Faecal analysis - lab session Flashcards
What is the purpose of faecal analysis?
Allow us to identify:
- endoparasites and their eggs
- gastrointestinal disease
- digestive function
- diagnose bacteria/viral GI infections
What factors can effect the diagnostic quality of a faecal sample?
freshness of sample
amount
drying
contamination
What crude analysis of faeces can be performed?
smell
colour
consistency
presence of mucus
presence of worms
Different faecal collection methods? how should we store and preserve samples?
Can be collected rectally or as a fresh stool sample (<2 hours old)
Sample tube - fill to top - aim for 3-5grams
or clean plastic container
Label with animal’s details, date and place of collection
Can be kept up to three weeks in a fridge until processing – up to 2 months for parasites
Can add 10% formalin and keep it indefinitely
- not suitable for culture and may damage protozoa
What is a pooled sample? why do we do it?
Taking 3 separate samples across 3 days
Reduces the risk of a false negative or missing bacterial/ parasitic egg shedding.
Also reduced the chance of false positives due to contamination.
Faecal samples can be stored in the fridge between collections.
what are the different types of faecal testing?
McMaster Technique
Centrifugal flotation
Passive flotation
Baermann
How do you perform a passive flotation test?
Place faecal material into a disposable container
Add chemical solution
Macerate and mix gently
Add further chemical solution to dilute
Add sufficient to produce a rounded meniscus
Place a coverslip over the top
Leave for 15-20 mins
Remove the coverslip and place it on microscope slide
Positive and negatives of passive flotation?
Positive
- Less equipment
- Minimal steps
Negative
- Not as reliable - fecal debris may cover eggs
- longer time
How do you perform a centrifuge flotation?
Place fecal material into centrifuge tube
Add small amount of chemical solution
Macerate and mix gently
Add further chemical solution to dilute
- Add sufficient to produce a rounded meniscus
Place a coverslip over the top
Place into centrifuge
- Ensure to balance with the same tube and solution
Centrifuge for 3-5 minutes at 1000-1500RPM
Remove coverslip and place on microscope slide
Positives and negatives of centrifuge flotation?
Positives
- Reduces time by not waiting for passive flotation
- Increases yield of parasitic eggs
Negatives
- Requires more equipment
Advantages and disadvantages of faecal flotation?
Advantages
- Fast results
- Easy to obtain solutions
- Equipment easy to maintain
Disadvantages
- Can have contaminants from the environment - pollen, grass etc
- Can ‘miss’ or get false negative due to varying shedding of parasites
- Coprophagy (eaten faeces from another animal) may lead to false positives
- Some eggs may not float to the top and attach to the coverslip - false negative
What can you diagnose with floatation tests?
Roundworms
Hookworms
Whipworms
Giardia
Toxoplasmosis
Coccidia
How do you perform the McMasters technique?
Place 4g of fecal material and 56ml of chemical solution into measuring cyclinder
Macerate and mix gently
Using a sieve strain into a beaker
- keep liquid and dscard of solid waste
Leave faecal liquid for 5 mins
Place a small amount of the sample into a double-chambered microscopic slide
How do you analyse a McMaster’s sample under microcope?
Use 10x lens
Count the number of eggs within the grid of each chamber
- ignore all outside the squares
Multiply the total by 50
- this gives the eggs per gram of faeces
How do you perform the Baermann technique?
Place 5-10 grams of faeces on cloth
- tie four corners and apply an elastic band
- thread stick though to suspend on top of funnel
Fill funnel with lukewarm water to cover the sample
- leave to stand for 24hrs.
Take the bottom few mls,
- leave to stand for 30 mins
-or centrifuge for 2 mins at 1000 rpm
Remove sediment into petri dish
- some large nematodes may be seen.
Remove sediment from petri dish
- Place on slide
- Add drop of iodine and place cover slip
