ICEH Resources Information Sheet

TOXOCARIASIS

Pronunciation: Tox-o-car-eye-ass-iss

What causes Toxocariasis?

Toxocariasis is a usually mild zoonotic (animal related) disease caused by the parasitic worm Toxocara canis, or Toxocara cati (rarer cause). Infection is most common in children, and sickness is from larvae (immature worms) spreading into organs and tissues, or the eyes. Human infection with this parasite was first observed in 1950. Toxocariasis is not a Nationally Notifiable Disease.

Toxocara canis occurs in dogs and Toxocara cati in cats. It cannot reproduce in humans or other end-stage hosts like cattle and sheep. However, it can live in their tissues for many years.

What does it look like?

Adult worms are large (6-18 cm long and 0.2-0.3 cm wide), but the larvae are very small (0.4mm long and 0.02mm wide). The eggs can only be seen with a microscope, and have a very sticky outer coat that allows them to be transported long distances. Eggs can survive for up to 2-4 years in cool moist conditions.

Toxocariasis in Australia

Where does it occur?

Toxocara spp. is found worldwide in dirt and sand, and most often is present in wet tropical areas.

Australian / Indigenous Significance

A study in Brisbane found infectious eggs present in 1% of all dirt samples collected from local parks.

In the 1970s T. canis was found in 70-80% of dogs in North Queensland. However, it is thought to now be less common in this area, as well as in the Northern Territory and Western Australia. Currently, around 1 case of toxocariasis is reported every 2-3 years.

Symptoms: What to look out for?

It is common for people with light infections to be asymptomatic (not feel sick). Symptoms may vary depending on the severity of infection, where the larvae enter the body, and the body’s natural responses to the infection. There are two main forms of toxocariasis:

1. Eye infection (Ocular larva migrans or OLM)
   This type of infection may cause blindness or partial permanent vision loss, due to larvae entering the eye and causing inflammation and retina scarring. Symptoms include red eyes and impaired vision. This form is more common in children aged 5-10 years.
2. Infection of body organs and tissues (Visceral larva migrans or VLM)
   This form is rarer, and is caused by heavier or repeated infections. The spread of worms through body tissues and organs causes symptoms such as fever, rashes, pale skin, coughing, asthma, headaches, abdominal pain and pneumonia. This infection is more common in children under 5 years of age.

How do you diagnose (confirm) a case?

People who think they may be infected can visit their local health clinic for an examination. Blood tests are required to confirm cases of toxocariasis.

How does it spread?

Toxocariasis does not spread from human to human. Illness starts when people swallow infective eggs. This may occur when people swallow dirt or dust soiled with dog or cat faeces (shit), or eat food contaminated with infective soil (raw vegetables etc). Flies also transfer eggs onto foods, which can lead to infections. Scientific studies have found that hands can pick up eggs by patting infected dogs, which then may be transferred onto food or other itmes. A person may also become infected from eating raw liver from infected chickens, sheep or cattle.

How does it reproduce?

Toxocara canis is of more concern to humans than T. cati, and its lifecycle will be discussed in this section.

Adult dogs swallow eggs that hatch in their intestines. The larvae then spread into body tissues where they can stay for several years.

Larvae become active again when a female dog becomes pregnant. Puppies become infected either before birth, or after by drinking their mother's milk.

Larvae become adults in the puppy’s intestine, and produce eggs when 3-4 weeks old. The eggs are released in the puppy’s faeces, and become infective after incubating in dirt for 1-3 weeks. Eggs can stay alive in the dirt for months, and are only killed by heat greater than 30-35ºC or drying out.

Worm activity may stop or become dormant when the dog reaches sexual maturity.

Toxocara canis cannot reproduce in end-stage hosts. Eggs swallowed by humans hatch in the intestine, and the larvae go through the walls and into the liver. The larvae may then spread to other body tissues in the case of VLM (mainly lungs and gut), or infect the eyes causing OLM. Larvae can live for years in the tissues of end-stage hosts like humans and sheep and cause infection when eaten by other animals.

How infectious is it?

Toxocariasis is not spread from human to human. However infectious eggs can survive in dirt for up to 4 years.

How long does it take for symptoms to appear?

Symptoms can take one week or a couple of months to appear after eggs have been swallowed, and may continue for a year or more. Eye-related symptoms can take 4-10 years to appear. Eating raw liver from an infected animal may result in an infection where symptoms appear wihin hours or a day.

Who is most at risk?

Severe cases of toxocariasis are rare, sporadic, and most common in children aged 14-40 months. Children that regularly play in or who eat dirt have a greater risk of developing toxocariasis, as well as owners of dogs and cats. Human and animal reinfection can occur.

How do we prevent it from occurring?

