Environmental Health Practitioner Manual: A resource manual for Environmental Health Practitioners working with Aboriginal and Torres Strait Islander Communities

5 Parasites

Page last updated: November 2010

5.1 What are parasites?

Parasites are animals or plants which must live on or in another plant or animal to survive (go on living). There are several parasites in the environment and when they get into a person's body, his/her health can be affected. Some parasites enter the body by way of contaminated food or water and some live on the skin and the hair. Examples of parasites include:
  • stomach and gut worms (threadworm, hookworm)
  • skin mites (scabies)
  • hair and body lice (head lice and crab lice)
  • protozoa (Giardia)
Most of these parasites cannot be seen without the help of a magnifying glass. Like a microscope, this is another kind of special instrument which makes things look bigger than they really are. Some adult worms are big enough to see without the help of a magnifying glass.
It is often easy to see where parasites have been, such as when they cause rashes on the skin.

Protozoa

Protozoa are tiny single-celled animals which can move about on their own. Protozoa are so small they can only be seen with the help of a microscope and only some of them cause disease in humans. An example of one of these is Giardia lamblia.
Fig.  1.10: Giardia, a disease-causing protozoan
Fig. 1.10: Giardia, a disease-causing protozoan.

Worms

Parasitic worms are small animals which can live inside the body. Their eggs are taken into the body, usually by swallowing. The worms then hatch out of the eggs and live in the body. Some types of worm larvae (young worms) can also burrow their way into the body through the skin.
When the worms live in the body they can cause sickness. They may get into the stomach and gut and eat the food before the body has digested it. This means that the body does not get enough nourishment. Sometimes the worms will find their way into other parts of the body, such as the blood or liver. When this happens these parts of the body may not work properly.
Fig.  1.11: Worms
Fig. 1.11: Worms

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Mites and lice

These are small animals which affect the skin and hair of the body. They cause the skin, especially the scalp, to become very itchy.
Fig.  1.12: Lice
Fig. 1.12: Lice.

5.2 Diseases caused by parasites

Common diseases in Indigenous communities which are caused by parasites are described below.

Giardiasis

This is a parasitic infection caused by the protozoan Giardia lamblia getting into the small intestine. Giardia is a single celled animal which is so small it can only be seen with the help of a microscope.

This disease can occur anywhere in Australia and is very common in Indigenous communities. The symptoms (signs) of this disease are:
  • very severe or chronic (long-lasting) diarrhoea
  • stomach cramps and pain
  • fatigue (tiredness)
  • weakness
  • weight loss
There is special medicine which can be taken to get rid of Giardia from the body.

Hookworm infection

This is a widespread disease in warm, tropical and sub-tropical places, especially where sewage disposal is inadequate. It is common in the Kimberley and other parts of tropical northern Australia.

Hookworm is a parasitic worm. The adult worm is about 1 cm in length and is about the thickness of a pin.
The worms suck blood from the human host. The disease becomes serious when there are many worms in the intestine sucking blood from the host. When this happens, the host loses too much blood which contains the body's important nutrients (nourishing food).

This can cause:
  • the body to become anaemic (pale and weak)
  • fever
  • diarrhoea or constipation
In extreme cases hookworm infestation can stop the person from thinking and moving properly. It can also slow down children's growth.

To get rid of these worms from the body, the person must be treated with special medicine.

Threadworm (or pinworm) infection

This is a disease which can occur in any part of Australia. It is another disease which is caused by a parasitic worm which lives in large numbers in the human intestine.

Threadworm causes anal (bum hole) itching. This can lead to disturbed sleep and can cause people to become grumpy. Excessive scratching can lead to broken skin which may become infected (pus sores).

Threadworms are easily passed from one person to another and frequently whole families or groups become infected.

There is also special medicine to get rid of these worms from the body.

Dwarf tapeworm infection

Dwarf tapeworm is the most common human tapeworm in Australia. It is a parasitic infection of the stomach and intestine.
Infection with this tapeworm can cause:
  • diarrhoea
  • stomach pain
  • weight loss
  • weakness
There is special medicine which will get rid of these worms from the body.

Scabies infection

This is a skin disease caused by a tiny animal which is called a mite. It is usually about 3 mm long. The female burrows into the skin to lay her eggs and this irritates the skin and makes it very itchy. As a result, the person scratches the skin a lot.
If the skin breaks as a result of the scratching, germs can enter the break in the skin and cause an infection. When treating the infection it is important to also get rid of the mites or lice; otherwise the irritations will continue and cause more infections.
To get rid of scabies a specially medicated lotion is used.

Pediculosis (head lice infection)

These tiny bloodsucking animals live their whole life on a person's head. The lice stab an opening through the skin and suck up blood from the host. This causes irritation. The resulting scratching can lead to broken skin which can become infected.
Special shampoos are used to get rid of head lice. The eggs which are stuck to the hair need to be removed with a special fine-toothed comb.

