Yep, it’s coming up to that time of year. All of Microbiology is excited as there is about to be a holiday and eggs are likely to feature in a big way… no not Easter!!! Its holiday time and people will be going to exotic countries and bringing back souvenir parasites and their eggs will be involved in working out what is wrong with them. Yep us Microbiologists’ love eggs, not just the chocolate variety. I don’t know, you lot all have chocolate on the brain :-)
Most intestinal parasites occur when someone ingests the eggs of a parasite, usually from faecally contaminated soil, which then hatch in the patient’s intestine and the parasite starts causing an infection.
Diagnosing intestinal parasite infections is actually quite difficult. There is sometimes a clue in the clinical history such as foreign travel or drinking potentially contaminated water, but most of the time in the UK we only tend to look for parasites when the clinical details say that diarrhoea has been going on for more than 2 weeks. Remember, clinical details are really important and where diarrhoea is concerned it is critical; so include travel history, pets, symptoms (e.g. bloody diarrhoea), contact with other people who are unwell and duration of symptoms.
Laboratory diagnosis of intestinal parasites
There is no easy way to say this; to diagnose most intestinal parasites you have to look at poo! Okay, some labs can do molecular tests for common parasites like Giardia lamblia and Cryptosporidium parvum but for most of the others it all comes back to looking at poo.
More particularly the laboratory is looking for the eggs of the intestinal parasites in the stool sample because the adult parasite itself is usually attached higher up in the bowel where it is laying eggs into the bowel lumen which are then mixed with faeces and passed.
The eggs of parasites are bigger than bacteria but you still need a microscope to see them; parasite eggs are usually >5 micrometres in diameter but sometimes >100 micrometres, whereas bacteria are usually about 1 micrometre. Rather than using x1000 magnification on a microscope, which we use for bacteria, we tend to use x100-400 instead.
Before we look for parasites in the stool sample we need to concentrate the sample so that we get as many eggs under the microscope as possible. This is usually done using a kit that filters out as much “organic debris” (yuck) from the sample whilst concentrating smaller particles in sediment at the bottom of the tube (see picture). The sediment is then put on a microscope slide and a cover slip placed on top so that it can be looked at in more detail.
Diagnosing intestinal parasite infections is actually quite difficult. There is sometimes a clue in the clinical history such as foreign travel or drinking potentially contaminated water, but most of the time in the UK we only tend to look for parasites when the clinical details say that diarrhoea has been going on for more than 2 weeks. Remember, clinical details are really important and where diarrhoea is concerned it is critical; so include travel history, pets, symptoms (e.g. bloody diarrhoea), contact with other people who are unwell and duration of symptoms.
Laboratory diagnosis of intestinal parasites
There is no easy way to say this; to diagnose most intestinal parasites you have to look at poo! Okay, some labs can do molecular tests for common parasites like Giardia lamblia and Cryptosporidium parvum but for most of the others it all comes back to looking at poo.
More particularly the laboratory is looking for the eggs of the intestinal parasites in the stool sample because the adult parasite itself is usually attached higher up in the bowel where it is laying eggs into the bowel lumen which are then mixed with faeces and passed.
The eggs of parasites are bigger than bacteria but you still need a microscope to see them; parasite eggs are usually >5 micrometres in diameter but sometimes >100 micrometres, whereas bacteria are usually about 1 micrometre. Rather than using x1000 magnification on a microscope, which we use for bacteria, we tend to use x100-400 instead.
Before we look for parasites in the stool sample we need to concentrate the sample so that we get as many eggs under the microscope as possible. This is usually done using a kit that filters out as much “organic debris” (yuck) from the sample whilst concentrating smaller particles in sediment at the bottom of the tube (see picture). The sediment is then put on a microscope slide and a cover slip placed on top so that it can be looked at in more detail.
Click for larger image
In order to get the best chance of seeing any parasite eggs in stool it is good practice to look at at least 3 different stool samples before saying they are negative. The stool samples should be as fresh as possible, ideally within an hour of passing; otherwise the eggs may start to break down!
Appearance and size really does matter
Once the sample is under the microscope it is then a case of trying to find what looks like an egg and measuring how big it is. In this complicated world, we rely on human methods. Some of the more common eggs are easily recognisable such as Ascaris lumbricoides, Fasciola hepatica and Trichuris trichuria (which I always think looks like a tea tray) but others require an experienced eye to tell them apart. If you are unable to tell them apart by appearance then size matters and measuring them with a graduated eyepiece in the microscope (not a ruler!!) allows you to compare your image to pictures in order to identify what you are seeing.
So how many of these do you recognise?
Appearance and size really does matter
Once the sample is under the microscope it is then a case of trying to find what looks like an egg and measuring how big it is. In this complicated world, we rely on human methods. Some of the more common eggs are easily recognisable such as Ascaris lumbricoides, Fasciola hepatica and Trichuris trichuria (which I always think looks like a tea tray) but others require an experienced eye to tell them apart. If you are unable to tell them apart by appearance then size matters and measuring them with a graduated eyepiece in the microscope (not a ruler!!) allows you to compare your image to pictures in order to identify what you are seeing.
So how many of these do you recognise?
Answers at the bottom...no pun intended!
Okay the last one was chocolate, but you will be glad to know that all of the others, however grim they look, are easily treatable with the right antimicrobial. The trick though is to work out which parasite you are dealing with and for that you really do need to take a close look at poo!
Have a great Easter and remember as far as I know eating Easter eggs is not a risk factor for infection!
Okay the last one was chocolate, but you will be glad to know that all of the others, however grim they look, are easily treatable with the right antimicrobial. The trick though is to work out which parasite you are dealing with and for that you really do need to take a close look at poo!
Have a great Easter and remember as far as I know eating Easter eggs is not a risk factor for infection!
Answers
1) Ascaris lumbricoides, 2) Entamoeba histolytica, 3) Enterobius vermicularis, 4) Fasciola hepatica, 5) Giardia lamblia, 6) Tinea sp., 7) Trichuris trichuria, 8) fizzy worm Easter egg
1) Ascaris lumbricoides, 2) Entamoeba histolytica, 3) Enterobius vermicularis, 4) Fasciola hepatica, 5) Giardia lamblia, 6) Tinea sp., 7) Trichuris trichuria, 8) fizzy worm Easter egg
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