TO: WormMail list (recip. undisclosed).
WRML.20110628.1 Frosts don’t finish Haemonchus 2 Naphthalophos resistance 3 article in The Land – quarantine drenching
Frosts don’t finish Haemonchus
(I wrote this little piece for elsewhere, mainly because I get the impression that some think winter spells the end for problems with Haemonchus)
It is well known that the eggs of barber’s pole worm of sheep (Haemonchus contortus) are particularly sensitive to cold and desiccation. It is wrong to conclude from this, however, that this worm will not be a problem over winter. Here’s why.
The top three worms of sheep in Australia are barber’s pole worm (Haemonchus), black scour worm (Trichostrongylus) and small brown stomach worm (Teladorsagia(Ostertagia)). These have differing preferences when it comes to climate and weather. This is largely due to differences between the eggs of these three worm types.
Although the eggs of these worms look similar – almost identical – under the microscope – they have different needs. Haemonchus eggs are most sensitive to cold and desiccation: they need it to be more than 10 degrees by night and 18 degrees by day. And compared to the other important roundworms, they need lots of moisture. This explains why Haemonchus is mainly a warm weather parasite and is particularly a problem in summer rainfall areas – or other areas experiencing unseasonably wet summers.
Barber’s pole worm’s other Achilles Heel is that the eggs are short-lived, being viable for just 5 days or so once deposited in dung on pasture. It’s strength however is its fecundity: barbers pole worm produce a lot more eggs -around 10,000 per day- than most other important worms except for liver fluke.
But the third stage or infective larvae of these top three worms are a different story. While barbers pole worm is the weakling in terms of its eggs, it keeps up with the others when it comes to survivability of infective larvae on pasture.
So, the barber’s pole worm life cycle stops in winter, because its too cold for the eggs, assuming it’s consistently below 10 degrees overnight.
But the larvae live on. Sure, their numbers won’t be topped up with new hatchings over winter, but all those larvae produced on pasture in late summer and autumn won’t die in a hurry. In fact the larvae live longer if it is cool to cold – about twice as long – compared to when it is warm to hot.
Come early Spring, there will still be some infective larvae on pasture surviving from autumn. As an aside, the liver fluke situation is similar to that for barber’s pole worm: it’s infective stages on pasture (metacercariae) will survive over winter, albeit in dwindling numbers, especially if moisture is available.
So, if conditions on your farm were good for barbers pole worm in the several months leading up to winter, don’t rest on your laurels and think that frosts have fixed the problem. Your sheep could still be picking up barber’s pole worm – not to mention scour worms – over winter.
Not surprisingly the last ‘word’ is: Don’t guess, WormTest.
(‘Eaves-dropping on a conversation I had with a veterinary colleague. Let’s call him ‘Alphonse’).
"Alphonse, ‘sorry for the lateness in replying: bulging INBOX syndrome.
Naphthalophos(NAP; ‘Rametin’, Combat’ etc) intrinsically is not highly effective ( ie not >95% effective) against Trichostrongylus sp, Teladorsagia (Ostertagia), or immature (L4) Haemonchus (Hc). Typically it is only 70-90% effective. (I don’t have a peer-reviewed source for the statement re L4 Hc, but it seems to be accepted).
( Neil Cooper and others (1996, Naphthalophos combinations with benzimidazoles or levamisole as effective anthelmintics for sheep. Aust. Vet. J. 74, 221–224) showed that NAP alone, in a number of worm egg count reduction tests, produced egg count reductions ranging from 58-98% (presumably burdens dominated by Trichostrongylus and/or Teladorsagia). NAP in combination with either a BZ or LEV produced better results)
So, this might explain what appears to be resistance in many if not most worm egg count reduction tests (WECRT, aka FECRT, ‘DrenchTest), eg WEC reduced by less than 95% 7-14 days post-treatment.
However, there ARE some fair dinkum, reported cases (peer reviewed journals) of resistance to NAP (one for Haemonchus, one for Trichostrongylus). The two I know of are Green et al and Le Jambre et al.
(I mentioned these two references in a recent WormMail
. If I wasn’t so lazy and dying to have some lunch, I would dig them up for you…:-).
Alphonse, there was a suspicion of fair dinkum resistance of Hc to NAP in your backyard, at the famous Wallangra
farm, from which came the first Australian reports of Haemonchus resistant to closantel
(first detected by Warialda District Veterinarian Phil Kemsley; confirmed, characterised and reported by Rolfe et al
(including Kemsley), and to moxidectin.
But the NAP situation was never clarified.
Then look at some of the results for NAP-combinations in WECRTs by Andrew Biddle…(eg the Glen Innes property with resistance to abamectin+BZ+LEV+CLOS – also mentioned in recent WormMails
). The NAP results may just be due to lots of Hc L4s being there at time of treatment, or………….
Very cold here…. Haemonchus is not happy (the eggs at least. ). Pity.
NSW Northern Tablelands.
I dug up the references:
Green PE, Forsyth BA, Rowan KJ and Payne G (1981). The isolation of a field strain of Haemonchus contortus in Queensland showing multiple anthelmintic resistance. Australian Veterinary Journal 57(2): 79–84.
Le Jambre LF, Geoghegan J and Lyndal-Murphy M (2005). Characterization of moxidectin resistant Trichostrongylus colubriformis and Haemonchus contortus. Veterinary Parasitology 128: 83–90. (" the TcMOX-R strain* should be considered resistant to NAP…" ) * ie moxidectin-resistant T.colubriformis. ("Both NAP and LEV are effective options for the
control of HcMOX-R." **) ** ie moxidectin-resistant Haemonchus contortus. ("The TcMOX-R strain is one of the first, if not the first, MOX resistant strain of this parasite to be described. The existence of this strain proves that Australian T. colubriformis has sufficient genetic variability to develop MOX resistance."). By way of background: these worms originated from goats in SE Queensland.
Sheep drench resistance and quarantine drenching
– Vet Talk-The Land (NSW, Australia) 23 June 2011
Read no further…
Popper and Black Swans
"Popper set the standards by which hypotheses should be structured. A well-stated hypothesis should be able to be falsified. That doesn’t mean it will be falsified, but it should be structured in a way that it can be. And real scientists – of which, sadly, there are all too few in the field of nutrition – don’t try to confirm their hypotheses: they try to refute them.
One of the examples Popper used in explaining how a hypothesis should be established involved swans – white and black.
He used the following as an example of a good hypothesis: All swans are white. He made the case that this hypothesis cannot be confirmed by simply pointing out more and more white swans. The hypothesis can be strengthened by doing so, but it can’t be proven.
It can, however, be disproved by the discovery of even a single black swan. Popper argued that scientists should be working to find black swans instead of simply adding more and more white swan sightings to their data. The more effort scientists expend to find a black swan without finding one, the more their hypothesis is strengthened. Diligently searching for black swans is a much more valid scientific endeavor than simply looking for more white swans.
Many scientists don’t want to hunt for black swans, however, because they don’t want to blow up their hypotheses. The easy way to bolster their hypotheses is to continue to tally up all the white swans they find and forget about looking for black ones". – Michael Eades