Gungahlin Vet Hospital

Hydatid disease in humans and dogs

The tiny hydatid tapeworm of dogs can cause severe health problems for humans. This award winning essay is by medical student Joannah Chappel. She is a qualifed veterinary nurse who we are lucky enough to employ on some weekends.

Hydatid Disease: Worth Our Attention 

Hydatid disease is arguably the most important parasitic disease in Australia. Public awareness of it, however, is surprisingly low. The disease occurs in humans when the tapeworm egg is ingested and a larval cyst forms inside a bodily organ. This thriving and versatile parasite has the potential to affect numerous farming and rural communities as many mammals including cattle, sheep, dogs, native mammals and even wild pigs may act as a reservoir.  By understanding the disease and by being aware of potential exposure risks and taking precautions every day, we hope to prevent transmission to humans and decrease the threat to public health. The changing patterns of rainfall resulting from climate change may alter the epidemiology of hydatid disease, therefore we should take its surveillance more seriously and educate people in the many regions potentially at risk.   This is a reminder for both the public, health professionals and policy-makers that hydatid disease is still in our midst and can be prevented.

 Hydatid disease can be found on all continents of the globe, more frequently in rural grazing areas1. The tapeworm Echinococcus granulosus arrived with dogs and livestock to Australia at different phases of European colonisation. By the 1860s there were 20 million merino sheep and rampant human hydatidosis to accompany them2. Even though we now know the lifecycle of E. granulosus, it remains an important public health issue because of its ability to replicate in Australian native wildlife and transmit back to livestock and domestic dogs1. This makes the tapeworm resistant to normal public health interventions aimed at domestic animals. Dingoes and wild dogs are highly susceptible to infection as well as foxes3; kangaroos, wallabies and other native mammals, are also highly vulnerable1. In wallabies that have been studied, the cysts grew more rapidly and became fertile earlier and they also suffered significant lung disease from the cysts4, 5.

 Unfortunately, E. granulosus has a complex life-cycle that is important to understand in order to control transmission to humans and between species. Like all tapeworms it requires a “definitive” host in which the adult worm lives, a canine, and an “intermediate” host in which the larval form of the parasite lives, traditionally the sheep, but it can also infect goats, swine, cattle and native wildlife. The adult tapeworm, which is only 3-6mm long, lives in the small intestine of the dog, dingo or fox and releases eggs that are then excreted in the faeces. A grazing animal ingests the egg which then hatches and burrows through the small intestine wall into the blood stream. From here it can now travel pretty well anywhere but mostly migrates to the liver and lungs where it develops into a fluid-filled cyst containing tiny little heads of the tapeworm. The lifecycle is complete when a dog, dingo or fox then eats the organs of the prey animal containing the cysts and the little tapeworm heads attach to the small intestine and grow into adults within 32 to 80 days6. The disease in humans occurs when we act as an inadvertent intermediate host by ingesting eggs from dog faeces on the ground or transferred to us by flies, then developing a larval cyst up to years later in an internal organ. Children may be particularly at risk because they are still honing their hygiene habits.

 In humans, the hydatid cysts tend to form in the liver (50-70% of patients) or in the lung (20-30%) but may be found in any organ of the body, including brain, heart, and bones (less than (10%)7. They grow to 5-10cm in size within the first year and can survive for decades. Symptoms are often absent but when they are present it is usually from the mass pressing on an organ. If the cyst ruptures, secondary bacterial infection and abscess may occur or anaphylaxis (extremely dangerous allergic reaction). The most important complication of cyst rupture is secondary seeding of daughter cysts into other areas of the body which can then subsequently grow and cause critical failure of other organs.7 This process could be likened to the malignant spreading of cancer.

 In a 2006 study it was found that 29% of rural domestic dogs sampled from 95 farms in south eastern New South Wales and 17.5% of dogs sampled from 43 farms in Victoria had evidence of infection with E.granulosus8. Many of the owners revealed that they fed raw meat and occasionally offal from domestic livestock and wildlife to their dogs and few owners wormed their dogs frequently enough to eliminate human health risks. Most owners said they did not know that kangaroos, wallabies and feral pigs could also be infected8.

 The main source of infection of domestic animals and humans now seems to be through native and feral wildlife rather than a domestic animal transmission pattern9. In wild dogs and dingo hybrids the prevalence of E. granulosus has been found to be between 76% and 100% in eastern Queensland10, 11 and between 25% and 100% in Victoria and New South Wales12.  Wild dogs infected with E. granulosus have even been found encroaching on urban areas in Townsville13 and the Sunshine Coast14.

 Hydatid disease is not a nationally notifiable disease, which means that it is not mandatory for doctors to report it to the Commonwealth’s National Notifiable Diseases Surveillance System (CNNDS)15 nor to the local public health unit. One study audited NSW and ACT medical records from 1987-1992 and found that the average annual number of people needing treatment for hydatid disease was 2.6 cases per 100 000 rural population16. However, this number ranged between 0.3 to 23.5 (cases per 100 000) throughout the north-eastern and south-eastern tableland shires. (There was one case in the Bega Valley during this time). These numbers were much higher than the official figures suggested16. The real prevalence of hydatidosis in Australia is unknown and probably still underestimated as this study showed. At the moment there is also no routine recording of hydatidosis in Australian abattoirs2.Hydatid disease is thought to be costing the Queensland meat industry $2.7 million annually through lost offal sales17. The distribution of E. granulosus is restricted by rainfall18; with changing rainfall patterns, improved vigilance seem very wise.