5.3 Methods on how some important parasites are spread

Giardia

Giardia occur in the intestines of humans. When Giardia are inside the body they can move about quite easily, but they often leave the body as tiny egg-like cysts in faeces.

Infection happens when these cysts are taken back into the body of someone who does not have Giardia in their intestines. Once inside the intestine they become mobile (able to move) again and start to reproduce themselves by dividing and redividing.

Giardia cysts can be passed:
  • directly by the faecal/oral route from an infected person to one who is not infected
  • indirectly by taking in the cysts in contaminated water or food when eating or drinking

Hookworm

When hookworms get inside people, they lay their eggs inside the person's intestines. These eggs get into the soil or water when infected human faeces has been left on the ground or from faulty or broken sewage systems.

Tiny larvae (young worms) will hatch out. If the soil is wet the larvae will develop to a stage where they can infect people. They can survive in wet soil for several weeks and are able to burrow through unbroken skin. This happens when people's skin comes into contact with water, soil or faeces which is infected with hookworm larvae.

People can become infected with hookworm directly by the ingestion of larvae or by larvae burrowing through the skin.

People in the tropical parts of northern Australia who walk around in contaminated wet places without shoes are very likely to get infected.
Fig.  1.13: Life cycle of the hookworm
Fig. 1.13: Life cycle of the hookworm.

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Inside the body the larvae travel through the blood stream to the lungs where they are coughed up and then swallowed. They finally reach the intestines where they develop into adult worms. Adult worms are able to attach themselves to the walls of the intestines. They have hooks around the mouth which allow them to do this. They live there and suck blood from the human host.
Fig.  1.14: How hookworm gets into the body and where it lives in the body
Fig. 1.14: How hookworm gets into the body and where it lives in the body.

Threadworm (or pinworm)

These worms look like tiny white threads and live in the intestine. The female worm will travel to the anal opening to lay its eggs on the skin around the anus. It is this activity which causes the itching. The eggs and the worms leave the body in faeces. The eggs hatch when they are taken into the same or another person's intestine.

The worms or their eggs can be passed from one person to another:
  • directly through the faecal/oral route from an infected person to one who is not infected
  • indirectly through contact with contaminated clothing, bedding or food

Dwarf tapeworm

The dwarf tapeworm occurs in the stomach and intestines of humans. The adult tapeworm lays its eggs in the body. The eggs are passed out of the body in the faeces. If these eggs are ingested by other people indirectly or directly, the eggs will hatch in the intestine. The immature worm goes through two further stages of development before it becomes an adult.

Humans become infected with dwarf tapeworms:
  • directly by touching the mouth with fingers which are contaminated with faeces containing the egg
  • indirectly by ingesting eggs in contaminated food or water, or by swallowing an insect which has ingested eggs which have then hatched into larvae inside the insect

Roundworms

Roundworms are nematodes and are found in northern parts of Australia and in many tropical countries. Strongyloides stercoralis is a roundworm which causes a life threatening disease called Strongyloidiasis.

People can become infected through contact with soil contaminated by faeces containing the parasite.

People can often get sick where hygiene and sanitation are poor. Infection can be detected with a special blood test and people can be cured with special tablets.

Scabies

These small animals are a type of mite. The female burrows into the skin where it lays its eggs. When the mites hatch they climb out onto the surface of the skin and then enter hair follicles. These are the small openings in the skin which hold the hair roots. The young mites grow into adults in the hair follicles. They then climb out and mate and start the process all over again. It is the burrowing activity of the mites which causes the skin irritation associated with scabies.
Fig.  1.15: Scabies' life cycle
Fig. 1.15: Scabies' life cycle.

Scabies prefer to live in certain places in the body. These are body creases such as the backs of the knee and elbow and in the armpit and groin.
Fig.  1.16: Scabies rash on the body
Fig. 1.16: Scabies rash on the body.

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Scabies can be passed from an infected person to an uninfected person by:
  • direct contact; or
  • indirect contact with contaminated clothing or bedding. Infection happens more frequently when people live in overcrowded conditions
Fig.  1.17: The spread of scabies from person to person
Fig. 1.17: The spread of scabies from person to person.

Head lice

Adult lice live their whole lives in the hair of a person’s head. The lice stab openings in the skin to suck blood. The eggs of the head lice, which are also called nits, are glued to the hairs on the person's head. The nits are about 1 mm in size and are whitish in colour. They take about a week to hatch.

The lice can be passed:
  • directly from person-to-person, such as when small children play or sleep together; or
  • indirectly through the sharing of infected combs, brushes and hats
While head lice can be killed with special shampoos, the nits are difficult to kill in this way. For this reason, nits must be removed with a special fine toothed comb.