McMaster Egg Count
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McMasters Counting Technique
The McMaster counting technique is a quantitative technique for determining the number of eggs (Ova) present per gram of faeces (e.p.g.).
A prescribed amount of stool sample is mixed with salt solution and added to a special microscope slide (Whitlock Universal or Whitlock McMaster). Segments etched into the slide allow the observer to easily count the number of eggs per standard area. While the salt solution makes the worm eggs float to the top.
Sir Frederick Duncan McMaster founded the CSIRO in Australia. The work of developing the counting technique was developed by the CSIRO institute in the mid 1900's for the care of pastoral animals.
The McMaster method is used for measuring patients’ stool samples with egg load varying from very low (15–60 epg for T. trichiura) to moderate (1650–4500 epg for A. lumbricoides).
Egg count does not tell you the exact number of hookworms you are infected with. However we can make a guess.
- The Nottingham allergy trial gave everyone 10 hookworms and did quantitative egg count. Participants had egg counts from 90 – 200 epg.
- A light infection is considered < 2000 epg.
- Average egg count for a single adult female in the prime of her life is estimated to be around 50 epg. So a count of 700 epg could assume 14 females.
These notes were gleamed from Debora web site who has been measuring and studying worm eggs for some time now.
Most pathology labs will have a faecal (stool) test called something like "Ova, cysts, and Parasites" or "Ova and Parasite". When choosing a testing lab try and find one that is experienced in counting eggs. Note that some labs only note the presence of hookworm ova without actually reporting the egg count.
The Argument Against Egg Counts as an Indicator of Helminth Number
- Parasitology texts note that per day female hookworm and whipworm ova production varies from 2,000 to 20,000 total. For this reason alone any estimate based on an ova count must have a variance of x10. That is the answer can only be expressed as a range, with the higher end of the range being ten times the low end. So a typical answer would be "from 20-200 hookworm". So this indicator may be only a rough gauge of infection.
- Egg counts are a measure of density. So any count is going to be affected by things like the speed of material through the intestines (constipation or diarrhoea at the extremes), amount eaten, amount of fluid drunk, fibre content of food, etc. If you think of the extremes one can see this is going to have an enormous impact on density of ova per gram of faeces. Different foods and drugs affect the speed of material through the intestines.
- Any count depends on extreme precision and replication of methods and precision from test-to-test. Only an experienced lab technician is capable of accurately counting ova in stool, stains are no aid and identifying each and every ova in a gram of faeces is difficult work. In someone producing 100 ova per gram .1 grams will contain 10 ova, so the slightest variation in weight can have a big effect on the number observed, that effect then being amplified by the multipliers used to derive worm population from egg counts.
- Ova production varies tremendously with time. Hookworm ova production falls by an estimated 50% about one year after infection. But there is little information on whether this is invariably 50% or exactly when it happens or how fast.
- Ova production in all helminths is affected by various drugs, some known, some inevitably unstudied. So, antibiotic use so profoundly reduces ova production that parasitology texts recommend not doing ova tests for two weeks after the subject stops taking the antibiotics. Other drugs almost certainly have various effects as well.
A New Counting Technique
Traditional counting techniques, such as McMasters, have poor sensitivity for measuring light infections of hook worm. In Helminthic therapy our focus is maintaining a light infection. For an inoculation of 25 hookworms we might only observe 2 or 3 ova on a McMaster slide (so maybe 2x60 = 120 epg depending on the technique). Given the inherent error associated with egg counting (see section above) it's not uncommon for pathology labs to completely miss seeing ova in people undergoing the therapy.
However using a fecalyzer gives much better sensitivity. A number of us undergoing the therapy are trialling the following technique:
- Added 1 gram of poo to a fecalyzer (prepare as per fecalyzer instructions).
- Let 22x22mm slide cover slip stand on top of fecalyzer for 20mins.
- Place the slip on slide and using a microscope at 100x magnification count all ova observed under the cover slip.
For more information on the new counting technique see: countingclub.bluesina.com