In this issue
- WormFaxNSW – April
- Lambex 2016 – Albury in August
- Cold weather and barber’s pole
- Sheep measles – again
- Bush fire? Go to sleep – echidnas do
- Phalaris poisoning in wallabies
- Taking malaria breath markers to the world
The latest edition is up on the NSW DPI website: http://www.dpi.nsw.gov.au/about-us/publications/publications/wormfax
WormFax is a summary of WormTest results (in sheep) from around NSW.
WormFax is based on sheep WormTest (faecal worm egg count (WEC) monitoring) data from the NSW DPI Veterinary Laboratory at Camden/Menangle (EMAI) as well as from Armidale-based private laboratory, Veterinary Health Research (VHR). Owner details are not disclosed.
Some mobs had high WECs. How are your sheep going? If you recently drenched your sheep, do you know if the drench was effective? See, DrenchCheck.
Lambex 2016 – Albury in August
Lambex is the biggest sheep-related conference in Australia. The last Lambex, held in Adelaide in 2014, was a sold-out event, with 930 attending, and another 200 missing out.
NSW DPI’s Lambex coordinator / Lambex committee member is Tracy Lamb*, located at Cowra. E: firstname.lastname@example.org M: 0408 443 267 (* Yes, she has probably heard all the jokes).
Cold weather and barber’s pole
It stops egg development (on pasture) dead in its tracks, but doesn’t bother infective stages (3rd stage larvae) on pasture too much. So, yes, you can still get barber’s pole worm problems in winter, especially if you also inadvertently have been using ineffective drenches, and also if your grazing management hasn’t been ‘crash hot’. (It’s hard to be perfect all the time).
Barber’s pole worm eggs: delicate like little princesses. It’s L3 larvae: as tough as old boots.
Sheep measles – again
Sheep measles (Taenia ovis) was mentioned in the last WormMail. In that edition of WormMail, there was discussion of a survey finding that farmers on average only treated their dogs for tapeworms 2-4 times a year, Dr Patrick Kulver, of the Livestock Biosecuity Network, suggesting that farm dogs should be treated monthly, based on T ovis having a pre-patent period (PPP) of 35 days. (Others say 5-8 weeks) (PPP=time from infection of host until eggs / proglottids appear in the faeces).
Foxes and sheep measles – 10 years ago
Several or more years ago it was thought that foxes did not play an important role in Australia as a host for Taenia ovis.
From the NSW DPI Primefact (2008 edition) on sheep measles, we have this:
“The fox is not an important definitive host for Taenia ovis in Australia. While foxes can become infected with this tapeworm, field experience indicates that this happens rarely. In contrast, foxes quite commonly are infected with the tapeworms Taenia pisiformis and Taenia serialis, from eating rabbits. Less commonly, foxes can also be infected with the tapeworm Spirometra erinacei, from eating reptiles and amphibians. As to dingoes and wild dogs, field evidence indicates that they are only very occasionally infected with Taenia ovis in certain areas (David Jenkins, personal communication, 2007)”
Back to the present – more or less
Then, more recently we have this (Jenkins and others, 2014):
“Foxes (n = 499), shot during vertebrate pest control programs, were collected in various sites in the Australian Capital Territory (ACT), New South Wales (NSW) and Western Australia (WA). Wild dogs (dingoes (Canis lupus dingo) and their hybrids with domestic dogs) (n = 52) captured also as part of vertebrate pest control programs were collected from several sites in the ACT and NSW. The intestine from each fox and wild dog was collected, and all Taenia tapeworms identified morphologically were collected and identified to species based on the DNA sequence of the small subunit of the mitochondrial ribosomal RNA (rrnS)
gene. Taenia species were recovered from 6.0% of the ACT/NSW foxes, 5.1% of WA foxes and 46.1% of ACT/ NSW wild dogs. Taenia ovis was recovered from two foxes, 1/80 from Jugiong, NSW and 1/102 from Katanning, WA. We confirm from rrnS sequences the presence of T. ovis in cysts from hearts and diaphragms and Taenia hydatigena in cysts from livers of sheep in Australia. T. ovis was not recovered
from any of the wild dogs examined but T. hydatigena were recovered from 4(8.3%) wild dogs and a single fox. With foxes identified as a definitive host for T. ovis in Australia, new control strategies to stop transmission of T. ovis to sheep need to be adopted”. (Abstract from Jenkins et al 2014).
If I read this correctly, and all 499 foxes were successfully examined for T. ovis (and other tapeworms), then 0.2% (2 out of 499) foxes were found to have T. ovis. At the two locations (Jugiong, NSW and Katanning, WA) where T. ovis was found in foxes, more foxes (~ 80-100) were sampled, with one fox at each location (roughly 1% of each sample) being positive for T. ovis.
The 2014 Jenkins paper can be accessed by clicking the reference.
