Yugesh Raj Panta,
MBBS student, UCMS

Review Article:

    
Debunking the myths of Acid fly…

                            With self experimentation… 

Abstract:

Paederus, notorious in UCMS as ‘acid fly’ affects almost all the students residing at the UCMS hostel in one or other part of the hostel life. It neither bites nor stings the human beings. It is the human’s activity of crushing the creature against the skin, knowingly, or unknowingly during sleep, that releases its ‘blood’ called hemolymph containing a vesicant toxin ‘Pederin’ that induces irritant contact dermatitis to produce the characteristic blisters commonly named among the students as a ‘acid fly bite’. The lesion heals on its own but administration of a combination of strong topical corticosteroid and oral antibiotic (ciprofloxacin) and oral antihistaminic (cetrizine) accelerate the healing and prevent secondary infections and residual dermal lesions.

Key words: Paederus, Acid fly, dermatitis, student hostel, UCMS, Nepal

Introduction:

Paederus (so called 'acid fly')

The so called ‘acid fly’ in UCMS is Paederus by genus of the family Staphylinidae ("commonly called as rove beetles") and includes over 622 valid species (10). Paederus beetles are small, soft bodied and are roughly 1 cm (¼ to ⅜ inch) in length. They are dark orange in color with their head, front wings (elytra) and the tip of their abdomen colored black. As other insects, they lay eggs and pass through larva and pupa stages before adulthood. Both the larva and adults are predators against several crop-damaging insects and occurs in warm tropical climates. The insect breeds in wet rotting leaves and soil (that are found abundantly behind the UCMS hostels). The immature stages of Paederus beetles develop in moist areas such as marshes, irrigated croplands and wetland areas surrounding freshwater. The larvae usually feed on the algae, small insects and decaying plant and animal material found in these habitats. The population increases rapidly at the end of the rainy season and then rapidly diminishes with the onset of dry weather. At night, light towers and other bright light sources can attract the adult beetles from habitats that are miles away. The beetles live in moist habitats and are often beneficial to agriculture because they will eat crop pests. Adults are attracted to incandescent and fluorescent lights, and as a result, inadvertently come into contact with humans (2).

The toxin:

Contrary to the name ‘acid fly’ given to the creature at UCMS, the toxin ‘Pederin’ that its hemolymph contains, is not an acid but a vesicant toxic amide. Paederin is considered to be 12 times more poisonous than the cobra venom (17). At least 20 species are known to be associated with Paederus dermatitis (7). The manufacture of pederin is largely confined to adult female beetles—larvae and males only store pederin acquired maternally (i.e., through eggs) or by ingestion. Actually, the toxin is manufactured, not by the beetles themselves, but by endosymbiont bacteria, probably some species of Pseudomonas. (4)

Pathophysiology:

It is an irritant contact dermatitis, i.e., an inflammatory response of the skin to exogenous agents, in which inflammatory mediators may be activated but memory T-cell function or antigen-specific immunoglobulins are not involved. The main pathophysiological changes observed in irritant contact dermatitis are skin-barrier disruption, epidermal cellular changes, and cytokine release mainly from keratinocytes. Irritants produce various responses on the skin that range from stinging, burning, and tightness to erythema, urticarial reactions, frank eczema, or chemical burns (1). In addition, Pederin blocks mitosis at levels as low as 1 ng/ml, by inhibiting protein and DNA synthesis without affecting RNA synthesis, prevents cell division and causes skin barrier disruption leading to blister formation(11). Acantholysis is probably caused by the release of epidermal proteases (3).

Clinical features:

Typical linear lesion on fore arm

Erythemobullous lesion on neck

The lesions of Paederus contact dermatitis are usually in the form of a typical bizarre linear vesicles and sterile pustules on an erythematous skin. The lesion appears on the skin about 12-36 hours after contact (2). Different responses are seen in the skin depending upon its concentration, duration of exposure, and individual characteristics. Mild cases are limited to slight erythema lasting for a couple of days. With moderate cases, the erythema evolves into vesicles and bullae over a few days, after which the blisters dry out over a week leaving hyper- or hypo pigmented patches that may last for years. Scarring usually does not occur.  Symptoms are limited to little discomfort in mild to moderate cases, unless the area becomes secondarily infected. The lesions are characteristically linear due to smearing the crushed insect across the skin. Patients may unknowingly transfer the toxin to other areas like genitals and face or the toxin may spread to contagious site through skin apposition to give ‘kissing lesions’ or ‘mirror image lesions’ especially over the flexure of the elbow, adjacent surfaces of the thighs etc. Severe cases, in addition to showing more extensive blistering, may demonstrate additional symptoms, such as fever, neuralgia, arthralgia, and vomiting (12). If the periorbital area is affected, conjunctivitis may develop referred to “Nairobi eye” in eastern Africa. It may even result in intense pain and temporary blindness (1).

Differential diagnosis:

The clinical features of Paederus dermatitis are most commonly confused with phytophotodermatitis (5). The lesions may also vary to simulate with the lesions of herpes simplex, herpes zoster, liquid burns, acute allergic or irritant contact dermatitis and millipede dermatitis (3).

Diagnosis:

The characteristic linear appearance of the lesions, their predilection for exposed areas, the presence of kissing lesions, and most importantly epidemiological features (occurrence of similar cases in a given area, the seasonal incidence and identification of the insect) should enable the clinician to arrive at the right diagnosis (3).

Treatment:

The cases should be managed as irritant contact dermatitis-removal of irritant, initial washing with soap and water, application of cold wet compresses (11). Once the lesion appears, healing can be achieved faster by administrating a combination of topical steroids and oral antibiotics (ciprofloxacin) and antihistaminic (cetirizine) than with steroids and antihistaminic alone (1). It is hypothesized that the better response with the antibiotics may be because of the possible contamination of skin by pederin-producing endosymbiont bacteria while crushing the insect (1).

