Parasites
There are a number of tiny pests that can be passed from animal to human or human to human that at best will make you very uncomfortable and at worst can transmit disease.
Bed bugs
Bed bugs are blood-feeding insects that come out at night to feed. They are small, 4 to 5 mm in length and typically oval shaped, thin and flattened. They will hide and lay eggs close to where humans sleep which, due to their small size, can be mattresses, bed frames, furniture, behind skirting boards, loose wall paper, floorboards and in the cracks and crevices of walls.
They typically feed on exposed, bare skin which may result in small areas of swelling and itching. Some people don't react at all while others can show a delayed response (up to 9 days). Still others react immediately. While irritating, they are not known to transmit disease. Eradicating them can be quite tricky.
Bird mites
Bird mites are naturally found where birds (such as pigeons, starlings, sparrows and poultry) and their nests are located.
However, in the first few weeks after birds leave their nests, bird mites may infest homes in search of a blood-meal from humans. Bites from bird mites can cause severe irritation. They are tiny mites - less than 1mm long - and semi transparent until they've fed. They are generally associated with humid conditions and are most active during spring and early summer.
Bites from bird mites can cause itching, swelling and raised reddish spots but are not known to transmit any infectious disease. Eradicating them involves removing nearby birds' nests and using an approved insecticide.
Head lice
Head lice are social pests and can live in clean or dirty hair. They only live on human heads and are transferred mainly by direct head to head contact. They do not carry disease but bacterial infections can occur from scratching the scalp. They are 2-4 mm long and 1 mm wide with a flat body and are pale to dark brown in colour. Their eggs are tiny and hard, white to yellow in colour and are attached firmly to the hair shaft close to the scalp.
Outbreaks can be controlled if parents regularly check their children's hair and follow recommended treatment methods. Not all people with head lice will feel itchy, so regular weekly checks of all members of a household are recommended. In the event of an outbreak, daily checks are suggested.
For more information, visit the Healthy Heads - Without Head lice program pages on the South Australia Government Department of Health web site.
Scabies
Scabies is a highly contagious mite infection of the skin causes by a parasitic mite. It spreads from person to person mainly via prolonged (several minutes) direct skin to skin contact - although sharing the same bed, clothing or even living in the same house as an infected person can cause infection. Scabies mites tunnel under the skin where they lay eggs. This action leaves squiggly burrows in the skin, usually less than a centimetre in length. Scabies are most commonly found on the hands (particularly between the fingers), wrists and feet although it can also appear in other folds of the body. Scabies can take two to six weeks to present and its onset is typified by intense itching, particularly at night. It is not an indication of poor hygiene. Affected people and environments must be treated to eradicate scabies.
For more information on symptoms and treatment of scabies, visit the Scabies information page of the Australasian College of Dermatologists or download the information fact sheet - Scabies: Prevention and treatment fact sheet