Advice on Prevention on Fly for Hospitals / Home for elderly

Background

Myiasis is the invasion of organs and tissues of human or vertebrate animals with fly larvae. Fly larvae such as Chrysomya bezziana (the old world screw worm fly), is a parasite of man and other vertebrates and cause myiasis. Myiasis may cause severe health consequences as the fly larvae may cause major and irreversible damage to human body.

Since old-aged people with physical disability may be bed-bound, they are vulnerable to fly invasion of their exposed parts such as wounds and mucous membranes.

Biology of Chrysomya bezziana

Female adult fly lay eggs in wounds, open sores, scabs, ulcers, gums, scratches or even mucous membranes, especially those contaminated with discharges. A female fly can lay as many as 150-500 eggs each time. The eggs hatch within 8-24 hours and newly emerged larvae burrow through the skin to the underlying tissues where they commonly remain congregated together. Larvae tend to penetrate deeply into tissues so that infections near the eyes, nose and mouth can cause considerable destruction of these areas, often accompanied by putrid smelling discharges and ulcerations. Larvae complete their development in 5-6 days and then wriggle out of the wounds and drop to the ground, where they bury themselves and pupate. The pupal stage lasts about 7-9 days in warm weather, but is prolonged to several weeks or even months during cold weather. The life-cycle from egg to adult under ideal conditions is about 22 days. Adult flies frequently found feeding on decomposing corpses, decaying matter, excreta and flowers.

Prevent and control of fly

To effectively prevent the invasion of fly into premises, good sanitation and sound proofing measure are the keys to success. Insect electrocuting device (IED) should not be used as the first line in defence against flies. Without appropriate proofing measures, the number of fly visiting a premises will not be reduced significantly by IED alone. IED can only be used to kill flies that have accidentally broken through the barrier methods employed. The following points should be noted in prevention and control of fly.

Animal attraction

Ø      Do not keep pets particularly dogs in the compound.

Ø      Should pets, particularly dogs, be kept in the compound, the pets have to be examined regularly by veterinary surgeon.

Ø      Report to the Department of Agriculture, Fisheries and Conservation for the control of stray dogs found inside or near the compound.

Environmental sanitation

Ø      Store food in refrigerator or cover the food with screen.

Ø      Collect, store and dispose refuse in containers with tight-fit lid.

Ø      Keep animal remains properly without exposure to air.

Barrier methods

Ø      Screen windows, ventilation openings and doors with 10 mesh screens (10 X 10 mesh per inch). Using 16 mesh screens can concurrently prevent mosquitoes from entering.

Ø      Install self-closing device to doors / screen doors.

Ø      Use anti-fly curtains by fixing strips of beads or plastic strips, etc. in doorways.

Ø      Install electric fans to create air curtains with air velocity 8 m/s or more across doorways.

Installation of insect electrocuting device

Selection of IED

Ø      Ultraviolet (UV) light as the light source, preferably with wavelength at 330-350nm.

Ø      Brighter UV source (higher wattage) with reflector behind.

Ø      Equipped with catch pans that can be cleaned.

Positioning of IED

Ø      Place IEDs along the most critical insect pathways e.g. entrances, doorways and other bottlenecks, vestibules.

Ø      Place the first IEDs according to the areas of the premises.

Ø      Install sufficient number of IEDs according to the areas of the premises.

Ø      Do not place two IEDs farther than 12-15 metre apart for better results.

Ø      Spread out IEDs evenly throughout the facility.

Ø      Install IED at about 1.5m from the floor where most flies are found.

Ø      Place IED at a place where the light is visible from all directions, but avoid placing them near windows or doors where the light may attract insects from outside.

Ø      Do not place IED in direct sunlight or near to sodium vapor lights / mercury vapor lamps as they emit a good bit of UV. Standard incandescent and fluorescent lighting has little or no effect on IED performance.

Ø      Place IED in warm areas where flies are attracted by the temperature.

Ø      Place an IED near to the entry point of the food production area. keep IED at least 1.5m (preferably 4.5-6m) away from exposed product. Use only low mounted wall-type IED. DO NOT use ceiling-hung IED in food processing area.

Ø      Do not use IED in explosion sensitive areas.

Maintenance of IED

Ø      Dead insects in the catch pans must be cleaned out at least weekly, preferably twice a week.

Ø      Light source and the electrifying grid should be cleaned at least monthly.

Ø      Change UV lamp once a year, preferably prior to the spring season.

Ø      To ensure maximum efficiency of the IED, follow product instructions from the manufacturers.

Protecting yourself against screw worm fly attack

As a precautionary measure, inmates are advised to take the following actions:

Ø      Maintain good personal hygiene.

Ø      Maintain good oral health

Ø      Keep wounds clean

Ø      Keep home environment clean.

To learn more about oral care and wound care skills, staff of Residential Care Homes for the Elderly are welcomed to contact the corresponding Visiting Health Teams of the Department of Health. Information could also be obtained from the website of Department of Health (www.elderly.gov.hk).

The management of hospital/home for elderly could appoint a pest control company for providing services on fly control and prevention.  Advice on fly prevention could also be obtained from the Pest Control Advisory Section of the Food and Environment Hygiene Department. (Tel: 2319 8559 or 2314 1352)

Pest Control Advisory Section

Food and Environmental Hygiene Department

January 2005 updated