, flies and rodents.
8. Wear gloves when handling raw meat before cooking!
9. If you are “at risk” and want to get a cat, get a healthy adult cat from a private family. Faecal and blood tests (2 of then 2 weeks apart) should be performed for safety, but remember - direct contact with individual cats rarely causes toxoplasmosis.
© Forrest Hill Vets (2000) Ltd