Worm Egg Counts Flashcards
What are Faecal Egg Counts
Method of detecting and quantifying worm eggs in faecal samples
Useful for gastrointestinal parastites
Selective/targeted therapy
Only treating animals which exceed a certain cut-off value of parasite burden
Reduces a selection pressure for anthelmintic resistance
Refugia
An area in which a population of organisms can survive through a period of unfavourable conditions
What is a Direct Smear test?
Small amount of faeces mixed with saline
(or iodine for better contrast)
Placed on microscope slide
Advantages and Disadvantages of Direct smear tests
Advantages
* Cheap
* Short processing time
Disadvantages
* Qualitative
* Very low accuracy, precision and sensitivity
What is a Cornell-Wisconsin test?
Centrifugal flotation of eggs in a salt solution in a tube
Collection onto a coverslip
Counting under a microscope
Advantages and Disadvantages of Cornell-Wisconsin tests
Advantages
* Cheap
* High limit of detection
Disadvantages
* Time-consuming
* Low accuracy
What is a McMaster test?
- Faeces is mixed in a flotation solution
- Loaded onto chambers of a slide
- Floated eggs are counted
Advantages and Disadvantages of McMaster test
Advantages
* Cheap
* Medium processing time
Disadvantages
* Sensitivity limit is 50 eggs/g of faeces
* Requires specialised slide
* Required ability to distinguish between eggs
What is a FLOTAC test?
Centrifugal-flotation of eggs in a specialised device
Subsequent examination of the top layer
Advantages and Disadvantages of FLOTAC test
Advantages
* Cheap
* High sensitivity
Disadvantages
* Time consuming
* Requires a centrifuge
What is a Mini-FLOTAC test?
A modified version of FLOTAC
Without centrifugation step
Requires less volume
Advantages and Disadvantages of Mini-FLOTAC test
Advantages
* High sensitivity
* Accurate
* Precise
* Medium processing time
Disadvantages
* Detection of some parasites
○ E.g. trematodes
* Requires centrifugation
What is a FECPAK test?
Eggs are floated in a flotation solution
Accumulated into a single viewing area and imaged
Advantages and Disadvantages of FECPAK test
Advantages
* Does not require technical skills as eggs identified and counted remotely
* Digitalised images
Disadvantages
* Low accuracy and precision
* Medium sensitivity
* Time-consuming
What is a Parasight System test?
A faecal sample is mixed with water and filtered to remove debris
Eggs are labelled with a fluorescent dye
Imaged and counted using an automated algorithm
Advantages and Disadvantages of Parasight System test
Advantages
* High precision
* Does not require technical skills
* Fast
* Automated counting
* Digitalised images
Disadvantages
* Expensive
* Some results need to be confirmed visually
* Does not detect overlying eggs
* Cannot differentiate in the presence of high debris background
FECR
Fecal Egg Count Reduction Test
Considered gold standard in detecting anthelmintic resistance
Method:
* Measure FEC at time of treatment
* Measure again at defined times after treatment
(times depend on which anthelmintic group used)
FECR times for different anthelmintic groups
3-7 days after using levamisole
8–10 days after using a benzimidazole
14–17 days after using a Macrocyclic lactones
* If unsure or using multiple anthelmintics then repeat FEC after 14 days
FECR Calculation
Find reduction in eggs/gram of faeces as a %
1-(T2-T1)/100
Cut off is 95% (resistance is inferred if FECR <95%)