WRML: blasts from the past – some strategic sheep worm control programs, NSW Australia (1940s-1980s)

‘A quick WormMail while I am working on another job.

Here are copies of three PowerPoint slides (see below) from what I am currently working on.

(Hopefully you can make out sufficient detail)

Hugh Mcl Gordon, scientist with CSIR (later CSIRO) developed an early epidemiologically based worm control program. (Australian Vet. Journal (AVJ), 1948 etc).

Keith Dash, also from CSIRO, built on this earlier work somewhat (eg KM Dash AVJ 1986), aided by the serendipitous launch of closantel in Australia (1982), and the two New England Drench Resistance Surveys (1978 (Webb et al AVJ 1979) and 1984 (Love et al AVJ 1992)), which put a bomb under everyone.

Shortly after WormKill’s launch in 1984, DrenchPlan was developed for the non-seasonal and winter rainfall areas of southern NSW. Similar programs were launched in other states

‘Must go…back to work.

Regards

SL

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Liver fluke – update

From WormBoss News (May 2012)

Stephen Love, State Coordinator – Internal Parasites, NSW Primary Industries, Armidale, comments on the liver fluke situation:

For those with liver fluke on their farms, now is the time for the most important liver fluke drench of the year.

With above average seasons in many areas for the last 2 years or so, liver fluke (Fasciola hepatica) numbers have built up. There have already been reports of liver fluke disease in sheep and other livestock, some with low liver fluke egg counts (typically less than 100epg of faeces) and some with spectacularly high counts e.g. over 2000 fluke epg in an alpaca.

About now (May) it is getting too cold (below 10°C overnight) for liver fluke eggs to develop, so now is a good time to strategically drench sheep with a highly efficient flukicide (i.e. triclabendazole-based) to clean sheep out. Cattle producers also have the option of Nitromec® (ivermectin+clorsulon+nitroxynil), another highly efficient flukicide.

Remember, however, that just like barber’s pole worm (Haemonchus) in sheep, the infective stages of fluke (metacercariae), which were produced in summer and autumn, will survive over winter, especially if moisture is present. So, as with barber’s pole worm, it may be too cold for the eggs over winter, but the infective stages produced in autumn will survive, albeit in declining numbers, through to spring. In the case of fluke, these infective larval stages are found in wetter areas on a farm, where the intermediate host snails are found.

Come spring, sheep could still have some liver fluke in them, even if they were treated with a highly efficient flukicide in May. Firstly, even the best flukicides do not kill every single fluke. In Australia, ‘effective’ – in the case of flukicides – is defined as 90% kill or better. (The yardstick for broad-spectrum drenches is better than a 95% kill of target roundworms). Also, some of the very young fluke (harder to kill) will be left behind after the May drench. By spring these will be adult flukes, living in the bile ducts, munching away, producing eggs, causing protein and blood loss, leading to clinical signs similar to Haemonchosis (‘bottlejaw’, anaemia), but with the possible addition of jaundice as well.

There are two other reasons the sheep may have some fluke come spring. One is that they picked up some Metacercariae over winter from pasture, and the other is resistance to the flukicide you used.

Yes, there are cases of liver fluke resistant to triclabendazole and to closantel, but as yet we really do not have a good handle on how common this is.

If you want to check how well your triclabendazole drench worked, do a fluke egg count 28 days after they were drenched (and preferably a count on the day of drenching as well). The reason for waiting 28 days is that it can take this long for all the eggs left inside the liver (the bile ducts) to clear from the system.

In passing I should mention that Charles Sturt University at Wagga is trialling an immunodiagnostic test (an ELISA) that detects liver fluke antigen in faeces. They hope this will be useful as a fluke resistance test. If you are a cattle producer, and you are interested, contact your local Virbac rep. (Virbac is assisting CSU in this work.)

Wormfax May 2012

TO: WormMail mailing list (recip. undisclosed).   WormFaxNSW – May 2012 edition. More high egg counts. More sunshine.The May edition is now online.http://www.dpi.nsw.gov.au/aboutus/resources/periodicals/newsletters/wormfax

Many thanks again to the State Vet lab at EMAI and VHR at Armidale for supplying summary data each month.

Here (table below) are some of the highest strongyle worm egg counts (WECs) from various districts in NSW:

LHPA or District Highest WormTest Mean egg count Highest individual egg count Larval culture (Hc=Haemonchus)
Central North 7 608 25 200 92% Hc
Central West 17 740 30 600 No cult.
Darling 3 724 12 600 No cult.
Lachlan 13 660 17 000 94% Hc
South East 8 536 64 000 100% Hc
Tablelands 6 320 11 600 92% Hc
Armidale 4 072 13 520 93% Hc
Ctrl Tblnds 1 460 8 360 77% Hc, 20% Trich
C’bran 9 224 19 120
Narrabri 2 624 10 880 100% Hc
Nrthn New Englnd 1 240 5 200 No cult.
Yass 9 44 2 160 99% Hc
Riverina 376 800 11% Hc 48% Trich  37% Tel
Hume 736 1736 86% Hc

 

Go to WormFax on the web (see URL above) to scan the results for yourself and to check the map if you don’t know where all these districts are.

