In this issue:
Rommel drove a Skoda
WormFaxNSW – October issue now on-line
WormFax is a monthly summary of sheep WormTest results from around NSW, with data provided by parasitology labs at NSW DPI’s State Vet Diagnostic Lab (SVDL, Menangle) and Veterinary Health Research (Armidale).
Given above average rain for the last 3+ months, it’s more important than ever to regularly monitor worm burdens using worm egg counts (WECs). And test drench efficacy when you treat: do a WEC on or just before the day of treatment, and again 14 days later. Money well-spent.
Here is a simple exercise: Let’s say the Gross Margin for your sheep enterprise is $25 per dry sheep equivalent (DSE). Your feed is good (quality/quantity) but the sheep aren’t doing well. You haven’t done any egg counting because WEC on 10 samples costs (ball park figures) about $55 plus about $25 if you want a ‘worm type’ (larval culture/differentiation) done as well. Plus there have been few deaths and just a bit of scouring. ‘Can’t be worms. You start drenching more often anyway, just in case. The sheep do better but not a whole lot better. Your neighbour nags you into doing a DrenchTest. That means two WormTests, one on the day of drenching, and another 14 days later. Good grief! That’s about $160 bucks worth ((55+25) x 2). Your Scottish grandfather is rolling over in his grave, especially as you are using a premium drench – whatever that means. The test results come back. It seems the premium drench is about 40% effective against black scour worm and 75% against barber’s pole worm. Further down the track, you are using less drenches and your productivity has jumped and your GM is up to $33/DSE. You have 3000 DSEs, so that’s an increase of $24 000. For an investment of $160.
These figures are wild guesses – and the scenario is an oversimplifcation – but the main point holds true: the return on investment (in WormTesting, DrenchChecks etc) is very, very good.
To back this up a bit: back in the day (several years ago), when Gareth Kelly did his PhD, part of his study – done on real farms in the New England (haemonchosis-endemic area) region of NSW – was on comparing the cost of parasitism on farms with ‘typical’ worm control vs those with IPM (integrated parasite management), as detailed in WormBoss, for example. Ball park figures: the cost of parasitism on typical farms was ~$11/ewe vs $6/ewe on IPM farms. The IPM figures included recommended levels of wormtesting and drench resistance testing. So, a difference of roughly $5. Let’s apply this to say 3000 sheep: $15 ooo.
You have probably heard of PGP inhibitors. Below are a couple of papers if you are interested. The abstract below (from Lepine and others, 2011) gives an inkling of what this is about. (Private vet practitioners reading this may have heard of PGPs / ‘MDR’ in relation to the test available in dogs (collies etc) to check to see if they have a mutant MDR gene that renders the dog more susceptible to macrocyclic lactone toxicity). (Thanks Dr Ebert)
“Parasitic helminths cause significant disease in animals and humans. In the absence of alternative treatments, anthelmintics remain the principal agents for their control. Resistance extends to the most important class of anthelmintics, the macrocyclic lactone endectocides (MLs), such as ivermectin, and presents serious problems for the livestock industries and threatens to severely limit current parasite control strategies in humans. Understanding drug resistance is important for optimizing and monitoring control, and reducing further selection for resistance. Multidrug resistance (MDR) ABC transporters have been implicated in ML resistance and contribute to resistance to a number of other anthelmintics. MDR transporters, such as P-glycoproteins, are essential for many cellular processes that require the transport of substrates across cell membranes. Being overexpressed in response to chemotherapy in tumour cells and to ML-based treatment in nematodes, they lead to therapy failure by decreasing drug concentration at the target. Several anthelmintics are inhibitors of these efflux pumps and appropriate combinations can result in higher treatment efficacy against parasites and reversal of resistance. However, this needs to be balanced against possible increased toxicity to the host, or the components of the combination selecting on the same genes involved in the resistance. Increased efficacy could result from modifying anthelmintic pharmacokinetics in the host or by blocking parasite transporters involved in resistance. Combination of anthelmintics can be beneficial for delaying selection for resistance. However, it should be based on knowledge of resistance mechanisms and not simply on mode of action classes, and is best started before resistance has been selected to any member of the combination. Increasing knowledge of the MDR transporters involved in anthelmintic resistance in helminths will play an important role in allowing for the identification of markers to monitor the spread of resistance and to evaluate new tools and management practices aimed at delaying its spread“.
(ABC = ATP-binding cassette (ABC) transporters. None the wiser? Me either.).
Regarding the safety of macrocyclic lactones in mammals:
” Mammalian safety appears to depend on p-glycoprotein activity in the blood-brain barrier. A p-glycoprotein deficiency in certain animals decreases the ability to pump avermectins, milbemycins, and other drugs across cell membranes” “There have been cases of CNS depression in cattle breeds (Murray Grey) and in individual dogs of multiple breeds, but these were first recognized in purebred and crossbred Collies.” Source: http://www.merckvetmanual.com/mvm/pharmacology/anthelmintics/safety_of_anthelmintics.html
Lespine A and others, 2011. Review: P-glycoproteins and other multidrug resistance transporters in the pharmacology of anthelmintics: Prospects for reversing transport-dependent anthelmintic resistance. Int J Parasitol.
Razaa A et al 2015.Effects of third generation P-glycoprotein inhibitors on the sensitivity of drug-resistant and -susceptible isolates of Haemonchus contortus to anthelmintics in vitro. Veterinary Parasitology
211. 1–2. 30 June 2015 pp 80–88
If you are not too proud to read wiki (with discernment, as with everything):
Skoda Superb – Rommel had one
Competing/conflicting interests: none to declare (Trust me: I work for the government)
My antecedents were Scottish: I can mock them as much as I like. It’s the Australian way.