Diagnosis of Internal Parasitism and the effect of worms on the host
|There is a relationship between the number of worms and the number of their egg in faeces|
|Different types of worms produce different types of eggs|
|All the trichostrongylid worms produce similar eggs which we can’t tell apart|
Eggs in Ruminant Faeces
"Normal strongylid egg – the..."
|Normal strongylid egg – the main egg type we are interested in when doing counts|
"Normal strongylid egg with smaller..."
|Normal strongylid egg with smaller Strongyloides eggs – these contain a first stage larvae when they are passed in faeces|
McMaster Egg counts
|Most common technique used|
|Relies on the use of a floatation fluid in which eggs float and heavier debris in faeces sinks|
|Floatation fluid needs to be at least Sp. Gravity of 1.2|
|Common floatation media are various salt solutions including|
|Saturated common salt (NaCl)|
|Sodium nitrate (specific gravity of 1.2)|
"The other key to this..."
|The other key to this technique is the use of a special counting chamber called a McMaster slide|
"2g of faeces is added..."
|2g of faeces is added to 28ml of floatation fluid within the coarse sieve (tea strainer)|
"The faeces and fluid are..."
|The faeces and fluid are mixed until all the lumps are broken down and the eggs “liberated”|
"The sieve containing coarser material..."
|The sieve containing coarser material is then removed leaving the floatation media and smaller faecal material including eggs|
"The fluid is then thoroughly..."
|The fluid is then thoroughly stirred with a back and forth motion. If not evenly stirred the eggs come to the surface and you do not end up with a representative count|
"Fill each chamber of the..."
|Fill each chamber of the counting slide separately going back and refilling the pipette each time|
"Focus on the gridlines in..."
|Focus on the gridlines in the chamber which are on the underside of the top slide|
|Use the 4X objective lens first and then change to the 10X|
|It should then be possible to see a line of each grid on each side of your field of view|
|Strongylid eggs are about the same length as the gridlines are wide (don’t confuse with coccidial oocysts|
|Count the number of strongylid eggs in each chamber, add them together and multiply by 50 to give you a count of egg per gram of faeces|
|US recommendations are that a cut-off value of 1000 eggs/g indicates the goats need treating|
|Goats can die with egg counts of only 2000 eggs/g so be careful|
|Haemonchus is a very prolific egg layer with about 6000 per day but Trichostrongylus only produces about 600 per day and Nematodirus many fewer than this|
|The immune response can reduce the ability of individual worms to produce eggs so more eggs per worm in young than old, especially with sheep|
Haemonchus and FAMACHA
|This is a system that has been developed by the South Africans and is only suitable for Haemonchus|
|Relies on examination of the colour of the conjunctiva of the eye, more particularly the bottom conjunctiva of the eye|
|They have produced a chart and an experienced operator can detect wormy goats|
|Remember other causes of anaemia such as liver fluke|
"Note the sheep on the..."
|Note the sheep on the left is normal and the black one on the right has pale conjunctiva – it is suffering clinical haemonchosis|
|Haemonchus is big enough to see with the naked eye|
|Trichostrongylus and Ostertagia are not|
|Counting worms is a skilled job for trained professionals but nevertheless a big burden of Haemonchus is generally easy to spot with some experience|
|Haemonchus in a goat abomasum|
|Mature adults are 2-3cm long|
"Haemonchus doesn’t cause scouring but..."
|Haemonchus doesn’t cause scouring but all the other trichostrongylids do when the infection is large|
Effect of other trichostrongylid species on the host
|Mucus browsers essentially induce the host to try to get rid of them|
|The host then redirects protein metabolism to the gut to produce more cells, more mucus and antibodies and other immune mediators to fight off the infection, not necessarily effectively|
|Has a dramatic effect on the protein metabolism|
|Wormy sheep look like starved goats/sheep|
|Slightly wormy goats/sheep don’t grow as well as uninfected sheep|
"Abomasum of a goat showing..."
|Abomasum of a goat showing nodules and unevenness associated with the host’s response to the worms|
|Goat abomasum: note the nodule formation, this is particularly caused by Ostertagia|