Red foxes (Vulpes vulpes) and wild dogs (dingoes (Canis lupus dingo) and dingo/domestic dog hybrids), as definitive hosts for Australian Taenia hydatigena and Taenia ovis. (2014) Jenkins DJ., Urwin NAR., Williams TM., Mitchell KL., Lievaart JJ., Armua-Fernandes MT. International Journal for Parasitology: Parasites and Wildlife 3; 75-80.
“The article below by Dr David Jenkins of Charles Sturt University Wagga Wagga first appeared in WormBoss News (now incorporated into ParaBoss News).
“Foxes, the culprit for high levels of sheep measles in Australian sheep?
“Sheep measles is a parasitic infection of sheep occurring as small white masses in meat. The importance of this parasite is that it causes financial losses to the Australian sheep meat industry and is a potential barrier to the international trade of Australian sheep meat. Data collected in the National Sheep Health Monitoring Program (co-ordinated by Animal Health Australia and supported by the Sheep Meat Council Australia and Australian Wool Producers) clearly shows sheep measles to be widespread and often at high prevalence levels in sheep from all sheep producing areas of Australia.
“During the last two years, Meat and Livestock Australia (MLA) funded a two-year study charged with determining why sheep measles is so common, revisiting the life cycle, identifying on-farm risk factors and then determining the financial impact on processors.
“The sheep measles parasite, Taenia ovis, has a two-host lifecycle with a different body form in each host. Large tapeworms (up to two metres) occur in the intestine of dogs and small cysts about the size of a small pea grow in the muscles of sheep. Mature tapeworms in dogs produce thousands of eggs that are shed daily into the environment via the faeces of infected dogs. These eggs are accidentally ingested by sheep whilst grazing. They hatch in the sheep releasing microscopic 6-hooked larvae that exit the sheep’s intestine, enter blood vessels and are passed to the muscles. Here, over two months, each develops into a cyst containing a tapeworm head. If these cysts are eaten by a dog (via the infected meat), the dog becomes infected with a sheep measles tapeworm.
“Sheep measles does not infect humans, in contrast to its closely related cousin the hydatid tapeworm (Echinococcus granulosus), and it appears to be of no veterinary importance to either dogs or sheep. Its importance is all down to aesthetics associated with the presence of cysts in meat for human consumption. Cysts in sheep remain infective to dogs for 2–3 months after which time they are killed by the immune system of the sheep, developing into a small pus-filled abscess. These abscesses become mineralized transforming into a gritty masses, evolving to hard calcified nodules that remain in the muscle for the life of the sheep. None of these manifestations is popular with consumers!
Figure 1. Degenerated sheep measles cyst in sheep heart. Source: David Jenkins
Figure 2. Viable sheep measles cysts in sheep heart. Source: David Jenkins
“The MLA sheep measles study was undertaken in WA, NSW and Tasmania. These states were selected since abattoir infection data regarding sheep measles identified high prevalence in WA, medium levels in NSW and low levels in Tasmania. In addition, from a potential for wildlife involvement, Tasmania is wild dog and fox-free*.
“About 100 producers were involved in the study, about two thirds with a sheep measles problem and one third without. We also undertook financial impact studies in 5 abattoirs (3 NSW; 1 WA; 1 Tasmania). Abattoirs killing mainly lambs suffered the lowest losses but mutton abattoirs in NSW were losing about $1,100/day whilst in WA losses averaged $2,200/day with peaks up to $4,000/day. Losses for individual producers are often unexpected and substantial. One producer in this study lost $4,000 on two consignments of lambs sent for slaughter in 2012.
“We found no identifiable on-farm risk factors pre-disposing farms to having sheep measles. We examined the faeces of 245 farm dogs and found only one infected with tapeworms. Coincidently, these turned out to be T. ovis in a dog from a farm in Tasmania. The low level of tapeworm infection in dogs is the likely result of the common use of dry dog food and wide availability of relatively cheap all-wormers for dogs containing the highly efficient tapeworm-killing drug praziquantel. We concluded that domestic dogs may not be the major source of infection for sheep now, as they once were in the past.
“We examined the intestines of 499 foxes and 52 wild dogs. We found T. ovis in two foxes (one from NSW and one from WA). The sample sizes of foxes collected from the various locations were variable. The two infected foxes were recovered from the localities where the largest samples were collected, equating to a prevalence of about one percent in each location. Although not high, given the fact eggs of T.ovis remain infective on pasture for at least 300 days and foxes are highly mobile covering anything from 4 to 16 km/night, only a few infected animals need be present in a given geographical area to maintain high exposure pressure on the local sheep population.
“Of the 52 wild dogs examined none was found infected with T. ovis, however, this may be a reflection of the small sample examined. Nevertheless, there was no doubt some wild dogs had been consuming sheep because T. hydatigena tapeworms (bladder worm) were recovered from 4 (8.3%) of the animals. We also identified two foxes infected with T. hydatigena.
