586 



THE ANIMAL PARASITES OF MAN 



Musca domestica, Linn. (Common House-fly). 



It is not only on account of a few larva? of the common house-fly (Musca 

 domestica} being found in the intestines of man that it is of importance medically. 

 It is far more important on account of the part it plays in the spread of diseases 

 of the intestines, such as typhoid fever and cholera, infantile diarrhoea and 



dysentery. 



Howard and Clark (Journ. Exp. Med., 1912, xvi, No. 6, pp. 850-859) have shown 

 that the house-fly is capable of carrying the virus of poliomyelitis for several days 

 on the surface of the body and for several hours in the gastro-intestinal tract. 

 The house-fly may also distribute the ova of Tcenia solium and the white worms 

 (Oxyuris and Ascaris). It has also been proved that they may carry the germs 

 of tuberculosis, and it is said that they play an important part in the spread 

 of infectious ophthalmia in Egypt. 



This insect is found in all parts of the world. In warm countries it breeds 

 all the year round, and it may do so even in temperate climates in warm places, 

 such as stove houses. Most, however, die off in the autumn ; but some survive the 

 winter as adults, in such places as kitchens, restaurants, and warm houses. I have 

 never failed to find a few Musca domestica in houses during the winter. The 

 majority, however, hibernate as puparia. 



The females deposit from 120 to 150 eggs in a batch in stable manure, rotting 

 vegetation, house refuse, spent hops, old soiled bedding, etc. A single female 

 may lay as many as six batches of ova during her life. The eggs are shiny white, 

 and hatch in from eight to twenty-four hours in warm weather to three or four 

 days in cool weather. The white footless maggots are cylindrical, tapering to 

 a point at the head end, truncated posteriorly. The head consists of two dark 

 mandibular hooks and two short antennas. ,On the tail end are two plates, the 

 stigmata, in which the main tracheal trunks open ; in the second segment are 

 a small pair of projecting stigmata. The larval stage lasts from seven to five 

 days in hot weather ; but in cold weather in temperate climes it may last six or 

 eight weeks. 



The larva on reaching maturity becomes a barrel-shaped puparium of a dark 

 brown to black colour, and in this case changes to the pupa. This stage lasts from 

 three days in the tropics to four or five weeks in cold weather, the life-cycle thus 

 varying from ten days in the tropics to fourteen in warm weather in Europe up to 

 three or four months under unfavourable conditions. 



All breeding grounds should be burnt or otherwise done away with, such 

 as stable manure, house and kitchen refuse, human excrement and soiled substances, 

 also decaying vegetation as soon as possible, certainly by every sixth day. Stable 

 manure should be kept in closed receptacles and should be removed by every sixth 

 day to at least one mile from habitations and sprinkled with chloride of lime. 

 All kitchen and household refuse should be burnt at once or buried in pits and 

 covered with soil. Latrines should be as far as possible from hospitals, mess rooms 

 and tents. Food especially milk, sugar and fruit should be kept screened with 

 muslin when house-flies are about. Mess rooms and tents and hospitals should 

 have doors and windows screened with fine wire gauze during the fly season. 

 All possible steps should be taken to prevent them contaminating man's food and 

 from breeding in human excrement and from entering hospitals. When present 

 in dwelling-houses in numbers they may be killed by fumigation with pyrethrum 

 or sulphur. 