Outbreaks:

The outbreaks of Paederus dermatitis occur most commonly at the end of the rainy seasons when the population of the adult insect grows rapidly. It is also endemic in many tropical areas. Many outbreaks are reported in the literature from countries like Iran (13), Iraq (14), Malaysia (15), China (16), Srilanka (9) and India (3). Some examples include the outbreaks in medical mission boat in Amazon (5); United Nations Hospital at Koidu Sierra Leone (West Africa) (1); a primary school at Terengganu, Malaysia; Sri Jayawardanapura General Hospital, Kotte, Sri Lanka (9); and Manipal University Karnataka (3). However, no cases are reported from Nepal till now.

Prevention:

Preventing human-beetle contact is the primary method of avoiding Paederus dermatitis. Learning to recognize Paederus beetles and avoiding handling or crushing these insects will help decrease these eruptions. If a beetle lands on the skin, it should be blown off or encouraged to walk onto a piece of paper and then removed. The area in contact should be immediately washed with soap and water, and any clothes in contact with the beetle should be washed as well. Doors should be kept closed and window screening should be kept in good repair to help reduce entry of these insects into buildings. Since beetles are attracted to light, these should be switched off near areas where people sleep. Removal of any decaying vegetation around buildings and work areas helps to eliminate potential harborage for the beetles and their larvae (2). The application of deltamethrin dust to vegetation may help to reduce beetle numbers in small areas (8).

A small experiment:

While writing this article, the author encountered a Paederus running on his forarm. The insect was caught and stored. The writer took a bath and crushed the insect onto the flexor aspect of the forearm. The crushed insect was smeared on the skin and the area marked. An ant was also taken and the process was repeated with the ant on the opposite hand which was taken as a control.

The reaction in the skin was observed every 4 hours and noted. The first changes observed was 12 hours after the experiment which included irregular erythemas on the skin inside the marked area of the ‘case’ hand.The reaction is still on observation.

References:

1.      “Paederus dermatitis In Sierra Leone” Syed Nurul Rasool Qadir MMBS, Naeem Raza MMBS, Simeen Ber Rahman MD; Dermatology Online Journal 12 (7): 9 

2.      "Just the facts…Paederus Beetles". US Army Public Health Command. Retrieved 30 July 2011.

3.      Paederus dermatitis Singh Gurcharan, Yousuf Ali Syed; Indian Journal of Dermatology, Venereology and Leprology, Vol. 73, No. 1, January-February, 2007, pp. 13-15

4.      Piel J (2002). "A polyketide synthase-peptide synthetase gene cluster from an uncultured bacterial symbiont of Paederus beetles".

5.   Journal of clinical and aesthetic dermatology, 2011 November; 4(11): 44–46. PMCID: PMC3225135: Paederus Dermatitis. “An Outbreak on a Medical Mission Boat in the Amazon” Jere J. Mammino, DO, FAOCD

6.      “Paederus Dermatitis Amongst Medical Students in USM”; KelantanN. Mokhtar, MSc (Derm), R. Singh, MRC ,W. Ghazali, Dip (Derm)

7.  Mullen, Gary; Gary Richard Mullen, Lance Durden (2009). Medical and Veterinary Entomology. Academic Press. p. 102. ISBN 978-0-12-372500-4. Retrieved 31 July 2011. "Pederin contacts human skin only when a beetle is brushed vigorously over the skin or crushed."

8.    Sichuan journal of zoology. “Effect of Four Kinds of Insecticides on Predatory Function of Paederus fuscipes Curtis” MENG Qing-yu, College of Life Science, China West Normal University, Nanchong, Sichuan Province 637002)

9.    International journal of dermatology. “An outbreak of paederus dermatitis in a suburban hospital in Sri Lanka” Satheeka D. Kamaladasa MBBS, MD, W.D.H. Perera MBBS, FRCP^*,  L. Weeratunge DOI: 10.1046/j.1365-4362.1997.00009.x

10.   Frank, J.H. (1988). "Paederus, sensu lato (Coleoptera: Staphylinidae): An index and review of the taxa.". Insecta Mundi2 (2): 97–159.

11.  Frank JH, Kanamitsu K (1987). "Paederus, Sensu Lato (Coleoptera: Staphylinidae): Natural History and Medical Importance". J. Med. Entomol 24 (2): 155–191.PMID 3295241

12.  Borroni G, Brazzelli V, Rosso R.M. Pavan. Paederus fuscipes dermatitis: a histopathological study. The American Journal of Dermatopathology. 1991;13:467–474. [PubMed]

13.  Zargari O, Kimyai-Asadi A, Fathalikhani F, et al. Paederus dermatitis in northern Iran: a report of 156 cases. Int J Dermatol 2003;42:608-12.

14.  Al-Dhalimi MA. Paederus dermatitis in Najaf province of Iraq. Saudi Med J 2008;29:1490-3.

15.  Rahmah E, Norjaiza MJ. An outbreak of Paederus dermatitis in a primary school, Terengganu, Malaysia. Malays J Pathol 2008;30:53-6.

16.  Huang C, Liu Y, Yang J, et al. An outbreak of 268 cases of Paederus dermatitis in a toy-building factory in central China. Int J Dermatol 2009;48:128-31.

17.  Huang, Fu-Chin MD; Chen, Wan-Ju MD; Shih, Min-Hsiu MD. Paederus-Induced Keratitis. Cornea 2010;21:941-4