Community education on good personal hygiene practices is the main means for reducing the number of toxocariasis cases. Emphasis should be placed on the importance of:

• Washing hands after soil contact or touching animals, and before handling or eating food.
• Teaching children not to eat dirt or put dirty objects in their mouths.
• Keeping cats and dogs out of areas where food is grown, and stopping them defecating (shitting) in areas next to houses or where children play. Sandpits should also be covered when not in use.
• Worming dogs and cats regularly. Worming treatment should start when animals are 3 weeks old, and be given every 2 weeks for 6 weeks, and then once every 6 months.
• Cleaning of animal living areas regularly. Faeces should be hygienically collected and disposed of to prevent dirt contamination.

How can it be controlled?

The VLM form of this disease is sporadic, and the majority of infected people recover without treatment. Antiparasitic drugs can be used to treat more severe VLM cases. Anti-inflammatory drugs may also be required to reduce inflammation caused by the larvae moving through the body.

OLM toxocariasis is more difficult to treat and usually requires medical attention to prevent further damage to the eye.

Extreme heat and prolonged dryness will kill eggs. Contaminated sandpits (or suspected ones) can be steam treated to kill any eggs present, and blow guns may be used to clean kennels of infected animals.

Bleach (hypochlorite) solutions remove the sticky outer coating of eggs, making it easier to wash them off concrete surfaces like those in kennels. However, bleach will not kill eggs, and the eggs may enter the soil.

Treatment of contaminated dirt is difficult. One suggestion is to break up topsoil and flame several times to kill eggs present. Alternatively, the top 10-20cm of dirt may be removed and replaced with clean dirt.

Case Study

Human toxocariasis is rare in Australia, and no Australian case studies were located for this disease.

The best way to prevent/control this disease is to educate people about why it is important to:

• prevent dog faeces contaminating the environment,
• keep animals out of living areas,
• worm domestic dogs and cats regularly, and
• cull stray or unwanted dogs or cats.

For more information on controlling parasites in dogs, check out Environmental Health for Aboriginal Communities, The Public Health Bush Book, or A Better Dog’s Life, which are listed under resources.

Glossary

Resources

Community Education Flyer to print out
Available at: iceh.uws.edu.au/fact_sheets/toxo_flyer.pdf
[1 page sheet for community information, 129KB PDF file]

Blatz, S. 2000, ‘How to stop the spread of toxocariasis’, Nursing, Vol January, p. 17.
[Journal article on ways to prevent the spread of toxocariasis]

Carden et al. 2003, ‘Toxocara canis: egg presence in Melbourne parks and disease incidence in Victoria’, Clinical and Experimental Ophthalmology, Vol. 31, pp. 143-146.
[Journal article on Toxocara sp eggs in Melbourne parks (technical)]

Chin, J., 2000, Control of Communicable Disease Manual, 17th edn, American Public Health Association, Washington DC, pp. 497-499.
[Book on infectious diseases that is often referred to in health departments (technical language)]

Coghlan, A. 2003, ‘Dog stroking can transmit debilitating parasite’, New Scientist, Available: http://www.newscientist.com/news/print.jsp?id=ns99993651
[Article on how patting dogs can cause infections]

Currie, B. 1995, ‘Dogs and human health in Aboriginal communities: how important are zoonoses’, Aboriginal and Torres Strait Islander Health Information Bulletin, Vol 20, pp. 19-29.
[Journal article on diseases that occur in dogs (technical language)]

Dickson, D.D., Gwadz, R.W. & Hotez, P.J. 1995, Parasitic Diseases, Spinger-Verlag, New York, pp. 61-70.
[Book on diseases caused by parasites (technical language)]

Fernando, R.L., Fernando, S.E. & Leong, A.S.Y. 2001, Tropical Infectious Diseases: Epidemiology, Investigation, Diagnosis and Management, Greenwich Medical Media Ltd, London, pp. 99-101.
[Book that focuses on infectious diseases in Australia (technical language)]

Griffiths, O. & Henderson, H. 1997, Environmental Health for Aboriginal Communities: A Training Manual for Environmental Health Workers, Office of Aboriginal Health, East Perth, pp. 16-28.
[Training manual for Environmental Health Workers in Western Australia]

Lloyd, S. 1998, ‘Toxocarosis’, in Zoonoses, eds S.R. Palmer, Lord Soulsby & D.I.H. Simpson, Oxford University Press, New York.
[Book on diseases that spread from animals to humans (technical language)]

The Public Health Bush Book, 2nd edn, 2002, Northern Territory Health Services, Darwin. Available at:
www.nt.gov.au/health/healthdev/health_promotion/bushbook/
[Book that provides relevant environmental health information for people working in remote Aboriginal communities in the Northern Territory]

Thielberger, N. & McGregor, W. 1994, Macquarie Aboriginal Words: a dictionary of words from Australian Aboriginal and Torres Strait Islander languages, Macquarie Library Pty Ltd, NSW.

Created November 2003
by Margaret Davidson