Dermatology Online Journal

A sticktight flea removed from the cheek of a two-year-old boy from Los Angeles
John C Carlson¹, Mark S Fox²
Dermatology Online Journal 15 (1): 4

1. Department of Allergy, Clinical Immunology, and Rheumatology, Tulane University, School of Medicine, New Orleans, Louisiana. john.carlson@tulane.edu
2. Department of Ecology & Evolutionary Biology, Tulane University, New Orleans, Louisiana. mfox@tulane.edu

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Abstract

Species-level identification of an ectoparasite often requires outside expertise. Patients are increasingly turning to the internet for medical information, in part to gain access to experts. We present a case of a flea identified after contact was made between a patient's father and the authors via an insect-related forum on the internet. The flea had been attached for 12 hours without inducing symptoms before it was removed. The specimen was identified as a sticktight flea Ectoparasites in the differential diagnosis for this case are discussed.

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Introduction

Zoonotic ectoparasites are of concern both because they pose a risk to human health (e.g., the rat flea Xenopsylla cheopis transmits plague) and because they induce intense pruritus (e.g., the cat flea Ctenocephalides felis) [1]. It is typical for an ectoparasite to be discovered by the patient (or in the case of children, by a parent) rather than by a physician. The recovered specimens, when retained, are frequently brought to a physician when sufficient concern exists over the parasite. Because most medical schools in developed countries no longer train physicians in invertebrate identification techniques, definitive arthropod identification requires consultation with a shrinking pool of parasitologists and entomologists [2].

Access to experts is an important motivator for seeking medical information online. Although healthcare professionals remain the dominant source of trusted health care information, the internet is cited as an important source of medical information for 75-80 percent of internet users and significantly affects their medical behaviors [3]. Online methods for providing rapid feedback range from user-generated forums where the general public is invited to ask and answer the questions [4], to ask-the-expert sites in which the public is invited to submit questions to be answered online by pre-selected experts [5, 6].

Case

Figure 1
Figure 1. Sticktight flea bite. Left inset: Macroscopic photograph taken of the flea attached to the patient's cheek. This image was posted to a number of insect-themed websites in hopes of identification. Right inset: Microscope photograph taken of the cleared, slide-mounted flea, identified as E. gallinacea. Background image: Slight erythema around the site of attachment was noted several days after removal of the flea.

The patient is a 33-month-old Caucasian male in good health that was found to have a "small black speck" on his right cheek one morning. The parents initially assumed that it was dirt or food, although attempts to remove it were unsuccessful. The lesion was unchanged over a 12-hour period of time, with no surrounding redness, swelling, itching, or tenderness. Finally the child's father took a macroscopic photograph (Fig. 1) and noted bands from the picture that suggested an insect. He posted the picture to several insect-themed websites asking for help with identification.

After the photograph was taken, the specimen was removed using tweezers and placed in alcohol. Pulling on the insect with tweezers "pulled his check out about a centimeter before it popped off." Although no skin discoloration or swelling was noted initially, a faint ring of erythema was noted surrounding the site of attachment several days later (Fig. 1). This resolved spontaneously and he remained without other signs or symptoms.

Figure 2
Figure 2. Griffith Park. Background: Aerial image of Griffith Park, located within urban Los Angeles (USGS 2004). Inset: Photograph of Griffith Park demonstrating habitat characteristics found near the patient's home (Clinton Steeds 2005).

The patient lives with his parents and an infant sibling across from Griffith Park (17 km² city park) in Los Angeles (Fig. 2). No contacts have reported insect bites or other skin lesions. Exposure to animals includes one dog and one cat as pets and stray cats outside the home, in addition to the number of birds, squirrels and other animals living in the park, which is visited several times per week. The child's father notes that squirrels, raccoons, coyotes, skunks, and possums have all been seen in the yard.

The child has experienced multiple mosquito bites and a single bee sting in the past, all with normal local reactions. The child's review of systems was otherwise unremarkable, as were his past medical history and family history.

