Are indoor-housed or free-range pigs more susceptible to infestation by nematodes that cause PGE, and why?
Free-range pigs are more susceptible because they encounter more eggs and larvae that accumulate in the soil.
There is also greater access to intermediate hosts for nematodes. For example, earthworms are intermediate hosts for pig lungworms.
What are the four main nematode parasites that affect pigs to cause PGE, and what nematode superfamilies do they belong to?
Hyostrongylus rubidus - Trichostrongyloidea
Oesophagostomum spp - Strongyloidea
Ascaris suum - Ascarida
Trichuris - Trichinelloidea
Which of the porcine nematodes is a "typical" strongyle nematode, very much like Ostertagia that affects ruminants in terms of appearance, life cycle, pathogenesis and epidemiology?
What is the main difference between pigs affected by Hyostrongylus rubidus and ruminants affected by Ostertagia species?
Unlike cattle and ewes (adult animals), sows and pigs in general do not develop any useful immunity to the worm. They remain susceptible throughout their lives.
Where in the pig GIT does Hyostrongylus rubidus target?
Abomasum (like Ostertagia in ruminants)
Why is Hyostrongylus rubidus only seen in outdoor pigs?
Fecundity is too low to maintain life cycle when faeces are regularly removed from buildings.
What can happen to piglets and sows affected by Hyostrongylus rubidus?
Severe weight loss & even death in lactating sows.
Remember strongyle worms like Ostertagia destroy the epithelial lining in the glandular stomach, increasing permeability to macromolecules and lower acidity so diarrhoea becomes an issue.
Aside from Hyostrongylus rubidus, what is the other strongyle parasite to affect pigs? What is its target organ in the pig's GIT?
It targets the caecum & colon (large intestine)
What is the main condition Oesophagostomum spp can exacerbate in sows?
What is the pathogenesis of this condition?
Thin Sow Syndrome
Hungry sows eat bedding → eat lots of L3 → intestinal damage, lots of eggs excreted → lots of L3 in bedding → downward spiral → excessive weight-loss during lactation
Thin Sow Syndrome is a sporadic condition occurs with the economy is bad for the pig industry & pig welfare falls below standard & sows go hungry. It is exacerbated by caused by the ingestion of Oesophagostomum spp L3.
Under normal circumstances in an otherwise healthy herd, what is the impact of Oesophagostomum spp?
It's not very pathogenicm but large numbers cause ↓ in milk production & growth rate of young pigs
What is the morphology of Ascaris suum? What about its eggs?
A typical ugly ascarid that's enormous with three lips in the head (remember Parascaris equorum).
Grow to 40 cm long!!!
Its eggs, like all ascarid eggs, has a thick brown sticky coating that enables it to live in the environment and be spread passively.
What is the life cycle of Ascaris suum?
The pig eats the infective stage -- embryonated egg with L2 larvae inside.
Like all ascarids, the larvae then migrates to the small intestine via hepato-tracheal migration. It enters the liver as L2 via the hepatic portal system, then via hepatic vein and inferior vena cava to the right side of the heart , then via pulmonary arteries into the lungs where they crawl through capillaries and alveoli back up into the trachea, where they are then swallowed. That's how they end up in the small intestine as adults.
What is the cause of milk spot in pig livers that have been condemned?
Damage caused by Ascaris suum larvae as they migrate via hepato-tracheal migration to the small intestine. Usually this is a result of a small number of worms.
Can pigs develop immunity to Ascaris suum?
Pigs develop strongly protective immunity several months post-infection:
Early (first) infection: L4 killed after passing liver as they reach intestine (immunity developing);
Only when Ascaris infects pig a SECOND TIME are the L2 killed by pig’s immune system before they reach the liver ∴ few hepatic milk-spot lesions seen in sows
What is the fecundity of the Ascaris suum female?
She can lay up to 200,000 eggs per day and they can persist in the environment
At what age of pigs most susceptible to Ascaris suum and where?
Young piglets in the farrowing house.
What type of damage is caused by the massive, 40cm long Ascaris suum worms in the pig?
Reduced weight gain due to blockage of intestine by worms of blockage of bile ducts in liver
Trichuris suis is also known as "whipworm". What is it about its morphology and behaviour that give it this name? What part of the porcine GIT does it prefer?
It has a very thin head and a thick tail. See photo.
All you can see are the thick tails as the thin head is burrowed into the superficial mucosa of the large intestine, which it prefers.
Is Trichuris suis a big problem in the UK?
No. It prefers warmer climates. It is mainly seen in pigs kept outdoors or in deep-litter systems.
What problems and clinical signs can Trichuris suis cause in pigs and how?
Linked with diarrhoea & dysentery as holes made by burrowing worms into superficial mucosa leave pigs open to secondary infection by spirochaetes
What is the relationship between Trichuris suis and human Crohn's disease?
Interestingly, human Crohn's (Th-2 response almost ￼disappeared) due to over-protectiveness from immune stimulation; artificial Trichuris infection can restore balance, stimulating Th-2 response and down-regulate Th-1 response.
The main approaches to controlling nematodes in pigs are:
Routine dosing & Strategic dosing
What are the advantages and disadvantages?
Routine dosing is most common, with farmers feeding pigs medicated feed usually at three-month intervals. It's pretty easy as you can put the medication into the shoot feeder.
Problem with this is potential anthelmintic resistance.
Strategic dosing is better: Time the dosing to specific husbandry activities such as dosing when moving sows to farrowing house, moving weaners to finishing pens, etc.