L. H. Dunn.
Rearing the Larvæ of Dermatobia hominis Linn, in Man.
Psyche 37:327-342, 1930.

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19301 Development of Dermatobia hominis 327 REARING THE LARVB OF DERMATOBIA HOMINIS
LINN., IN MAN
Medical Entomologist and Assistant Director, Gorgas Memorial Laboratory,
Panama, R. de P.
The following article presents some observations on the development of the larvae of Dermatobia hominis when reared in man, and on the effects of an infestation of these larvae upon the host. The results of studies on other phases of the interesting life-history and habits of this species of parasitic diptera will be presented in later reports. In October, 1929, while seated at the edge of a small stream near Summit, Canal Zone, I captured a fly which was hovering about and which had several times alighted on my right knee.
This fly proved to be a species of
Limnophora, not a blood-sucker, and a number of eggs were found attached to her abdomen. An examination of these showed them to be eggs of Dermatobia hominis. Many of them had developed to the larval stage, the operculum at the hatching end being open and the minute larva inside of each being active and ready to leave its shell when a suitable host was provided. Through the acquiring of these eggs a good opportunity was afforded for studying the development of the larval stage of D. hominis with man as the host, and in view of this it was decided to allow two of the larvae to enter the skin of my arm.
October 9. At 4 P. M., about six hours after capturing the egg-bearing fly, the glass tube in which it was confined was unstoppered and inverted on the skin of my left fore- arm. The tube, which was about four inches long and one inch in diameter, allowed room for considerable move- ment .on the part of the fly. The latter was quite active



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328 Psyche [December
and would not rest on the skin except very momentarily, but kept up a continual dashing about in the tube. The larvae were all protruding from the egg shells, but the swift movements of the fly seemed to prevent them from remain- ing on the skin for a sufficient length of time to allow them to crawl from the shells. This continued for about five minutes, and it was then noticed, with the aid of a hand lens, that as the fly dashed against the side of the tube one of the larvae was left hanging to the glass. About one minute later this was repeated and a second larva was left crawling about on the inside of the tube. The fly was then removed and the two small larvae inside the tube were picked up on the point of a needle and gently placed on my left forearm at about the upper third of the median flexor region. Since there were no abrasions of the skin at this area, an opportunity was given for observing the entrance of the larvae into unbroken skin.
The two larvae were placed in the skin slightly less than an inch apart, and each remained at exactly the site where it was placed. Neither of them could be detected as having moved even a quarter of an inch. They remained so motionless that at first it was feared that they had been '
injured by the needle in transferring them from the tube to my arm. After watching them closely with a 10 X lens for a few minutes, however, a few faint contractions could be seen, and it was also noted that the anterior, or larger, end of each larva seemed to be sinking very slowly into the skin. This large end of each larva seemed to be about one-third, horizontally, pressed into the skin, and was evi- dently securing traction through the use of the oral hooks and dermal spines, while the posterior end exerted a pro- gressive forward motion. The larvae were lying nearly parallel with the skin, and with but a slight arching near the posterior end, so that their position in relation to the skin surface was thus very oblique, and the penetration was at first beneath just the outer part of the skin. One of the larvae had practically all of its large anterior part imbedded in the skin in about thirty minutes. It was then able to obtain sufficient purchase with its spines, so that rapid progress was made and the posterior end was soon inside. At the end of 42 minutes from the time this



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19301 Development of Dermatobia horninis 329 larva was placed on my arm it was completely out of sight in the skin and could not be seen even with the aid of a lens. There was absolutely no sensation caused by the entrance of this larva until after the first thirty minutes. Then, as the posterior end was being drawn inside, a sharp pricking, which lasted for about two minutes, was experienced. The second larva was much slower in effecting an entrance and required an hour and thirty-five minutes to bury itself completely in the skin. At the end of an hour approximately half of the anterior end was inside. At
this time I rolled down my shirt sleeve and put on my coat to determine if the rubbing of clothing would loosen the larva or have any apparent effect upon its entrance. After spending about thirty minutes in walking about and in doing some work in the laboratory which necessitated using my arm rather actively, I removed my coat and in- spected the larva. At this time it was all buried in the skin with the exception of the tip of the posterior end, and five minutes later that also was inside. During the night following the entrance of these two larvae into my skin a marked itching and pricking sensa- tion at the sites of their location was experenced at inter- vals. Although this did not last more than half a minute at each time it occurred, it was sharp enough to awaken me several times during the night.
October 10.
Fourteen hours after the entrance of the larvae it would have been nearly impossible to locate them. Since I had ringed the sites with ink, however, and thus knew their exact situations, they could with the aid of a lens be detected as pinpoint raised areas which were slightly reddish. After twenty-four hours they were visible to the naked eye as slightly elevated tiny red dots. When viewed closely with the lens the tiny posterior ends of the larvae could be detected slowing moving up and down in a pump- ing movement and forcing out minute quantities of fluid. October 11.
This evening a sharp itching was felt at two small pimples which were at first thought to be caused by mosquito bites. One of these was located at the mid- ulnar margin of my right arm, approximately four and a half inches from the wrist joint. The other was on the internal surface of my right thigh about midway between



