A can of worms?

We all have background knowledge that we rarely question and just assume as fact. Even those of us who love our dogs very, very much probably think worms in dog poo have made lots of people go blind. Some people think it happens a lot.
How many cases of Toxocariasis a year do you think there are? Take a guess. Answer will be revealed a little later in this blog.
Toxocariasis is seen as a serious enough threat to public health for some councils to have installed secret cameras to film dog owners who don't clean up.
We all know that not cleaning up our dog's poo is unsociable and unacceptable. It's smelly stuff that no one wants on their shoes. But the blindness health 'fact' puts the poo leavers in a very different category to the vile gum spitters, binge drinking spewers and the careless dog end tossers.
Archie Bryden worked for many years at the Public Health Laboratory Service - now called the Health Protection Agency. He's now retired.
How many cases of blindness caused by dog poo did he encounter?

"When I was looking into toxocara, I did not find any references to bilateral ocular involvement. If you understand the life-cycle in human infection you would find that bilateral infection was remote. You could not say that it could never occur but the chances of it occurring are minute. I seriously doubt if anyone has ever been blinded in both eyes in proven toxocara infection."

So how do you catch Toxocariasis?
I'm going to quote from an article Archie wrote in the 1990s for the Kennel Gazette.

"The principle source of human infections is probably infected soil, with geophagia pica (soil eating) in infants being an important risk. Intimate contact with very young puppies by children may also be associated with increased risk."

How can you reduce the risks

"The prevention of human toxocariasis infection is good hygiene and common sense. For all ages, washing of hands before eating is a must for all sorts of reasons. Parents should supervise closely infants playing on grass, preventing them from putting dirty toys in their mouths and especially from indulging in pica (dirt eating).
Hygiene in the kitchen is also important by ensuring that any vegetable which is to be eaten raw and has had close contact with soil (eg lettuce, celery, radish) is thoroughly washed.
We have become increasingly aware of many unanswered questions. One of these concerns the relation between infections in dogs, foxes and cats. Much further research is required."

So Toxocariasis can come from cat and fox poo and unwashed salad are likely culprits for transmission? How come we don't all know that...? Does Max Clifford do PR for pussies and foxes?

"It is assumed that human cases of toxocariasis are caused by T canis. However, recent reports (Ed's note: this was written in the 1990s) suggest that in Japan T cati in cats has been shown to be very variable. Early studies of domestic and stray cats found that 5-45 per cent had ova in their faeces, which a more recent investigation showed that 63 per cent of farm cats were excreting ova, often in large numbers. However, our investigation of cats in an RSPCA cattery in the North West of England has shown an excretion rate of 6-7 percent. It should also be noted that 50-60 per cent of foxes, adults and cubs, are excretors and while it is impossible to assess their role in disseminating ova in the environment, this may not be insignificant, considering the increasing numbers in urban areas."

But dogs are still some risk?

"The vast majority of dogs in public places are adults and thus unlikely to excrete ova and, of the few young puppies, all are well past the age of maximum excretion."

So what are the statistics? In May last year according to Hansard the following question was asked in parliament:

Mr. Denis Murphy: To ask the Secretary of State for Health how many reported cases of toxocariasis in humans there were in the last three years. [204904]

Dawn Primarolo: The number of toxocariasis cases reported in the last three years in England and Wales is as follows:

	Number of cases
2007	1
2006	1
2005	5

So why do we all have such a fear of dog poo?

"One reason for such variation is confusion of toxocariasis with toxoplasmosis caused by a different organism. Toxoplasma gondii, which also causes eye defects."

So what causes Toxoplasmosis? And how do you get it? (This answer comes from patient.co.uk - a GP driven website.)

"Toxoplasmosis is caused by Toxoplasma gondii, an intracellular obligate parasite (i.e. it can only feed on the living tissues of the host). It is one of the commonest human parasites and has features in common with the pathogen that causes malaria. Human domestic cats are the main source of infection. Infectious oocysts are excreted by the cat for up to two weeks after the initial infection and can survive in warm, moist soil for more than 1 year. Humans acquire infection from cats or from eating raw or undercooked meat from another intermediate host. Pregnant women should avoid contact with cat litter and wear gloves when gardening and during any contact with soil or sand."

So how many people have lost babies to Toxoplasmosis ? Going back to the 1990s again, but according to Hansard:

Mrs Ray Michie
To ask the Secretary of State for Health if he will list the number of cases of congenital toxoplasmosis recorded in England and Wales as a fraction of total pregnancies for each year since 1979; and if he will make a statement.
Mr Dorrell
Congenital toxoplasmosis is not a notifiable disease, so comprehensive figures are not available. However, reports of cases to the public health laboratory service from the Toxoplasma reference laboratories in England and Wales have averaged about 12 per year. As a proportion of the number of conceptions (between 750,000 and 850,000 per annum over the past decade), the figure is minute.

I have to say 12 people a year losing their babies sounds far too many!
Instead of spending money covertly filming people not cleaning up dog poo, couldn't councils leaflet people about the risk of handling litter trays when they are pregnant, eating poorly washed salad and eating undercooked meat on the BBQ? Now that might actually save lives! Sounds like soil is the problem and even if we shot every dog in Britain there'd still be a real danger in eating dirt!
We all need to clean up too, and keep worm free - but how on earth did the dog get all the blame when there are so many other factors and much worse lurgies hiding in our soil?
What's Max Clifford's phone number? Think the poor old dog has been left in the stinky stuff by the cat and the fox!

• See the Think Tank for a lively discussion on worming!