HOUSEFLIES - THE PORTERS OF INFECTION

HOUSEFLIES - THE PORTERS OF INFECTION

Houseflies are the most common and familiar insects living in close proximity to human beings. They occur in abundance all around the year in India. The most important of this species are Musca Domestica, Musca Vicinia, Musca Nebula, and Musca Sorbents.

Houseflies are potential vectors for transmission of many diseases to the human being, like typhoid and paratyphoid fevers, diarrheas and dysenteries, cholera, salmonellosis, gastroenteritis, amoebiosis, helminthic infestations, tuberculosis, poliomyelitis, enterovirus, viral hepatitis (A&E), conjunctivitis, anthrax, yaws, etc.

Houseflies are exceptionally efficient mechanical spreaders of microorganisms. The legs and body of houseflies are covered with numerous short and stiff hairs, called the tenant hairs, which secrete a sticky substance. They transport microorganisms on their feet and hairy legs and body. While feeding on garbage and other such materials that have been disposed of, the fly cover itself with microorganisms.

A single fly can carry 6,500,000 bacteria. Pathogenic organisms, ova, and cysts have been recovered from the bodies of the most common houseflies. Houseflies are therefore called “porters of infection”. One will be shocked to know that houseflies can keep and carry various microorganisms in their digestive system for as long as four weeks, only to be transmitted by their succeeding generations!

The majority of house-frequenting flies are non-biting. It is attracted to food items by their sense of smell. It cannot eat solid food; it transfers its food to a liquid or semi-liquid state by regurgitation of some of the liquid it has already swallowed – such as sewage and bacteria-laden saliva – on the food. The regurgitated stomach contents or “vomit drop” is a rich bacterial culture. The liquefied food is then sucked up and parts of the regurgitated liquid are left behind. Due to this habit of frequent vomiting and defecation constantly all day, it deposits countless bacteria on exposed food.

The excrement of houseflies has been found to contain numerous micro-organisms as well as cysts and ova of intestinal parasites. It is a restless insect and moves back and forth between food and filth. It helps in the spread of infection mechanically. Thus the housefly infects food. When human beings consume these contaminated food items, the microorganisms can be transmitted to them and disease occurs.

Controlling the housefly population can be best achieved by making food inaccessible (covering food, water and other items from the houseflies; screening of houses, hospitals, fruit markets, restaurants and other such establishment) and eliminating breeding sites of flies (fresh horse manure, human excreta, manure of other animals, garbage, decaying fruits and vegetables, rubbish dumps containing organic matter, ground where liquid wastes are spilled, etc.). Implementing these measures will bring about an overall improvement in the environmental sanitation on a community-wide basis.

This, in effect, implies the followings:

(1) Storing garbage, kitchen wastes, and other refuse in bins with tight lids till their disposal (2) Efficient collection, removal and disposal of refuse by incineration, composting or sanitary landfill

(3) Making provisions for sanitary latrine

(4) Stopping open-air defecation

(5) Sanitary disposal of animal excreta and

(6) Stepping up general sanitation.

A clean house with clean surroundings is the best answer to solve the menace of houseflies. Houseflies should be regarded as a sign of insanitation.

Houseflies first showed its resistance to DDT in 1948. Musca Domestica has developed resistance to other organochlorine compounds as well as organophosphorus and carbamate pesticides.

Use of residual spray, space spray, solid or liquid poisoned baits, hanging of insecticide-impregnated ribbons, cords and sticky flypapers in places where flies abound can reduce the population of flies. But these measures can, at best, be used only as supplements, and there cannot be any substitute for sanitation.

Dr. Dharmakanta Kubhakar

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