CASE NOTES

CYSTICERCUS BOVIS: BACKGROUND TO THE NSW PROGRAM AND REVIEW OF CASES

Graham Bailey, Cattle Health Coordinator, NSW Department of Primary Industries, Orange

Posted Flock & Herd April 2017

Introduction

The metacestodes (or larval cestodes) of Taenia secies tapeworms are the cause of cysticercosis in various farmed and wild animals and in humans. Adult tapeworms are found in the small intestine of carnivore definitive hosts: humans, dogs, and wild canids. Taenia saginata of humans causes bovine cysticercosis, which occurs virtually world-wide, but particularly in Africa, Latin America, Caucasian and South/Central Asia and eastern Mediterranean countries. The infection occurs in many countries in Europe and sporadically in the United States of America, Canada, Australia and New Zealand. Diagnosis in cattle usually is based on identification of the metacestode at meat inspection or necropsy.

Adults in definitive hosts are acquired by the ingestion of viable metacestodes in meat and offal that has not been adequately cooked or frozen to kill the parasite. Gravid segments are shed by the adult tapeworms. These release about half their eggs through the site of the break into the faecal mass. Approximately 50% of the segments of T. saginata then migrate spontaneously out of the anus to fall to the ground, the rest of the segments are passed with the faeces. The segments migrate, shedding most of the remainder of their eggs on the soil and herbage or on the faeces, respectively. Eggs may be disseminated from faeces by physical means or transport hosts. Flies particularly ingest eggs and transport these eggs, so eggs are deposited at high intensity within 150 m of the faeces and at low intensity for 10 km. Eggs are immediately infective when passed. Animals acquire infection from ingestion of food or water contaminated with sticky eggs, ingestion of segments or faeces containing eggs. Disease clusters where a human carrier exists.

Background to listing Cysticercus bovis as a notifialbe disease

Animal Health Committee considered Cysticercus bovis policy in 2010 and 2011. Prior to 2010, C. bovis was not included on the national list of notifiable diseases. The proposal to include C. bovis on the national list of notifiable diseases was prompted by:

Australia seeking that its food inspection and certification system be recognised as equivalent to those of the European Union (requirement for routine notification of ante- and post-mortem C. bovis findings between slaughter establishments, holdings of origin and back to slaughter establishments).
Industry request to consider modifying the current inspection protocol as described in the Australian Standard for the Production and Transportation of Meat and Meat Products for Human Consumption so that it is based on risk. If changed, it is likely the protocol would be simplified (inspection of fewer organs).

C. bovis has been a notifiable disease in NSW since 2011.

Occurence of C. bovis in NSW

The prevalence of C. bovis infection in cattle in Australia and NSW is thought to be low. The state wide prevalence in NSW from 1970-1972 as shown by meat inspection was 0.05-0.06% (Bryden personal communication cited by Rickard and Adolph 1977).

Collins and Pope (1990) cited records of the Meat Inspection Service in the period between 1984 and 1988. The biggest concentration of farms was in the vicinity of Bowral, Berrima, Mittagong and Moss Vale where there were 71 affected farms.

Pearse et al. (2010) conducted the first national survey of C. bovis infection. During February 2008, 493 316 cattle slaughtered at 48 export abattoirs in Australia, excluding those that slaughtered only calves, were subjected to the standard post-mortem procedure including incision of the heart and masseter muscles. Tissues from 23 animals were submitted for laboratory examination by histopathology and molecular characterisation. C. bovis was not confirmed by laboratory examination of the tissues. The authors concluded that bovine cysticercosis in Australia was extremely rare.

An exception was a “cysticercosis storm” reported by Jenkins et al. (2013). In the period 5 July to 13 December 2010, 138 animals maintained exclusively in feedlot enclosures were slaughtered with 80 (58%) positive. In contrast none of the 234 animals grazed exclusively on pasture on the property were infected. The suspected source of infection was imported copra meal which was used as a feed supplement.

Since C. bovis was listed as a notifiable disease, notification has been received about 6 animals that were suspected of having cysticercosis at slaughter. The presentation at the 2017 DVs conference will provide details of the animals and on-farm investigations.

Acknowledgements

Thanks to abattoir on-plant veterinarians who submitted samples for testing and District Veterinarians who conducted field investigations following receipt of positive C. bovis reports.

Information in the section “Introduction” was modified from the OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals 2016.

References

Collins GH, Pope SE. Cysticercus bovis in cattle in New South Wales. Australian Veterinary Journal 1990; 67:228-9
Jenkins DJ, Brown GK Traub RJ. 'Cysticercosis storm' in feedlot cattle in north-west New South Wales. Australian Veterinary Journal 2013; 91:89-93
Manual of Diagnostic Tests and Vaccines for Terrestrial Animals 2016 Chapter 2.9.5 Cysticercosis 1 March 2017
Pearse BHG, Traub RJ Davis A et al. Prevalence of Cysticercus bovis in Australian cattle. Australian Veterinary Journal 2010; 88:260-2
Rickard MD, Adolph AJ. 1977. Med. J. Aust. 1977; 1:525-527