Maggie Fisher, the parasitologist and chairman of ESCCAP (European Scientific Counsel Companion Animal Parasites), has highlighted studies which demonstrate an association between the common parasite, Toxocara spp. and human disease, and has called on the profession to help reduce the damaging and widespread effects of this parasite.Maggie Fisher MRCVS, the parasitologist and chairman of ESCCAP (European Scientific Counsel Companion Animal Parasites), has highlighted studies which demonstrate an association between the common parasite, Toxocara spp. and human disease, and has called on the profession to help reduce the damaging and widespread effects of this parasite.

Maggie says that many in the profession may not be aware that Toxocara eggs aren't actually infective when they are first passed in an animal's stools, sometimes taking weeks to develop to this stage. Eggs persist long after pet waste has naturally washed away too, so the risk of infection still exists even in environments that appear to be clean and safe. Interestingly, there seems to be only a very loose (and according to some studies, entirely absent) link between owning a pet and an increased risk of human Toxocara infection, suggesting that most infections are acquired from the environment1,2 . Education of pet owners about responsible pet ownership, including appropriate worming and picking up their dog's waste quickly is essential to reduce this environmental infection risk.

The parasite's larval stages cause disease in humans as they migrate through body tissues, with retinal damage a previously well identified consequence. However, Maggie has identified studies which suggest a whole range of common conditions that may also be attributable to Toxocara infection. One study3 included 425 children displaying signs of a persistent cough and 1600 asymptomatic children as controls. Blood tests confirmed that a statistically significant 32% of the symptomatic group were positive for Toxocara antibodies, compared to just 17% of the asymptomatic control group. What's more, when given a week's course of an appropriate anthelmintic, the vast majority of symptomatic children had a greatly reduced and frequently absent requirement for inhaled corticosteroids to control their symptoms when re-examined by the study team a year later.

Numerous other studies from around the world have shown similar strong associations with asthma, allergies and epilepsy. One nationally representative US study even showed an alarming association with Toxocara infection and reduced cognitive function in children2 . Those that were positive for antibodies to the parasite on blood tests (proving prior exposure) scored significantly lower on tests assessing verbal and manual dexterity as well as maths and reading abilities2 .

So, what should veterinary staff and SQPs be telling clients? Maggie says you should be advising pet owners to worm pets regularly (at least four times a year) with an effective anthelmintic from an appropriately young age (2 weeks of age for puppies and 3 weeks of age for kittens, because transfer of the parasite to puppies before birth and to kittens via milk is a feature of the parasite lifecycle). Reducing pets' access to raw food and hunting activities can also help. This is in addition to more general recommendations including cooking food well and making sure children wash their hands before eating.

Maggie said: "Vets, nurses and SQPs are perfectly placed to make sure that pet owners are aware of the risks and take precautions to protect themselves and the wider general public."

For further information about effective control of Toxocara and a wide range of other companion animal parasites, visit www.esccapuk.org.uk. To view all the presentations from the 'Everyday Parasites' CPD day, visit www.esccapuk-cpd.co.uk.

References:

  1. Taylor, M.R., 2006. Ocular Toxocariasis. In: Toxocara, the enigmatic parasite. Holland, C.V., Smith, H.V., Eds. CABI Publishing, Ch. 9, 127-144.
  2. 2. 3rd US National Health and Nutrition Survey Walsh, M.G., 2010. Toxocara infection and diminished lung function in a nationally representative sample from the United Sates population. Int J Parasitol.41(2):243-7
    Walsh, M.G., Haseeb, M.A., 2012. Reduced cognitive function in children with toxocariasis in a nationally representative sample of the United States. Int. J. Parasitol. 42, 1159-1163
  3. Bede, O., Szénási, Z., Danka, J., Gyurkovits, K., Nagy, D., 2008. Toxocariasis associated with chronic cough in childhood: a longitudinal study in Hungary. J. Helminthol. 82, 357 - 63.

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