Medical importance of housefly

House fly is very common insect. Some insects are friendly to human society, while others are dangerous in transmitting human diseases. House fly is medically important. They belong with the Order Diptera, which means two winged flies.

House flies are 6-9 mm in length. Four stages in their life cycle are the egg, larva, pupa, and adult. In summer, the eggs generally hatch within 3 hours into larva. The average hatching time of egg is 48 hours. Larval period lasts up to 2 days, at the end of which larva transforms into pupa. Pupa stages lasts for 4 to 5 days in summer, but may be prolonged in winter. The adult emerges from pupa through a circular slit. Male and female mates within 24 hours after emergence from pupal case.

The female lays 75-150 eggs per batch at an interval of 3 to 4 days. On an average, the fly live for 15 days. The maximum life span is known to be 70 days. Usually, the adult tend to remain within a radius of 100-500 meter from their breeding places. They can fly up to 20 miles with the help of wind, and are active at daytime. At night, they take shelter in the dark corners of the room, under the roof, and behind the clothes. They prefer milk, fruit, cough, pus, blood, sugar, and stool, and always in search of food. Horse manure, cow manure, hog manure, chicken manure, human excreta, garbage, organic manure, fishmeal, blood and bone meal, sewage, and waste food behind trough attract house flies to oviposit there. The fly feeds intermittently, and defecates at the interval of 5 minutes, and vomits frequently. The fly sits on sputum, pus, and stool for purpose of feeding, or not and indiscriminately feeds on feces, sweets fruits, sugar, and milk. 

Owing to this habit, the fly can contaminate human food with the micro-organisms form the filth.

The whole body including the legs of a housefly is studded with numerous hairs. Microorganisms get attached to these hairs, and carried over to different food substances. The fly transmits germs by vomiting the ingested material, and by passing the ingested pathogens along with stool.

House flies can mechanically transmit bacterial infections such as Salmonella typhosa, S. paratyphi. S. enteritidis, Shigella dysenteriae complexa, Vibrio chlolerae, Mycobacterium tuberculosis, and M. leprae; viral diseases such as poliomyelitis, and infectious hepatitis. They also spread protozoan like Entamoeba histolytica, E. coli, and Giardia lamblia. The egg of Ancylostoma duodenale, Ascaris lumbricoides, and Echinococcus granulosus can be carried both internally and externally by this fly. The ova of helminths like Taenia solium, Enterobius vermicularis can be carried extrenally.