Specimen identification

Although the specimen could not be identified from the photograph, arrangements were made to mail the specimen to another user of a website to which the photograph was posted (bugguide.net). Upon arrival, the specimen was placed in clearing fluid for 24 hours and then slide mounted in PVA medium before examination under a compound microscope. It was identified as a female specimen of sticktight flea (Echidnophaga gallinacea Westwood 1875) based on the presence of two preantennal bristles, a patch of spinelets on the hind coxa, the shape of the head, the shape of the spermatheca, and the lack of pronotal comb, genal comb, or rod-like sclerotization dividing the mesosternite [1]. (Fig. 1) Notably, the mouthparts were severed, presumably retained in the child's skin, and possibly the cause of the subsequent erythema.

Discussion

We agreed to assist in the identification of the specimen because of the unusual characteristics of the bite. Most arthropod bites are brief and often induce pruritus or pain; this specimen had attached for over 12 hours and induced no symptoms. Ticks are notable for asymptomatically attaching to their hosts for long periods of time. However, the shape of the specimen from the initial photograph was inconsistent with any ticks with which we were familiar. Contrary to popular belief, human head lice (Pediculus humanus capitis) most often do not induce itch, but they are rarely found off of the scalp and conduct brief feedings [7]. Pubic lice (Phthirus pubis) can also be found on the head in children but do not often remain away from follicles for extended periods of time [8]. Of fleas recorded on humans, only two species regularly attach for prolonged periods of time: Tunga penetrans and Echidnophaga gallinacea. The females of T. penetrans can embed for years, usually in the feet, where they become encased in a tender nodule. Tungiasis is not transmitted within the US, but is seen in travelers coming from endemic areas [9].

E. gallinacea (commonly referred to as sticktight or stickfast fleas) are principally found on birds, but will attach to mammals when preferred hosts are unavailable. For example, in Los Angeles County sticktight fleas have been collected from the California grey fox, California bob cat, and California ground squirrel [1]. These small fleas can reach large population levels in domesticated chickens as well as wild bird nests, with fleas becoming a problem for humans venturing nearby. Although many textbooks state that sticktight fleas are an occasional cause of bites on humans, we were able to uncover only a single report in the literature that dealt with a girl bitten by fleas over several months [10]. This paucity of published reports is probably a result of a once-common phenomenon (not worthy of reporting) that has subsequently become rare due to urbanization and changes in farming practices. In particular, large farms now use cement floors or metal cages in which flea larvae have difficulty living and pupating. Given the similarity between attachment patterns of ticks and sticktight fleas, removal of sticktight fleas is probably best accomplished by applying slow, gentle traction to allow time for the flea to disengage the mouthparts [11].

In contrast to other species of flea, lesions due to cat fleas (Ctenocephalides felis) are commonly reported in humans [12]. These fleas are the cause of nearly all flea infestations in cities world-wide. Host factors play an important role in determining the severity of the reactions, with papular urticaria (clusters of firm, intensely pruritic, deeply erythematous papules with a central punctum) being most common in children older than 2 years (following a period of sensitization) [13]. The intensity of reactions typically wanes by adolescence. With the exceptions of Pulex irritans and T. penetrans (often connected with pig farming) fleas cannot reproduce while feeding on human blood alone. Thus prevention of flea bites is centered around eliminating infestations in the reservoir hosts (e.g., dogs and cats) or reducing contact with them (e.g., removing nests of birds or rodents). Especially in the case of an on-going infestation, species-level identification of the flea can help identify the reservoir host so that obscure sources can be located [14].

Acknowledgments: The authors wish to thank M. Garon for contribution of the photographs used in Fig. 1 and consent to publish the patient details presented in this article, Clinton Steeds for the photograph in Fig. 2 (creative commons, attribution license), BugGuide.net editors J. VanDyk and E. Eaton for their feedback and L. Wild for review of the manuscript. Reproduction of the images in this article for non-commercial purposes is permitted without prior consent provided attribution to the relevant copyright owner is made.

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