Haemonchus (barber’s pole worm) is dominating the picture through much of NSW (coast, tablelands and slopes at least (eastern third of the state)), whereas in ‘normal’ years, Haemonchus/haemonchosis is mostly significant in the summer rainfall zone of north eastern NSW only (and SE Queensland of course!)

Two to three ‘La Nina’ years in a row have favoured worms in general, not least Haemonchus, and also liver fluke in areas where it occurs. We are likely approaching an El Nino situation in Spring (so, sheep might be chasing green pick in marshy areas in Spring/Summer??…   risk of liver fluke disease???…although the risk is generally higher in autumn….)

Although the life cycle of various worms might stop over winter, especially cold sensitive ones like Haemonchus and Fasciola, the infective larvae from these species on pasture from autumn are much more cold tolerant (than the eggs). Some of these larvae will survive winter and able to infect grazing livestock.

Don’t guess, WormTest. (You may need to get a fluke WEC done as well if you live in a ‘flukey’ area. Don’t forget the possibility of liver fluke in sheep bought from elsewhere when considering your ‘quarantine treatment’ procedures).

Some more ‘record’ high counts:

121, 800 epg at Lithgow:

Adding to our list of high counts, Dr Zoe Spiers (NSW DPI State Vet Lab, EMAI) told me of a case (M12-03656) managed by Dr Mel Gabor. Nine sheep were sampled. WECs ranged from zero up to 121,800 (Larval culture: 100% Haemonchus).  The sheep with the count of 121,800 had died. The next highest count was 2240. The sheep had apparently been drenched 3-6 months before with fenbendazole. Possibly the sheep with the count of 121,800 had missed a drench. Another likely factor is drench resistance: Haemonchus is resistant to BZs on the great majority of properties in the eastern third of NSW.

107 000 epg at ‘Condo’:

In the May 2012 edition of WormBoss News [http://www.wormboss.com.au/news/outlooks/nsw/may-2012.php] ,  Dr Katherine Marsh, District Vet., Condobolin mentioned ‘one property with an average count of 14012 epg, with individual counts ranging up to 107 000 epg.  The property was losing lambs due to barber’s pole worm’.

Other  remarkably high counts mentioned previously:

High liver fluke egg counts from an alpaca in the Central Tablelands (>2,217 Fasciola epg. Case M12-07437-F-V1  ) and from sheep at Berrigan (Riverina, NSW): ~ 750 Fasciola epg (the latter reported by Dr Gareth Kelly, Virbac).

Astonishingly high Trichostrongylus sp counts (~ 60,000 epg) in sheep at Brewarrina (March 2010) were reported by Dr Kylie Greentree who was then Veterinary Officer, Bourke (shared with Dr Charlottle Cavanagh).   Not quite as high, but Dr Steve Eastwood (Armidale) came across sheep in April 2010 with WECs up to 16, 400 (100% Trichostrongylus). (‘Pretty high for ‘Trichs’)

 

https://wormmailinthecloud.wordpress.com/2012/05/23/wormfax-april-2012-time-to-treat-for-liver-fluke-fasciolosis-on-the-increase-big-fluke-counts-and-flukicide-resistance/

https://wormmailinthecloud.wordpress.com/2010/03/17/redux-sky-high-counts-at-bre/

https://wormmailinthecloud.wordpress.com/2010/04/09/more-sky-high-trichostrongylus-counts-armidaleguyra-area-this-time-join-the-fao-animal-nutrition-network/

Good news!   More sun!

Winter Solstice in Australia tomorrow Thurs. 20 June at  0909 EST.   By week’s end I think the sun will be setting at 17:01 instead of 17:00.   🙂

 

Regards

SL

WRML. sheep immunity to worms (McClure)

To WormMail mailing list (recip. undisclosed).  WRML.20120606. sheep immunity to worms (McClure).

immunity, sheep, worms, McClure,

Following is a nice overview of sheep immunity to worms by Dr Susan McClure.

This appeared recently in ‘Plains Talk’ (Issue 2, February 2012), edited by Edward Joshua (NSW DPI). The current issue can be found here:

http://www.sheepconnectnsw.com.au/files/blogs/000057/Plains%20Talk%20-%20Issue%205%20-%20June%202012.pdf

Susan McClure is a Research Scientist/Veterinarian working with the Central West LHPA in NSW. http://www.lhpa.org.au/districts/centralwest

Previously she was a research scientist working for CSIRO.   e.g. see here: http://www.publish.csiro.au/?act=view_file&file_id=EA03002.pdf

Sheep immunity to worms – Dr Susan McClure

"Sustainable worm control programs should aim to optimize host immunity as one element of the armory. Immunity (or host resistance) is the ability of the sheep to block infection with worms and reject established worms. The outcome will be protection of susceptible stock and reduction of pasture contamination in successive seasons.