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330 Psyche [ December
the knee and perineum.
When these were rubbed there
seemed to be more soreness present than usually accom- panies mosquito bites. My suspicions becoming aroused, a closer examination was made, and it was then found that each of the small lesions contained a larva of D. horninis. A further search showed two more of the larvae infesting me. One of these was on the flexor side of my FIG. 1.-Diagram showing locations of the larva?. right wrist and the other on my right shin, about two inches below the lower margin of the patella. I had felt nothing which might indicate the presence of these last two larvae, and it was only the tiny red pimples caused by them that revealed their presence to the naked eye. Apparently it had been just a case of carrying coals to



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19301 Development of Dermatobia hominis 331 Newcastle when I allowed the two larvae to enter my left arm, since I evidently was already infested with four of them at the time. It is quite certain that these four larvae were deposited on me by the carrier fly while it was alight- ing on me just prior to its capture. This placed their - entrance into my skin at about six hours earlier than when the two entered my left arm. Finding myself now infested with six of the larvae I decided to allow them all to remain until they began to produce too great a reaction, either local or general. In order to record observations on the larvae each one was given a number. The two on the left arm were numbered 1 and 2; the one at the right wrist was No. 3, in the right forearm No. 4, in the upper right leg No. 5, and below the right knee as No. 6. Nos. 1, 2, 4 and 5 were located in areas surrounded by considerable adipose and muscular tissues, while Nos. 3 and 5 were in situations surrounded mainly by fibrous tissue and with much less softer tissues.
October 16. Each lesion, or site of each larva, now ap- pears as a bright red area, about three-eighths of an inch in diameter, and slightly elevated in the center. There is sufficient itching and pricking occurring to cause consider- able discomfort. The irritation seems to be much greater during the evenings and nights than throughout the days. No. 6 proves an exception to this, since there is frequently a prolonged stinging or burning sensation experienced when I am walking. While I am at rest this larva seldom causes any annoyance. No. 4 seems to be causing the greatest irritation. This may be due to the location of this lesion on the lower surface of my right forearm, and thus sub- jected to considerable rubbing on desk and tables while I am at work.
October 17. Last night I was awakened by a severe itch- ing and dull burning sensation at No. 4. The burning
sensation seemed to feel more like an erosive burn caused by a strong acid than to contact with a hot surface. All the lesions are exuding serous fluid at times. That which comes from Nos. 1 and 4 is slightly tinged with blood. October 18. Last night the lesions on both arms became very irritating and awakened me several times. There
has also been considerable itching and pain today.



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332 Psyche [December
October 20.
Yesterday and today there has been but
little discomfort.
The lesions now have the appearance
of small boils. They are a deep red in color, swollen and with some induration of the surrounding area. The indu- rated area surrounding No. 4 is about an inch and a half in extent.
October 21. A severe stinging pain is occurring at inter- vals at Nos. 1 and 2 on my left arm. These two lesions are so close together that it is difficult to determine whether it is only one or both that cause the pain. There is also a severe itching at No. 5 and an occasional sharp, stabbing pain in No. 6.
October 22. During the night I was awakened several times by sharp stinging pain in Nos. 1 and 2. There was intense itching in No. 3 and on two occasions when I awak- ened during the night I found that apparently I had been scratching this lesion while still asleep. This morning a considerable area of the ulnar surface of my wrist was greatly swollen and an intense itching occurs when the skin is touched, even though it be at some distance from the lesion.
October 24. The lesions have increased in size and have more of the appearance of small boils which have "pointed" and erupted slightly. There is considerable oozing of serous fluid, blood-stained pus and dark-colored matter which I believe is digested blood being defecated by the larvse. The exudate from the lesions is now sufficient to be quite disagreeable, owing to its staining clothing and bedding, and it is necessary to bandage all the lesions. It is to be regretted that the bandages were not applied earlier, so that the date of possibly a first molt of the larvae might have been noted. It is my opinion that this molt occurred about October 21, and that the small amount of discomfort present on October 19 and 20 was due to the larvae being in the first pre-molting period at this time and were not feeding and were quite inactive. Had the bandages been on the lesions at the time it is possible that some traces of the molted skins might have been found which would denote the time of the molt. October 26. There seem to be three kinds of local sensa- tions connected with the presence of the larvae. The first



