NOSOCOMIAL MYIASIS IN AN EXTREMELY PREMATURE INFANT CAUSED BY THE SHEEP BLOWFLY LUCILIA SERICATA

Abstract

Myiasis is the infestation of body tissues of humans or animals by the larval stages of dipterous flies.1 It is common worldwide but occurs more often in hot and humid climates. Myiasis has been classified into three categories: (1) obligatory-flies require a living host tissue to complete their life cycle1; (2) facultative-gravid fly lays eggs in decaying flesh or vegetable matter but may also be attracted by the odor of necrotic wounds or mucus. Eggs are laid in wounds or natural body orifices1-3; (3) accidental-eggs are laid in food, thus eggs or larvae are ingested and survive in the gastrointestinal tract.4 Almost any exposed human surface may be involved in myiasis. Skin, either intact or damaged,5 eyes,6 nose,7 ears,7 mouth8 and the urogenital tract9, 10 are prime targets. Myiasis occurs mainly in indigenous populations or in travelers to endemic areas. Most reports of nosocomial myiasis have been of sporadic facultative infestations, particularly in debilitated patients, some of whom were diabetic.3 Contributing factors include hypoesthesia or disturbed consciousness, which prevent the patient's sensation of fly contact, or paralysis or immobility, which prevent the patient from fending off the fly once detected.2, 11 A literature search between 1966 and 1998 (Medline Silver Platter International, NV) did not reveal any reports of nosocomial myiasis in a premature infant; the following is a brief report of such. Case report. A 630-g female infant was born by spontaneous vaginal delivery after a 26-week gestation. At delivery the infant was cyanotic and bradycardic but responded well to intubation and ventilation. During the hours after admission a fly was noted in the neonatal intensive care unit (NICU). At 24 h of age the infant was irritable and required sedation, although no obvious cause was identified. At 48 h of age 25 to 30 wormlike organisms were seen in or emerging from the vaginal orifice and a provisional diagnosis of myiasis was made. The organisms were whitish-gray and ∼7 mm long (Fig. 1). A sample of the organisms were fixed in 10% formalin and sent for identification. The vagina was thoroughly flushed with saline until no larvae were seen.Fig. 1: Sample of second instar larvae of L. sericata.The infant remained stable for the next week and then developed two episodes of Gram-negative sepsis during the subsequent 2 weeks. The second and fatal episode was fulminant sepsis caused by Pseudomonas aeruginosa. Permission for postmortem examination was refused. Identification of the larvae. The larvae were examined at the Department of Veterinary Parasitology, Liverpool School of Tropical Medicine, UK, and were identified as second instar Lucilia sericata (Meigen).12 Discussion.L. sericata is a facultative ectoparasite belonging to the family Calliphoridae and is commonly known as the sheep blow fly or the green bottle fly.13 It is found worldwide but is more common in cool temperate rather than warm temperate and subtropical habitats. Its rate of development after oviposition (laying eggs) is temperature-dependent. In the sheep, which has a body temperature of 39°C, larvae in a wound mature by 43 h and then exit the wound for pupation.12 In the patient described larvae were noted at age 48 h; thus it is likely that the infestation occurred within the first few hours of life. The mother did not have any evidence of vaginal myiasis; thus it is highly unlikely that larvae were acquired from the mother. In addition the unusual presence of a fly in the NICU may have been related to the infestation. Facilitatory conditions in this case include the infant's inability to fend off the fly, the likely presence of bloody mucoid secretions in the vaginal orifice immediately after delivery, the hot and humid climate in central Israel during the summer and the ground floor location of the NICU. Historically L. sericata organisms were utilized as "surgical maggots" because of their propensity for debridement of necrotic wounds while ignoring living tissue.14 However, certain strains have been known to invade healthy tissue if the amount of accessible necrotic tissue is inadequate.15 In this infant no gross evidence of local tissue damage was noted, although in the absence of postmortem examination, microscopic damage could not be ruled out. Furthermore absence of obvious tissue damage can be explained since the larvae had not reached the final third instar, the stage that causes most damage because of its size and large mouth hooks which are used to macerate tissue.16 Potential morbidity caused by myiasis includes intense pruritus and irritability, transmission of other infectious agents and local tissue damage.2, 15, 17, 18 Preventive measures should include appropriate hygiene and meticulous wound care, efficient waste disposal (including insecticides, as required), window screening and air conditioning.11 Myiasis is extremely rare in infancy. In a series of 254 cases of myiasis in India during a 6-year period, 94 (37.9%) were seen in children, the youngest being 11 months of age.7 Most of the pediatric cases were aural myiasis. To the best of our knowledge no case of nosocomial myiasis has been reported in a neonate. Moshe Amitay, M.D. Moshe Efrat, M.D. John W. McGarry, Ph.D. Eric S. Shinwell, M.D. Department of Neonatology; Kaplan Medical Center; Rechovot and Hebrew University; Jerusalem (MA, ESS) Department of Pediatrics; Carmel Medical Center and the Faculty of Medicine; Technion Institute of Technology; Haifa (ME) Israel Department of Veterinary Parasitology; Liverpool School of Tropical Medicine; Faculty of Veterinary Science; Liverpool, England (JWM)