Stool testing (egg counting)
Stool testing for helminth hosts
For the purposes of helminthic therapy, it is only necessary to test for the presence of the human helminths, Necator americanus (NA) and Trichuris trichiura (TT). The non-human helminths, Trichuris suis (TS) and Hymenolepis diminuta (HD) do not normally survive for long enough in humans to produce eggs. (The exceptions to this are a small percentage of very young children and severely immunocompromised patients, in whom HDC can develop and persist.)
A DNA polymerase chain reaction (PCR) stool analysis is the ideal method of determining whether any helminths are present, as was shown in a 2023 study that found PCR testing to be superior to traditional microscopy for identifying soil-tranmitted helminth infections. [1]. A PCR test can be ordered internationally online from Diagnostic Solutions in Atlanta Georgia, US. Make sure your clinician specifically asks for the helminth test.
Stool sample microscopy was the method used traditionally, and most pathology labs will still have a faecal (stool) test called something like "Ova, Cysts, and Parasites" or "Ova and Parasite". Unfortunately, most commercial laboratories have insufficient experience to accurately identify helminth eggs by this method, [2] especially when the number of eggs is low, as it usually is in the stool of helminth self-treaters.
Microscopy is therefore best carried out by one of the following.
- A helminth provider. Currently, only one helminth provider offers a stool testing service, details of which can be found here.
- A laboratory associated with a school of tropical medicine.
- A veterinarian. (Vets are very familiar with helminth eggs.)
Eventually, artifical inteeligence (AI) will be used to test stool samples for helminths. [5] In the meantime, anyone with a microscope can carry out a stool test themselves, using a fecalyzer, although some practice may be required in order to develop adequate proficiency with the technique.
- Stool testing (Equipment) - Equipment required for stool testing.
- Stool testing (Method) - A simple stool testing method.
McMasters egg counting technique
The McMaster egg counting technique is a conventional quantitative technique for determining the number of eggs (Ova) present per gram of faeces (eggs/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.
A new egg counting technique
Traditional counting techniques, such as McMasters, have poor sensitivity for measuring light hookworm infections.
In Helminthic therapy, our focus is maintaining a light infection. Even an inoculation of 25 hookworms might only produce 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 fail to find any ova in the stool of hookworm self-treaters.
However, using a fecalyzer gives much better sensitivity, and those who are using helminthic therapy have found the following technique preferable.
- 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 detail, see the following page.
Egg counting is not a reliable means of assessing colony size
The number of eggs found in a single stool sample is not a reliable indicator of the number of worms being hosted, for the following reasons.
- 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 at which material passes 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 also affect the speed of material through the intestines. In subjects who are only hosting a few NA, it will be more difficult to find eggs due to their reduced density and, when only a very small number of worms is being hosted, these may all be of the same gender so unable to produce any eggs at all.
- 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 gram 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. NA only begin to produce eggs between 4 and 6 weeks post inoculation. [6] Thereafter, the number of eggs produced increases gradually up to a maximum at about 20 weeks. After approximately one year, ova production falls by an estimated 50%, although 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. For example, antibiotics suppress egg production for at least 2 weeks after completion of a course of treatment, and production might not recover fully for 3-6 months. Certain foods and other substances can also affect egg production, as can be seen in the Human helminth care manual.
In spite of the foregoing considerations, someone who regularly monitors the egg output of their worms over a prolonged period of time may be able to use the results of their testing to gauge the health of their colony.
Alternatives to egg counting
Some people find egg counting difficult.
Some hookworm hosts find it easier to check for the presence of worms by incubating a stool sample rather than attempting to count the eggs via a fecal float.
Another way to determine whether or not you are hosting helminths is to have a blood draw to see if your eosinophil levels are elevated. Although this is not a foolproof test for the presence of helminths (eosinophils are not always raised), it is fairly reliable. It is also quick, and is a method that a medical insurer might pay for.