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19301 Development of Dermatobia homims 333 of these is an intense itching of the skin of the area sur- rounding a lesion. This may be due to an infiltration of the tissues with the faeces of the larva and other fluids present in the lesions causing a slight cellulitis. This itch- ing was not constant but occurred at frequent intervals, and is induced by even very slight friction in the vicinity of the lesion. The second sensation is a very irritating prick- ing which takes place in the lesion. This is probably caused by the rasping of the cutaneous spines or hooks on the larva during any movement of the latter. The third sensation is a sharp, stinging pain, which is believed to be produced by the tearing of the tissues by the oral hooks of the larva when it becomes necessary to use the hooks in order to excite the flow of serum or blood to serve as food. October 29.
Nos. 3 and 6 are now much more swollen
than are the other four lesions which are located in areas of more adipose and muscular tissues.
The four located in
more favorable situations are but little swollen on the out- side, but can be felt as hard nodules, each as large as a good-sized marble and seeming to extend into the sub- cutaneous tissues. During the past three days there has been less of the pricking sensation occurring. This may be due to the lesions becoming walled off so that each larva is to some extent encapsulated. Or, again, it may be due to wearing bandages over the lesions. When the latter were exposed to the air the exudate soon dried and formed small scabs that at times seemed to seal over the small openings of the lesions, and it is quite plausible to believe that in order to burst through these scabs some struggles were required on the part of the larvae when it was necessary for them to take air or discharge faecal matter. With the lesions bandaged the exudate is being continually absorbed and the holes left open and moist around the edge. A quite pronounced vesicular eruption has now ap- peared on both hands and wrists and on my right leg. This is accompanied by an intense itching and a slight oozing of serum from the vesicles.
October 31. During yesterday and today there have been several attacks of excruciating pain experienced from Nos. 3 and 4. This pain was possibly a nerve irritation caused by the oral hooks of the larvae tearing the tissues. These



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334 Psyche [December
attacks lasted from one to three minutes each time they occurred. Squeezing the arm just below the lesions seemed to stop the pains to some extent. These two lesions bled sufficiently to stain through the bandages several times today.
November 3. Drops of apparently unchanged blood oozes at intervals from Nos. 1 and 3 when the bandages are removed. Blood-stained serum is exuding from Nos. 2, 4 and 5. No pus is in evidence except a small amount from No. 6. When viewed with a lens at this time each larva may be seen pushing liquid from the hole with a quick, pushing, upward movement somewhat after the ac- tion of a plunger of a pump. The downward movement seems to draw back some of the fluid with each jerking back of the posterior end of the larva. When the end of a larva is retracted an occasional air bubble can be noticed coming up through the liquid. There has been very little pain or irritation caused by any of the lesions today. November 4. A sharp pricking lasting several minutes has occurred at intervals during the day and early evening in No. 6. This lesion and the area surrounding it is quite red, considerably swollen and very sore to the touch. At about seven o'clock this evening when the bandages were removed for a while this larva was found to be pushing out a cast skin. The larva had molted, and since it prob- ably needed more room in the hole for its futu're growth, was disposing of the cast skin. The movements of the larva caused the skin to emerge in its natural, round, tube-like form. As it came slowly out it formed a tiny crater about 2 mm. high around the hole and then continued to turn back upon itself with the posterior end of the larva pushing up through the center. From the manner in which the molted skin moved slightly from side to side it appeared as though the larva was pushing it up first at one side and then at the other, but keeping it about even so that the rows of hooks of each segment were all out before those of the next segment appeared. After observing the efforts of the larva with a hand lens for about three hours, it was estimated that about one-third of the cast skin was still in the hole. None of the other five lesions have caused very much discomfort.