“Our study showed for the first time that foxes in Australia are able to act as hosts for T. ovis tapeworms, providing an additional (important?) source of infection to sheep. These findings highlight the need to modify current sheep measles control strategies. This does not mean abandoning de-worming of dogs and feeding safe foods; this should continue as it has been highly effective, but we need to consider how we can protect sheep.
“In 1989 data were published in the scientific press reporting the development of a highly efficient vaccine for sheep against sheep measles. A few years later, this vaccine was commercialised in New Zealand as a stand-alone vaccine. However, the marketing blunder of producing a stand-alone product ensured the failure of the vaccine because most financial losses were felt by the processors and not the producers. Despite the effectiveness of the vaccine, almost nobody bought it. To be used, the vaccine should be combined with something farmers need to use to ensure the well-being of their sheep (such as the current 6-in-1 vaccine). Over time, with wide uptake by producers, this vaccine has the potential to solve the sheep measles problem in Australia, despite the presence of T. ovis-infected wildlife.”
Some notes on T ovis /sheep measles
I cobbled together some notes on sheep measles, in the first place for my own benefit, but it may be of use to others. Love S Taeniid tapeworms incl T ovis – NOTES 2016-05
Although a little repetitive, following are some points from my notes. (See the notes for references, more detail etc).
- Prevalence of sheep measles (T. ovis metacestodes / Cysticercus ovis). Based on National Sheep Health Monitoring Program (NSHMP) data, sheep measles is common and widespread, but varying between regions. At least it’s relatively common for lines of sheep inspected under the NSHMP to have at least one sheep with ‘measles’. However the proportion of individual animals affected is somewhat less, around a few to several percent. (It varies). But, there are occasional cases which perhaps reflect ‘Ovis storm’-like conditions. For example, in one case I recall, 400 lambs were sent to an abattoir in NSW, 100 of the carcasses were condemned or severely trimmed because of sheep measles (B McLeod, pers comm). As to inspections under NSHMP: about 3 million sheep (incl. lambs are inspected per year, which is about 10% of the sheep (incl. lambs) slaughtered in Australia. Also, two of the bigger mutton processors in NSW (Dubbo, Goulburn) are not part of NSHMP. So, we need to be careful when interpreting results from the program. However, some mutton processors not currently involved in NSHMP were part of the study (on costs to processors) by Jenkins et al, 2014.
- Prevalence of adult T. ovis tapeworms. The definitive (final) hosts are canids: domesticated and wild dogs, and foxes. Theoretically cats could (very) rarely be infected, but it’s highly unlikely these infections would be patent (i.e. shedding eggs onto pasture). T. ovis has never been reported in feral cats in AU or NZ.
Jenkins et al opine that foxes are more important now (in mainland Australia) in the spread of T. ovis than domestic dogs, with the role of the latter seemingly declining in importance in recent decades. Apparently not all agree, for example, Palmer, in Western Australia. Even if foxes are now more important, it seems, on current evidence, that even the prevalence of infected foxes is quite low (and probably variable), possibly (?) around the 1% mark (?).
- Fecundity of T. ovis. T ovis is fecund, with about 3 segments being shed per day, each segment containing about 60,000 – 80, 000 eggs. According to “NZ”: one T. ovis tapeworm can produce 250 000 eggs/day and some dogs can carry 3-4 T. ovis tapeworms. Compare this to say Haemonchus (about 5-10 000 eggs/female/day) and Fasciola hepatica (about 20,000 eggs/fluke/day). But, dogs with T. ovis have perhaps 1-4 tapeworms. (But, they are up to 2 metres long!). The numbers of adult Haemonchus and Fasciola carried (in sheep etc) can be in the hundreds to thousands. On the other hand, just a few T. ovis cysts in a sheep can be economically important, even without health consequences to sheep/goats or humans.
- Spread of T. ovis eggs. The eggs on pasture are infective to the intermediate hosts, sheep/goats. These can be spread far and wide by free-ranging wild canids (foxes and wild dogs), but are further spread by wind, rain and coprophagous flies. (‘No accounting for taste).
- Viability of eggs on pasture. Jenkins et al says eggs can be viable for 300 days or more, whereas ‘NZ’ (see notes) say they can be viable for 6 months, but more likely around 4 months (but some can last 18 months), depending on conditions. (Infective stages of H contortus (L3 larvae) and F hepatica (metacercariae) are viable for weeks to several months (and even more) depending on temperature in particular).