Immunity can be either innate or acquired.

        * Innate immunity is the inherent ability of some sheep and breeds to resist infection with worms.

        * Acquired immunity develops in sheep after they have been exposed to worms. Most adult sheep have good acquired immunity to worms, whereas lambs do not.

Acquired immunity takes several months to develop following exposure to worms. During this time animals, such as lambs, will be vulnerable to infection and disease. It is important to increase the immunity of young lambs to worms, especially before weaning. The sooner they become immune, the less they will need to be drenched. Immunity to worms can be improved by implementing some of the other arms of sustainable worm control. These include good grazing management & nutrition, breeding programs and reducing the number of drenches.

 Immunity is rarely complete, so even immune sheep carry a few worms. However, immunity reduces worm numbers and production losses. How long it takes for immunity to develop depends on the age, liveweight and nutritional status of the sheep, whether it has been exposed to worms previously and the number of worm larvae it is exposed to.

Immunity to worms affects worm burdens in 3 stages:

        * Fewer incoming worm larvae establish and become adults.

        * Established female worms lay fewer eggs.

        * Established adult worms are rejected by the sheep.

Exposure to worms is needed for immunity to develop and be maintained. This exposure must be large enough to stimulate the immune response, but not so large as to overwhelm the animals and cause production losses or disease. This is especially a problem with Barber’s Pole Worm. Lambs that are continuously drenched from birth in the absence of vaccination cannot develop immunity, and adult sheep moved from worm-free districts are similarly naïve and therefore susceptible. When a sheep develops immunity to one species of worm, especially Black Scour Worm, it acquires partial immunity to other worm species as well.

The development of an immune response to worms requires extra nutrients. In well-fed animals the development of immunity occurs over the first 6 weeks for Black Scour Worm, but takes longer for Barber’s Pole. In young worm-infected sheep nutrients are diverted from muscle and wool growth to developing an immune response to the worms. Once immunity has been established it is less sensitive to malnutrition, as the mechanism is a rapid hypersensitivity response which ejects incoming larvae very quickly. An exception is in ewes at peak lactation, where the demands of milk compete successfully and immunity wanes unless nutrition is improved.

Thus immunity to worms is influenced by a number of factors (predisposing factors). The first approach to sustainable control is to identify and remove the predisposing factors which slow down the development of immunity.

Individual animal-related predisposing factors include:

        * Age – Adult sheep have better acquired immunity than lambs and recently weaned sheep, although this may be because of other associated factors such as available fat reserves rather than age itself.

        * Sex – Dry adult ewes seem to have better immunity than males.

        * Pregnancy and lactation – During late pregnancy and early lactation immunity in ewes wanes. This can be largely countered by feeding a higher quality diet, in terms of digestibility, bypass protein and/or readily available carbohydrate.

        *Liveweight – In general, animals less than 23 kg at first exposure to worms have poorer immunity than heavier animals unless fed a very high quality diet (essentially a monogastric diet). Lambs less than 15 kg do not develop any degree of immunity. The exception is neonatal lambs, which appear to develop good immunity quickly if infected within a week of birth.

        * Health – Sheep in poor health because of other diseases will have reduced immunity to worms. However, there is some evidence that concurrent mild inflammation of the gut can hasten the development of immunity to Black Scour worm. In this case the initiators of the gut inflammation were navy beans or polyunsaturated fatty acids from sunflowers (high in omega -6), while polyunsaturated fatty acids from fish oil (high in omega-3) suppressed gut inflammation and impaired immunity (i.e. increased worm egg counts).

        * Breed and sire line – Some breeds and sire lines have better immunity to worms than others. However, some caution should be used when applying results of genetic selection beyond the managemental and environmental conditions under which selection was made. (This applies to other parameters as well as worm resistance).

External predisposing factors

        * Inadequate nutrition – Sheep need adequate nutrition to develop and maintain immunity to worms, and in many districts problems are observed only in weaners when the feed goes off. Young growing sheep should be given priority access to high quality pasture or nutritional supplements when first exposed to worm larvae. Protein, energy, vitamins and minerals are all important for the optimal development of immunity. Poor seasons or grazing management may result in previously immune sheep becoming more susceptible to worms.

        * Stress – Weaning, transport and inclement weather can all reduce immunity to worms. Weaning onto clean pasture limits pick-up of worms at a time when the lamb is particularly vulnerable.

Immune sheep are a good insurance against the developing resistance of worms to drenches, and are especially useful in breeding or wool enterprises. In addition, animals managed so as to be capable of developing good immunity to worms are also better able to mount immune responses to other diseases."

——

Regards,

SL

IGNORAMUS, n. A person unacquainted with certain kinds of knowledge familiar to yourself, and having certain other kinds that you know nothing about.  – Ambrose Bierce, Devil’s Dictionary