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19301 Development of Dermatobia hominis 335 November 5. This morning the molted skin from No. 6 was found all outside of, and still surrounding, the hole. This larva was quite active and caused considerable irrita- tion during the day. None of the other five lesions caused much discomfort. The fluid is exuding in a smaller amount than usual, and it seems to be comparatively clear serum with the exception of that which is coming from Nos. 1 and 5, which is rather heavily tinged with blood. The other five larvae are probably also preparing to molt. November 6. The larva in No. 3 molted and ejected the cast skin during the A. M. Following the ejection of the skin, which was found adhering to the bandage, this lesion exuded a considerable amount of blood during the day. Frequent sharp, stinging pains at No. 6. This pain is so severe that at each attack it is necessary to remove the bandage and place a hand on each side of the lesion and press upward in order to stop the action of the larva. There is only a small amount of deep tissue surrounding this lesion and the larva is situated parallel with the sur- face of the skin.
November 8. Cast larval skins were ejected from Nos. 1, 2 and 4 this P. M. This leaves all the larvae molted except No. 5. Both arms are now very sore, and sufficient bloom and serum is exuding from the lesions to stain through the bandages soon after they are applied. November 10. No. 6 has caused excruciating pain at intervals throughout the day. During the evening one at- tack lasted for fifteen minutes and became almost unbear- . able. Pressing on the sides of the lesion and allowing cold water to run on it seemed to have but little palliative effect. This attack was followed by bleeding. Blood oozed from the lesion in a thin stream and continued until it had soaked three gauze pads that were applied one after the other. No. 1 also bled sufficiently at one time this evening to stain through the gauze pad, bandage, shirt sleeve and coat sleeve. During the night I awakened to find that this lesion was again bleeding and to the extent of soaking through the dressings and sleeve of my pajamas. November 11. No. 1 gave the most trouble today. Dur- ing the afternoon it suddenly developed a severe, deep- seated pain which seemed to extend for some distance up



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336 Psyche [December
and down my arm. After this pain had lasted for about a minute, bleeding began. From the way in which the blood bubbled from the lesion it appeared as though it came from a small artery. This continued for several minutes until by applying cold compresses to the lesion it was in- duced to stop.
November 12.
The exudate from No. 3 today consists
largely of pus with a very fetid odor. Serum mixed with dark-colored digested blood and pus is oozing from No. 4. Several spasms of pain occurred during last night and today in No. 5. This pain was severe enough to awaken me several times during the night. No. 1 again bled pro- fusely on two occasions today. The bleeding started both times soon after the bandage had been removed. The blood welled out in a small stream, and it was necessary to hold my arm beneath running tap water for some time before it ceased. These hemorrhages were sufficiently severe to cause me to consider the advisability of having No. 1 re- moved in order to prevent the possibility of losing a con- siderable amount of blood during the night while asleep. I have decided, however, to delay any action and await developments for another day or so. Both times that the bleeding occurred from this lesion it was preceded by a sharp, deep-seated pain which was sufficiently acute to cause a slight nausea.
November 13. The sharp pain and bleeding from No. 1 again occurred this afternoon just after a fresh bandage had been applied. Blood-stained serum is exuding from Nos. 2 and 5. Serum mixed with blood and pus is issuing from No. 5, while pus only is being discharged from No. 3. A cast larval skin was expelled from No. 5 today. All the larvae have now molted with nine days' difference between the time the molted skin was ejected from No. 6 and No. 5. Both arms are now very sore and a lymphangitis extending almost from the elbow to the axilla of my left arm is evi- dent. The epitrochlear and axillary lymph nodes of the left arm are enlarged to about the size of marbles and are tender to the touch. The nodes of the right arm are also swollen and tender, but not to the same extent as on the left side. A general feeling of lassitude which is quite marked has been experienced during the past few days.



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19301 Development of Dermto bia hominis 337 This may be due to absorption of toxins from the lesions and may also be influenced by the many times that I am awakened each night by the larvae. The lesions are now emitting a fetid odor which becomes very disagreeable if the bandages are not changed frequently. When they re- main unchanged during the night the odor is extremely offensive in the morning.
November 14. During the night I was awakened by a severe pain in No. 3 and a contraction of the muscles of the wrist and forearm. This served to draw my hand back on the wrist, and I was unable to straighten the hand except by using my left hand. It was necessary to place the hand and wrist in cold water before relief was afforded. Considerable blood and serum oozed from this lesion fol- lowing the pain and contraction. During the past few days this lesion has become much swollen and is very red and inflamed. The center of the lesion is taking on a dark purple appearance, although the aperture is well down on one side near the base of the swelling.
November 17.
No. 5 is very painful and the muscles
of the leg are stiff and sore to the touch, and is causing some lameness. All the lesions are oozing considerable serum and pus. I seemed to be quite feverish at one time when I awakened last night, but the feeling of lassitude was so great that no temperature was taken. November 19. No. 3 has been causing severe pain and muscular contraction at intervals during the past four days and the wrist is very painful. No. 6 has been quite sore for several days, and this evening it was found that an- other opening had developed in it. This new opening is located on the side opposite the original opening and about where the anterior end of the larva seems to be. It is a