What is fasciolosis caused by and what are the clinical signs? What are the species that can suffer from fasciolosis?
Fasciola hepatica, a trematode (flat worm)
Fasciolosis is a seasonal disease that is characterised by different degrees of liver damage, depending on whether infection is acute, sub-acute or chronic.
Sheep, cattle, rabbits and horses (and humans) can suffer from fasciolosis.
What are the main differences in acute, sub-acute and chronic fasciolosis?
Acute - Animals can die. Haemorrhagic liver, enlarged, pale, firable liver with mroe than 1000 immature flues in parenchuma. This is seen more often in sheep but less in cattle.
Sub-acute: rapid weight-loss over 1-2 weeks, enlarged haemorrhagic liver, >500 flukes, immature and adult
Chronic: progressive weight loss over weeks/mos. hypoalbuminaemia, oedema, small, distorted, cirrhotic liver, enlarged bile ducts, >250 adult flukes
What is special about the appearance of a cow's liver that is infected with chronic fasciolosis?
Calcification of bile duct so you get "pipe-stem" liver. See photo.
Where do adult Fasciola hepatica reside?
Bile ducts. See graphic.
What is the life cycle of Fasciola hepatica and other trematodes? What is the protozoa's intermediate host in the UK?
F. hepatica's intermediate host in the UK is the mud snail, Galba truncatula.
Life cycle (see diagram):
Sheep excrete oocysts in faeces
Oocysts hatch: free-swimming miracidium looks for snail
Miracidium ingested by Galba truncatula mud snail
Sporulates into sporocyst inside snail
Turns into Redia still inside snail
Turns into free-swimming cercaria, still inside snail
Turns into metacercaria on vegetation
Eaten by sheep
Migrates via peritoneal cavity to liver, bile ducts
What is Blacks Disease? What causes it & what animal does it occur in? Why is it commonly associated with liver-fluke infestation?
Caused by a toxin produced by the Gram (+), spore-forming bacilli bacteria, Clostridium novyii Type B.
Migrating flukes that cause liver necrosis produce anaeronic conditions in which clostridium can multiply, produce toxin and cause disease.
What do adult liver flukes feed on? What two blood conditions does this lead to in chronic infestation?
Blood and epithelium. This leads to anaemia & hypoalbuminaemia (proteins lost due to whole-blood loss and increased vascular permeabililty).
How does Fasciola hepatica evade the host immune response?
The tegumental cells covering the Fascioloa trematode have rapid turnover, so they slough off antibody and adhering host cells.
In the case of Schistoma, another trematode, the tegument conducts molecular mimicry so the host doesn't recognise it as foreign antigen
Fasciola tegument releases certain factors that cause the immune system to switch to useless Th-2 response, which produces IgG)
Fasciola tegument releases enzymes that cleave antibodies & presents many different anitgens to the host (antigenic variation)
How big is the Fasciola hepatica egg?
It's 150 µm, about 2x the size of a strongyle egg.
How would you identify a Lymnaea snail aka Galba truncatula?
it's 5-10 mm long, has a brown-black shell with 5-6 spirals and its first spiral is half its total length. The snail eggs hatch in June, kicking off the miracidia-penetration cycle.
When is acute Fasciolosis most prevalent?
Acute: September to November.
Chronic: January onwards
What is the zoonotic potential of Fasciola hepatica infection, causing Fasciolosis?
Humans can end up eating vegetation infected by encysted metacercaria.
Chronic fasciolosis in sheep can lead to bottle jaw. What is this and how does it happen?
Oedema caused by protein loss in blood, so water flows out into tissue.
What are the differences in F. hepatica's pre-patent period and its patency period?
PPP= 8=12 weeks, from metacercaria to eggs in faeces. NB the sporocysts can overwinter in the snails.
Patency is up to nine months in cattle and several years in sheep; they continue to produce 5000 to 20,000 eggs per fluke per day.
What is the only broad-spectrum anthelmintic that can kill liver flukes?
It kills them at all stages of the trematode cycle.
What are the morphological differences between Dicrocoelium dendritica & Fasciola hepatica?
D. dendritica is much smaller than Fasciola hepatica.
How does the life cycle of the smaller Dicrocoelium dendritica differ from that of Fasciola hepatica?
Dicrocoelium dendritica has two intermediate hosts compared with F. hepatica's one (the mud snail, Galba truncatula).
D. dendritica's intermediate hosts are:
What happens if one of Dicrocoelium dendritica's small dark-brown eggs are ingested by a land snail?
If the miracidium is ingested by a LAND SNAIL, The miracidium sporulates, becomes cercaria-filled redia, then cercaria.
The cercaria are excreted as faeces in slime-balls that are collected and eaten by WOOD ANTS. Now miracidium develop inside the wood ants, which are eaten by the final host, ruminants or other herbivores. See diagram.
Why is the Dicrocoelium dendriticum "lancet fluke" less pathogenic than the liver fluke?
1. It's smaller as an adult. It's 1/3 the size of the liver fluke.
2. Its tegument is NOT covered in spines, the way F. hepatica's tegument is. So, less tissue damage.
3. D. dendriticum migrates DIRECTLY TO THE BILE DUCT from the intestine, so doesn't cause liver damage.
How are Paramphistomum spp trematodes similar and different to F. hepatica?
Paramphistomum spp colonise the RUMEN, not the bile ducts.
They are plump, not flat.
Rare in UK.
Eggs are big, 2x size strongyle (like F. hepatica)
Life cycle is similar - uses snail as intermediate host
Eggs are colourless