HISTORY: The larvae of the African tumbu fly, Cordylobiaanthropophaga, were first discovered by Coquerel and Mondière in 1862 in Senegal in both humans and dogs. The adult fly was unknown to them (Zumpt, 1965). It was not until 1893 that Blanchard described the adult and gave it the name Ochromyiaanthropophaga. In 1903, Grunberg placed the fly in a new genus, Cordylobia (Rice and Gleason, 1972). Infestations with these fly larvae were common in the district of Cayor, hence the parasites are often referred to as "vers de Cayor" or "worms of Cayor." (Zumpt, 1965)
GEOGRAPHIC DISTRIBUTION: This parasite is responsible for cutaneous myiasis in the sub-Saharan region of Africa (Zumpt, 1965). However, with the extensive travel patterns of today's "air mobile" world citizen, the parasite has been diagnosed in travelers (Rice and Gleason, 1972, Laurence and Herman, 1973, Scholten and Hicks, 1973, Kozminska-Kubarska, 1981, Ockenhouse etal., 1990, Veraldi etal., 1993) and their accompanying pets (Idowu and Olote, 1976, Roberts etal., 1982, Fox etal., 1992) in geographic areas where the parasite does not exist.
LOCATION IN HOST: The parasite produces a painful boil-like (furuncular) swelling in the skin in both man and animals (Idowu and Olote, 1976). The lesions caused by the developing larvae are localized to the skin or subcutaneous tissue (Ockenhouse etal., 1990). In animals, the chief sites of infestation are the feet, genitals, tail and axillary region; however, in heavy infestations any area of the body may be affected, including the nose (Zumpt, 1965).
IDENTIFICATION: Adult Cordylobiaanthropophaga are non-parasitic and as a result will not be observed by the client or the veterinarian. They are stout, compact flies, averaging about 9.5 mm long. Their general color is light brown, with diffuse blue-grey patches on the thorax and a dark grey color on the posterior part of the abdomen. The face and legs are yellow. The body length of the adult fly is variable, between 6 and 12 mm (Zumpt, 1965). It is very difficult to recognize the adult fly if it has not been reared from a larva extracted from the host (Zumpt, 1965).
The second and third stage larvae of Cordylobia. anthropophaga are the stages that will be usually observed in the skin of an infested cat. The second stage larva is slightly club-shaped and exhibits large, black, posteriorly directed cuticular spines irregularly distributed over the third to the eighth segments. Segments nine to eight are almost bare when compared to the preceding segments. The segments have a few rows of small pale spines posteriorly. Segment twelve is densely covered with these spinules. Segment thirteen is indistinctly demarcated, lacking spines but possessing two pair of short processes. Each tracheal tube opens through two slightly bent slits. The cephaloskeleton is strongly schlerotized and armed with two hook-shaped labial sclerites. The early second stage larva is from 2.5 to 4.0 mm in length. Great variation is seen in the size of the advanced second stage larva.
Great variation is also seen in the size of the third stage larva; the fully mature larva is from 1.3 to 1.5 cm in length. The body is cylindrical with twelve identifiable segments. The two hook-shaped labial sclerites are projected. On either side of the sclerites is a ridge of yellow schlerotized integument. Posteriorly-directed curved spines are densely arranged at least up to segment seven; the last five segments may be either partially covered or densely covered with spines. The posterior spiracles open through three sinuous slits located on a weekly schlerotized peritreme (Zumpt, 1965). The presence of a dermal swelling with a central opening may lead to a tentative diagnosis of myiasis due to Cordylobiaanthropophaga. A definitive diagnosis can be made only after extraction and identification of the typical larva.
Diagnosis is often made by a history or either residence in or travel to an area endemic for Cordylobia. anthropophaga. There are other flies from different areas throughout the world that might produce a lesion similar to Cordylobia. anthropophaga. These should also be considered in a differential diagnosis. These myiasis-producing flies include: Dermatobiahominis, the South American tórsalo fly; Wohlfahrtiavigil, the grey flesh fly; Chrysomyiabezziana, the Oriental fly; Cochliomyiahominivorax, the New World primary screwworm; and Cuterebra species, the rabbit botflies. These obligatory myiasis-producing flies should be considered in the differential diagnosis in cats with an appropriate residence or travel history.
LIFE CYCLE: The adult flies are rarely observed during the daytime but instead rest on the ceilings of huts and open porches. They are active from seven to nine in the early morning and from four to six in the late afternoon. The adults feed on the juices of plants (bananas, pineapples), decomposing animal tissues and excreta. For egg laying, the female is attracted to dry sand contaminated with urine or feces. A cat's litter box (either clean or soiled) may be a prime medium for egg laying (Author's personal opinion). If the sand is too moist, the eggs are not laid there, but are deposited nearby on a dry spot. The flies never lay their eggs on the exposed skin or attach them to hairs.
