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24 August 2017
Myiasis  

Myiasis is the invasion of body of animals and humans by larvae of fly (maggot). Elderly people with physical disability or bed-bound are more vulnerable to fly invasion of their body parts not protected by skin such as wounds and mucous membranes.

Causative agent

Many types of flies can cause myiasis in animals or humans, such as Oestroidea, Calliphoridae and Sarcophagidae.

Chrysomya bezziana of the Calliphoridae family is the more common species that cause human myiasis in Hong Kong.

Development of disease

For Chrysomya bezziana, there are 4 stages of the life cycle, from egg, larva, pupa and then to adult. An adult female fly only lays eggs on live animals. The sites of larvae infestation are usually on superficial wounds, or mucous membranes in body orifices such as the mouth, the ear and the nose of debilitated persons. The eggs hatch within 24 hours and the larvae burrow into the host's tissue and feed on the host's dead or living tissue.

Clinical features

Feeding activity of the larvae may cause serious tissue damage, often accompanied by putrid discharge and ulceration, resulting in loss of function, injury to the skin, secondary bacterial invasion and death.

Prevention

To prevent myiasis infestation, members of the public, especially staff of elderly homes while taking care of their residents, are advised to observe the following measures:

  • Observe good personal hygiene
    • Bathe daily and keep skin clean.
    • Maintain good oral hygiene.
  • Proper wound management
    • All wounds should be treated immediately and dressed properly. Wash hands before and after touching wounds.
    • Wounds should be observed regularly. Dressings should be kept clean and dry.
    • Seek medical attention should the wound does not heal well or shows symptoms of infection.
  • Ensure good environmental hygiene
    • Store food in refrigerator or cover the food with screen.
    • Refuse should be kept in containers with tight-fit lid and disposed of regularly.
    • Dead bodies of animals should be disposed of properly.
  • Fly proofing measures
    • Install fly screening, insect electrocuting device, or fly trap.
  • Keeping of pet
    • All wounds on animals should be treated immediately and properly.
    • Pets, particular dogs and cats, have to be examined by veterinary surgeon regularly.
    • Do not feed stray animals or keep them as pet.

Staff of elderly homes should ensure good environmental hygiene, be alert to inmates developing symptoms of the disease and seek medical consultation promptly for inmates feeling unwell.

Further advice on fly prevention could also be obtained from the Pest Control Advisory Section of the Food and Environmental Hygiene Department. (website: http://www.fehd.gov.hk/english/safefood/Pcas.html)

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