Dermatobia hominis: Life cycle and Morphology

Since we’ve talked about transmission of the egg into some unlucky human or other mammal, let’s go from what happens after that…
(Also, this is a cycle so, the end loops to the beginning again)

lifecycle

Figure of Dermatobia hominis life cycle taken from Guimarães, J.H. & N. Papavero. 1999. Myiasis and animals in the Neotropical region: bibliographic database. São Paulo, Ed. Plêidade, FAPESP, 308p. From <http://www.sel.barc.usda.gov/Diptera/oestrid/Dermatobia%20life%20cycle%20expanded.html> 21

 

Eggs
The yellow-white eggs are about 1.3 mm long. The ventral portion of the egg has been described as "relatively flat and has small ridges, whereas the dorsal portion has a curvature that is more pronounced at the anterior end. The eggs are laid side-by-side along their longitudinal axis with subsequent rows of eggs tiered one above the other. This orientation ensures that opercula (lid-like structures) are not obstructed and thus allow larvae to readily exit the egg." 21

The eggs are deposited near the bite wound. They hatch with the stimulus of a rise in temperature and commence burrowing! This takes between 5-60 minutes.23

 

Larvae
So the first-stage larvae have burrowed into the skin! Now what?

The larvae typically hangs out where it’s burrowed, and breaths through the “breathing hole” it’s created. The time the larvae takes to develop has been cited to be anywhere between around 5-10 weeks (this is how long it stays inside you!).23

During this time it undergoes morphological changes. Specifically, there are 3 transformations occurring (called instars), and the parasite will migrate to deeper layers of the host’s skin. A dome-shaped cavity forms (the furnicular lesions we’re now so familiar with). During this time, people might complain of “painful gnawing and drilling sensations.”23

Second stage larva, Markell, Medical Parasitology  p. 367 8th edition 4

 

Eventually, it develops into third-stage larvae (also called the instar stage). This version can become 2 cm or greater in length.

3rd

SEM of 3rd larval stage, Courtesy Dr. David A. Henderson, Markell, Medical Parasitology  p. 367 8th edition 4

as = anterior spiracles
oh = oral hooks
ah = abdominal hooklets
ps = posterior spiracles

Morphology: The way the larvae make sure they stay well embedded in the skin is through rows of spines along the larvae’s back. The spines are all dark brown, parallel, concentric and posterior pointing.


It also has a unique body shape, with a wider anterior end than posterior end, anchoring it in the skin10. In 1910, Henry Ward described “The early larva of Dermatobia is curiously flask-shaped with the narrow end towards the open air”22.  

By the end of this time (5-10 weeks) within the host, the larvae must have taken enough nutrients/sustenance to supply its transformations, sexual reproduction and adult life. The larvae then wiggle out and fall to the ground, searching for an area in the soil to pupate (they can pupate above ground, but won’t develop into adults) 10, 17, 21.

 

 

Pupua
The incubation period is between 14-30 days 10, 21. The botfly emerges as a mature adult!

Morphology:

These photographic images were captured by Jonathan Eibl using a Wild Photomakroskop M400 with Leica Apozoom 1:6 and Syncroscopy Auto-Montage imaging software. 21

 

 

Adult fly
The adult fly has diminished mouth parts, compared to other flies that cause myiasis- this is indicative of how key the host is in it’s life cycle. The adult doesn’t actually feed at all!
Adults quickly mate and reproduce! They only have a very short time to do so- the female adult fly’s lifespan is 8-9 days (10) while the males die around the 4th day after emerging 21. As Oldroy notes, this means the adults have to stick close to their host, in order to maintain the overall life cycle 6.

 Morphology:

Female adult human botfly (here's looking at you, kid!)

These photographic images were captured by Jonathan Eibl using a Wild Photomakroskop M400 with Leica Apozoom 1:6 and Syncroscopy Auto-Montage imaging software. 21

 

 

U.S. Dept. of Agriculture, Miscellaneous Publication No. 631

 

 

The circle continues back to eggs!

 

The entire life cycle is complete within 3-4 months10.