Fertilization and oviposition continue all year round. The female fly lives for about two weeks and produces 300 to 500 eggs, deposited in two batches of 100 to 300 eggs each. The larvae hatch after one to three days and remain alive without food for about nine days. Some may persist for as long as 15 days. The larvae remain just below the surface of the sand, in anticipation of a passing host. If the surface of the sand is disturbed, the larvae quickly crawl out. They adhere to grains of sand and by means of their posterior end, raise the body and wave about actively, seeking a host to which they can attach. Once the larva attaches to the skin of the host, it immediately begins to penetrate. The time required for penetration depends on the thickness of the host's skin. At the end of the invasion process, the larva is covered by a thin layer of skin. Its last segment protrudes slightly through the aperture, but it can be withdrawn if touched. The first larval stage molts to the second after two to four days. The molt to the next stage takes place on the fifth or sixth day after invasion. In the rat, maturity is reached on or about the eighth day. The larva then leaves the boil, drops to the ground and pupates within 24 hours. At room temperature, the fly hatches after ten to eleven days. At lower temperatures, the pupal stage lasts longer (Zumpt, 1965).
CLINICAL PRESENTATION AND PATHOGENESIS: Penetration of the skin by the first stage larva may not be noticed by the owner. A small red pimple forms at the penetration site. The reaction caused by the entrance of the larva is said to be palpable for the first two days. The symptoms then subside and the infected area may be overlooked. Serous fluid exudes from the opening made by the larva for breathing. The skin becomes inflamed, and there is tenderness on pressure. The lesion now resembles a small boil. There may be multiple sites of infection (Patton and Evans, 1929). As mentioned previously, the lesions caused by the developing larvae are localized to the skin or subcutaneous tissue (Ockenhouse etal., 1990).
With the increase in size of the furuncular lesion and the surrounding inflammation of the tissues, more serious symptoms develop. The tissues surrounding the swelling, now large, are hardened, and erythematous. During this period, the larva is very active and can cause great pain. The larvae can be observed moving in the swellings as they attempt to enlarge the cavity and the respiratory opening as they grow. For this process, the larvae produce a lytic reaction. The secretions from the opening now contain more and more larval feces (Gunther, 1971).
One or two larvae normally do not produce conspicuous stress, but when they are numerous, considerable irritation and restlessness may arise, resulting from septic absorption. Where larvae are close together, swelling and edema occur. The tissues may become gangrenous. The larvae may invade deeper tissues and may cause severe destruction leading to the death of the host (Zumpt, 1965).
Furuncular myiasis due to Cordylobia. anthropophaga is characterized by the simultaneous finding of four clinical signs: (1) occurrence of boil-like lesions; (2) the indolence of the lesions; (3) a small opening in which lies the caudal end of the larva with its spiracular plate; and (4) the secretion of a serous fluid, sometimes stained with blood or larval feces (Gunther, 1971).
TREATMENT: As with all subcutaneous tissue dwelling flies, treatment is based on the fact that the larvae need communication with outside air for respiration. Air exchange is accomplished via the larva's posterior spiracles. The airway may be occluded using heavy oil, liquid paraffin, sticking plaster, pork fat or petroleum jelly (Ockenhouse etal., 1990).
Surgical intervention involves the injection of lidocaine hydrochloride into the furuncular lesion producing local anesthesia for the cat and also anesthetizes the larva, allowing it to be manually extracted using thumb forceps. Antibiotics should be prescribed. Ockenhouse etal. (1990) state that 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 the larva insitu, although no mention is made of anaphylaxis as occurs when larvae of Cuterebra species are ruptured during extraction. In suspect cases, the extracted larva should be submitted to an entomologist for definitive diagnosis. Parasitologists (and veterinarians) not well acquainted with the taxonomy of these myiasis-producing flies should always contact an expert when correct identification is needed (Zumpt, 1965).
EPIZOOTIOLOGY: In the tropics, cordylobiasis occasionally spreads during the flies' breeding season and during the period of animal migration, especially among rats during floods occurring in the rainy season (Gunther, 1971). Young animals are much more susceptible than older ones, and are more heavily infested (Patton and Evans, 1929).
HAZARDS TO OTHER ANIMALS: Of domestic animals, the dog is primarily affected and must be regarded as an important reservoir host; the rat is the most important wild reservoir host (Gunther, 1971). In addition to cats, other domesticated animals naturally infected are the goat, pig, rabbit, guinea pig and chicken. Wild animals infected include mice, monkeys, mongooses, squirrels, leopards, boars, and antelopes. Reptiles and amphibians are never infected (Veraldi etal., 1993).
HAZARDS TO HUMANS: The larvae are capable of penetrating any part of the skin surface of humans. Young children may demonstrate involvement of the scalp and the face. Children are more frequently infected that adults due to the thinness of their skin. Thin skin facilitates penetration of the larvae (Veraldi etal., 1993). The lesions in humans are often found on covered parts of the body, such as the waist, buttocks, arms, armpits, and sometimes the legs, suggesting that the larvae may have become fixed to some article of clothing (Patton and Evans, 1929)
CONTROL/PREVENTION: Adult flies should be killed if observed 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 (Patton and Evans, 1929).
In Africa south of the Sahara Desert, Cordylobia. anthropophaga is a common parasite of dogs and rabbits. Prevention of an infestation depends on cleanliness and regular disinfection of the animal's sleeping quarters. In the case of valuable animals (e.g., Angora rabbits), protection can be provided by keeping flies out of rabbit pens using gauze wire (Zumpt, 1965).
With regard to cats in an area endemic for the tumbu fly, feces should not be allowed to accumulate in litter boxes.
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