Faecal Sampling Flashcards
Why do we collect faecal samples?
Provide info on GI tract and how well it’s functioning - can aid diagnoses of parasites in GI tract
What are the 2 ways in which faeces can be collected and what are the advantages/disadvantages?
- Direct from Ground
- has to be fresh!
- has to be from correct pet!
- Easy for owner to do - Direct from Rectum
- PPE and lube (to avoid skin flora in sample)
How should faecal samples be stored?
Ideally, should be examined within 2 hours or stored in the fridge with as little air in the sample as possible (or can add double the volume of formal saline).
Ideally 5g of sample should be collected.
If anaerobic examination required then as much faeces as possible should be put in tube to minimise air and prevent the reduction of viable anaerobic bacteria in the sample.
What are the normal contents of carnivore faeces?
Water Small amounts of undigested food Pancreatic secretions - enzymes Bile Products Small amounts of mucus Bacteria Small numbers of Epithelial cells Small amounts of blood or hair from prey
What are we looking for in a faecal sample?
Signs of undigested food or ingested materials
Parasites
Blood
What are the 3 ways faeces can be examined?
Gross examination (observation) Microscopy (Smears) Concentration Methods (Flotations, sediment)
What do the colour variations in faeces mean?
Brown - normal
Black - melaena (bleeding from SI)
Red - Haematochezia ( bleeding from LI)
Yellow - malabsorption of nutrients / liver disease
White - eaten too many bones or too fatty a diet
What does a rancid smell of faeces indicate?
Malabsorption of nutrients
What does fatty or mucoid faeces indicate?
Exocrine Pancreatic Insufficiency or Colitis
What can a direct smear be used to look for?
Worm eggs
Partially digested food (presence would suggest EPI)
Protozoan oocysts
Describe the method for a direct smear
- Place a drop of saline in the centre of a microscope slide
Add an equal volume of faeces
Add a stain
Mix well, make a thin smear and add a cover slip
Low power to look for worm eggs and high power for protozoa
What are the stains you can use for a faecal smear?
Lugols iodine - stains starch blue/black
Methylene Blue - shows undigested meat fibres
Sudan IV - shows fat globules red
What are the adv and disadv of a direct smear?
Cheap and Easy But Qualitative (I.e. it only detects heavy infestations)
What does the floatation method depend on?
The weight of certain debris and the use of liquids with different SGs
What is the specific gravity of
water
parasite eggs
salt/sugar solutions?
- 000
- 100-1.200
- 200-1.350
What happens to faeces in a salt/sugar solution?
Heavy debris sinks to the bottoms - light eggs rise to the surface
What is the most common faecal flotation? what do you have to be careful of when using it?
Sodium nitrate
- it will form crystals and distort the eggs if left to stand for more than 20 minutes
What are the 3 types of flotation tests?
- Standard
- Test tube used where faeces are mixed with flotation solution. Cover slip left on top. Parasitic eggs float up and stick to slide. Then examine. - Centrifuge
- quicker and more effective
- spin tubes at 1000-1500rpm for 3-5 minutes - Commercial Kits
- come with tubes, sieve and solution
- expensive!
Describe the standard flotation method
Mix faeces with water (3g faeces + 50ml)
Put mixture through a sieve
Put the filtrate in a test tube and leave for 5 mins
Pour off supernatant and add flotation solution
Fill the test tube to top and add meniscus
Place a cover slip over the top and leave for 15-20 mins
Lift cover slip off vertically and examine under microscope at 25x
What does a sediment test do?
It allows the parasitic eggs and oocysts to sink to the bottom of a liquid (usually water)
When is a sediment test used?
Used if suspected infective eggs are too heavy to float for a flotation test
Describe the method for a sediment test
Mix 2g faeces with tap water and strain
Half fill a centrifuge tube with filtrate
Spin at 1500rpm for 5 minutes
Pour off the supernatant
Put some of the sediment onto a slide with a pipette and put cover slip on
Lugols iodine can be mixed with the sediment but can be difficult to see the eggs in all the debris
What is the outcome of the Modified McMaster Technique?
Determines the number of eggs per gram of faeces
Quantitative assessment
What are the disadvantages of the Modified McMaster Technique?
Clinical signs are not caused by the eggs
Egg numbers are different across species and may be sporadic
Describe the method for the Modified McMaster Technique
Add 3g of faeces to tap water Sieve and collect filtrate Pour filtrate into 15ml centrifuge tube Centrifuge at 1500rpm for 4 mins Pour off liquid at top Add sodium chloride to the tube and mix Fill McMasters chambers Put under the microscope Count the number of eggs in each grid and add together Multiply this number by 50. This gives you the number of eggs per gram of faeces.
When would you see occult blood?
In chronic bleeding form ulcers, neoplasia, parasites
Define malaena
Changed blood in faeces
Define Haematocheza
Fresh blood in faeces
How do we determine if occult blood is present?
Chemical reaction
- place animal on meat free diet for 3 days prior
- Use reagent (either ortholudine or benzidine)
- both react with hb peroxidase with occult blood in the faeces to produce a colour change
What other faecal tests are there?
Faecal trypsin
Undigested fat - use Sudan IV stain
Bacterial Culture
Baermann Technique - add faeces to warm water to encourage larval parasites to move and sink to bottom.
