THE FLIES THAT CAUSE MYIASIS IN MAN 



103 



available, the female may oviposit on foliage. The embryo hatches 

 after 5 to 15 days, and abandons the empty chorion while the carrier 

 is in contact with the host. If the carrier is a blood-sucking fly, it 

 may further serve the parasite by providing a puncture in the skin to 

 allow easier ingress. In the absence of such an opening the larva may 

 penetrate the skin through a hair follicle, a fold, or some point where 

 clothing, bedding, or the ground may come in contact with the moist, 

 sweaty skin. 



Each larva makes a separate lesion. It develops under the skin in a 

 boillike pocket, opening to the outside, where it finally reaches matu- 

 rity. The generally accepted number of larval instars is three, al- 

 though Townsend claims that there are four. The duration of the 

 larval life within the body of the host is usually from 5 to 10 weeks but 

 sometimes runs over 3 months. 

 The mature larva enlarges the 

 opening and drops to the ground to 

 pupate. 



The larva produces a furunculous 

 wound, which may be painful at 

 intervals, usually of short duration. 

 However, the discharges from the 

 wound may be even more trouble- 

 some than the pain, when they foul 

 bedding and clothing, and often 

 acquire a fetid odor; furthermore. 

 they invite infestation by other 

 parasites, such as screwworms. A 

 loss of energy and longer sleep re- 

 quirements of the patient are noticed, 

 those containing dead larvae, may 



Figure 51. — A, A Psorophora mos- 

 quito carrying a load of Derma- 

 tobia eggs; B, egg, enlarged. 



Infection of wounds, especially 

 have serious crippling effects. 

 Cattle and dogs are often so heavily parasitized that death results. 



The furunculous swellings frequently occur on exposed parts of the 

 body, but they are also found on parts covered by clothing. The lesions 

 occupy the area of the looser subcutaneous or areolar connective tissue. 

 One fatal case resulting from the invasion of the brain of a child is on 

 record (Dunn 36). 



The larva may be removed by pressure; but notice should be taken 

 of the shape of the larva, with its narrower posterior end toward the 

 opening. Since the larva depends on the outside atmosphere for its 

 respiration, it may be forced to the surface by temporarily plugging 

 the opening; if some such substance as soft beeswax or chewing gum 

 is used, the larva may be trapped in it and in this way be more easily 

 removed. Care should be taken to remove the larva intact, and, if 

 possible, alive. A technique for removal, after anesthetizing the larva 

 and the surrounding tissue. of the host, is described by Harrell and 

 Moseley {55). 



In addition to man, Dermatobia ho?ninis parasitizes cattle, dogs, and 

 a number of other mammals, both wild and domestic; however, it 

 apparently bothers Equidae relatively little. It has been reported 

 from birds. It is a very serious cattle pest in many parts of tropical 

 America. 



Vernacular Names. — Some of the many vernacular names in use 

 are as follows : Beef worm, macaw worm, mosquito worm, ver macaque, 



