A Risky Business: Toxocara cati
By Susan McKay
The second European Meeting on Toxocara and toxocariasis, supported by Pfizer Animal Health, recently took place in Paris. The aim was to gather together public health workers, doctors and vets to discuss a way that more data can be gathered about the Toxocara worm.
Researchers have dubbed it ‘the enigmatic parasite’ because so much work still needs to be done to find out what, to scientists, are still quite basic facts. However, information is building on the impact of Toxocara in human and animal populations and cat breeders would be well advised to prick up their ears.
For those who know little about the Toxocara worm here are the facts: the worm can live in cats and dogs while causing no outward signs of infection.
The worms can produce eggs which are passed out in the cat’s stools. Within two weeks the eggs develop larvae within them (an immature worm). The eggs are now infectious and if eaten by a child, the larva can hatch out in their body, migrating through various tissues (in a process called larva migrans) and in some cases causing damage to the eye and even blindness. Cats get re-infected through picking up the eggs and kittens can get infected through their mother’s milk.
In the past dogs were blamed for larva migrans but this was mainly because the eggs of the cat and dog worm are so hard to differentiate. It is now known that Toxocara cati – the cat worm - can also be held responsible.
Speakers at the conference told the invited audience that in fact, things are even more complex than previously imagined. Professor Peter Schantz, the key note speaker at the conference began by making a plea for vets to advise their clients to worm their pets.
Vets have been sued in the USA for failing to do so and there is also a message there for breeders in this increasingly litigatious society, given that many vets do not see the new kitten owner immediately after purchase. All cat breeders should consider asking their vet about what they should be recommending to new kitten owners regarding worming, especially if the kitten is purchased by a family with children.
Cat breeders also need to know about this parasite in order to protect themselves and their families. Although there is no conclusive research relating to cats, it has been found that dog ownership increases the likelihood of Toxocara infection in owners by three times.
Having a litter of puppies in the household increases the risk five times and the risk also increases with ownership of two or more dogs. Professor Schantz quoted Woodruff’s research which indicated that dog breeders were at significantly higher risk than the general population and were more likely to be sero-positive (have antibodies showing that they had been infected by the worm at some point) the more dogs they owned1.
Soil surveys show that anywhere between 10-20% of gardens contain Toxocara eggs, nearly 25% of school playgrounds and up to 39% of sandpits2 3 4, presenting a significant health hazard. While most cat breeders do not allow their cats to roam freely, there is no denying that these sort of statistics can give cats a bad press, especially as dogs don’t tend to have access to neighbours gardens, or sandpits.
Blind to the Risks
The speakers also highlighted that the consequences of human infection by Toxocara are now known to go beyond sight impairment and blindness. Some individuals are infected and like many cats, show no signs at all. Dr Mervyn Taylor has carried out some studies in Ireland and found that from the ages of six months up to five years, about 30% of children will show antibodies in their blood to Toxocara, showing they have been exposed to the parasite and about ten in every 100,000 will develop eye problems5 6. People up to 70 years of age have been diagnosed as having eye problems due to Toxocara infection in childhood.
Two new conditions have also been described. In ‘covert toxocariasis’ there are very vague signs, making it difficult to diagnose the condition but it is associated with antibodies for Toxocara rising in the blood as the signs develop. One finding is that more signs are seen the higher the antibody titre. Even worse is ‘cerebral toxocariasis’ which is due to larval migration into the brain. Several studies now show a strong association between children who have eye damage as a result of Toxocara and who have also eaten dirt and had convulsions (fits) in the past7 8.
What About Cats?
Vet and parasitologist, Maggie Fisher, speaking at the conference, reminded everyone that dogs do develop granulomas in their eyes as a result of Toxocara migration and some kittens do die due to Toxocara larva in their lungs. One study showed that 37% of earthworms are also infected by Toxocara and cats that eat earthworms may also be infected by this route9. Rodents are another possibly source of infection.