- Infectivity and longevity of T. ovis. The host response to adult T. ovis is not that strong, and tapeworms possibly live from a few months to a few years in the intestine of canids. As to the metacestode (sheep measles, ‘Cysticercus ovis‘) stage, the cysts require about 1-2 months to become infective/mature, and then they are highly infective (one cyst consumed by a dog will likely result in infection), but then, unlike the closely related taeniid, T. hydatigena, the cysts are only infective for a short time: about 2-3 months. The immune response of the intermediate host (sheep/goats) is relatively strong: the cysts die, fill with pus and mineralise. (Not attractive to consumers). But, “lambs not exposed to Sheep Measles eggs on pastures develop no natural immunity (‘NZ’).”
More on immunity…”Exposure to T. hydatigena suppresses infection by T. ovis, but not by E. granulosus. This has important epidemiological consequences where these parasites co-exist.” (Gemmel et al Parasitology 1997. See notes).
- Control. Traditional control consists of preventing dogs from consuming sheep meat/offal containing viable cysts, and regular treatment with a tapewormer (praziquantel is the most effective) to remove T. ovis from the dog’s intestines. Given the role, according to Jenkins et al, of a sylvatic pathway, with foxes in particular playing a part (in mainland Australia), traditional control measures, while necessary, are insufficient, the authors say, and vaccination of sheep against T. ovis is necessary.
- T ovis vaccine. A Melbourne-based group (Joh or TAS?nstone et al) in 1989 reported on the development of a T. ovis vaccine and this was subsequently commercialised and marketed in NZ, but then went off the market. Jenkins et al, 2014, comment on possible reasons for this.
Theoretically the sylvatic cycle (apparently not an issue in NZ? or TAS??) could be interrupted to some extent by using cestocide-laced baits (trialled in Germany) but this would be impractical in countries like Australia. Jenkins et al much prefer the use of a T ovis vaccine to augment traditional control measures.
More on vaccines…”Highly effective recombinant vaccines have been developed against the helminth parasites Taenia ovis, Taenia saginata and Echinococcus granulosus. ” Lightowlers et al Vet Parasitol 2003 (See notes).
- Resistance to praziquantel (PRZ)? To control T.ovis with its pre-patent period of 35 days (others say the PPP is 5-8 weeks), monthly treatment of rural domestic dogs has been recommended. This is logical to optimise control, but on the other hand, it may increase selection for resistance. However, I know of no cases of taeniid tapeworm resistance to PRZ, although I am aware of reports from NZ of Monezia app resistance to PRZ. There is discussion about PRZ resistance of Schistoma (blood-flukes), but I gather it is not currently considered an issue.
- More information, and modelling, needed? My impression is that there is still a lot to be leaned about the ecology, epidemiology and economics of T ovis / sheep measles, at least in Australia. As to the role of various definitive hosts, although quite a few dogs and foxes have been examined over the years in Australia, it seems to me the numbers are inadequate to result in reliable estimates of prevalence. I wonder also if modelling may help to better understand the epidemiology of T. ovis in Australia. (On the one hand, T ovis is fecund (but each dog/fox has few tapeworms) and the eggs are viable for several months, but then the prevalence of T ovis in definitive hosts seems to be low, and also the cysts in intermediate hosts are only viable for 2-3 months.. But then it doesn’t take many cysts in a sheep or goat at an abattoir to make a case significant economically……) – SL.
Bush fire? Go to sleep
That’s what echidnas do.
Phalaris poisoning in wallabies?
From Animal Health Surveillance Quarterly | Volume 20 | Issue 4 – page 4:
“Chronic phalaris toxicity in Bennett’s wallabies:During the six months preceding October 2015, it is estimated that up to 100 Bennett’s wallabies (Macropus rufogriseus rufogriseus) died on a single property located just north of Hobart, Tasmania.”
“Chronic phalaris toxicity has previously been reported in eastern grey kangaroos (M. giganteus) in Victoria and red kangaroos (M. rufus) and wallabies grazing phalaris-dominant swards in captivity (Munday, pers comm, 2009). Affected macropods display a variety of neurological signs, including ataxia, muscle tremors, a wide-based stance and sporadic collapse. Often, these clinical signs are exacerbated when the animals are approached.”
“Other documented plant poisonings in Australian wildlife include hepatotoxicity and secondary photosensitisation in red kangaroos following ingestion of lantana (Lantana camara), suspected pyrrolizidine alkaloid hepatotoxicosis in southern hairy-nosed wombats (Lasiorhinus latifrons) associated with consumption of potato weed (Heliotropium europaeum)and crystal- associated hepatopathy consistent with intoxication by steroidal saponins in eastern grey kangaroos (AHSQ Vol. 19 Issue 2)”
Taking malaria breath markers to the world
‘Australian scientists will be field testing their ground-breaking breath markers for malaria, thanks to a $1.4 million research grant from the Bill & Melinda Gates Foundation.’ Link to article.
(Paraphrasing Mark Twain): I was going to write a short WormMail, but I didn’t have time, so I wrote a long one instead.
SL, Armidale 2016-05-30