Richard makes a good point about infectivity (or viability)
falling off with time. I believe Oshima published a paper on this around
1960 or 1961 in the Journal of Parasitology. Its been sometime since I
read it but I believe he found significant loss of infectivity after only
90 days when eggs were maintained at room temp. On the other hand,
regardles of the total decline, it only takes one infective ovum to give
an infection and there is ample reason to believe that very, very light
infections tend to favor the development of ocular larva migrans which
might be far worse than visceral larva migrans. Again, I recognize that
OLM is a rare condition, but to a person who has it, its 100% of the cases.
On 31 Jan 1996, Richard Speare wrote:
> In the current discussion on viability of Toxocara eggs, the point has
> been made that Toxocara eggs survive a "long time" in soil. However, I
> think it is also important to take into consideration quantitative
> aspects. Key information must be the rate of death of eggs with time.
> So even if viable eggs could be found for years, what proportion of the
> initial inoculum survives 1 wk, 1 mth, 1 yr, etc. I have not yet made
> the effort to chase this up, but it is important. Do any subscribers
> have good data on this?
>> Remember that the zoonotic hazard is probably dose related. One of the
> key factors in the risk of disease to a person will be inoculating dose.
> (Apart from a range of host factors as well). Without quantitative
> considerations, a qualitative argument may serve to make the situation
> appear much worse than it is.
>> Also dog faeces does not equal Toxocara eggs. Has the soil been checked
> for Tozocara eggs?
>> Rick Speare
>> Department of Public Health and Tropical Medicine
> James Cook University
>> Phone: -61-(0)77-225710
> Fax: -61-(0)77-715032
> email: Richard.Speare at jcu.edu.au>>>>