African Tumbu Fly
(
Mango fly,
Skin maggot fly, Ver du Cayor, Worms of Cayor) |  |
| The African tumbu fly,
Cordylobia
anthropophaga
, is responsible for another boil-like (furuncular) myiasis in both humans and animals in Africa, particularly in the subSaharan regions. |
| The adult flies are nonparasitic and as a result are not seen by owners or veterinarians. They are stout, compact flies, 6-12 mm long. They are light brown, with diffuse blue-gray patches on the thorax, and dark gray on the posterior part of the abdomen. The face and legs are yellow. The second- and third-stage larvae are the stages usually seen in the animal’s skin. |
| Second-stage larvae are slightly club-shaped and exhibit large, black cuticular spines that are directed posteriorly and distributed irregularly over segments 3-8. Segments 9-11 are almost bare when compared with the preceding segments. The segments have a few rows of small, pale spines posteriorly. Segment 12 is densely covered with these spines. Segment 13 is indistinctly demarcated, lacking spines but possessing 2 pair of short processes. Each tracheal tube opens through 2
slightly bent slits. The second- stage larvae are 2.5-4.0 mm long. The size of advanced second-stage larvae varies greatly, as does the size of third-stage larvae. Fully mature larvae are 1.3-1.5 cm long. The body is cylindrical with 12 identifiable segments. Curved spines that are directed posteriorly are densely arranged at least up to segment 7; the last 5 segments may be either partially or densely covered with spines. |
| After fertilization, female flies produce 100-500 banana-shaped eggs, usually depositing them in dry, shady, sandy soil that has often been contaminated by urine or feces. Eggs are never deposited on the skin of the host. Eggs hatch after 1-3 days, and the larvae are initially 0.5-1.0 mm long. Larvae can survive up to 15 days while waiting for a host and can penetrate the host in as little as 25 sec. After penetration, larvae reside in a cavity in the dermis and hypodermis. This
cavity communicates to the external environment by means of a central breathing pore, which corresponds to the caudal end of the larva with its spiracles. A single larva is found in each cavity, within which the larva develops to the second and third stages. Larvae require 7-15 days to mature and then emerge through the breathing pore and drop to the ground, where they pupate. Adult flies emerge 10-20 days later, and the cycle begins again. |
| Rats and dogs are the usual definitive host; however, humans, mice, monkeys, mongooses, squirrels, leopards, boars, antelopes, cats, goats, pigs, rabbits, guinea pigs, and chickens can be infested. |
| Pathology: |
| Clinically, the infestation is characterized by a small erythematous papule that appears 2-3 days after larval penetration. Within days, the papule enlarges until it becomes a nodule that resembles a boil (furuncle); hence, the description
furunculoid myiasis. At the center of the nodule is a pore through which serous fluid oozes. This fluid can be hemorrhagic or purulent and contains larval feces. |
| Dogs with thin, soft skin seem to be more suitable hosts for larval development than dogs with thick skin. Preferential sites of infestation are the feet, genitals, tail, and axillae. In endemic areas, mild infestations in dogs do not produce clinical distress. Massive infestation may induce marked swelling and edema, especially if larvae are in close proximity to each other. Larvae can penetrate deep into tissues and cause considerable damage and even death. |
|  |
| Diagnosis: |
| The presence of a dermal swelling with a central opening may lead to a tentative diagnosis of myiasis due to
C
anthropophaga
. A definitive diagnosis can be made only after extraction and identification of typical larvae. The identification of adult flies and their associated larval stages should be left to an entomologist. |
| A tentative diagnosis may often be made by a history of either residence in or travel to a geographic area endemic for
C
anthropophaga
. However, the parasite has also been diagnosed in travelers and their accompanying pets from geographic areas where the parasite does not exist. |
| |
| Treatment and Control: |
| Larvae can be removed by coating the breathing pore with a thick, viscous compound, such as heavy oil, liquid paraffin, sticking plaster, pork fat, or petrolatum jelly. Clogging the pore causes the larva to become hypoxic and leave the cavity in search of oxygen. Light pressure at the edge of the lesion also aids in larval removal. |
| Lidocaine hydrochloride can be injected into the furuncular lesion to facilitate larval extraction with thumb forceps. Surgical excision is usually unnecessary and unwarranted while the larvae are alive but is used to remove dead or decaying larvae. Great care should be taken during the extraction process to avoid rupturing larvae in situ, although anaphylaxis has not been reported. Antibiotics should be prescribed. |
| Adult flies should be killed if seen indoors. Larvae should be removed from animals entering the house and destroyed. All rats should be killed and burned. Clothes should not be left lying out; they should be ironed and put away. Prevention of an infestation depends on cleanliness and regular disinfection of the animal’s sleeping quarters. In the case of valuable animals (eg, Angora rabbits), flies may be kept out of rabbit pens using wire gauze. |
| Because the adult female flies lay eggs in sandy soil contaminated by feces or urine, the parasite can be controlled in the pet’s environment by prompt removal of the pet’s feces and by covering urination sites on the premises with a layer of dirt. |
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