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Originally Posted by Monkey Orchid  Worming might help reduce Toxocara parasite loads in domestic pets, but of course the use of veterinary drugs to kill parasites does have a serious knock-on effect on wildlife via the food web. E.g. Ivermectin, a commonly-used worming treatment for domestic grazing animals such as cattle and horses, persists in the animals' dung, where it then kills dung-feeding insects such as Dor beetles. This in turn seriously affects the Greater horseshoe bat, for which Dor beetles are an important prey item. It's a demonstration of an important ecological principle, essentially "What goes around, comes around."
There will always be feral dogs and cats transmitting Toxocara, not to mention wild species such as foxes which also carry the parasite. Research has shown that there are high levels of contamination of soil with Toxocara eggs anyway: 87% of soils tested in Germany, 66% in the UK, 42% in Japan. Cats are considered by some authorities to be less responsible for transmitting Toxocara to humans than dogs, partly because of cats' habit of burying their faeces, and partly because dogs are usually in more direct contact with humans. One of the most effective countermeasures against potential ingestion and infection by Toxocara is one of the simplest: thoroughly washing hands after outdoor activities such as gardening, playing etc. If pet owners were to pick up/clear away their dog or cat faeces and dispose of it properly via a contained composter/wormery system then that should reduce the pathological load of eggs in the soil in general, too. |
Soil load is a key issue, and while Toxocara eggs are long lived a persistent load needs replenishment, feral dogs and foxes certainly do not exist in numbers sufficient to account for more than a tiny proportion of the area infections you quote.
Because the domestic dog is a human creation we can't make a direct equivalence between its ecological contribution and that of its ancestor the wolf, however the wolf is the only comparitor we have for a 'natural environment' comparison. On assessment of present day environments a single wolf needs the equivalent of 10 square kilometres of territory to make a living and while richer environments provide a better wolf/land density it is difficult to see the British Isles ever having supported more than a few tens of thousands of wolves at any one time.
Even if we allow, because of the lesser stature of dogs, a biomass eqivalent of dog to wolf of 3:1, at no time could the British Isles have supported more than the equivalent of 100,000 domestic dogs - yet today's dog population is 7 million ! Until mass ownership of dogs began in the 20th Century, the soil load of Toxocara canis eggs in Britain would have been barely measurable. Similar calculations can be made for the relationship between the wild cat and domestic cat where the current population runs at perhaps 200 times what would naturally be supportable.
As to disposal of faeces - ironically if managing Toxocara were the main consideration - street fouling would likely be the best option because dessication, which is the most effective non chemical destruction of the eggs, is more likely to occur on a pavement slab than in the soil.
CM