 So how do we avoid hydatid disease? The most obvious thing to do is to keep your dogs wormed and do not feed them offal (anything that is not muscle meat) from livestock or wildlife including feral species like wild pigs19. Worming should be done every 6 weeks with a tapewormer containing praziquantel. If you are unsure if your worming product covers tapeworm, as not all of them do, ask your veterinarian. [Interceptor™, Drontal™, Popantel™ and Virbac Tapewormer™ available from Gungahlin Veterinary Hospital all contain Praziquantel.]

Do not approach any wild dogs or foxes and be wary of dogs and puppies with an unknown past. Wild dogs and foxes are drawn to camping and barbecue areas in parks and forests. They can be treated with praziquantel baits every 4-6 weeks to decrease the risk of hydatid transmission to humans, as has been done in Germany20.  An effective vaccine has been produced for sheep and other intermediate hosts, EG95, which should be used in areas where hydatid disease is prevalent21. This would stop an important avenue of transmission from wildlife to domestic animals but may not decrease disease in humans necessarily. And, of course, wash your hands with soap after gardening and wash vegetables well that may have been in contact with dog faeces.

 Because of the infection of wildlife, it is very unlikely that hydatid disease could ever be eradicated from mainland Australia as it has been in Tasmania1. Therefore good public education is key for prevention on a personal level and to sway political agenda on a national level. Monitoring human infection is important to identify regions where transmission may be happening. We need to be reminded and be aware of this parasite that lives alongside us.

Joannah Chappel

 References

1.         Jenkins D. Echinococcus granulosus in Australia, widespread and doing well! Parasitol Int. 2006;55:S203-6.

2.         Jenkins D. Hydatid control in Australia: where it began, what we have achieved and where to from here. Int J Parasitol. 2005;35:733-40.

3.         Jenkins D, Craig N. The role of foxes Vulpes vulpes in the epidemiology of Echinococcus granulosus in urban environments. Med J Aust. 1992;157(11-12):754-6.

4.         Barnes T, Hinds L, Jenkins D, Bielefeldt-Ohmann H, Lightowlers M, Coleman G. Comparative pathology of pulmonary hydatid cysts in macropods and sheep. J Comp Pathol. 2011;14(2-3):113-22.

5.         Barnes T, Hinds L, Jenkins D, Coleman G. Precocious development of hydatid cysts in a macropodid host. Int J Parasitol. 2007;37(12):1379-89.

6.         Centers for Disease Control and Prevention. Parasites and Health- Echinococcosis.  2009 [cited 2012 27 Feb]; Available from: www.dpd.cdc.gov/dpdx/HTML/Echinococcosis.htm

7.         Cestodes.  Principles and Practice of Infectious Diseases. 6th ed. Philadelphia: Elsevier; 2005.

8.         Jenkins D, McKinlay A, Duolong H, Bradshaw H, Craig P. Detection of Echinococcus granulosus coproantigens in faeces from naturally infected rural domestic dogs in south eastern Australia. Aust Vet J. 2006;84(1-2):12-6.

9.         Jenkins D, Macpherson C. Transmission ecology of Echinococcus in Australia and Africa. Parasitol. 2003;127:S63-72.

10.       Baldock F, Thompson R, Kumaratilake L, Shield J. Echinococcus granulosus in farm dogs and dingoes in south eastern Queensland. Aust Vet J. 1985;62:335-7.

11.       Durie P, Riek R. The role of the dingo and wallaby in the infestation of cattle with hydatids in Queensland. Aust Vet J. 1995;28:249-54.

12.       Jenkins D, Morris B. Echinococcus granulosus in wildlife in and around the Kosciuszko National Park. Aust Vet J. 2003;81:81-5.

13.       Brown B, Copeman D. Zoonotic importance of parasites in wild dogs caught in the vicinity of Townsville. Aust Vet J. 2003;81:700-2.

14.       Jenkins D, Allen L, Goullet M. Encroachment of Echinococcus granulosus into urban areas in eastern Queensland, Australia. Aust Vet J. 2008;86(8):294-300.

15.       Department of Health and Ageing. Australian national notifable diseases case definitions.  July 2011 [cited 2012 27 Feb]; Available from: www.health.gov.au/internet/main/publishing.nsf/Content/cdna-casedefinitions.htm

16.       Jenkins D, Power K. Human hydatidosis in New South Wales and the Australian Capital Territory, 1987-1992. Med J Aust. 1996;164(1):18-21.

17.       Thompson M. Hydatids:an emerging issue. Queensland Country Life. 2003 September 4:35.

18.       Gemmell M. Hydatid disease in Australia III. Observations on the incidence and geographical distribution of hydatidosis in sheep in New South Wales. Aust Vet J. 1958;34:269-80.

19.       Lidetul D, Hutchinson G. The prevalence, organ distribution and fertility of cystic echinococcosis in feral pigs in tropical North Queensland, Australia. Onderstepoort J Vet Res. 2007;74(1):73-9.

20.       Schelling U, Frank W, Will R, Romig T, Lucius R. Chemotherapy with praziquantel has the potential to reduce the prevalence of Echinococcus multilocularis in wild foxes (Vulpes vulpes). Ann Trop Med Parasitol. 1997;91:179-86.

21.       Lightowlers M, Jenson O, Fernandez E, Iriarte J, Woollard D, Gauci C, et al. Vaccination trials in Australia and Argentina confirm the effectiveness of the EG95 hydatid vaccine in sheep. Int J Parasitol. 1999;29(4):531-4.

This award winning essay is by medical student Joannah Chappel. She is a qualifed veterinary nurse who we are lucky enough to employ on some weekends.