Maggie has been investigating Toxocara on an ongoing basis across boarding and rescue catteries for some years. She has found that 4.5% of boarding cats have Toxocara cati, compared with 15.2% of rescue cats10. On average the egg count was over 500 eggs in every gram of faeces. For those who combine breeding with boarding and rescue, this gives much food for thought.
And just in case you thought that basic hygiene would completely protect your breeding cats, a German study involving dogs shows just how complex this parasite may be. Some Toxocara free bitches were walked in a park for three hours a day, five days a week for three months. They were then mated and when the pups were born seven pups from five out of the nine bitches shed Toxocara eggs and 12 pups had adult worms11.
In summary, the effects of Toxocara are long lasting and potentially severe and according to Maggie Fisher, ‘acquisition is easy’: a study of London parks in 1987 showed 66% were positive for Toxocara eggs12. It is known that over the period of one year Toxocara eggs penetrate the soil by only 1-3cm and the eggs can remain infectious for two years13.
The second European Meeting on Toxocara and toxocariasis has provided us with a timely reminder: developing a good worming programme in your cattery is good for your cats’ health and good for the health of you, your customers and the public at large.
Good Toxocara Control
• Toxocara has a pre-patent period of four to five weeks - this is the time between the cat picking up an infection and the adult worms producing eggs. A logical conclusion is that monthly worming for adult cats and dogs will be required
• Instigate a good worming regime for breeding cats and kittens.
• Advise new kitten owners that children should wash their hands after handling pets and before eating (and so should adults!) and that sandpits should always be kept covered when not in use.
• Clean up cat faeces immediately – it takes two weeks for the eggs to develop infectious larva within them.
1. Woodruff, A.W., De Savigny, D.H. and Jacobs, D.E. (1978). Study of toxocariasis in dog breeders. BMJ 4, 1747-1748.
2. Smith, R.E. and Hagstead, H. (1984). Visceral larva migrans : a risk assessment in Baton Rouge, Louisiana. International Journal of Zoonoses 11, 189-194.
3. Childs, J.E. (1985). The prevalence of Toxocara species ova in backyards ans gardens of Baltimore, Maryland. American Journal of Public Health 75 (9), 1092-1095.
4. Dada, B.J.O. and Linquist, W.D. (1979). Studies on flotation techniques for the recovery of helminth eggs from soil and the prevalence of Toxocara spp. in some Kansas public places. Journal of the American Veterinary Medicine Association 174, 1208-1210.
5. Taylor, M.R.H., Keane, C.T., O’Connor, P., Mulville, E. and Holland, C. (1988) The expanded spectrum of toxocaral disease. The Lancet i, 692-695.
6. A Holland C V (2004) Clinical Infectious Diseases 39 173 Ocular Toxocariasis in School Children
7. Good, B., Holland, C.V., Taylor, M.R.H., Larragy, J., Moriarty, P. and O’Regan, M. (2004) Ocular toxocariasis in schoolchildren. Clinical Infectious Diseases 39, 173-178.
8. A Holland C V (2004) Clinical Infectious Diseases 39 173 Ocular Toxocariasis in School Children
9. Mizgajska, H. (1997) The role of some environmental factors in the contamination of soil with Toxocara spp. and other geohelminth eggs. Parasitology International 46, 67-72.
10. Fisher, M. BSAVA 2004 Scientific Proceedings No 41 Assessment of the Zoonotic importance of Toxocara cati and examination of the prevalence of T. cati in domestic cats staying in rescue and boarding catteries in England.
11. Stoye M (1993) J Vet Med 40 453-458 Studies on the infection risk for helminth-free raised dogs kept under conventional conditions in an urban area (article in German)
12. Snow K R et al (1987) Prevalence of Toxocara species eggs in the soil of five east London parks. Vet rec 120 66-67
13. Mizgajska, H. (1997) The role of some environmental factors in the contamination of soil with Toxocara spp. and other geohelminth eggs. Parasitology International 46, 67-72.